Shaft Generators for Low Speed Main Engines · 8 Shaft generators for low speed main engines As illustrated in Fig. 3, at 124 rpm, the right-hand power range curve No. 1 is located

Shaft Generators for Low Speed Main Engines

Contents

Preface ........................................................................................................5

Introduction .................................................................................................5

PTO/GCR (power take off/gear constant ratio) ..............................................7

PTO/RCF (power take off/RENK constant frequency) .................................. 10

PTO/CFE (Power Take Off/Constant Frequency Electrical) ........................... 11

Characteristics of electric power from shaft generators ............................... 13

Engine mounted front-end installation (BW I) ............................................... 15

Tank top mounted front end PTO installation (BW II) .................................... 16

RENK installation (BW III) mounted on engine side ...................................... 18

Aft-end installation (BW IV/GCR) mounted on tank top ............................... 19

Aft-end installation (SMG/CFE) mounted on propeller shaft ......................... 21

Front-end PTO installation mounted on engine (DMG/CFE) ......................... 22

Layout for engine driving a fixed pitch propeller ........................................... 25

Layout for engine prepared for driving a fixed pitch propeller and

shaft generator ........................................................................................... 26

Special layout for engine with fixed pitch propeller and shaft generator ........ 27

Engine layout with controllable pitch propeller and shaft generator .............. 28

Layout for engine driving a fixed pitch propeller and shaft generator/motor . 28

Engines with small PTO applications ........................................................... 30

Engines with large PTO applications ........................................................... 30

PTO advantages ........................................................................................ 32

PTO disadvantages .................................................................................... 32

PTO used with shuttle tankers .................................................................... 35

Auxiliary electric propulsion system ............................................................. 37

Auxiliary hydraulic propulsion system .......................................................... 38

RENK propeller shaft clutch ........................................................................ 39

Power turbine generator ............................................................................. 41

MHI hybrid turbocharger ............................................................................ 41

MHI electro-assist turbocharger .................................................................. 42

The combined RENK shaft generator and waste heat recovery system ........ 43

Introduction ............................................................................................... 44

Summary ................................................................................................... 44

References................................................................................................. 46

Shaft generators for low speed main engines 5

Preface

The purpose with this paper is to

provide detailed information about

different categories of shaft gen-

erators driven by a MAN B&W low

speed marine engine used for ship

propulsion.

The paper describes different types

of marine shaft generators and their

configurations, with the physical

connecting interfaces to the main

engine or to the intermediate propel-

ler shaft. It will provide a description

of relevant aspects and can be used

for reference.

Introduction

After the first MC engine was intro-

duced in 1982, MAN Diesel & Turbo

started investigating the possibility for

using a low speed main engine driven

shaft generator for generating the elec-

tric power on ships as an alternative to

the four-stroke gensets.

This was motivated by the rising fuel

prices and the fact that, at that time,

most four-stroke gensets could only

operate on the more expensive marine

diesel oil. The low speed main engine

was able to operate on the cheaper

heavy fuel oil, and the marine industry

therefore looked into the possibility for

using a main engine driven shaft genera-

tor alternative. Various reliable shaft gen-

erators were developed, and the electric

power generated from shaft generators,

combined with the prolonged length be-

tween overhaul for the shaft generator

and low speed main engine compared

to the four-stroke genset, rapidly be-

came popular among operators.

However, references have shown that

a number of shipowners and opera-

tors still consider a shaft generator as

an attractive investment for ships like

container vessels, product tankers and

shuttle tankers. This is probably as-

cribed to the fact that shaft generators

and low speed main engines are con-

sidered to be highly reliable and offers

savings from prolonged time between

overhauls compared to a four-stroke

genset solution. This means that by

selecting the right shaft generator and

main engine layout, operating hours can

be saved on the four-stroke gensets

because they can be shut down during

voyage.

Supported by examples of typical and

special shaft generator installations,

this paper describes the most com-

monly used systems and the connect-

ing interface to the low speed main en-

gine or propeller shaft.

In the following, the term “shaft genera-

tor” is used for any arrangement where

a power take off from the main engine

prime mover or its shaft line is used to

drive an alternator for the purpose of

generating electric power.

Shaft generators for low speed main engines

Shaft generators for low speed main engines6

MAN Diesel & Turbo distinguishes be-

tween three main categories of shaft

generators:

PTO/GCR (power take-off/gear con-

stant ratio) consists of flexible coupling,

step-up gear and alternator.

PTO/RCF (power take-off/RENK con-

stant frequency) consists of flexible cou-

pling, step-up gear, torsion rigid toothed

coupling, RCF gear and alternator.

PTO/CFE (power take-off/constant

frequency electrical) consists of slow

running alternator with electrical control

equipment.

PTO/RCF and PTO/CFE shaft genera-

tors incorporate various frequency con-

trol systems that allow them to generate

electric power with constant electrical

frequency at varying engine speed.

The designations BW I, BW II, BW III

and BW IV distinguish between various

physical configurations.

In MAN Diesel & Turbo terms, a 700 kW

(60 Hz) GCR shaft generator type in-

tended for installation with an S50ME-

C engine is designated: BW III S50ME-

C/GCR 700 - 60.

Descriptions of PTO/GCR, PTO/RCF

and PTO/CFE shaft generator types

and the various configurations possibili-

ties appear from the principles sketched

in Fig. 1 and represent the most typical

shaft generator layouts, based on infor-

mation from the suppliers.

Fig. 1: Alternative types and layouts of shaft generator systems.

Definitions and designations of shaft generators

Alternative types and layouts of shaft generators Design Seating Total efficiency (%)

PT

O/R

CF

1a 1b BW I/RCFOn engine

(vertical generator)88-91

2a 2b BW II/RCF On tank top 88-91

3a 3b BW III/RCF On engine 88-91

4a 4b BW IV/RCF On tank top 88-91

PT

O/C

FE 5a 5b DMG/CFE On engine 84-88

6a 6b SMG/CFE On tank top 84-88

PT

O/G

CR

PT

O/C

FE 7

BW I/GCR

BW-I/CFE

On engine

(vertical generator)

92

81-85

8BW II/GCR

BW-II/CFEOn tank top

92

81-85

9BW III/GCR

BW-III/CFEOn engine

92

81-85

10BW IV/GCR

BW-IV/CFEOn tank top

92

81-85


PTO/GCR (power take off/gear con-stant ratio)Layout for operating at constant propeller

speed

The PTO/GCR system is the most

simple and cheapest of the shaft gen-

erators, and it comprises a standard

synchronous alternator and a simple

step-up gear. Its simplicity is attractive,

and many shipowners use it to gener-

ate all the electric power at constant

electrical frequency during the voyage.

Since the frequency produced by the

alternator is proportional to the en-

gine speed, the operation of this type

of shaft generator normally takes place

at constant propeller speed. The GCR

shaft generator system is therefore

normally utilised in connection with a

controllable pitch propeller, with which

constant propeller speed and relatively

constant frequency are available over a

wide engine power range.

The small engine speed and frequen-

cy variations that occur even for the

main engine running at constant speed

mode means that the GCR system is

not normally utilised for long term par-

allel running with the gensets. Conse-

quently, the electric power generation

from the GCR generator type only takes

place during the voyage supplying all

the electric power while the gensets are

out of operation.

Layout for operating at combinatory curve

At near zero propeller pitch, the con-

stant speed CP-propeller sees a sig-

nificant drop in propeller efficiency.

This means that ships with a typical

low speed profile, i.e. ships trading in

coastal areas or rivers, can benefit from

operating the CP-propeller at a lower

propeller speed at low engine loads.

To be able to benefit from an improved

CP-propeller efficiency at a lower pro-

peller speed, the GCR shaft generator

is disconnected and the gensets are

employed.

However, to avoid disconnecting the

shaft generator at reduced propeller-

and ship speeds, it is possible to install

a more expensive two-step gear solu-

tion that can be utilised at the alternative

power range found at lower propeller

speeds to maintain the right electrical

frequency from the alternator.

The lower propulsion power for differ-

ent CP-propeller speed and pitch diam-

eter ratio is illustrated in the power and

propeller speed diagram in Fig. 3.

Fig. 2: Shaft mounted BW IV/GCR system

Categories of shaft generators


As illustrated in Fig. 3, at 124 rpm, the

right-hand power range curve No. 1 is

located 2-3% below the 100% rpm. At

this propeller speed, one of the two gears

of a two-step GCR system can generate

electric power with constant frequency

at, for instance, 60 cycles. But thanks to

the two-step gearbox layout, the same

60 cycles can be achieved with the sec-

ond alternative gear selection found on

the left-hand power range curve No. 2

at 109 rpm.

This means that the two-step gearbox

can generate power with the same out-

put at two different propeller speeds.

The improved propeller efficiency ob-

tained at 109 rpm allows the ship to

travel the same speed (11 knot) at ap-

prox. 600 kW lower main engine power.

The gain from the two-step gearbox so-

lution and the propeller running with a

combinatory curve at lower ship speed

can be summarized as follows:

1. Electric power with the same fre-

quency generated from a shaft gen-

erator is possible within two propel-

ler speed alternatives.

2. Improved propeller efficiency for part

load operation is possible.

3. Slightly improved engine thermal ef-

ficiency is achieved because of the

lower engine speed.

For ships with bow thrusters and a

CP-propeller, the switchboard is often

arranged in such a way that the shaft

generator supplies the electric power

to the thrusters, and the gensets take

care of the hotel load.

11.000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,00090 95

P/D=1.0

0.9

Design

Lower ME powerfor same ship speed

MCR

0.8

0.7

0.6

0.50.4

100 105 110Propeller Speed [rpm]

Propulsion Power [kW] Ship Speed

2. 1.

115 120 125 130

16.0

15.5

15.0

14.5

14.0

13.5

13.0

12.5

12.0

11.0

10.0

12.000

9.0

Fig. 3: CP-propeller efficiency map and a PTO/GCR two-step gear dual electric power range solution utilised for low ship speed


The investment in a GCR shaft genera-

tor type is much smaller than the more

sophisticated PTO/RCF or other PTO/

CFE systems which are ready for paral-

lel running with gensets.

The total efficiency of a PTO/GCR unit

is around 92%, corresponding to a 2

and 6% loss from gear and alternator.

