Of
all the many materials and fittings required to build this boat, I did not for
one minute expect that the supply of the centre plate would be a problem, I
contacted several companies inviting them to submit a quotation and received a
very mixed response. It seemed that they could supply the plate cut to profile
but were unable or unwilling to drill the holes or machine the edges, some
never even bothered to reply. To obtain a quote for the machining was a real
challenge, citing excuses about handling the weight or just submitting a silly
price to make me go away, no one really wanted the job. Out of frustration I decided
that I would undertake the drilling and machining myself and placed an order
with the most accommodating company to have the 25 mm thick 316 grade stainless
steel plate cut by laser to a DXF file supplied by the architect. When I turned
up to collect, it was loaded into the back of my pickup with a fork lift.
The
plate is very heavy at around 100 kg and I was handling it by myself, I therefore
decided to keep it low down to the floor on a pallet and blocks then take my
bench pillar drill to the plate. I created the rounded profile on the forward edge
by grinding with an angle grinder fitted with a ceramic grinding disc. The
chamfer on the aft edge I machined using a milling machine in a friend’s
workshop, I blended in the end of the chamfer again using the angle grinder.
The centre board case is very tight, prompting a concern that the shackles
connecting the blocks might chafe the sides of the case and cause wear,
allowing possible water ingress into the plywood. I therefore decided to
machine a 5 mm rebate either side of the plate around the anchor points to
compensate for some of the thickness of the fittings, I then used Allen key
shackles as opposed to the conventional type to further increase the clearance.
Set up for
drilling on the barn floor
Clamped down on the milling machine bed ready to machine the chamfer
The machined rebate
to minimise the projection of the shackles
The finished
article ready for installation
Installing
the plate into the boat proved to be a challenging operation. It became
apparent that the whole assembly would not feed in from above so it had to go
in from beneath. The boat had to be moved back on the trailer cradles to give
clear access to the centre plate case which was partly obscured by the beam
axle of the trailer, I then jacked up the boat as high as possible from a
position just aft of the case opening. The plate was slid under the boat on
timber battens then reared vertically on its edge whilst attaching the hoisting
blocks, shackles and line. I then raised the plate into the case hauling on the
installed tackle plus an additional lifting rope passed through the pre-drilled
handling hole, lining up and inserting the pivot pin proved to be easy, an unexpected
bonus. Because of the extended clearance between the keel and the ground, I was
then able to carry out a test run lowering and raising the plate to check that
everything was in line and working as intended.
All
that remains is to cap and seal the centre plate case, carry out some further improvements
to the rigging and she’s ready for
launch.
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