January '06
1. The Lofting Table
2. The Scarfing Jig 

1. The Lofting Table

In the end, the attractiveness of stitch and glue for a first time boat builder was the deciding factor, so the first step was to make a table which could be sturdy enough to act as a base for the construction cradle, and would allow for scarfing and lofting of the plywood panels. Therefore it needed to be 1.2 metres wide and long enough to accommodate the first and last support frames, which were to sit under bulkheads A and F, ie. just over 5 metres long. There would be six support frames, and six sets of legs. Aprons were of 40mm x 150 mm Oregon, and legs were of 90mm x 60mm Western Red Cedar. The table top was to be of two sheets of 19mm. ply, plus an offcut to fill in the rear 200 odd millimetres.

Hull supports were fashioned from 9 mm. ply, which were cut to the same profile as the bulkheads, and were located beneath each bulkhead. The number of supports used might have been excessive, according to the recommendations of some of the books I have read, but this number was chosen so that they would fit directly underneath the boat's bulkheads. That way I could cut the angles as laid out in the plans rather than extrapolating a shape from a computer program. (While they were adequate in the early stages of construction, they were a bit weak as the weight of the boat increased later, especially when it became necessary to get into the boat at times.) But they served the purpose. If they had been cut from thicker stock it may have been necessary to bevel them to fit, and that would have defeated the purpose of copying the bulkhead profiles.

The table under construction, and finished with supports.

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2. The Scarfing Jig

In order to achieve an 8 to 1 ratio in the scarf joints, the cut needs to be 7.2 degrees off horizontal. A jig designed to hold a portable saw at that angle was devised and published on a web site concerning canoe construction: Scarfing plywood sheets - scarfing jig . I used this design to make one myself. In retrospect, I would probably not do so again. The weight of the saw (about 7 Kg.) made it difficult to keep a straight line during the cut, and the scarfs were not ideal.

The jig in construction.

The jig in action.

The saw is held at about 7 degrees above horizontal.

With 9 mm. ply, the width of the scarf is over 70 mm., so a 235 mm. saw blade is needed. The scarfs were a bit uneven, but perfectly functional with epoxy. However, there is no possibility of using a bright finish on the boat because of the plainly visible glue line. Next time I might try the Gougeon Bros. Scarfing Attachment
The Scarfer from West System Epoxy

 
My slightly wavy scarf...and the resultant joint.

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