The shaft generator layout operation

range should be based on the expect-

ed ship operation profile, in order to

ensure the longest possible operation

time for the shaft generator.

Layout for operating with a fixed pitch pro-

peller

Due to the nature of the fixed pitch

propeller, the speed of the propeller

and engine, vary with the required ship

speed and the resistance acting on the

ship. Consequently, the electric power

generated from a PTO/GCR system

would have a variable frequency.

Most electrical equipment can operate

with a frequency at between 50 and 60

Hz without problems. This means that

the PTO/GCR system can be utilised in

the 52% to 90% engine power range,

corresponding to an engine speed

range of 80% and 97%. This indicates

that the PTO/GCR shaft generator type

can be used to supply electric power

for that equipment most of the time,

see also page 13.

When utilising the cheap PTO/GCR sy-

atem in combination with a fixed pitch

propeller speed, the limited part of

sensitive electrical equipment that re-

quires fixed frequency then have to be

powered by smaller adapted frequency

converters close to the few critical con-

sumers that rely on constant frequency.

Summary

Several manufacturers are able to sup-

ply different kinds of PTO/GCR systems.

Fig. 4: Small adapted rotating frequency converter


PTO/RCF (power take off/RENK con-stant frequency)

The PTO/RCF system produces elec-

tricity with a constant electrical fre-

quency over a wide propeller speed

range, and the shaft generator type can

be utilised in combination with a fixed

pitch propeller and continuous opera-

tion in parallel with gensets.

The PTO/RCF incorporates the RCF

speed controlled planetary gearbox

ensuring a constant speed for the al-

ternator within a certain propeller speed

range. This mechanical-hydraulic RCF

gear unit has been developed by RENK

and is only available from this supplier.

Based on the detected output speed

from the crankshaft gear, the RCF gear

transmission can serve a constant

speed to the alternator over an engine

speed range of 35%. It consists of an

epicyclic gear with a hydrostatic super-

position drive.

The hydrostatic motor is controlled by

an electronic control unit and is driven

by the built-on hydrostatic pump.

The hydrostatic system drives the an-

nulus of the epicyclic gear in either

direction of rotation and continuously

varies the gear ratio according to the

engine speed.

In the standard PTO/RCF layout, the

output speed range of the gearbox is

set between 70% to 105% of the en-

gine’s specified MCR speed, but this

could be selected otherwise.

The speed range from 70% to 105%

equals an engine power of between

34% to 105%, see page 13.

PTO/RCF–BW IIIRENK

42-98MC

To panel

Hydrostaticcontrol

Hydrostaticmotor

Toothed coupling

Alternator

Operator control panel(in switchboard)

Hydrostatic pump

Multi-disc clutch

Toothed coupling

ControllerTerminal

Elastic damping coupling

Toothed coupling

Fig. 6: The engine side front end mounted installation BW III RENK PTO/RCF solution


with fixed pitch propellers and continu-

ous operation in parallel with gensets.

The most commonly used PTO/CFE is

as a slow-running alternator type oper-

ating at the same speed as the propel-

ler shaft. Alternative and faster step-up

gear systems with a low-cost synchro-

nous alternator are possible, but only a

limited number of step-up-gear-based

PTO/CFE systems have been intro-

duced. The PTO BW III/GCR-CFE step-

up solution from RENK is shown on

page 19.

The PTO/CFE slow-running alternator

is available as an engine-mounted front

end DMG/CFE solution, or installed as

a tank-top-mounted aft end SMG/CFE

solution with the rotor integrated on the

intermediate propeller shaft.

More poles are necessary for a low

speed operated synchronous alterna-

tor. This means that the alternator type

becomes bigger than for the step-up-

gear based alternative. The slow-running

alternator type does not need any kind

of flexible coupling, necessary for the

faster-running step-up gear shaft gen-

erator types.

Both the DMG/CFE and the SMG/

CFE are able to operate in parallel with

the gensets and serve full rated elec-

tric power output when the speed of

the main engine is between 75% and

105%, which equals an engine power

range of 40% to 105%.

The CFE system also has the capac-

ity for a reduced electric output that is

proportional to the engine speed of be-

tween 40% to 75% of the SMCR speed,

The PTO/RCF system can serve elec-

tric power to all power consumers on

the voyage.

During parallel running with gensets, the

internal electronic control box system,

included with the RCF unit, ensures that

the control signals to the main electric

switchboard are identical to those of the

gensets. This allows the PTO/RCF to

operate alone or in parallel with gensets

throughout a 35% speed range.

Internal control circuits and interlocking

functions between the epicyclic gear

and the electronic control box provide

automatic control of the functions nec-

essary for the satisfactory operation

and protection of the RCF gear. By the

extent of deviation or severity from the

permissible values, caused by incidents

or failure, a warning or alarm will be

shown on a display.

Summary

PTO/RCF is suitable for ships with a

fixed pitch propeller.

During operation, the multi-disc clutch

integrated into the RCF gearbox input

shaft permits disengaging of the epicy-

clic RCF gear and alternator from the

step-up gear driving by the main engine.

Depending on the actual engine speed

relative to the maximum speed layout of

the RCF unit, the total efficiency of the

RCF shaft generator system varies be-

tween 88% and 91%.

PTO/CFE (Power Take Off/Constant Frequency Electrical)

The PTO/CFE generates electric power

with constant electrical frequency over

a wide engine speed range. The shaft

generator can be used in combination

Fig. 7: The hydraulic speed controlled planetary gear box supplies constant speed for the alternator.


which equals an engine power range of

6.4% and 40%, see page 13.

A traditional PTO/CFE shaft generator

is installed with a thyristor converter

and synchronous condenser.

The alternator generates a three-phase

alternating current with a varying fre-

quency that corresponds to the pro-

peller speed. This is then rectified and

conducted to the thyristor converter

system in the engine room, which pro-

duces alternating current with constant

frequency. The synchronous condens-

er is necessary because the DC inter-

mediate link used by the thyrister con-

verter system has the effect that there

will be no reactive power served to the

main switchboard. A synchronous con-

denser is therefore necessary to gener-

ate the reactive power needed.

A novel marine shaft-driven genera-

tor system with two PWM-pulse width

modulated converters has been intro-

duced. With this system, one of the

PWM converters is used to convert

the varying current into the DC energy.

Afterwards, the other PWM converter

converts the DC energy into AC energy

with the fixed frequency and voltage.

Thanks to the space vector control

used with this converter system, the

generator can maintain a constant volt-

age and frequency. The PWM pulse

width modulated converter system is

able to supply effective power and re-

active power to load on ships without a

synchronous condenser and, thereby,

simplifies the installation and later on

maintenance processes.

The traditional thyrister converter run-

ning with a synchronous condenser is

illustrated by the control principle for a

DMG/CFE unit, Fig. 8.

However, the tank-top-mounted aft end

SMG/CFE solution with integrated ro-

tor on the intermediate propeller shaft

is much more frequently used than the

DMG/CFE, because it is not subjected

to any limitations from the installation on

the main engine and the limited space

between the bulkhead and PTO.

Summary

The CFE shaft generator system is suit-

able for ships with fixed pitch propeller.

The total efficiency of the slow running

CFE types varies from 89% to 91%.

Fig. 8: PTO DMG/CFE engine-mounted front end design

Mains, constant frequency

Excitationconverter

Synchronouscondenser

SmoothingreactorStatic

converterDMGDiesel engine


Fig. 9: Possible el-power output from shaft generators operating with variable propeller speed.

Fig. 10: Possible el-power output from shaft generators operating with variable main engine power.

0

50

100

0 10 20 30 40 50 60 70 80 90 100 110

Electric power [%]

Propeller speed %

CFEGCR CFE

RCF

0

50

100

0 10 20 30 40 50 60 70 80 90 100 110

Electric power [%]

ME power

CFE GCR

RCF

CFE

Characteristics of electric power from shaft generators

The range of electric power available

from a shaft generator system depends

on the shaft generator type selected.

To illustrate the variation, the electric

power diagrams are shown for the CFE,

RCF and GCR principles. The diagrams

are shown for basic layouts, but it is im-

portant to note that other shaft genera-

tor layout ranges based on a particular

engine load profile could be selected to

ensure that the electric power from the

shaft generator is available for most pre-

ferred main engine load conditions.

Normally, the most inexpensive GCR

solution is operated with the controlla-

ble pitch propeller running at constant

speed. This means that electric power

is available throughout the main engine‘s

power range.

If the variable frequency is acceptable

for the ship, the GCR gear system

could be matched according to a suit-

able speed range for the fixed pitch

propeller layout, See page 9.

The RENK RCF solution offers constant

frequency at parallel running with gen-

sets and have a full electric power ca-

pacity available within a wide range of

engine power and propeller speed.

The CFE constant frequency applica-

tion is offered by several suppliers and

and can be selected for constant fre-

quency, parallel running with gensets

and for generating electric power for an

even wider engine power and propeller

speed range.

The PTO/GCR solution can be select-

ed for electric power generated within

a 50-60 cycles range obtained at be-

tween 81-96% propeller speed range,

see Fig. 9.

The PTO/GCR solution can be select-

ed for electric power generated within

a 50-60 cycles range obtained at be-

tween 52-90% ME power range, see

Fig. 10.


Engine power and speed ranges available in PTO operation mode

PTO layout PTO used with Propeller speed ME power Max. electric power output Frequency

% % % Cycles

CFE 40 6.4 50 60

CFE 75 42.2 100 60

CFE 105 105 100 60

RCF 70 34.3 100 60

RCF 105 105 100 60

GCR Variable frequency 80.6 52.1 100 50

GCR Variable frequency 96.5 90 100 60

Fig. 11: Electric power output from shaft generator based on PTO layouts given by Fig. 9 and Fig. 10.


Encoder system used with electron-

ically controlled engines

The electronically controlled low speed

engine system relies on the robust en-

gine encoder system developed by

MAN Diesel & Turbo. For most applica-

tions, this encoder system is mounted

on the foremost shielding system con-

nected to the front end of the crankshaft

flange, where it continuously sends the

exact position of the crankshaft to the

ME control system.

Shop testing of electronically con-

trolled engines prepared for a front-end

mounted PTO normally takes place with

the standard encoder system mounted

on the front-end shielding system with-

out the PTO unit installed.

