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> Building Kayaks and Kayak Accessories > Building "Sofistry"

Anatomy of a Skin-On-Frame Form:
I’ll be building this kayak on a bunch of forms raised above an external strongback. The strongback will be a simple 8’ long box beam of 1/2in plywood with dimensions of 8” wide by 4” high. This wide size will allow the whole boat assembly to be stable wherever placed.

The external strongback approach is chosen because this kayak cannot be split open to remove an internal assembly. This build approach will also sacrifice ALL the forms as they will have to be cut into little pieces in order for them to be removed from the built frame. Stupid, huh? Good thing that I'm using Daren’s shop and all his handy handy tools!

Mounting
The forms will be attached to risers coming up from the strongback with 1/4" diameter bolts, but their centrally located bolt holes are 3/4" diameter to allow lots and lots of movement for leeway to set all of them in line.

Alignment
Outside of the bolt holes are two 1/2" diameter holes centred on bulls-eyes. Two stringlines will be tensioned through each of these two sets of holes so that one can readily check alignment at all stages during the build.

Stringer notches
Deep notches are put in the forms so that the stringer assemblies won't fall out too easily. Each notch has 1/16" extra stringer clearance all around to allow for glueup discrepancies and to assist in actual placement. I am guessing that the natural self fairing qualities of the wood stringers will overcome this 1/16" leeway. The notches are 7/8" diameter, the stringers are four 3/4" wide strips cut to 3/16" thickness to make a 3/4" square. The first and last strips will have the outer edges chamfered to allow twist.


Rail notches
Rail notches are cut only to rail depth, but are cut over size at the top. The driver shape is the notch bottom so there is 3/4" thickness of plywood left there to support hard clamping of these shapely members. This area could have been improved if I had cut the outside lower edge to the same angle as the rail bottom in order to seat the clamps better. In the end, it doesn’t seem to matter, but it would have been better. The oversize slot allows wedges to be driven at the top of each rail to jam the assembly together on setup and through the build.

One other funny thing about forms like these is that they are larger than any other type of internal kayak form that Daren or I have made and that the outside shape is quite immaterial to the eventual yak shape – only inside location of the stringer and rail holes matters. This form is marked -2-6, which means 2'-6" sternwards from what I mark as the centre of the yak.


there's an ongoing discussion in our forums about this project if you have any questions or comments.
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