8/10/2019 And Just What Do Deep Vees Do

1/3

-\

-.

A 27ft deep

vee from Magnum of Miami.

John

Teale

continues

his

thesis

in the

third

extract

from his new book

High

Speed

Motor

Boats

@

1969 by John Teale. Published by the Nautical

Publishing Company at 32s

IT

WOULD be as well at

this stage to

put

forward

a

definition.

A deep

vee

will

be

considered

to

be any

hard

chine

boat that

has a minimum deadrise of

20

deg

or

more.

In

practice

this

will

mean that the deadrise

at

the transom

will

be

that

amount,

and

elsewhere

along the

hull

it

will

probably

be

greater.

So

many craft are

claimed

to

be

"deep

vees", when

in

fact they are

nothing ofthe

sort,

that it

seems

worth

while

to lay

down

those

limits;

genuine

high

deadrise

vessels

have

disadvantages

as

well

as

advantages

and anyone

hunting

for

a boat to suit

his

particular

requirements could

well choose

something

quite

unsuitable

on

the basis of

a manufacturer's

advertising

blurb.

Since builders make

this

deep

vee

claim

it

is

obvious

that they are trying

to cash

in

on something.

In

fact what they are doing

is

attempting

to bask

in

the

reflected

glory

of

the

racing successes of

craft from

the

a

20ft,

seven-step

hydroplane

with

a

constant

28

deg deadrise

and

powering

this

with

a

30h.p.

motor

achieved

the

very

respectable speed

of

27 knots.

Litde

more

seems to

have been

done

with the very

vee'd

type

of

hull

form

until

after

the 1939-45

war

when the American Ray

Hunt,

and

Italian

based,

British-passport-holding

Renato

Levi

both turned out

genuine

deep

vees and

proceeded

to

dominate

the

racing

field.

Certainly

the

long lack

of

interest

between 1908

and

the

1950s was due to

the difficulty

of

obtaining

high-powered,

lightweight

motors

in

commercial

production.

A deep vee takes

more

power

to

drive

it

than

does

its

equivalent

flatter-bottom craft and comes

into

its

own

only when

really high speeds are

required.

Why

is

this? Well consider

the case

of

an

aeroplane.

Its wings

are

generally

set

fairly

well

parallel

to

the

ground

with only

a

slight upwards

angling.

By this means

the

even

a

high

speed

powerboat

will not

normally be driven

so

fast that

it

becomes

completely

airborne. What may well

happen

is that

the forward

third

of

the

hull

will

leave the

water from time to time

and then

slam back again

in

rough water.

The more

veed the bottom

forward the smaller

the

bang will be

on

re-entry.

That

is

pretty

obvious,

for it will

tend

to slice

back

through

the sea

rather than bang

on

its

surface as would

a completely

flat bottom.

Hence

it

is

clear

that

a good

vee

given by

a

high chine

line forward

is indicated for

any sort

of

comfort

in bad

weather.

An

example

of

such

a

shape

is

the

112ft

Fairmile

D

which were

built

in

great

numbers

during

the war, and numbers

of

which

can

still

be seen

round

our estuaries

and rivers as

houseboats.

A

deep

vee boat has this high chine

forward

but

continues

it

all

the

way

back

to

the transom.

This is

very

nice

if

one

is

contemplating becoming airborne, for most

fast

boats

will

come down again stern

first

and

the

cushioned descent

given

by

the

steeply angled transom

will

soften the drop

considerably.

But

how

often

does

the

cruising man

take

off

completely? You

might

say that all orher things being equal

the vee'd transom

is

worth having

for

its

occasional

real

usefulness.

Unhappily

all

other

things are

not

equal.

The

power

question

has

been

mentioned but there

are

other factors too. Firstly, the deep vee

is

a

very

wobbly boat

in

the water

until

it

is

going

fast.

To

put

that

technically, its

transverse stability

is

low

because

of

the

shape of

the bottom.

It

is clear that

it

will

take

more effort to

give

initial heel to

a flat

bottom than

to a vee'd one.

Further, the vee

taken to

extremes

interferes

with

the

accommodation

since

it

reduces

useful

space,

but more

important,

perhaps,

is the

fact that the

genuine

deep vee

craft

actually has

a

more

violent

pitching

and

slamming

movement than a shallower

boat

stables of,

to name a

few, Ray

Hunt, maximum

lift

is

obtained.

