The bottom line

Plating the bottom. I started by cutting some limber holes, just along the bottom chines. I left the forward bulkhead without, the space there will be completely water tight.

The limber holes are glassed to protect the end grain:

 

Also, some minor defects are filled, no reason for them to collect dust and moisture.

For the plating itself I decided I want to try to scarf join the plates instead of using butt joints like on the sides. There will be 2 layers of plating so the scarfs will complement each other and make for a nice and flat bilge. I cut the scarfs by hand on 2 plates simultaneously in order to get the angles right. The scarf ratio is 10. Gougeon bros recommend 8 for epoxy joints, some poeple say 12, I went with 10.

As always, all mating surfaces are pre-wetted:

Then the plate goes on (with a squiggly line of thickened epoxy inside the joint) and is screwed tight using 3.5mm self drilling steel wood screws. Those will be replaced with 5mm stainless screws.

The loose scarf gets some additional clamping:

The scarf joint if screwed between a piece of scrap plywood (to force it to follow the bottom line) and a plank from below (don't have any pictures though, it is kinda hard to try to get everything done before the epoxy gels AND take pictures with all glued up hands...)

First layer done. Was not too hard, although it was stressful and kinda fiddly and time consuming.

The joint came out perfect, with some squeeze out on both sides; curving where it needs to curve.

After some trimming the temporary fasteners were replaced with the larger stainless screws. 30mm long along the chines, 35mm along the frames and 50mm at the transom. I filled the holes with slightly thickened epoxy to improve holding power - the wood surrounding the fastener becomes tougher and should make the bond stronger (to be tested). Just an extra precaution since I am using quite soft wood. I would not have done this in oak or ash for example.

The second layer went on in a similar fashion, first I prepared the plates and scarfed them.

I troweled slightly thickened epoxy on the first layer without pre-wetting the surfaces. Should the bond be slightly worse the large surface area will make up for it. I used 20mm fasteners to provide some clamping force (the bottom is relatively flat so not much force is needed). The scarfs are clamped using some scraps of plywood screwed to the plates on both sides of the joint to force them into shape.

After it all cured I trimmed the overhangs almost to where I want them. I will leave the final shaping/sanding for later when I'm ready to glass the hull.

The joints look quite ok:

It did took quite some hours of work but the final result does, finally, look like a boat:

Next step will be attaching the stem cover plate, replacing the rest of the temporary fasteners in the hull, filling and fairing the screws and holes and, finally, turning the hull to start working on the interior and the deck. I want to do the interior first, before installing the deck, otherwise it might get a bit cramped in there.

Tot de volgende keer.

Turn of the bilge - done. The story of a bitter victory.

Bending plywood proved to be a challenge. Maybe it's just the plywood/stringer material I'm using, but the results are not quite as good as I was going for. To cut to the chase: plywood does not like to be bent and is trying to go straight again exerting quite some forces on the skeleton. So if that is not stiff enough the water lines turn out not as smooth and fair as intended. This specific design does not seem to have enough stiffness, at least the way I'm doing it:) (maybe that is the problem). In hindsight I wish I had made an additional station between frames D and E (first and second counting from the stem). Also maybe an additional stringer or two. The deviations from the hull form lines are not very large, but noticeable, I'm not worried, it's all still structurally sound and hydrodynamically it will also not matter - not at the speeds a 5m sailboat is capable of. It's also very unlikely anyone but me will ever notice:) So enough yammering, on with the pictures:

Installing the bow section went fine as it was already pre-bent as described earlier. Installing the section directly aft of it was tricky due to the curvature at the front side and the length of the panel. I started at the bow, fastening one corner with a temporary bolt. This made bending the panel into place easier:

I used bolts also to force the butt blocks into shape, went with 8mm plywood, the 10mm was impossible to bend in such small pieces. I will reinforce the joint with extra glass on both sides.

While the epoxy it still malleable I clean up the squeeze out and make fillets on the inside. 

Trimming is quite easy:

No plywood is perfect:

Below, the subtle flaws in the curvature along the water lines are visible. I may have minimised this by choosing to join panels closer to the frame, but the effect would still be there. Just in between the stations, where nothing rigid supports the stringers the plywood tries to flatten itself out. It both pulls the unsupported bottom chine to the outside and the middle stringer to the inside.

Other things I could have done: install the bottom plating first. Would have prevented the bottom chine from developing the complication. But would have made installing the bilge plating way tougher. I could have gone the way most setka builders go: make it all flatter, avoid the large compound curvatures, would have helped some. I could have installed a (half-) frame and additional stringers. Next time maybe:)

Checking the global geometry shows all is well in terms of symmetry, straigntness and trueness of the hull:

On to installing the bottom now.
tot ziens.