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SUB-COMMITTEE ON SHIP DESIGN AND EQUIPMENT 56th session Agenda
item 24
DE 56/249 December 2011
Original: ENGLISH
PROVISIONS FOR THE REDUCTION OF NOISE FROM COMMERCIAL
SHIPPING
AND ITS ADVERSE IMPACTS ON MARINE LIFE
Proposed framework for non-mandatory guidelines
Submitted by the United States
SUMMARY
Executive summary: This document presents information on the
issue of "Noise from commercial shipping and its adverse impact on
marine life" and offers recommendations and a framework to the
Sub-Committee concerning the development of non-mandatory,
technical guidelines to minimize underwater noise
Strategic direction: 7.1
High-level action: 7.1.2
Planned output: 7.1.2.3
Action to be taken: Paragraph 7
Related documents: MEPC 62/11/10; DE 56/2/1; MEPC 61/19 and MEPC
58/INF.19
1 At the most recent session of the Marine Environment
Protection Committee (MEPC 62), the Committee instructed this
Sub-Committee to address the issue of noise from commercial
shipping and its adverse impacts on marine life. Resolution
A.1012(26) regarding the High-level Action Plan for IMO and
Priorities during the 2010-2011 Biennium, identified provisions to
reduce noise from commercial shipping and its adverse impacts on
marine life as a priority output for IMO. 2 At the fifty-eighth
session of the MEPC, it established a correspondence group to
review existing knowledge on ship-quieting technologies and their
potential applications for large commercial vessels in order to
minimize the effects of underwater noise. Specifically, the
correspondence group has operated under the following terms of
reference: "(to) identify and address ways to minimize the
introduction of incidental noise into the marine environment from
commercial shipping to reduce the potential adverse impact on
marine life, in particular develop non-mandatory technical
guidelines for ship-quieting technologies as well as potential
navigation and operational practices".
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3 The correspondence group, as reported in documents MEPC 59/19,
MEPC 60/18, and MEPC 61/19, discussed ship design and operational
modifications potentially relevant in the reduction of incidental
noise produced by large vessels. These documents include technical
responses by the correspondence group members, shipowners, and
engineers. The correspondence group agreed that the propeller is
the main source for ship generated underwater noise and also
highlighted the demand for reliable underwater noise data. 4 In
document MEPC 61/19, the correspondence group proposed that IMO
develop non-binding, technical guidelines and consider solutions to
reduce the incidental introduction of underwater noise from
commercial shipping and, in turn, reduce potential adverse impacts
to marine life. Further, in document MEPC 62/11/10, the United
States proposed development of non-mandatory technical guidelines
that would be applicable for both new and existing ships to reduce
underwater noise from ships taking into account guidance from the
MEPC and the correspondence group. 5 We note the final
recommendations of the MEPC correspondence group for approaches
that have emerged as the most plausible design and/or retrofit
options and the further recommendation that these specific
high-priority focus areas be assessed by naval architects and
engineers. In particular, the correspondence group recognized that
the primary cause of underwater noise is propeller cavitation and
identified four specific high-focus areas that should be assessed
for potential underwater noise reduction: .1) propulsion, .2) hull
design, .3) onboard machinery and .4) operational modifications.
The recommendations of the MEPC correspondence group on these
specific high-priority focus areas are restated below:
.1 PROPULSION
A) Propeller design and modification to reduce cavitation Basic
design optimization of propellers Fixed vs. variable pitch
propellers Contra-rotating propellers Propellers with tip (Winglet)
engineering
B) Propulsion systems
Twin screw design systems to allow for reduced tip speed Screw
systems with open (high) screw propulsion to allow for
a smoother (less turbulent) wake field Podded propulsion
(azimuth electric propulsion drive)
systems to allow for an improved wake field by placing
propellers deeper
C) Propeller/hull form optimization (requires model basin
testing)
Determining optimal hull design for propulsion system and
propeller type, in order to reduce hull resistance and minimize
turbulence in the wake field
Propagation and radiation of pressure fluctuations induced
structure-born noise
.2 HULL DESIGN
Flow noise associated with various hull forms Flow noise as
function of vessel speed Flow around underwater appendages, e.g.
skeg shape,
trailing edge, bow thruster, rudder, other hull openings
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Bow shape and form Use of dampening coatings and variability
among coating
types
.3 ONBOARD MACHINERY Passive and/or dynamic equipment mounts
for: main
engines, generators, reduction gears/gear boxes, and pumps
(fixed and variable speed)
Other equipment isolation techniques (filters, hangers) for
pipes/pumps
Damping/shrouding systems or isolation chambers Engine
synchronization Purchasing focus on selection of low-noise profile
equipment
.4 OPERATIONAL MODIFICATIONS
Speed variations, including the impact of vessel speed on the
noise profile of a given vessel
Load variations (full load, partial load, ballast) Hydrographic
variations (shallow vs. deep water operations,
water column characteristics) Maintenance periodicity and
type
6 In order to assist the Sub-Committee in its development of
non-mandatory technical guidelines, the United States offers a
draft framework (see annex), largely drawn from the work of the
correspondence group, which can serve to guide this Sub-Committee
in the development of non-mandatory technical guidelines that would
be applicable for both new and existing ships to reduce underwater
noise from ships. Action requested of the Sub-Committee 7 The
Sub-Committee is invited to consider the above comments and the
draft framework (see annex) as it develops non-mandatory technical
guidelines that would be applicable for both new and existing ships
to reduce underwater noise from ships.