If

one

saw

a

Renato

Levi,

Jim

rWynne

and

Chris

'plane

with the

wings

raking

skywards

Tremlett.

The operative

word there

is

common sense

would tell

you that

it

"racing",

for

it

cannot be disputed

that

would take more

power

to keep

it

up

in

the

with

suitable spray

rails

slung

along

the

air,

and

that

if

the

engine

should

suddenly

bottom, to

decrease

wetted

surface

and

fail

the

aeroplane would tend

to

come to

effective beam,

a

deep

vee

power

boat

is

earth

pretty quickly.

Exactly

the

same

a very

potent

racing

machine. Whether the

thing

applies

to a boat.

If

the bottom

is

flat

average

owner

really needs such a

vessel is

or

nearly

flat it

will

tend to rise up and

a matter of some doubt,

and

it is

significant

start

planing

along more easily than

if

it is

that when,

for example,

Jim

Wynne

designs

heavily veed,

and

it

will

require less

power

a high speed cruising

boat

for

commercial

to

keep it

up

in

this

planing position.

production

the

chine

is often &opped

That

being so,

the high

deadrise

boat

towards the stern

giving

a

flatter bottom.

must have

some

advantages

to

counteract

The result is called

a

"modified

deep

vee"

its inherent weakness

as far as

powering

is

when

in fact it is a normal

warped

bottom concerned.

So

it

has,

and

these

apply

or

monohedron

hard chine boat.

Ah

well, especially to

racing boats which

we

will

this

is

the

age of the catchpenny

phrase.

consider later

on'

but its

most commonly

Anyway,

before we

dive

into the

quoted

superiority

over

a

craft

with

a

technicalities,

pros

and cons, and so

forth

it

flatter

bottom

is

that

it

gves

a

softer ride

in

is

worth

mentioning

that,

despite

popular

rough water.

Let

us

ponder

on that a

morrF

superstition

to

the

contrary,

the deep

vee

is

ent and then

look at an

American tank test.

not

an exclusively

modern hull

form. Back

Well,

in normal cruising

when the

in

the dim, dark

ages

of

1908, Fauber

built

comfort of

the

crew

is

of

some

interest,

8/10/2019 And Just What Do Deep Vees Do

2/3

9,

l97O

cruising speeds.

Let

us take

that

tank test

report now.

Davidson

Laboratory

in

America

was

in 1963

to

carry out tests on three

types of boat to

find

the best shape

a

52ft

high speed

landing

craft.

Two

of

vessels

were conventional hard chine

boat types, though one

had convex

the other

concave bottom sections.

The

was

a

genuine

deep

vee,

by a

world-famous exponent of

forrr,

having

the

usual spray rails and

from

'midships

to the

ofabout

22

deg.

Various tests

were

run

to determine

requirements

in calm and

rough

and to

measure vertical

accelerations

rough

seas.

In

the

last-named, the tank

a State 3

sea where the

average

of

the

waves is about

2.5ft

and

period

about 4.4 seconds.

This sort

thing

happens

after

a

wind of

11-16

been

blowing

for

about

six

In

calm water,

it

was

found

that

the

needed

consistendy

more

power

to

it than

the

other

two.

750h.p.,

for

would

push

the two conventional

at

roughly

31

knots

and

the

deep

vee

bit undet

27

knots. To achieve 40

the high

deadrise

vessels required

and the other

two,

1,200h.p.

All

were running at a displacement

of

or

about

24j

tons,

and the

are e.h.p.----effective

horse

is

about

half that

of

brake

On

the

rough water runs,

it

was

that the deep vee

model required

more power

than

the

other two

the maximum

speed

run of 40

knots.

Bow accelerations are

measured in

"g's"

regardless

of

the technicalities

of

this

of

measurement

it

can

be taken that

higher the

"g's"

the

more

things

will

be

for

those

on

Astronauts are

subfected

to a

of

"g's"

on

take-ofF-sorry,

in

the

modern vernacularl

pilots

when

the

"g's"

exceed a certain

on

pulling

out of a dive.

It's all

same

measurement. However

it was

that

the

deep

vee,

complete

spray

strips

along the bottom,

pitches

more

violently than

the

two right up the speed

range. This

is

but very

rarely

appreciated

by

who

dash out

and buy

a

cruiser

for

the

fabled easier

ride

of

the

deep

They simply won't

get

it

and the whole

smacks

of another of

life's

great

the

maintenance-free

properties

They

fust

ain't

there

Well, well,

and how

do

we account

for

rum

state

of

affairs?