Afterwards, when the engine has fin-

ished the shop test running, the stand-

ard engine encoder system is reused

and mounted on the foremost PTO

shielding. Therefore, the PTO maker

must study the encoder system in ad-

vance and prepare a suitable and sta-

ble interfacing for the encoder housing

and pickup, ready for installation at the

shipyard at PTO assembly.

Engine mounted front-end installation (BW I)

The BW I system, available for GCR

and RCF shaft generators from RENK,

comprises a bevel gear and a step-up

gear bolted directly to the front-end en-

gine structure. The bevel gear allows

the alternator a vertical position on

top of the gear unit. This compact de-

sign gear system is only available from

RENK and is delivered with a combined

flexible toothed coupling.

Fig. 13: BW I S70/RCF 850-60 (RENK)

Physical shaft generator types and mounting configuration


Flexible toothed coupling and

lubrication

The flexible coupling used with RENK

shaft generators, supplied by Geisling-

er, is bolted in place between the crank-

shaft free end and the step-up gear. In

this way, transmission of torsion and

longitudinal excitations from the crank-

shaft to the step-up gear are avoided.

The integrated flexible elements con-

sist of packages of steel springs. The

damping of torsional excitations is

achieved with steel springs squeez-

ing oil from one chamber to the other,

when they are deflecting during opera-

tion. Together with the damping func-

tion, the oil provides the necessary

lubrication and cooling to the coupling

bolted to the crankshaft free end.

The toothed coupling allows a simple

separation of the step-up gear and

crankshaft if special events occur and

require full access to the limited space

behind the PTO gear unit.

If the torsion characteristics of the shaft

system require additional inertia mass

fitted to the crankshaft flange free end,

it is possible to mount a tuning wheel

or a torsional vibrations damper in the

space between the shaft generator

gear box housing and engine structure.

The bearings installed in the BW I gear-

box structure support the mass of the

gear wheels, the Geislinger coupling,

and any additional mass bolted to the

crankshaft flange in order to adjust the

torsional vibration damper according

to the final vibration analysis.

If a Geislinger damper needs to be

mounted on the engine crankshaft

flange, both the damper and flexible

toothed coupling will be lubricated and

cooled by the main engine lubricating

system through the hollow step-up

gear shaft.

The engine-mounted step-up gear re-

lies on the main engine lubricating oil

system, and with a lubricating oil load

level of 8, according to the standardised

FZG Gear Test (DIN 51354), the capac-

ity of the main engine’s lubricating oil

system must be increased accordingly.

The hydrostatic drive controlling the

RCF gear provides a constant shaft

speed input to the alternator and re-

quire a 5µm filtration of the oil of its own.

Normally integrated between the step-

up gearbox and alternator, the multi-

disc clutch is used for engaging or dis-

engaging of components during main

engine operation.

On an RCF gear unit, the multi-disc

clutch is mounted before the RCF gear

input shaft and will be lubricated by a

step-up gear driven pump.

The electrically driven PTO-integrated

lubricating oil stand-by pump supple-

ments the step-up gear driven pump

during engine start and if the gear driv-

en pump malfunctions.

PTO preparations (BW I)

Approved interface and connection for

ME engine encoder system.

Engine preparations (BW I)

� Weld on blocks machined for align-

ment of the gear unit

� Monitoring system for axial excitations

� Flange for lubricating oil

� Return flange welded on to bedplate

� To ensure a stiff connection between

the main engine parts and the PTO,

adapted machined steel washers are

placed between the PTO crankshaft

gearbox and the A-frame so as to

compensate for the approx. 3 mm

difference in length between the en-

gine structure parts.

Engine room preparations (BW I)

� External wiring of the control system

� Cooling water supply for built-on oil

cooler

� Wiring between alternator, switch-

board and to the control system

� Electric power supply for built-on

electric lubricating oil stand-by pump.

For the PTO BW I/RCF type it is recom-

mended that the shipyard install an ex-

ternal lubricating oil filling system with a

dosage tank having a specified volume

for one RCF gearbox oil change.

Tank top mounted front end PTO in-stallation (BW II)

The BW II works as a freestanding gen-

erator solution in front of the engine.

A rubber-type flexible damping cou-

pling needs to be installed between

the engine and PTO step-up gearbox

outside the engine. The engine drives

the shaft generator via an intermediate

shaft, bolted to the engine crankshaft

flange and passes through the engine

front-end cover made in two halves

with an oil sealing arrangement.


The installation length of the PTO BW II

in front of the engine normally exceeds

the built-in length compared with other

types of PTO arrangements. But, de-

pending on the space available, there

are some possibilities for limiting the

length. Fig. 15 shows a concept where

the alternator is placed horizontally

between the step-up gearbox and the

front end of the engine, thus utilising

the space anyway taken up by the flex-

ible coupling.

A small support bearing is often in-

stalled between the front end of the en-

gine and the flexible coupling. Whether

such a support bearing is required

can be determined from MAN Diesel &

Turbo specification of the permissible

shear force and bending moment on

the front end of the crankshaft.

The PTO BW II has its own lubricating

oil system, and an integrated electrical-

ly driven lubricating oil stand-by pump

supplements the gear driven pump

during engine start-up and in the event

of malfunctioning of the gear driven

pump.

The bevel gear solution in the step-up

gearbox enables a vertical installation

of the alternator, Fig. 16.

Various gearbox manufacturers are

able to supply the PTO BW II/GCR sys-

tems, but only RENK is able to supply

the PTO BW II/RCF system with possi-

bility for constant frequency operation.

Fig. 14: Tank top mounted front end PTO BW II installation in front of the engine.

Fig. 15: PTO BW II with alternator mounted between gearbox and engine structure

Fig. 16: PTO BW II installation with alternator mounted vertically above gearbox

AlternatorTorsionallyrigid coupling

Step-upgear

Main engineside

Supportbearing

Flexible coupling

Flexiblecoupling

Alternator

Step-upgear


Engine preparations (BW II)

� Replacement for the standard ME

engine encoder system on the en-

gine’s aft end turning wheel

� Intermediate shaft between the en-

gine and the flexible coupling

� Engine front-end cover with oil seal-

ing arrangement

� Axial excitations monitoring system.

Engine room preparations (BW II)

� Tank-top seating for bearings and

gearbox

� Cooling water supply for the built-on

oil cooler

� Electric power supply to the built-on

lubricating oil stand-by pump


board and control system

� For the PTO BW II/RCF solution,

the shipyard is recommended to in-

stall an external lubricating oil filling

system with a dosage tank having a

specified volume for one RCF gear-

box oil change.

RENK installation (BW III) mounted on engine side

The PTO BW III/GCR/RCF step-up gear

system is directly bolted to the front-

end engine structure, and the frame

supporting the alternator is placed hori-

zontally alongside on engine supported

brackets.

For the PTO BW III/RCF solution, the

RCF gear unit supplying constant

speed for the alternator is mounted on

the frame before the alternator, see Fig.

18.

The RENK gearbox is available for 40

bore engines and larger for standard

sizes of alternators at 700, 1200, 1800

and 2600 kW, but others are available

on request.

The flexible toothed coupling used by

the BW I and BW III RENK solutions,

supplied by Geislinger, is included in

the delivery from RENK.

The investment cost of the PTO BW

III system is typical higher than for the

other gear-based shaft generators. It

is bolted to the engine structure, and

there is no need for additional founda-

tion in the engine room. It is therefore

considered to be a compact and easy-

to-install PTO solution. The RCF gear-

box unit supplies the right input speed

to the alternator and a space requiring

frequency converter system in the en-

gine room is not necessary.

Fig. 17: RENK PTO BW III/GCR design

Fig. 18: RENK PTO BW III/RCF design

Alternator

Bedframe

Toothed coupling Multi-disc clutch

CombinedGeislingerand toothedcouplin

Crankshaftgear

Brackets

Operatorcontrolpanel

Alternator

Controller

Bedframe

RCF unitincl. multidisc clutch

Toothed coupling

Brackets

CombinedGeislingerand toothedcoupling

Crankshaft gear


Static frequency converter system

Synchronouscondenser Distribution cubicle

Converter cubicle

Excitation cubicle

Control cubicle

Toswitchboard

Alternator

Bedframe

Toothed coupling Multi-disc clutch

Combined Geislingerand toothed couplin

Crankshaft gear

Brackets

Flexible toothed coupling

See page 16.

PTO preparations (BW III)

� Interface between engine and crank-

shaft gear is coordinated between

MAN Diesel & Turbo and RENK

� Approved interface and connection

for ME engine encoder system.

Engine preparations (BW III)

� Welded-on blocks machined for

alignment of the step-up gear unit

� Oil tightness by fitting a rubber gas-

ket in the gap around the washers

� Axial excitations monitoring system

� Free flange end for lube oil inlet pipe

� Oil return flange welded to lower

main engine oil pan structure

� Bolted brackets welded to the main

engine lower structure part on the

exhaust side to support the alterna-

tor and RCF gear

� To maintain a stiff connection be-

tween the main engine parts and the

PTO, adapted steel washers are fitted

between the PTO crankshaft gearbox

and the A-frame to compensate for

the approx. 3 mm long difference be-

tween the engine structure parts.

Engine room preparations (BW III)

� Power supply for the lubricating oil

stand-by pump.


board and to the control system.

� Cooling water for the lubricating oil

cooler built on the RCF gear.

� For the BW II/RCF solution, it is rec-

ommended that the shipyard install

an external lubricating oil filling sys-

tem with a dosage tank having a

specified volume for one RCF gear-

box oil change.

Aft-end installation (BW IV/GCR) mounted on tank top

The PTO BW IV is placed on the aft side

of the engine as a freestanding PTO so-

lution. It has a tunnel gear with a hollow

shaft large enough to allow the interme-

diate shaft flange to pass through dur-

ing assembly.

Fig. 19: RENK PTO BW III/GCR-CFE step-up gear design

Fig. 20: PTO BW IV/GCR with tunnel gear and intermediate propeller shaft


Fig. 21: PTO BW IV/GCR with tunnel gear and hollow segmented flexible damping coupling fitted to the propeller shaft

Fig. 22: PTO BW IV/GCR tunnel gear and alterna-tor

Fig. 23: PTO BW IV tunnel gearbox from RENK

Vulkan Ratoflexible coupling

AlternatorToothedcoupling

Tunnelgear


A number of gearbox manufacturers

can supply PTO BW IV/GCR solutions

that do not increase the total built-in

length of the propeller shaft and the en-

gine, and the shaft generator can be in-

stalled within the space already available

around the shaft line aft of the engine.

