Practical Boat Owner - June 2018

PRACTICAL

than the original, moving the weak point in
the system into the structure of the boat.
Unfortunately, we don’t have the original
specification that would confirm this.
Given that the plan we were forming for
the new rig divorced the chainplate
position from the main bulkhead, Hugo was
happy for the damaged area to be cut out
and a new section of marine ply scarfed in
above it. This was a much easier task, with
lower material costs, than replacing the
entire bulkhead and had the advantage of
creating less trauma for the boat.
Conveniently, the damaged area was
just small enough to be cut from a single
sheet of ply. The only downside to this
plan was that the grain on the new and old
sections would not match, but we had
already discussed painting the bulkhead
white to brighten the interior. Extending
this white area a little further aft would also
include the new composite frames on
which the new chainplates would be
mounted, creating a neat cosmetic
appearance. There’s a well established
rule of thumb in boat repair that, if you
have to make changes, it’s often better to
make a feature of them than to
unsuccessfully attempt to disguise them.
Hugo also specified the areas of the teak
over plywood deck that would need to be
replaced, including which frames the
scarfs at the joins in the timber would
need to be above. Zest sustained some
hull damage when the jagged end of the
broken section of the mast was cut free
and released into the water. This had
punctured the epoxy/glass sheathing in a
number of places and had dug into the
outer double diagonal Douglas fir
planking at depths of around 2-7mm.

Structural engineering
While the bulkhead, without the
chainplates, would now be subject to
lower loads than previously, these new
frames clearly needed to be properly
structurally engineered. For this we turned
to StrucTeam in Cowes, where Jonathan
Evans and Martin Calmon calculated an
appropriate specification, with generous
margins of safety, including solid E-Glass
in way of the bolts for the new chainplates.
Chris Horne of CWH Composites –
whose background is as a laminator in the
Formula One world – then made up the
frames to specification and bonded them
into the boat. They span the width of the
side deck, and are tied into the carlin at
the coachroof/deck join, and the beam
shelf where the deck meets the hull. They
then extend down the side of the hull, and
along the bottom of the boat, tying into the
bunk fronts. The inner edge has a marked
concave curve, which means intrusion into
the saloon is minimal.
It might seem odd opting for a
composite solution here, instead of
plywood, which might appear more in
keeping for a wooden boat. However, the
ability to orientate immensely strong

uni-directional fibres in optimal directions

to support the colossal loads resulted in a

solution that’s aesthetically pleasing and

that’s neat in an engineering sense. Each

one is engineered to support a breaking

load that’s close to three times Zest’s

displacement. But the fabricating cost was

significantly higher than simply bonding in

big slabs of plywood.

Preparing the bulkhead

Martin Nott, who we engaged to do the

bulk of the woodwork, was not able to

start work straight away, so I kicked off by

removing the damaged section of the

main bulkhead. This had been one of the

first elements of the boat to be built, so it

was sandwiched between two substantial

laminated frames, with the hull planking,

deck and coach roof subsequently

assembled around it.

I started off by using a saw blade in an

oscillating multitool to make a rough cut

across the top to separate it from the

coachroof, taking care not to damage the

frames either side. The next stage was a

quick cut along the bottom with a jig saw

so the damaged section could be

removed easily.

I then used a small router to cut a

perfectly straight edge at what would

become the top of the scarf joint on the

lower section that remained in situ. To

achieve this I attached battens to use as a

fence to guide the router. This produced a

dead straight and clean cut, without risk of

splintering the top veneer.

After that it was time to remove what was

left of the bulkhead between the two

laminated frames. Again I primarily used

the router for this, being doubly careful to

set up a fence so that the laminated

frames could not be damaged. It generally

made quick work of the bulk of the task,

other than in a few inaccessible corners.

For these I used the multitool saw to

‘If you have to make changes, it’s often

better to make a feature of them’

The damaged

area of bulkhead

removed and

fences set up

to trim straight

edges with a

router

LEFT The two

laminated frames

that the bulkhead

fits between – the

gap had to be

cleaned out