TECHNICAL
MAY 2016 http://www.yachtingmonthly.com 79ABC(^1)
2
3
Hanging
locker
Heads
8in (20cm)
3
A
Flexible water tank
Waterline
Bunk platform
Forecabin area in a Sabre 27, showing
adaptations to create a partial collision bulkhead
around under-bunk lockers A, B and C
Fresh water plumbing
Position of bulkhead seal
KEY:
A serious ingress of
water can be too
much for a yacht’s
bilge pumps. You
may only have
PHOTO: ROEL ENGELS/PPLminutes to act
GRAPHIC: LIZA SAWYER
Will it work?
Although I have no intention
of testing this arrangement by
making a hole in the hull, I am
confi dent that it would help to
safeguard the boat. The most
likely impact position would be
below the waterline, or close
above it, and forward of the
keels. The protected zone covers
most of this area. Any infl ow of
seawater should only affect the
compartment where the damage
occurs and should only rise to
waterline level, which is 20cm
below the locker lids.
In principle, any water ingress
would add weight forward and
cause the bow to sink, but the
effect should not be critical
because the weight of water in
any of the compartments would
be quite small. In fact, the largest
compartment already contains
a 150-litre fl exible fresh water
tank and when full the tank’s
top surface is 10cm above the
waterline. If that compartment
was holed, very little additional
water would enter, even allowing
for the greater density of
seawater, and there would be
risk reduction.
I believe a signifi cant
proportion of GRP yachts (ie.
several thousand boats) could
benefi t from similar precautions,
if they have not already been
implemented. The foretriangle
berth has been near-ubiquitous in
small and medium-sized cruiser
designs since the 1970s and in
most instances the bunk platform
is above the waterline.
Many yachts with outward-
draining anchor lockers have
with sealed under-bunk
compartments, but these
have been pierced for
pipework or other services.
Sealing compartments
would be more diffi cult
where lockers are accessed
by doors or drawers, or
where the bunk structure
is not glassed to the hull.
In many cases it should
be possible to achieve at
least one semi-waterproof
compartment – giving
some peace of mind when
sailing over a dark sea that
may conceal nasty, hard
fl oating objects.W
Brown tape marks the outline of the
collision bulkhead, which should control
any leakage from an impact in this area
PHOTO: KEN ENDEAN
‘Several thousand GRP yachts could
benefi t from similar precautions, if they
have not already been implemented’
virtually no effect on the boat’s
trim. The other lockers would
admit only relatively small
volumes. There is a risk of water
sloshing up out of the locker
hatches but if we were holed we
would allow the boat to come
upright and the locker contents
would reduce water oscillation.
In big-ship damage control
terminology, what I have created
might be described as an open-
top cofferdam, rather than a
collision bulkhead, but it is a
perfectly respectable approach to