A flexible damping coupling based on

rubber elements is fitted around the in-

termediate shaft. The steel flanges used

for the coupling are made in halves to

allow assembly around the intermediate

propeller shaft. The flexible coupling is

connected between the hollow tunnel

gear shaft flange and the propeller shaft

flange on the engine. Alternatively, it

can be connected to a forged-on flange

anywhere on the intermediate propeller

shaft, which means that the PTO can be

moved further away from the engine.

When operating the PTO, the flexible

coupling only transfers a torque cor-

responding to the power of the shaft

generator.

The PTO BW IV has its own separate

gear-driven lubricating oil system and

an electrically driven built-on lubricat-

ing oil standby pump used to supple-

ment the gear-driven pump during main

engine start-up and in the event of any

malfunctioning of the mechanical gear-

driven pump.

Engine preparations (BW IV)

� No engine preparations for the instal-

lation of the PTO BW IV system are

needed

Engine room preparations (BW IV)

� Tank top foundation for gearbox and

alternator

� Cooling water supply to lubricating

oil cooler

� Electric power supply to lubricating

oil stand-by pump.


board and to control system.

The intermediate shaft flange must be

provided with additional screw holes

for the flexible coupling or an additional

forged on flange must be made for al-

ternative PTO positioning further away

from the engine.

Aft-end installation (SMG/CFE) mounted on propeller shaft

The PTO SMG/CFE has the same work-

ing principle as the PTO DMG/CFE.

The SMG/CFE alternator rotor is inte-

grated on the intermediate propeller

shaft away from the engine structure

and does not require a gearbox or flex-

ible coupling.

The intermediate propeller shaft is part

of the generator and is mounted by the

alternator maker. The stator housing is

mounted on a separate foundation pre-

pared by the shipyard, see Fig. 24.

The simplicity and low maintenance

costs of the shaftline alternator between

the low speed main engine and the pro-

peller has made it a popular choice. It is

mounted with a large air gap between

the stator and rotor without additional

bearings. The propeller shaft mounted

PTO/PTI SMG/CFE is more frequently

used than the DMG/CFE solution and,

moreover, it is offered at a somewhat

lower price. It is considered to be a

straightforward design with no physical

interface with the main engine itself.

Fig. 24: PTO SMG/CFE 1300-60 installation


Engine room preparations

(SMG/CFE)

� Tank top foundation for the alternator

stator housing

� Cooling water supply for water

cooled alternators

� Wiring between alternator, frequency

converter system, switch board and

control system

� For the traditional thyrister converter

solution additional seating for syn-

chronous condenser unit and static

converter cubicles are necessary,

but those can be avoided by the

shaft generator type using the PWM

converter technology.

Front-end PTO installation mounted on engine (DMG/CFE)

The PTO DMG/CFE is a large slow run-

ning alternator with its rotor mounted

directly on the crankshaft, and the sta-

tor housing is bolted to the front-end

engine structure, see Fig. 25.

The DMG/CFE does not require a gear-

box or flexible coupling, and the alter-

Fig. 25: PTO DMG/CFE

Static frequency converter system

Synchronouscondenser

Distribution cubicle

Converter cubicle

Excitation cubicle

Control cubicle

Toswitchboard

Oil seal cover

Rotor

Stator housing

Cooler

Supportbearing

nator is separated from the crankcase

by a plate and a labyrinth seal made by

the PTO supplier.

Depending on the torsion characteristics

and a vibration analysis, additional iner-

tia mass in the form of a tuning wheel

can be added, see Fig. 26.

If shear force and bending moment act-

ing on the fore-end flange of the crank-

shaft exceed the limits, the stator hous-

ing must be prepared with a front-end

support bearing to reduce the load on

the crankshaft.


� In order to secure the oil tightness a

rubber gasket is placed between the

gearbox and the A-frame.

� Monitor system for axial excitations.

Engine room preparations (DMG/

CFE)

� Foundation for the synchronous con-

denser unit and static converter cu-

bicles.

� Cooling water supply water cooled

alternator.

� Wiring between alternator, frequency

converter, switchboard and to con-

trol system.

Aircooler

Stator housingStuffing box

Crankshaft

Aircooler

Stator housingStuffing box

Crankshaft

Supportbearing

Polewheel

Mainbearing no. 1

Tuning wheelMainbearing no. 1

Standard engine, with directmounted generator (DMG/CFE)

Standard engine, with directmounted generator and tuning wheel

Pole wheel

Fig 26: PTO DMG/CFE structure can be made to accommodate a tuning wheel

In order to reduce weight carried by the

main engine structure further founda-

tions in ship may be necessary in order

to support some large DMG applica-

tion.

The electrical frequency generated de-

pends on the speed of the main engine

and the number of poles used for the

alternator. More poles increase the fre-

quency and diameter of alternator. The

alternator diameter is however con-

strained by ship hull geometry, which

means that alternator is not able to

produce a frequency of 50Hz or 60Hz

without the use a frequency converter

system between the alternator and the

main switchboard.

PTO preparations (DMG/CFE)

� Interface with engine and crankshaft

gear is coordinated between engine

maker and the licensee producing

the engine.

Engine preparations (DMG/CFE)

� ME operation encoder system can

be fitted to aft-end tuning wheel.

� Engine structure built-in stiffness and

strength for bolt connections.

� Weld on blocks machined for align-

ment of the gear unit.

� In order to maintain a stiff connec-

tion between main engine parts and

PTO, adapted machined steel wash-

ers are placed between the PTO

crankshaft gearbox and the A-frame

to compensate for the approx. 3 mm

difference in length between the en-

gine structure parts.


This chapter explains how a shaft gen-

erator system influences a fixed pitch

or a controllable pitch propeller engine

layout and provides guidelines to select

power and speed for an engine driving

a shaft generator.

Beyond the physical preparations con-

nected to the installation of a shaft gen-

erator, the engine power and speed

SMCR layout needs to be carefully

considered. Lack of power and propel-

ler speed will increase the heavy run-

ning condition for the engine and result

in increased thermal load and fuel con-

sumption. The heavy running condition

occurs when the engine is operated

without sufficient margins for engine

power and propeller speed. Without

that, the engine will be operated to the

left of the engine layout curve 2. This

means that there is less surplus power

and propeller speed available for ship

speed acceleration and 100% engine

power will not ba available, and 100%

engine power will not be available.

Operation of the engine to the left of

curve 2 can be minimised by an ap-

propriate investigation of the neces-

sary power and speed margins for bad

weather, fouling of hull and propeller

and, possibly, also utilisation of a shaft

generator application. The SMCR en-

gine layout point MP, is found on the

engine layout curve 2, Fig. 27.

Propulsion and engine running

points

In the design phase of a new ship, the

actual ship design speed that has to be

achieved is based on theoretical calcu-

lations for a loaded ship and the actual

combination of necessary engine pow-

er and propeller speed. Afterwards, it is

Fig. 27: Running points and engine layout for fixed pitch propeller

2 6LR (7%)

Engine speed

Power

MP

Sea margin(15% of PD)

SP

HR

PD´

PD

Engine margin(10% of MP)

Heavy propeller curve – fouled hull and heavy weather2 Light propeller curve – clean hull and calm weather6

MP: Specified propulsion MCR pointSP: Service propulsion pointPD: Propeller design point

LR: Light runningHR: Heavy running

PD´: Alternative propeller design point

Point M of load diagram

Line 1: Propeller curve through SMCR point (M=MP)

Line 7: Constant power line through SMCR point (M)

Engine speed

Power

M: Specified MCR of engineS: Continuous service rating of engine

M=MP

Propulsion andengine service curvefor heavy running

7

S=SP

2

16

Fig. 28: Engine layout diagram

Power and speed layout of engine


agram can be drawn, see Fig. 29. This

allows the actual load limitation lines of

validated by experimental tank tests for

the optimum operating conditions for

a new ship. The combination of power

and propeller speed obtained from this

analysis is called the ship’s propeller

design point PD, and it is found on the

dashed light running propeller curve 6

in Fig. 28.

Layout for engine driving a fixed pitch propeller

For a fixed pitch propeller layout, the

propeller speed depends on the resist-

ance from wind, waves and fouling of

hull and propeller.

When the ship has been sailing for some

time, the hull and propeller will become

fouled and the resistance acting on the

ship when sailing will be increased.

For a new ship without a fouled hull

and propeller trading at 15% sea mar-

gin, which means a little headwind and

small waves, about 15% more power

is necessary to achieve the same ship

speed compared to a situation of no

wind and no waves. In such circum-

stances the heavy running propeller

equilibrium pretty much follow the light

running curve, about 0.5% to the left of

the dashed light running propeller lay-

out curve.

However, for a very bad weather and

fouled hull condition, the propeller equi-

librium will be formed even more to the

left, and for that condition the engine

power and propeller speed layout has

to be prepared. To meet that require-

ment, it is normal practice to use an

extra engine power margin of 15%. To

ensure that a sufficient propeller speed

margin is available. Our recommen-

Fig. 29: Engine load diagram

4

7

5

2 61


Engine speed

M

Propulsion and engine servicecurve for heavy running

3.3% M

Power

S

3’

5% M

5% L1

4

3

75

2

61

dation for the propeller speed margin

(LRM) is between 4 to 10%.

Once the SMCR point MP has been

found in the layout diagram, the load di-

Fig. 30: Engine layout diagram for engine driving a shaft generator (normal case)

Shaf

t gen

erat

or

Propulsion curvefor heavy running

7

Engine service curvefor heavy running

MP

SGS

SG

SP

Engine speed

Power M


Point M of load diagram

Line 1: Propeller curve through SMCR point (M=MP+SG)

Line 7: Constant power line through SMCR point (M)

1 2 6


the diesel engine to be found from the

engine load diagram.