***
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ANNEX
DRAFT FRAMEWORK FOR NON-MANDATORY GUIDELINES 1 Underwater noise
computation/prediction Underwater noise computational/prediction
models are useful for both new and existing ships in understanding
what reductions could be achievable for certain changes in design
or operational behaviour. Such models analyse the noise sources on
the ship, the noise transmission path through the ship, and the
total predicted noise of the ship. This analysis will help
shipowners/shipbuilders to identify noise control treatments that
could be effective. Such treatments include: vibration isolation
mounts (single and double stages) for reciprocating machinery,
structural damping, acoustical absorption, and acoustical
insulation. 2 Standard Underwater noise should be measured to an
objective standard for any meaningful improvements. There are
several standards available to commercial ship designers. The first
standard is co-authored by the American National Standards
Institute and the Acoustical Society of America (ANSI/ASA)
S12.64-2009 "Quantities and Procedures for Description and
Measurement of Underwater Sound from Ships, Part 1: General
Requirements". Another standard is currently being developed by the
International Organization for Standardization (ISO/PRF PAS)
17208-1 "AcousticsQuantities and procedures for description and
measurement of underwater sound from ships Part 1: General
requirements for measurements in deep water". Also, several
research vessels have been designed using the standard set by the
International Council for the Exploration of the Sea (ICES)
Cooperative Research Report No.209 (CRR 209). It should be noted
that the ICES CRR 209 standard was purpose designed for research
vessels so that marine life would not be startled during biomass
surveys; it was not intended to be used as a commercial ship design
standard to prevent potential harm of marine life. However, certain
design arrangements used to meet ICES CRR 209 may still be useful
for new commercial vessels to reduce underwater noise.
Additionally, a number of classification societies have underwater
noise rating criteria, which may prove useful as guidance. 3 Design
considerations The largest reductions of underwater noise are made
possible during the initial vessel design; it is not practicable
for existing vessels to meet the underwater noise limits achievable
by new designs. The following design recommendations are primarily
intended for new vessels, but consideration should be given to
existing ships, depending on the practicality/cost of noise
mitigation measures. 3.1 Propellers: Propellers should be
designed/selected in order to minimize cavitation. Propeller
cavitation is the formation then collapse of water vapour bubbles
as water moves across a propeller blade. If propeller cavitation
occurs, it will be the dominant noise source and increases noise
levels by about 20 dB in the 80 Hz to 100 kHz band. While all
propellers will cavitate if sufficiently loaded, cavitation can be
avoided under normal operating conditions through good design, such
as optimizing load, ensuring uniform water flow into propellers
(which can be influenced by hull design), and careful selection of
propeller size and blade section, pitch and camber.
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3.2 Propulsion system: The best propulsion train configuration
for minimizing underwater noise is a diesel electric plant. This
allows for effective isolation of the diesel generators which is
not always possible with direct drive configurations. The use of
high-quality DC electric motors will also minimize vibration being
induced into the hull. The vessel transit speed should be less than
the cavitation inception speed of the selected propeller. 3.3 Hull
design: Underwater noise from new ships can be minimized through
the reduction of turbulence resulting from the underwater hull
form. An elliptical bow shape, the elimination of abrupt hull
changes at the waterline, minimization and alignment with flow of
appendages and fittings, flush welds, undistorted plates and smooth
paintwork will help to reduce turbulence. Hull form optimization
using computational fluid dynamics and model testing will further
reduce turbulence. It is anticipated that these recommendations
will decrease fuel consumption as well as reduce underwater noise.
3.4 Large reciprocating machinery (such as refrigeration plants,
air compressors, and pumps): Large reciprocating machinery should
have single isolation mounts, and diesel engines should have double
isolation mounts 3.5 Sea connected systems (such as sea water
cooling systems): The flow induced noise should be analysed and
reduced, and flexible hosing may be used to structurally isolate
the machinery and dampen the fluid noise. 3.6 Large HVAC fans:
These fans should be isolated from the structure. 4 Operational and
maintenance considerations Although the main components of
underwater noise are generated by the vessel design (i.e. hull
form, and the interaction of the hull and propeller), operational
modifications could be considered for both new and existing ships.
4.1 Propeller polishing: Propeller polishing done properly removes
marine fouling and vastly reduces surface roughness, helping to
reduce propeller cavitation. Information from technical articles
report that effective propeller cleaning and polishing can result
in a power savings of approximately 10%. 4.2 Underwater hull
surface: Maintaining a smooth underwater hull surface and smooth
paintwork may improve a ship's energy efficiency and will serve to
help minimize underwater noise emanating from the ship. There are
several advanced hull coatings commercially available that reduce
drag on the hull, reduce turbulence, and therefore reduce
underwater noise. 4.3 Speed reduction: Reducing speed of the vessel
below the cavitation inception speed of the propeller is the most
effective operational measure for minimizing underwater noise. 4.4
Routeing decisions: Consideration should be given to possible
routing decisions to avoid or reduce speed near sensitive marine
areas including well known habitats or migratory pathways.
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