In

fact with the

model run

in

State

3

sea,

with the

spray

rails removed,

lower vertical

were revealed.

In fact

the

boat

not much

inferior

to

the other

two

in

condition.

The Davidson

Laboratory sums up this

follows;

"The

Scheme

C model

(this

is

the

vee) encountered

larger accelerations

Schemes

A or B.

This

fact was

during

the tests

and is

confirmed

by

the

motion

pictures.

It is

attributed

to

the high trim characteristics

of the

Scheme

C model.

With a large

initial

angle of

attack the

model had a very

distinct

tendency

to lift

off

the crest of one

wave and slow down

on the

face

of

the

next. . .

. When

bottom strips are

removed

from the

Scheme model

C lower

accelerations

are

encountered.

Again,

removal

of

strips

resulted

in reduction

of

running

trim. This

reduction

is

the

probable

explanation

for

the

reduction

in

acceleration amplitude.

"

Although

the

three

models

all

started

floating level,

the

deep

vee took

a

much

higher bows up attitude than

the

other

two

and this

is

what

causes

it

to

iump

off

the

tops of

waves.

Its

trim

decreases though,

the faster

it

goes,

as

is the

case

with all

high

speed boats, and

at

,[0

knots

is

approaching

a reasonably efficient

level while the trim of

the

other

two

is

becoming

rather too flat.

This is the reason why

power

requirements

of

the deep vee are

not higher than those

of

its

conventional

rivals

in

rough water

at

around the

40

knots

mark.

The

high-

deadrise

craft

is

just

starting

to

come

into

its own at

these

velocities.

Translated into more everyday

terms

and

taking

the water-line length of

the

deep

vee

at

49ft,

we

have

the case

where

it is

inefficient and wasteful of

power

up to 40

knots

or a speed

flength

ratio of 5.7.

There

is

no

reason to suppose

that

a

smaller

vessel would

not behave

in

a

similar

way. Hence a

powerboat

25ft long

on

the waterline, say,

would be

a

better

and

more

comfortable

vessel

if

of

conventional

hard chine design

unless

it

were

designed

to run

at

consistently

above

a

speedAength

ratio

of 5.7.

Recall that

speedlength

ratio ofd-and

sothis, means

above a velocity

of

28.5 knots

(

I

5.7

therefore V

:'t/

L

x 5.7

or

'5'

'r.

5.7.

where

Z

is

speed

in

knots and

Z

waterline

length

in

feet).

Since

very few

cruising

boats, whatever

their

potential,

will

exceed

such

a

speed

at

sea except once

in

a blue

moon,

the deep

vee

appears a

fairly

unuseful

type for all round use.

Of

course that

does

not imply that

any

old

hard

chine

box

flopping round the

ocean

will

be

a

superior

craft to

a

well-designed

deep vee.

Far from

it,

we

must

assume

a

high

level

of

design

in

both

cases

and

a

recognition that

a

sharpish

bottom forward

is

essential

to

comfort at

sea.

All

that

we

have

discussed

simply

implies that

it

is not really wise to continue

that

sharpish

bottom

all

the

way to

the

transom, and rhen scntter

a

few

spray

rails

along

it in an effort to

improve

its

inherent

poor

lift

qualities,

unless

one

is

aiming

for

racing speeds

or

other

special

qualities.

The

gradually

reducing

trim

eventually

produces

a

more efficient attitude

in

the

water

than

is

the

case

with

the

normal

planing

boat.

That

is

part

ofthe

reason for

the success

of

the

deep

vee when

racing

but

only

part,

and

we

must now

bend our

minds to the subject

of

those spray

rails

along the bottom.

Such

rails have two

properties.

The first

is to

give

a

small

amount

of

lift,

though

not

so much

as would be

the

case by

213

simply

reducing

the

deadrise

a bit.

The

second

is

to reduce

wetted area by keeping

some

part

of

the bottom drier

than

it

would

otherwise

be by

deflecting

water away and

back down

to the

sea.

On

deep vees they

have a

special

function

in

reducing the

effective waterline beam as

well

as

making

for

a

smaller wetted surface.

Fig 1 Spray rails on a deep vee can reduce wsttsd

surface

more easily than on a

flatter-

bottomed craft.