Layout for engine prepared for driv-ing a fixed pitch propeller and shaft generator

For engines driving a shaft generator,

additional power and speed margins

must be considered to ensure opera-

tion hours for PTO during ship accel-

eration, bad weather and fouled hull

conditions. In many cases, the engine’s

SMCR power is found by a simple addi-

tion of the maximum power consumed

by the shaft generator to the propul-

sion point MP, Fig. 30. Accordingly, the

specified maximum continuous rating

point can be found by the calculation:

M=MP+SG, where SG shows the me-

chanical power needed for operating

the shaft generator including the ef-

ficiency loss through the shafting and

gearbox.

If the ship is trading at a low-load ship

operating profile, a further light running

propeller speed margin should be con-

sidered, as the shaft generator opera-

tion curve, through M, at low-load op-

eration is relatively closer to the torque/

speed limit curve 4, Fig. 31., and there-

fore has less propeller speed available

for a heavy running condition caused

by bad weather or fouled hull.

With the SMCR point established at

M, the combined ship propulsion shaft

generator layout and the load diagram

can be drawn, Fig. 31.

The extra power margin for a shaft

generator will ensure surplus power for

ship acceleration in bad weather condi-

tions, while keeping a suitable propeller

Fig. 31: Engine load diagram for engine driving a shaft generator (normal case)

Fig. 32: layout and Load diagram with the ship acceleration curve

L4

Shaf

t gen

erat

or


3.3% M

S

SG

5% M

5% L1

L1

L2

L3

M


MP

SP

Engine speed

Power


7

7

5

5

4

4

1

1

2

2

6

3 3’

6

L4

Shaft

gen

erat

or

Heavy runningpropulsion curve

Ship acceleration curve

S

SG

L1

L2

L3

M

MP

SP

75

4 1 2

3 3’

6

Heavy running(PTO) service curve


curve distance to the torque/speed limit

curve 4, Fig. 32.

Special layout for engine with fixed pitch propeller and shaft generator

An engine layout for a shaft generator

operated at maximum engine power

may put the intended SMCR point M’

of the engine outside the top of the

blue layout diagram. Consequently,

one more cylinder is necessary to meet

the power demand. Selecting an extra

cylinder for the engine implicates extra

costs and additional space require-

ments in the engine room. However,

selecting one cylinder more for the ME

can be avoided by restricting the load

on the shaft generator when the engine

is operated at close to the SMCR point.

By doing so, the propulsion point MP

can still be reached on the propulsion

curve 2, if a genset covers the partial

electric power gap between line 1 and

the horizontal line 7.

However, such a situation only occurs

rarely, as ships rather infrequently op-

erate in the upper propulsion power

range.

Point M is the highest possible engine

power available and it is found at the

Fig. 33: Special engine layout, with PTO (special case)

Fig. 34: Reduced power from the shaft generator close to specified propulsion point (special case)

Shaf

t gen

erat

or

Propulsion curve for heavy running

SG

S

1

7

2


MP

SP

MM´

Engine speed

Power

M´: Intended specified MCR of engineS: Continuous service rating of engineM: Recommended SMCR point of load diagram

Point M of load diagramLine 1: Propeller curve through service point S

M: Intersection between line 1 and line L1- L3Point

6

M´: Intended specified MCR of engineS: Continuous service rating of engineM: Recommended SMCR point of engine

Shaf

t gen

erat

or


3.3% M

SG

S

5% M

5% L1


MP

SP

MM´

Engine speed

Power

3’

6

6

2

2

3

7

7

5

5

1

1

4

4


intersection between line L1-L3 and SG

operation curve 1.

Engine layout with controllable pitch propeller and shaft generator

The hatched area shows a speed range

between 96.9 and 100% of the speci-

fied MCR speed for an engine driving a

shaft generator.

The service power point S can be lo-

cated at any point within the hatched

propeller speed range. Electric power

generated from the shaft generator is

available within the hatched area.

Although the speed margin is not rele-

vant for a CP propeller, as the pitch can

be adjusted to meet the requested pro-

peller speed, it is still relevant to inves-

tigate the power margin for PTO. This

applies if the ship speed must be main-

tained during heavy weather and fouled

hull conditions while retaining the ability

to operate the shaft generator.

Layout for engine driving a fixed pitch propeller and shaft generator/motor

In some projects for larger container

ships with a waste heat recovery sys-

tem installed in combination with a shaft

generator and a shaft motor (PTO/PTI),

it is ensured that any surplus electric

power generated from the waste heat

recovery can be utilised for shaft pro-

pulsion by the shaft motor.

Depending on the PTO and PTI power

available, the advice on an engine lay-

out with a combined PTO alone or PTI

alone solution can be followed.

In this example, a large shaft motor

has been installed. The contractual

ship speed is met at the service point

Fig. 35: Example with controllable pitch propeller running with a combinatory curve.

Min.speed

M

3.3%M

5

4

1

75%M

5%L1

Recommended rangefor shaft generatoroperation withconstant speed

3

5

1

7

Combinator curvefor loaded shipand incl. sea margin

Max.speed


Engine speed

Power

4

S

Fig. 36: Engine layout diagram for engine operating with a shaft motor (PTI)

Point M of load diagram:Point PD: Propeller design pointLR’: Normal light running (3-7%) of propellerPoint X: SMCR power on line 2’Point M: Same power as X but with X = 2.2% lower rpm

1

6’

6

2’

7

2

L4

SP

PD

LR’S

X

X = 2.2%

PTI

Engine margin(10% of M)

Sea margin(15% of PD)

PTI

PTI

M

L1

L3

L2

Engine speed

Power

Real propeller curve for heavy running

Real propeller curve for light running

Engine service curve for heavy running

Engine service curve for light running


SP=S+PTI and is based on the main en-

gine propulsion power S and the power

contribution from the PTI shaft motor.

In Fig. 36, for the purpose of illustration,

the propeller design point PD meets the

ship speed in calm weather and clean

hull condition. The resulting MCR point

X is valid for shaft motor operation and

is based on the normal light running

factor LR’ sea and engine margin.

When it comes to the engine layout,

and operating the shaft generator

(PTO) at engine part load (low load), it is

recommended to choose the specified

MCR engine speed M about X=2.2% to

the right of the point X, thereby forming

the engine layout curve 1 to which the

engine should be selected.

From curve 1, the real propeller light run-

ning factor LR can be found by using the

calculation LR=LR’– X, and the load dia-

gram of the main engine can be drawn

around the MCR point M.

Engines running with a PTI may some-

times need the possibility to operate

with increased light running outside the

standard load diagram. In such cases,

provided the torsion vibration conditions

permit, a speed derated engine offers

the possibility for extended speed limit. Fig. 37: Engine load diagram for engine operating with a shaft motor (PTI) and the light-running extended speed limit possibility shown by the hatched area.

Engine speed

Power

Line 1 : Propeller curve through M – layout curve for engineLine 2’ : Real propeller curve for heavy runningLine 2 : Heavy running curve for engine with PTI in operationLine 3 : Normal speed limit curveLine 3’ : Extended speed limit curve (provided torsional vibrations permit)Line 6’ : Real propeller curve for light running – layout curve for propellerLine 6 : Light running curve for engine with PTI in operationLR’ : Normal light running 3-7% of propellerLR = LR’ -X : Real light running of propeller (compared to curve 1)

M : Specified MCR of main engineS : Continuous service rating of main engineSP : Service propulsion power = engine service power S + PTI

L4

Power

Tak

e In

SP

LR’LR

2.2% MX=

3.3 M% 5% M

S

X

PTI PTI

M

L1

L3

L2

1

4

6’

6

3 3’

2’

75

5% L1

2

Real propeller curve for heavy running

Real propeller curve for light running

Engine service curve for heavy running

Engine service curve for light running


When dimensioning the layout of the

propeller and shafting system, the con-

tribution from extra PTI power for pro-

pulsion must also be taken into account.

Engines with small PTO applications

The gear-based PTO BW I, BW II, BW III

and BW IV systems all incorporate a flex-

ible coupling for protection of the gears

against hammering caused by torsional

excitations from the engine.

When the shaft generator power out-

put is less than 10% of the main engine

power, the vibration modes of the shaft

generator system will not influence the

vibration modes of the propulsion shaft

system. The choice and design of a pro-

pulsion shaft system can therefore be

made without making considerations to

a possible shaft generator later on.

The PTO/GCR gear constant ratio is

normally designed to operate at 100%

SMCR speed, and it is therefore tuned

so that the critical speed of significant

torsional vibration (t/v) orders is placed

outside the 80-120% range of propeller

speed.

The flexible coupling for the PTO/GCR

types is selected on the basis of the mis-

firing conditions and normal service con-

ditions. The normal service conditions

are therefore harmless to both the flex-

ible coupling and the gear. Irrespective of

the number of engine cylinders, a mis-

firing incident will increase the 1st order

excitation close to the natural frequency

substantially, which explains why it is es-

sential to tune the natural frequency of

the 1-node vibration mode in accord-

ance with the engine speed.

The position of the natural frequency for

the 1-node vibration mode in the shaft

generator branch mainly depends on the

torsional flexibility of the flexible coupling

and the inertia of the alternator. As a rule

of thumb, the lowest natural frequency

of the shaft generator branch should not

be less than 120%, or more than 80%,

of the frequency corresponding to the

SMCR engine speed. This means that

either under- or overcritical vibration

conditions for 1st order excitation can

be obtained with a satisfactory safety

margin.

For an incorporated alternator clutch,

the design criteria and operation of

clutch normal takes place according to

following:

� Alternator engaged: overcritical run-

ning (1st order critical speed at 55-

80% x SMCR speed)

� Alternator disengaged: undercritical

running (1st order critical speed above

120% x SMCR speed, higher orders

to be considered).

For the PTO/RCF (RENK constant fre-

quency), which normally operates at be-

tween 70% and 105% of SMCR engine

speed, the flexible coupling design leads

to a natural frequency of between 50-

60% of the frequency at SMCR speed.

Operation during misfiring is often pro-

hibited, so if the natural frequency in-

crease, due to a more rigid coupling

(breakage) or in the event of a misfiring

event, the alternator must be declutched

by the incorporated RCF gear clutch.

