Bulkhead C with top frame.
February
'06
3. Bulkhead Construction
4. The Hull Panels
5. The Stitch Up
The bulkheads are of 9 mm ply, and the original plan calls for them to be framed in 18 x 75 Oregon on the side and bottom, and 18 x 100 on the top. In the stitch and glue version these frames can be dispensed with, except for the top ones, which are needed to support the deck stringers. The clear Oregon frames are epoxy glued to the bulkheads and notches are cut for the eventual placement of sheer clamps.
Bulkhead
C with top frame.
Being inexperienced
in boat building, I made the mistake of taking the plans
literally, and cut out the bulkheads to the exact size specified.
This was a major miscalculation, as will be seen later.
The lofted and scarfed plywood panels were connected firmly to each other with dowel pegs and clamps, and cut close to the line with a jig saw. The final paring was done with a block plane. The two bottom panels were then drilled for the wires on the central seam, and the two side panels were drilled along the chine and bow.
Bottom
panel dowelled at the stern and clamped at the bow
Starboard
hull side attached
I used galvanised steel wire to stitch the panels. At the bow end where the tension is greatest, the stitches are spaced 25 to 30 mm apart. For the rest of the panel they are about 150 mm apart. The Selway Fisher plans suggest that bevels are not needed for the panels, and there is a bit of a struggle getting the parts to lie in the correct alignment, but the bulkheads are sized to fit non-bevelled hull panels, so there is not much to do about it. However, at the stern end of the bottom panels, where there is 180 degrees between them, there is no space for epoxy filleting. A partial bevel on the inside of the midline does not alter the measurements for the bulkheads, so I incorporated one there for the fillet.
All appeared to be going to plan, until the bottom panels were spread apart on the supports. After that the stiffness of the ply made it impossible to make the panels conform to the support profiles, which were supposed to be the profiles of the hull itself. Gradually the bow lifted higher off the supports as the side panels were stitched in, until a shape quite different to the A bulkhead was achieved, with predictable inconvenient consequences: gaps.
The gap as seen from the stern inside and from outside the bow.
The first problem
was a gap between the side and bottom panels, which was very
difficult to close. Eventually, with a lot of pressure from
outside and in, and half a day's labour, a reasonable
approximation was made. This involves a Spanish windlass inside
to wind the bottom panels in, and a wedge driven stake from
outside.
The
persuasion (left) and the
windlass (right).
The next problem was that the first bulkhead (bulkhead A) did not fit. It had been cut according to the plan, but it was grossly out compared with the hull shape. A new bulkhead had to be fashioned to fit the hull. At the end of a full day, only the B bulkhead was in position.
It took another day to fit the remaining bulkheads in their right positions, although it became much easier towards the stern.
Bulkheads
A to D are visible, along with temporary
sheer supports and the
girder
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Problems
shows higher resolution shots as well.