Kayak Shop 24- Bulkheads, foot braces


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24. Bulkheads

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Bulkheads partition the kayak into separate compartments. This serves two functions. It creates watertight storage but more importantly, provides flotation in case the entire cockpit floods. (The picture shows Cape Ann Double)

I usually make bulkheads from 3" Minicel foam for extra flotation or lightweight sandwich core panel. It can also be made from 1/4" plywood. The bulkheads fit loosely (1/8" gap all the way around) and are held in place by heavy silicone fillet.

The bulkheads here are made from 1/4" plywood coated with varnish.

Both are of exact shape as station 7 and 12 of the mold. This is only a dry fit for illustration. Note the holes in the rear bulkhead. The two in the center are for hardware to hold the rear hatch and the two on the sides are ports for rudder cable housing.

The black stuff is a band of unidirectional carbon fibers to reinforce the underside of the rear cockpit. The bulkhead further strengthens the area.

The best way to hold the bulkhead in place before applying a fillet of silicone from both sides is to 'stitch' it in place by a few beads of hot melt glue.
The last thing you want, is to dislodge the bulkhead and smear silicone all over the interior of the kayak.

The clamp is holding freshly bonded back rest attachment loop.

Apply a bead of marine silicone sealant (or any good quality silicone) on both sides and smooth it into a wide fillet.
The joint need not be reinforced with fiberglass and epoxy, in fact, the bulkhead need not be in contact with the interior of the kayak at all. The silicone can bridge the gap 1/8" (3mm) and it is strong enough to withstand the pressure of a completely flooded cockpit.

In general, bulkheads are rarely installed in full contact with the hull skin. Often, fillets and/or cushioning gaskets separate the hull from the bulkheads. One of the reasons is that the bulkhead can 'telegraph' through the thin skins or may worsen the damage to the flexible hull on impact near the bulkhead.
Practically speaking, neither of these circumstances apply in wood strip construction. The strip core is too stiff for the bulkhead to 'print through' and the skin may never flex to such degree that a stiff bulkhead would cause more damage on impact. Nevertheless, leaving a little gap for the silicone is a good practice.

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Mail:
Vaclav Stejskal
58 Wood Ln.
Acton, MA 01720
USA
Tel: 781-481-9261

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