When the alternator is declutched, the

magnitude of the alternator’s inertia it-

self must allow the natural frequency of

the shaft generator branch, which re-

mains coupled to the engine, to ‘jump’

to a sensibly higher frequency than the

corresponding frequency at 105% MCR

speed. In this respect, it may be neces-

sary to tune the inertia of the alternator

by fitting an additional mass (a tuning

wheel) to the alternator side of the clutch.

The DMG/CFE and the SMG/CFE do not

incorporate a gear or a flexible coupling,

but the inertia of the rotor may naturally

influence the torsional layout of the shaft-

ing.

Engines with large PTO applications

Such types of ships like shuttle tankers,

which have a high demand for electric

power, may use one or two large BW IV

shaft generators for the electricity pro-

duction. They are normally operated with

a controllable pitch propeller and some-

times also a propeller shaft clutch.

For such an installation, the torsional

vibrations analysis is very complex and

require a careful investigation of all pos-

sible operating modes during the design

stage.

In general, the flexible coupling between

the propeller shaft and the PTO should

be sufficient to ensure a natural fre-

quency in the shaft generator system at

below 75% of the corresponding engine

frequency when the generator is oper-

ated. If it is not, it could alternatively be

designed to have a natural frequency of

150%, corresponding to the frequency

of a main engine when a generator is op-

erated. This setup will provide main criti-

cal resonances (4th, 5th and 6th order)

in the shaft generator system at very low

speeds, and in case of a misfiring when

Torsion vibration aspects


the 1st and 2nd order excitation be-

come dominant, the resonance is found

outside the shaft generator operating

speed.

Adjusting of the natural frequencies will

normally require very flexible couplings.

The speed governor is an integrated

part of the ME control system and it

does not normally require special atten-

tion.

However, for plants where the power of

the PTO/PTI exceeds 15% of the main

engine’s L1 MCR power, and the PTO/

PTI is driven trough a flexible coupling

and/or a clutch, special precautions

may be necessary to maintain the sta-

bility of the speed control.

Such plants must be evaluated by MAN

Diesel & Turbo to determine any nec-

essary extra features such as speed

measurement on the generator/mo-

tor side of the elastic coupling and/or

clutch state signals.

Design requirements for shaft genera-tor makers

When a shaft generator is applied it

must be designed to operate on the

conditions of the main engine/propul-

sion system.

� A constant speed shaft generator

must be able to accept a ±5% sta-

tionary and ±10% transient speed

variation relative to the nominal

speed. The shaft generator must be

able to operate at least 5 seconds in

the transient range without setting off

an alarm or initiating disconnection

of the shaft generator.

� A variable speed shaft generator

must accept at least the same speed

variations within and at the end

points of the defined shaft generator

operating range.

� A variable speed shaft generator re-

quiring a wide operating range below

75% MCR engine speed must use

the absolute rpm limits calculated for

75% engine speed as tolerance.

In rough weather, the speed variations

will increase and may reach a level

where shaft generator operation is not

possible and, accordingly, the electric-

ity production must be shifted to the

auxiliary engines.

Engine Governing System


PTO advantages

Operating a shaft generator will make it

possible to:

1. Limit the operating time on the four-

stroke genset engines for mainly ma-

noeuvring operations in port.

2. Generate the same amount of elec-

tric power at a lower cost.

3. Save fuel for the charter.

4. Reduce the maintenance costs by

saving operating time on the four-

stroke gensets.

5. Improve the steam production from

the main engine, thanks to the high-

er engine load and exhaust gas tem-

peratures.

Small space requirement

Both the BW III installed close to the en-

gine or the BW IV installed in the shaft

line takes slightly more further space

than is already set aside for the engine

installation.

The DMG/CFE installed on the engine

front end and the SMG/CFE installed in

the shaft line need extra space elsewhere

in the engine room for the synchronous

condenser and the control cubicles.

Low investment cost (PTO/GCR)

The investment cost depends on the

generator type and make, but normally

the PTO/GCR shaft generator is avail-

able for a relatively low price, whereas

the PTO/RCF and PTO/CFE frequency

control types are relatively expensive.

The RCF type from RENK comes with

an inexpensive installation as no further

frequency control cubicles are needed in

the engine room arrangement.

The shaft generator requires no separate

or just a simple foundation, no exhaust

gas system, and only a few connections

to the auxiliary equipment. The installa-

tion time for a shaft generator is short.

Reliability

Shaft generators are generally consid-

ered to be highly reliable.

Low time use for maintenance

Planned maintenance of a PTO during

the first years of operation only involves

regular checks of proper functioning and

regular replacement of the lubricating oil

and oil filter if the shaft generator has a

separate lubricating oil system.

Low spare parts costs

As a result of the high reliability and low

spare parts consumption for the planned

overhauls, maintenance costs are low.

Long lifetime

A low wear rate for shaft generator parts

means long lifetime.

However, bearings, mechanically-driven

oil pumps, friction clutches, etc., will

need replacement or reconditioning after

many years in operation.

Saving running hours on the gensets

When the shaft generator can cover the

full electric power consumption on the

voyage, one genset can be omitted for

installation, and the running hours on

the remaining two gensets are reduced,

and they could perhaps be replaced by

smaller and cheaper high-speed genset

installations.

Low noise

The noise level of a PTO is considerably

lower than the noise level from a genset.

PTO can improve ship EEDI figure

PTO disadvantages

Increased spare parts costs

Normally, more parts are needed for gen-

sets, unless fewer gensets are installed.

No power production in port

Electric power from a shaft generator

is not available while in port, unless a

clutch is installed between the PTO and

the propeller shaft. This can be seen on

some shuttle tankers. In that case, the

electric power used for cargo pumping

is available from the shaft generator if the

propeller is de-clutched.

Higher load on main engine

Because of the higher load on the main

engine when operating the shaft gen-

erator, the specific fuel oil consumption

and the cylinder oil consumption may in-

crease depending on the engine layout.

Reduced CPP propeller efficiency at

reduced ship speed

PTO/GCR electric power production at

low load and SMCR propeller speed im-

plicate reduced propeller efficiency.

No long-time parallel running ability

for PTO/GCR

The PTO/GCR cannot run in parallel with

the four-stroke generators, except dur-

ing load take-over (shifting the electric

power production from gensets to PTO

and vice versa).

More complex shaft arrangement

Gears and flexible couplings are not

used for two-stroke diesel engines

used only for propulsion, and the inertia

from those components may influence

the torsional layout of the shafting.

A PTI can deteriorate the EEDI figure

if used for increasing the ship speed.

Pros and cons of shaft generators


This chapter gives a comparison of

the operating costs for a typical feeder

container vessel equipped with CP pro-

peller.

The first engine room layout has three

diesel gensets and the second engine

room layout has a low-cost shaft gen-

erator PTO/GCR combined with two

diesel gensets.

A CP propeller is used for both layouts,

but in order to utilise a low-cost PTO/

GCR, the main engine is running with

a constant speed for the whole power

range.

Engine room layout with gensets

One 7S50ME-B8 main engine, SMCR

9,760 kW at 127 rpm, NCR 80%.

One propeller running at reduced pro-

peller speed and engine power (combi-

nator propeller curve).

Three 6L23/30H Mk 2 diesel gensets.

Propulsion time and load profile:

1. 15% at 90% engine power




Engine room layout with shaft

generator

One 7S50ME-B8 main engine, SMCR

11,060 kW at 127 rpm, NCR 80%.

One propeller running at constant

speed.

One PTO BW IV/GCR/1,200 shaft gen-

erator.

Two 6L23/30H Mk 2 diesel gensets.

The cost comparison is made at run-

ning points for exactly the same ship

speed, but due to the efficiency loss

implication for CP propeller running at

constant propeller speed propulsion,

powers are increased at part load op-

eration for the engine running with PTO.

Time at sea: 250 days/year

Time in port: 115 days/year

Electric load at sea: 900 kW

Electric load in port: 500 kW

Operation costs for fuel oil, lubricating

oil and maintenance have been com-

pared, and it is concluded that the:

1. annual fuel and lube oil cost savings

are 2% lower for the PTO alternative.

2. annual maintenance cost savings are

5% lower for the PTO alternative.

3. annual total operation cost savings

are 2% lower for the PTO alternative.

The extra investment cost for one shaft

generator compared with one diesel

genset corresponds to a payback time

of three years. However, the investment

cost of both the PTO and the gensets

may differ significantly depending on

the supplier origin, but the installation

cost is expected to favour the shaft

generator layout.

Other installation aspects may also af-

fect installation costs, such as one ad-

ditional cylinder for the main engine in

order to ensure surplus power for the

PTO operation and ship acceleration,

together with appropriate engine derat-

ing for improved engine efficiency How-

ever, any extra costs for one more main

engine cylinder, its increased capacity

for auxiliary equipment, and the eco-

nomic impact from a possible increased

engine room length are not included.

Many factors influence the decision for

PTO, and whether the installation of a

shaft generator is attractive or not is

up to the shipowner. In the past, many

shipowners have preferred engine room

layouts that include three gensets, most

likely because of the simplicity and well-

known design offered by the yards.

Economic comparison between engine room layouts


The engine-mounted PTO BW III/RCF

is available for all engines larger than

40 bore.

Small ships installed with two-stroke

engines smaller than 40 bore and run-

ning with a fixed pitch propeller, will

typically be fitted with the PTO BW

II/RCF type, which offers an electric

power capacity of 250-700 kW.

The PTO BW III/GCR is mostly used

for 50 and 60 bore engines having an

electrical output of 800-1,800 kW.

For a large container vessel equipped

with a fixed pitch propeller and trading

with a large number of reefer plugs, the

PTO SMG/CFE type is often be speci-

fied with an electrical capacity of some

2,000 to 3,500 kW.

The most frequently installed shaft

generators are the BW IV/GCR, SMG/

CFE, BW III/RCF and BW II/RCF types

in the power range from 0.5 to 3.5 MW.

The GCR solutions are typically used

in combination with a controllable pitch

propeller. The PTO BW II/GCR and

PTO IV/GCR are used on container

vessels or chemical tankers with 60-

cm bore engines or smaller and with

an electrical output of 500-1,200 kW.

Fig. 38: Large PTO SMG/CFE installed on a large container vessel.

Typical Shaft Generator Applications


PTO used with shuttle tankers

Shuttle tankers are widely used to serve

oil fields where the cargo is loaded from

storage facilities at the oil field or direct-

ly from the production platform where

high performance and pods for accu-

rate positioning are required.

