Tuesday, January 30, 2018

Chine Stringers for Our Sportfisherman 26

Continuing with the 26ft sportfisherman project, the next step is to fit the chine stringers. This boat has a chine step that will be planked with Douglas fir strip. On the inboard edge of the step there is a stringer to support the outboard edge of the plywood bottom skin. These stringers fit into slots in the bulkheads and are housed at their ends into the transom and the stem.

That sounds like a simple process and for most of the hull length it is simple. Toward the bow it becomes more difficult because each stringer has to twist to follow the bottom panel and bend to follow the chine. It takes considerable power to pull that twist into the stringer as it goes into place.

The stringers also have to pass through the forward ends of the girders, with slots fashioned to fit the stinger path. The shapes of the slots through the girders are not easy to establish, so there is considerable work with saw, chisel and rasp to form the slots and filled epoxy is needed to fill in the inevitable gaps.

The end result is good. The photos and captions show the process.
The slots through which the stringer must pass on its way to the stem. The slot shape only applies on one surface of the bulkhead or girder, which must be used as a guide for shaping the bevel angles for the stringer through each member. In these photos the light coloured bulkheads are temporary formers, the darker ones are permanent and the horizontal members are the girders.
The slots through the temporary former and the girder have been shaped and the stringer is a reasonable fit. The upper edge of the girder will be bevelled to match the bottom skin, which will bring it into the same plane as the outer face of the stringer.
This photo shows how to establish the bevel shape of the stem to match the hull skin, also giving the front edge of the stringer when housed into the stem in the correct position. The stringer is now in the bulkhead slots but is short of the aft face of the stem, so it is lying at the correct angle relative to the stem. The saw is used to cut into the stem, down to the point that the saw teeth are touching the outer face of the stringer. The resulting saw cut is an extension of the line of the stringer.
The socket to receive the end of the stinger is easily made with a saw and a chisel. Housing it in like this is a stronger option than simply gluing and screwing to the side of the stem.
The socket for the aft end of the stringer in the transom is done in similar manner to the one in the stem. 
The stringer glued into its slots, passing through bulkheads and girders. The blue painters tape is there as a bond breaker to prevent adhesion where it is not wanted.
Here you can see how we pulled the twist into the stringers. We fitted the two in parallel, gluing both in the difficult twisted bow sections first before moving aft on one, then the other. The clamps are holding the twist in the forward ends, with the clamps lashed together with ropes pulled tight to provide the torque needed.
Stringers showing fair curves and securely lashed until the epoxy has fully cured.
The next stage of building will be to prepare the bottom framing to receive the bottom skin, by planing bevel angles on bulkheads, girders, keel and stem.

This design is not yet complete, so is not on our pricelist or website. See our full range of designs on our main website or our mobile website.