and just what do deep vees do
TRANSCRIPT
-
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.