Fig. 1 shows

how

this

reduction in

waterline

beam can be achieved on

a

high

deadrise

craft

but

not

on

its flatter

brethren.

The

water

will

simply

break away

over the

rail

on

the latter type and

reforrr

again on

the bottom a

bit

farther up.

Now

we

must

equate

narrow

effective

beam

with

the

high trim

angles inherent

in

the

deep

vee

and we find to our astonishment

and

gratification

that for

once

two

negatives

in life,

as

opposed

to algebra,

have made a

positive.

We

have

small beam,

which

has

really

not been

quite

the

accepted thing

for high-speed boats, and big

trim angles,

which

in

themselves

are not

always desirable.

This

is

thorny

ground

we

are

approaching

and much set about

with

abstruse technicalities.

Rather than

stumble over

the

prickles

we will

quickly

skirt

the

shambles

ahead

and

reproduce

instead

a

graph,

Fig.

2,

plotting

speed

against

power

for

tvto

22ft racing craft.

1$(/e

have

assumed

that one ofthem

can have

its

continued

overlegf

Fig

2

Speed/power curves

of two idortical

2z-footets but assuming that one can

reduce

its effective

waterline beam from five to three

feet.

40 50 60 70 80

90

Knots

8/10/2019 And Just What Do Deep Vees Do

3/3

214

..,.a[diust

what

iln

ilgg[

UEE$

ilo?

c.n

rud

beam

effectively

reduced from

5ft to

3ft.

It

will

be

seen

that

the

narrower

craft

has

a

smaller

power

requirement

for all

speeds

above

33

knots.

Since

racing

boats

may

be

expected to travel at

over

that velocity for a

reasonable

pan

of their

working

lives,

the

advantages in

using

a deep

vee

hull

together with beam reducing spray

rails are

obvious.

The

only

way

one

could beat

this

effectively

narrowed

22-footer

would

be to

use

either

a stepped hull with a very much

superior aspect

ratio,

or

a

catamaran

with

two hulls

of

even less than

that

3ft

beam.

Working in

opposite

directions,

really, for

one

is

a

craft with

a

very

wide,

short

planing

area in the vicinity

ofthe

step, and

the other

a

long,

thin

creation;

but

both

achieve the

same

end

ofhigher

speed.

Perhaps

one other

practical

lesson can be

learned

from

rhe

deep vee

discussion

so

far,

and that is the

imponance

of being able to

achieve high

speeds

in

a race and so

take

advantage of

the

form.

There would

be

little

point

in

slogging

it

out

with

a

more

conventional

planing

boat

in

conditions

that

limited

speed

if a

slightly

longer but

calmer course was available.

What has been

said on deep

vees

may

give

the

impression

that they are

fairly

useless obiects unless

employed

for

racing.

So

far as normal cruising is concerned that

is

probably

true,

but

many

people these

days buy a cruiser

with the thought

at the

back of

their minds thar they

might one day

race.

Further,

for

specialised

pursuits,

such

as water ski-ing,

the

deep vee

has

advantages

as

it

tends

to

turn without

skidding

and rhe depth of

boat in the water

makes

it difficult

for

the skier

to

swing

it

off

course.

Anci

these days even

quite

respectable size craft

are

used for

towing

water skiers.

The lines

of

one

such

boat,

a Tremlett

25-footer, are

shown

in

Fig. 3.

The

Tremlett boats

of

this

size

are normally

hot-moulded; that

is

the

hull

is

made up

of

a number of

veneers of timber or

ply

glued

together

over

a building mould, and then

finally

curved

and bonded together

under

heat and

pressure.

A

very strong

structure

results, especially

when

of

the

deep

vee

variety;

as can be

seen,

the

botton and

sides are

one smooth curve,

so can be made

of

continuous

laminations

with

no fear

of

leaks or cracking

at

the vulnerable chine

ioint.

Spray

rails

and

so

on

are

added

afterwards

to

the

bare

hull.

The convex

sections add their own

measure

ofstrength

compared with

flat

sheets, too.

Tremlett's

boats

are highly successful

competitors

in

offshore

racing, especially

among

the Class

111 boys.

This

particular

225-footer

is

capable

of

38m.p.h.-with

a

160h.p.

MerCruiser

inboard

/outboard

which,

incidentally,

develops

135

useful

horsepower,

not

160. Displacement

of

the

boat

is

1j

tons approximately.

