Chapter 2 From the Drawing Board to Reality
Here?s where the fun begins!
Having drawn out the hull shape the next step is to prepare the drawings for actually building the boat.
An allowance has to be made for the thickness of the hull material so that the finished boat is only as big as the drawings. In my case I offset the sections in 3mm (about 1/8? for the metrically challenged!), making each section that much smaller. By the time I strip plank the hull with 3.2mm balsa, sand it a bit, then glass & fair it, the hull turns out the same size as the linesplan.
I also make an allowance for the deck edge detail and slot each frame so that it all goes together kinda like one of those wooden dinosaurs skeletons you get for your kids.
The strongback
Because in this case I?m building a plug and not an actual boat, I don?t have to worry so much about weight, but there are other concerns. When the plug is used to make the female mould, a fair amount of compressive force is applied to the plug so I tend to build it a fair bit stronger than would otherwise be necessary. I make the frame spacing a little closer, run a full depth center girder down the middle and use a good, heavy strongback to attach everything to.
The strongback is made from 12mm ply (see photo above). Using a docking saw, I slot the ply about 5mm deep at the same spacing as the frames, as well as a longitudinal slot on the centreline. Because the kerf is almost exactly 3mm wide the frames (made from 3mm MDF) slide straight in allowing perfectly square set up. When these are glued into position the whole assembly is very neat and rigid and will not flex or bend.
Did someone say dinosaur?
Next step is the actual planking. I use planks that are a constant width. Its quick and easy. Another way is to measure the girth at each section and divide that up by the number of planks you plan to use. For example, If the girth at station five is 200mm and the girth at station 1 is only 100mm, and you plan to use ten planks then the plank needs to taper from 10mm wide where it hits station one to 20mm wide where it hits station 5. Geddit? Tapering each individual plank so that is wider in the middle (where the hull is fattest) and narrower at the ends means you end up with the same number of planks at each frame rather than having them run off into the keel line. I found this way pretty tedious and since I?m only building a plug here just stick with straight planks with tapered ends where they meet the centerline. It?s a slow and gluey process but there is a certain delight in seeing your baby take shape in the real world for the first time.
Gluing the planks
After a good sanding to eliminate any bumps caused by planks misaligning (okay, the secrets out, I?m no carpenter) the hull is ready to be glassed and faired. A story for next time??
Finished plug ready for glass
Please post any comments and suggestions??.
Troy
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fullhull.jpg
Jig.jpg
planks.jpg
strngbak.jpg