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SOF Siskiwit Bay Builder’s Log

Siskiwit Bay skin-on-frame kayak

Peter Lord writes:

I have almost completed the frame of my, shortened to 16’ (x 0.94 in length, frame spacings adjusted) to decrease the displacement slightly to suit my weight of 162 lb (73 kg). It will be for day trips and weekend touring on the Swedish lakes and in the archipelagoes.

It is a hybrid of “fuselage frames” and ribs, as I did not want a frame at station #4 getting in the way of my legs, and I wanted to try making ribs. I used all six ply frames of 5mm Baltic birch I already had,  3-ply glassed on both sides with 3oz cloth) to make the frame with gunwales, keel, stringers and stems, added 6 green oak ribs in the cockpit area and then took out frame #4 and replaced it with a masik beam.

I cut the ribs from a small oak tree growing nearby. I bent the ribs just where needed with a cheap steamer which has a focused nozzle. The wood got soft enough to bend after about 30-60s. Except for the keelson the longitudinals are pine ceiling mouldings which I got on sale at the local hardware store. They are wider and thinner than the usual rectangular pieces, and the outside has three faces at angles, which I will round off a bit to make a smooth curve for the cloth. Should look nice.

The inside of the upper chine stringers and the foredeck stringers is concave. They were cheap, and I also thought that their shape would add stiffness compared with rectangular longitudinals. The inside of the gunwales is like corrugations. The lower chine stringers were also on sale, and are a square U-shape in section, lighter than a similarly dimensioned solid piece. The inside shapes required some fancy cutting of the frames but the stringers fit well into the slots, and the masik ends are cut to fit the inside gunwale shape too. I fastened the longitudinals to the frames with cable ties to test their bendability. Based on previous experience of gunwales and stringers not bending up enough and/or hogging back, I cut 2 long kerfs from each end of the gunwales to frames 3 and 4, bent them in place, fastened them with cable ties to the frames, and epoxied the strips together. The wide upper chine strips were kerfed too, with one cut.

The frames and stems weighed 1586 gm before and 1918 gm after glassing, an increase of 0.73 lb, 332 gm. The lightening holes saved 1.15 lb, 521 gm.

The masik beam is made of two naturally J-shaped bent branches of juniper,  from trees around my house, epoxied and lashed together with a scarph and shaped to symmetry with a drawknife. I supported the foredeck with two ribs upside down and a thin longitudinal thin central stringer from the masik to frame #3.  I made a concave “Rolling Recess” (patent probably not pending) of a piece of 3 mm beech veneer I had lying around, across and supported by frame #3 and two crosspieces. So the back deck is about 1.2” (30mm) higher than the gunwale edge, and level with the top of the coaming. Should allow a good layback, and give a bit more room under the back deck for gear.

The coaming is fiberglass and carbon, bought from a Swedish kayak builder. Has to be supported at the sides by ply plates attached to it and the lower chine stringers. Everything is lashed, no metal parts on this kayak, just on principle to see if I could avoid metal. The ribs and masik are pegged with dowels and lashed to the gunwales and then cut off at the gunwale top. The gunwales are too thin for mortices. All this took some time, but I am not in a hurry, I have other kayaks, and my club has nice fiberglass ones to use.

The completed frame but without the skeg installed, weighs 27.5 lbs, (12.5 kg) on my bathroom scale.  I will glue a bought fiberglass skeg box beside the keelson and support it with wood struts. The aft hatch will go between frames 2 and 3 and the forward hatch in front of frame 5. Design not decided, but will be light. Then the frame has to be cleaned up and oiled before skinning it. Bulkheads will be fiberglass sealed with epoxy and glued to frames 3 and 5, and made watertight by strips of foam glued between the longitudinals.

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