That boat

is a

fairly

extreme

example

of

the type

having more or

less

wedge-shaped

sections

with

no

particular

demarcation

Fig 4 Sketch

plan

of

a 31ft

deep vee

designed by

the author for Dr Savundra.

Note

the full forward sections

towards the keel.

between

bottom

and

topside.

There

are

variations though, and one

is

shown

in

sketch

plan

form, Fig. 4. This was designed

by

the

author

for Dr

Savundra.

The

bottom

towards the keel

is

very rounded so

as to

give

a

quick

build-up of buoyancy

as

the

hull enters the water

having been flung

clear. The shape

may

give

a slightly harder

re-ntry but on the

other

hand it

will

also

mean

that

the

hull

may

be able

to

start

planing

again

after its

airborne

pursuits

without first

slicing

deep

into the

water

and being slowed down.

Both

hull

forms

Fig

3 The

lines

plan

of

a Tremlett

25ft deep

vee

MOTOR

BOAT

AND

YACHTING

illustrated have

their

advantages and it is

rather

a

matter of choice.

The

Savundra

boat was originally drawn

out

to

be

built

in

aluminium alloy.

This

should

have

been a

pretty

strong

structur,e

and

the

alloy weight

of

this

30-footer

would have

been

a little under

3,0001b.

It was then

decided,

largely

because

Vospers were also building an aluminium

racer

for

btr*-Flying

Fish

in fact-that

we would

change

to a sandwich

balsa

/glassfi

bre construction.

Here the balsa was laid

so that the end

grain

was

in

contact with the

glassfibre

and

the

timber was in

blocla 1in.

thick.

Depending

upon the

position

in

the craft

where

it

was

laid,

and thus the complexity

of

the curve, block size was not

constant

but

an

average

would have been

something

like

3in.

by

3in.

The

great

advantage

ofthis

construction

is

that the resin

soaks

into

the

end

grain

and

so

gets

a splendid

grip

on

things.

Between

each layer of blocks

a

1oz

chopped strand

mat

was inserted

to

key

things

together even

further.

Well the

end

grain

certainly

makes for

a

good

key but it

also soaks up resin at an alarming rate

and

it

appears

that resin/glass ratio

ofabout 3j

:

1 by weight is nearer

the

mark

than the

usual

3

: 1.

Even

so

it

is

possible

to

achieve

a

pretty

light

hull and

here

the

weight

works out to

be 2,2501b,

or

a fraction

over

a ton. The

strength

of this type

of boat is

rmpressrve.

Balsa itself comes

in

all

sorts

of

densities

and can be anything from 4 to about 24lb

per

cu.

ft.

With this

construction, the

lightest

type

is the

best,

for

we are looking

not

for

strength, but

for a

good

core

material;

however

there

are

interesting

possibilities

in

using

the

heavier

stuff

as

planking.

Balsa

at

16lb

per

cu.

ft. is, for

instance-, stronger

than

spruce at

28lb and

when covered

with

a

waterproof

skin of

glassfibre

it

might very well

be an answer

for some specialised

applications.

In

any

case,

when

employing

this

timber

it should

first of all be

kiln

dried

and then

kept

in

airtight

bags

until

it is used.

On

the

Dr

Savundra

ocean

racer a

norrnal wooden

plug

was

made

first

and

then

a mould

taken

from

it.

Inside

this

mould the

glass, resin and

layers

of

balsa

were

laid,

An expensive way of

making

a

"one-off' but

the

only

way

of

ensuring

a

good

finish without

a tremendous amount

of sanding of the

final hull.

Sandwich

construction boats

are

becoming fairly

popular

as a way

of

building a basically

glassfibre

hull without

the

need

of a

plug

and female mould.

The

normal

core material

is

expanded

p.v.c.

which after

hot

air

heating can be bent.to

the

required shape

over a

simple batten

malemould,

or

jig.

On this

p.v.c., glass

is

laid

to

the required thickness, when the

boat

is

removed from the

iib

and further

glass

laid inside. This

system seems to

work

very well

but

there is

always

a

sneaking

doubt

as

to

the

adhesion between

glass

fibre and the

core

material.

Ifit is not

perfect,

a thoroughly

suspect

iob

will result.

Balsa

ensures a

good

bond to the resin and

deserves to be used

a

bit

more

widely than

77

tr

t is.