The operating profile for those ships in-

clude long term running with accurate

Fig. 39: Engine room layout for shuttle tankers including shaft generators and clutches in the propeller shaft lines

Disconnectablethrust bearing

DG

ME

ME

DG

ME: Main engineSG: Shaft generatorDG: Diesel generator

Electric motors

MESG

Cargo pumps

Special shaft generator applications

dynamic positioning with the aid of the

bow and stern thrusters and main pro-

pellers during loading of the ship at the

oil field. The time required for loading

the oil depends on the loading facilities

and may vary from one to ten days in

each round trip.

To match such requirements, a typical

shuttle tanker is equipped with three

1,750 kW bow thrusters and two 1,750

kW stern thrusters for accurate position-

ing, which calls for equipment that can

provide sufficient electric power in the

form of gensets or shaft generators.

To reduce the complexity of such an

engine room layout, the cargo pump-

ing power is delivered by electrically


driven pumps, instead of hydraulically

driven pumps.

An efficient propulsion system that

meets the above requirements is the

diesel-mechanical twin propulsion sys-

tem with two low speed main engines

and CP-propellers, shaft generators

and propeller shaft clutches.

In port, the propeller can be discon-

nected and the main engine can be

utilised for electric power generation

without turning the propeller.

However, for safety reasons, a study

of the engine acceleration behavior is

required to establish the impact of an

immediate loss of electrical load on

the shaft generator when the propel-

ler is disconnected by the clutch. Such

a study normally results in the setting

of a minimum level of inertia for the al-

ternator, increased requirements to the

engine control system, including an ad-

vanced electronic governor with an ad-

ditional overspeed shutdown feature to

controlling a fuel cut-off device.

For safety reasons, the flexible coupling

between the PTO and the intermediate

shaft has a built-in torsion limiting de-

vice. If the flexible elements break, the

device will transmit the torque by the

help of steel parts until the safety sys-

tem has shut down the engine.

By using the main engine and PTO when

the propeller is de-clutched, the speed

of the cargo pumps can be adjusted

simply by varying the engine speed to

control the electrical frequency.

A frequency converter layout is neces-

sary if the shaft generator is serving

electric power for all consumers, at

all possible conditions during port op-

eration, sea state, dynamic positioning

and where, in some of these load con-

ditions, the engine speed is not kept at

a constant level. Alternatively, one gen-

set must serve electric power for critical

consumers.

Fig. 40: Propeller disconnected by clutch while low speed engine is driven the shaft generator

Shaft generator G1motor M1 1,800 rpmPTO load max. 1,400 kW

Clutch-engaged

Main engine

Propeller-0 rpm

120 rpm

PSC - Coupling

Propeller shaft disconnected

Main engine driving the shaft generator for cargo pumping

PTO gear


Auxiliary electric propulsion system

An auxiliary propulsion system for loi-

tering operations is especially of in-

terests for projects involving gas and

chemical tankers installed with small

bore low speed engines equipped with

a controllable pitch propeller.

MAN Diesel & Turbo can deliver an aux-

iliary system including electric propul-

Fig. 42: gensets driving the alternator/motor while the low speed main engine is disconnected from the propeller shaft.

Shaft generator G1motor M1 1,800 rpmPTO load max. 1,400 kW Clutch-C2-engaged

Clutch-C1-disengaged

Main engine

Propeller-85 rpm

0 rpm

2 Speed PTO / PTI gearRENK KAZ coupling

Fig. 41: Auxiliary propulsion system for low ship speed operations.

Oil distribution ring

Generator/motorHydrauliccoupling

Two-speedtunnel gearbox

Shaft Clutcher Main engine

Intermediatebearing

Flexiblecoupling

Hydrauliccoupling

sio, clutch, two-speed tunnel gearbox,

and a generator/motor that can drive

the propeller by means of the shaft

generator now operating as an electric

motor powered by a number of gen-

sets.

Before operating the system, the main

engine is disengaged by the clutch,

which is integrated on the shafting and

installed between the tunnel gearbox

and the main engine.

A combined propulsion mode includ-

ing both the main engine and genera-

tor/motor as power take-in is possible,

when increased propulsion power is

needed in order to maintain the ship

speed in rough weather conditions, or

if surplus electric power from a waste

heat recovery system is available.

When the propeller shaft clutch is en-

gaged, and the main engine is running,

the clutch statically transfer the thrust

force from the propeller to the main

engine`s thrust bearing.

When disengaged, Fig. 42, the clutch

build-in thrust bearing transfer the aux-

iliary propeller thrust force to the engine

thrust bearing.

Before starting up in auxiliary propul-

sion mode, a lower gear is needed from

the gear box to enable the generator/

motor to turn the propeller shaft.

Starting the generator/motor in auxiliary

propulsion mode is done with the help

from a start transformer and the two-

speed gear box built-in friction clutch,

allowing the propeller a clutch-in at full

alternator/motor speed where the full

torque is available.

The requirements of some classifica-

tion societies differ according to wheth-

er the auxiliary propulsion system has

been prepared as a take home system

in the event of a main engine failure at

sea, or as a take away from quay loiter-

ing propulsion system.


The auxiliary propulsion system of-

fered by MAN Diesel & Turbo fulfils the

requirements of both alternatives, pro-

vided sufficient electric power for aux-

iliary propulsion is available from the

gensets. Auxiliary propulsion controlled

from the engine control room and/or

bridge can quickly be established by

the system, even with unmanned en-

gine room. Re-establishing of normal

operation requires attendance in the

engine room, but it can be done within

a few minutes.

Auxiliary hydraulic propulsion system

In 2006, as an alternative to the genera-

tor/motor take-in solutions with gearbox

and electric motor powered by gensets,

Marinvest developed the MAPS auxiliary

hydraulic propulsion system for tankers

equipped with hydraulically driven cargo

and ballast pumps. When the hydraulic

propulsion system is engaged, the hy-

drauic power packs are used for driving

the shaft.

The special patented propeller shaft

clutch developed by Marinvest is used

for disconnecting the main engine.

In normal service, the rigidness of the

shaft line is ensured by a bolted con-

nection, and the MAPS system is fully

disconnected and at rest. In this way,

there is no wear and tear on the system.

The engagement of the MAPS system

for alternative propulsion mode takes

a trained crew about 15 minutes. In

this procedure, the special Marinvest

propeller shaft clutch is disengaged by

removing the bolts connecting it to the

main engine and inserting the bolts that

engage the hydraulic drive.

Fig. 44: The principle of MAPS, the alternative hydraulic propulsion system

Fig. 45: When disconnected from the main engine, MAPS can be used for take-away from quay or loiter-ing operations

Fig. 43: Main engine driving the propeller while the electric power is generated by the generator/motor

Shaft generator G1motor M1 1,800 rpmPTO load max. 1,400 kW Clutch-C2-disengaged

Clutch-C1-engaged

Main engine

Propeller-120 rpm

120 rpm

2 Speed PTO / PTI gearShaft Clutch


The MAPS is now ready to be started,

stopped and controlled via a local con-

trol panel. It is operated at constant

rpm and the controllable pitch propel-

ler is used to adjust the ship speed as

needed, reaching up to 10 knots.

Compared with electrically powered

auxiliary propulsion systems, the MAPS

Fig. 46: Exploded drawing showing the RENK propeller shaft clutch with casing to be mounted on a simple foundation below the propeller shaft line

is somewhat more manual in operation,

but also less complex and more robust

thanks to fewer moving parts and the

solid hydraulic drive.

RENK propeller shaft clutch

The RENK propeller shaft clutch is ap-

plicable for shuttle tankers, LNG tank-

ers equipped with twin-engine propul-

sion systems, and product tankers

with generator/motor systems. The

clutch type can be operated automati-

cally from the engine room for disen-

gagement, and semi-automatically for

engagement of the propeller shaft.


PS-clutch size

Torque Thrust engaged (max)

Thrust disengaged

PSC length

Spacer length

Max. Outer diameter

Flange diameter

PSC weight

Spacer weight

kNm kN kN mm mm mm mm tons tons

32 320 600 125 1.500 400 700 600 3,80 0,3

63 600 1.040 208 1.650 600 870 645 4,80 0,5

85 850 1.250 280 1.775 675 950 750 6,50 0,8

132 1.260 1.600 364 1.875 750 1.000 850 8,20 1,1

225 2.150 2.600 520 2.350 1.000 1.230 1.070 14 2,3

355 3.400 3.500 650 2.650 1.150 1.430 1.250 22 3,6

480 4.600 4.800 900 3.050 1.300 1.680 1.400 33 5,1

800 7.800 7.500 1.600 3.600 1.450 1.930 2.050 44 6,5

RENK propeller shaft clutch selection example:

Main engine power:................................................................................................................................... P = 12,640 kW

Main engine speed: ....................................................................................................................................... n = 127 rpm

Power factor: ...............................................................................................................P / n = 12,640 kW / 127 rpm = 99

Selected clutch size: ......................................................................................................................................... PSC 132*

Remarks:

* Coupling selection to be checked for compliance with class requirements for propeller shafting.

** PSC flange diameter adjustable according to main engine and propeller flange.

Fig. 47: The RENK propeller shaft clutch dimensioning


disengagement steps

1. Stop engine

2. Block engine

3. Slow down ship until maximum per-

missible shaft torque is achieved

(approx. 10% of nominal torque)

4. Disengage clutch.


engagement steps

1. Start hydraulic clutch pump

2. Engage turning gear of main engine

3. Engage disc brake

4. Align clutch by means of turning gear

and electric alignment indication

5. Disengage turning gear

6. Engage clutch

7. Disengage disc brake.


Waste heat recovery systems

The amount of air required for the diesel

engine’s combustion process is lower

than what is obtainable with high-effi-

ciency turbochargers. So when high-ef-

ficiency turbocharger systems are avail-

able, it is possible to reduce the supply

of energy to the turbocharger’s exhaust

gas turbine and utilise the excess ex-

haust gas heat for power production at

engine loads above 45% of SMCR main

engine power.

MAN Diesel & Turbo has published a

paper on waste heat recovery (Ref. 1),

which describes the more advanced

combined WHR systems that also uti-

lise the excess energy from steam for

electric power production.

