Assembling the mould
I assembled the mould by screwing 75 X 75 “legs” to the strongback at the correct spacing, and then used a laser cross level to both align the formers, and to ensure that they are at the correct level. The guide lines that I printed on the paper plans which are glued to the formers proved invaluable.
The next step is to plane the edges of the formers to the correct angles so that the strips will lie in a fair curve. This at first seemed a bit daunting as the bevel angle changes at a rate dependent on the size of adjacent formers from centre line to shear line. However, I made a jig that attaches to a very old Record rebate plane with an arm that runs from the plane to the adjacent former. One side of the jig runs against one face of the former being planed, and the rebate fence runs against the other side. This serves to keep the arm square to the former. This system is not mathematically correct for (at least) two reasons. Firstly the strips will not run as straights between formers, but as curves, and so the bevel needs to be greater to allow for the curvature. Fortunately, the back edge of the guiding former is too high, having not been bevelled, and so this increases the angle of bevel. Secondly, the strips will not always be laid at right angles to the formers, and so I expect some final adjustments will have to be made when I check the fairing before I start the planking process. On the small amount that I have faired to date, the result achieved with my jig have exceeded my wildest expectations.
A small diversion
Thinking ahead, I have been worried about the fibreglass sheathing process, as this is a technique that is new to me. I therefore enrolled on a course in the use of West System® Marine Epoxy at West System International in Wiltshire. The course content was comprehensive, and the presentation informal, making it easy to ask questions. The “students” got some hands-on practice, and came away feeling much more confident in their use of epoxy, and, for me, a feeling of relief that laying fibreglass sheathing is not nearly as terrifying as I thought. I picked up tips and experience in bonding and filleting. I also learned that I should lay the strip planks convex side up, and not concave as I thought, This is because the strips are only held in position at the mould formers, and a reservoir of glue in the concave edge would migrate away from the pressure points, thus slightly forcing the planks apart near the mid point between formers.With a large number of planks, this deviation could become noticeable.
West System® Epoxy was started in America by the Gougeon brothers, who invented the sheathed strip-plank method of boat building. They wrote a book “The Gougeon Brothers on Boat Construction”, and it can be downloaded free from the West System International website. It is a weighty tome of 400 pages, so not exactly bedtime reading, but it is superbly informative, and wonderfully indexed. As I move through my construction process, I just read the relevant chapter. A tip that I picked up for my mould assembly was to paint the edges of the mould so that as the bevels are cut, you can ensure that you do not cut into the “controlling edge”, as the Gougeon Brothers call it. The aim is to leave a hair-line of paint along all of that edge.