Power turbine generator

Electric power production from a waste

heat recovery system utilising only

the exhaust gas can be supplied by a

power turbine generator system when

by-passing a percentage of the exhaust

gas to a power turbine placed on a

frame in the proximity of an alternator.

The power turbine generator system

available from MAN Diesel & Turbo can

be operated as a stand-alone solution

to supply all the electric power on the

voyage.

MHI hybrid turbocharger

Electric power production from the

exhaust gas can also be effected by

means of an advanced turbocharger

solution designed with an integrated al-

ternator in the shaft line. Such a system

is available from Mitsubishi Heavy In-

dustries and is known as the MHI MAG

hybrid turbocharger system.

In the same way as a the standard tur-

bocharger, the MAG hybrid turbocharg-

Fig. 49: Cutaway view of MHI MET-MAG hybrid turbocharger

Fig. 48: Schematic diagram of a power turbine generator system

Board gridEfficiency between 3 to 5% ofmain engine SMCR power depending on size

Turbochargers

Funnel (boiler)

GeneratorCoupling

Exhaust gas turbine

Main engine

Exhaust gas receiverGearbox

er supplies supercharged air to the en-

gine, but at the same time the integrated

alternator in the turbocharger shaft line

generates electric power for the con-

sumers. In this way, the MAG system

utilises the excess exhaust gas rotation-

al energy produced by the turbocharger

to generate electric power from a simple

compact electromotor mounted with a

permanent magnet rotor (lower weight

and size) and directly attached to the

turbocharger shaft, without a waste heat

recovery bypass system.

The stator is held in place by a support

bracket attached to the housing.

Turbine

CompressorGenerator


Depending on the vessel type, the out-

put needed, and the size of the MET-

MAG system, an electric power output

in the range of 250-750 kW is possi-

ble. This could cover the electric power

needed on the voyage.

The three-phase alternating current

produced has a varying frequency

that corresponds to the turbocharger

speed. The converter system installed

in the engine room converts the current

to constant frequency electric power.

The MHI hybrid turbocharger system

allows a continuous switch-over be-

tween generating and motoring at

low-load engine operations where the

turbocharger does not supply a suffi-

cient scavenge air amount to the en-

gine combustion proces. In this condi-

tion, the standard scavenge air blowers

would normally be running, but they

can now be omitted and replaced by

the more advanced and efficient tur-

bocharger electro-assist function avail-

able with the MHI hybrid turbocharger.

MHI electro-assist turbocharger

Another variant of the hybrid turbo-

charger is the electro-assist MET tur-

bocharger. It incorporates a compact

electric motor with limited power func-

tions that assists the driving of the tur-

bocharger at low-load engine opera-

tions, where the scavenge air blowers

would normally be running.

The principle optimises the plant ef-

ficiency at low-load operations below

some 35% engine load. It improves

the main engine combustion efficiency

by serving more scavenge air to the

main engine. The same or even a bet-

ter performance is achieved, compared

with an auxiliary blower, thanks to the

improved efficiency from the electro-

assist permanent magnet motor, which

consumes less electric power.

Fig. 50: MHI electro-assist turbocharger type


The combined RENK shaft generator and waste heat recovery system

The engine-mounted BW III shaft

generator solution from RENK is also

available with a combined waste heat

by-pass power turbine solution to uti-

lise any excess heat available from the

exhaust gas. The power turbine is hy-

draulically coupled to the crankshaft

through the crankshaft gear already

available and used for the shaft genera-

tor mounted to the engine side.

These two systems are combined into

one unit offering the benefit of the two

without incurring the full first cost of

both, as the most expensive compo-

nent, the crankshaft gear, is shared.

The built-on shaft generator, which

serves all the electric power needed

on the voyage, will save running hours

and maintenance cost on the gensets,

and the power turbine feeds back the

mechanical power available from the

combustion processes, thereby reduc-

ing the main engine’s fuel consumption.

This system can benefit ships predomi-

nantly operated at load profiles higher

than 45% SMCR, for example contain-

er feeders.

Fig. 52: Sketch of turbo compound system/PTI without shaft generator type

Fig. 53: Schematic diagram of turbo compound system with and without a shaft generator

Fig. 51: RENK BW III turbo compound system


Introduction

One of the main goals in the marine in-

dustry is to reduce the impact of CO2

emissions from ships in order to meet

stricter IMO greenhouse emission re-

quirements.

The folowing two CO2 indexes came

into force on 1 January 2013:

1. Energy efficiency design index

(EEDI) evaluates the engine and

vessel design and measures the

gCO2 eimission per ton per mile.

2. Energy efficient operational indica-

tor guides the operator in develop-

ing the best practice on board the

ship.

The goal is to design future ships with

stepwise reduced design index figures

in 2013, 2015, 2020 and 2025 which

corresponds to a 30% reduction of CO2

emissions and fuel consumption.

Based on the assumption that electric

power generated by a shaft generator

connected to the two-stroke main en-

gine is more efficiently made than elec-

tric power generated from gensets, the

IMO rules give a preference treatment

for PTO applications. In this respect,

a maximum of 2.5% of the installed

SMCR power can be deducted from

the main engine power used to calcu-

late the EEDI figure.

However, the power take in (PTI) sys-

tems using electric power produced by

gensets will influence the EEDI number

in upwards direction for applications

designed to increase the ship speed at

normal service conditions. For waste

heat recovery systems, where excess

electric power is available, it is possi-

ble to take advantage of the PTI using

excess electric power for propulsion

on the voyage without having an EEDI

penalty.

A BIMCO EEDI calculator is available to

explore further possibilities.

Summary

A wide range of shaft generators with

frequency control systems are available

for installation with an MAN B&W low

speed engine. Relative to the propel-

ler, a shaft generator application affects

the installed engine power and the shaft

generator application must also be in-

cluded in the torsion vibration calcula-

tions.

Fig. 54: EEDI calculation formula.

EEDI – Energy Efficiency Design Index

Пfј (ΣΡМЕ*CFME*SFCME) + PAE*CFAE*SFCAE + (Пfj*ΣPPTI - Σfeff*PAEeff)*CFAE*SFCAE - Σfeff*Peff*CFME*SFCME

PME Main engine 75% rated main power = 75% *PMCR(i) - PPTO(i)

PMCR Main engine Rated main engine power at MCR

PPTO Power Take-off Rated shaft generator at MCR

fi * Capacity *Vref*fw

EEDI =

PTI will penalise EEDI figures(higher EEDI number)

PTO will improve the EEDI figures(lower EEDI number)

PPTO

PMCR


However, despite the prolonged mean

time between overhauls, references

have shown that most MAN B&W low

speed engines are operated without a

shaft generator. This reflects the fact

that many shipowners and shipyards

still prefer the simple engine room lay-

out including electric power generated

by gensets.

On the other hand, when surplus ca-

pacity is available from the main engine,

a shaft generator is still a viable solution.

Advantages:

� PTO improves the EEDI figures

� Small space requirement

� Low investment cost (PTO/GCR)

� Low installation cost

� Low manhour cost for PTO mainte-

nance

� Low maintenance cost for PTO

� Reliable

� Long lifetime

� Low noise

The requirements to the engine govern-

ing system is typically not influenced by

a shaft generators with a normal elec-

tric capacity of less than 15% of the

SMCR power. However, for shaft gen-

erators with no frequency control sys-

tem, the stability of the engine speed

needs special consideration.

For shaft generators used in special

applications such as shuttle tanker

propulsion arrangements, the propeller

can be disconnected by a clutch, and

the main engine can be used to drive a

large alternator supplying electric pow-

er for the cargo pumps. In rare cases,

where an auxiliary loitering propulsion

system is used, the main engine is dis-

connected and the shaft generator is

used as an electric motor driving the

CP propeller with electric power gener-

ated by a number of gensets.

Gensets have improved their cost ef-

fectiveness thanks to low prices, HFO

operation and improved reliability.

Auxiliaryengines

EEDI = ∑Р × CF SFCCapacity × Speed

Shaft motor PPTI

Shaft power PS Main engine PME

PAE

Main engine Pumps (2.5% PME)

Cargo heat

Thrusters

Cargo pumps

Cargo gear

Reefers

Powerexcluded EEDI

Powerincluded EEDI

Ballast pumps

Boiler

Accommodation(250 kW)

Waste heatrecovery etc. PME

Shaftgenerator PPTI

Switch board

Fig. 55: EEDI parameters

Disadvantages:

� PTI will penalise EEDI figures

� No power production in harbour

� Higher load on main engine

� No long time parallel running ability

for PTO/GCR

� Reduced propeller efficiency at low

propulsion power for PTO/GCR

� More complex shaft arrangement

Abbreviations:

Gear constant ratio (GCR)

RENK constant ratio (RCF)

Constant frequency electrical (CFE)

Direct-mounted generator (DMG)

Shaft-mounted generator (SMG)

MAN Diesel & Turbo (MDT)

Low speed engine (2-stroke main en-

gine)

Power take-off (PTO)

Marine diesel oil (MDO)

Four-stroke diesel generator (genset)

Power take-in (PTI)

Propeller shaft clutch (PSC)

Power management system (PMS)

Pulse width modulated (PWM)


References

BIMCO EEDI Calculator, link:

www.bimco.org/Products/EEDI.aspx

Waste Heat Recovery System,

MAN Diesel & Turbo, Copenhagen,

Denmark, Publication no.: 5510-0136,

Aug 2012

Image credits

http://www.mhi.co.jp/en/news/sto-

ry/1008261372.html


MAN Diesel & TurboTeglholmsgade 412450 Copenhagen SV, DenmarkPhone +45 33 85 11 00Fax +45 33 85 10 [email protected]

All data provided in this document is non-binding. This data serves informational purposes only and is especially not guaranteed in any way. Depending on the subsequent specific individual projects, the relevant data may be subject to changes and will be assessed and determined individually for each project. This will depend on the particular characteristics of each individual project, especially specific site and operational conditions. Copyright © MAN Diesel & Turbo. 5510-0003-02ppr Mdd 2015 Printed in Denmark

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Shaft Generators for Low Speed Main Engines · 8 Shaft generators for low speed main engines As illustrated in Fig. 3, at 124 rpm, the right-hand power range curve No. 1 is located