Tuesday 30 March 2010

Building Simbo

Having decided to build a small boat for small waters, I started the search for a suitable design. It needed to be quick, easy and cheap. Hannu's Simbo was the obvious choice, as the hull pieces are cut using practically straight lines out of one sheet of ply - it is very clever.
However, Hannu uses 12mm (half inch) ply to eliminate the need for any reinforcement. Unfortunately, this also means he has to build a jig to force the bottom into a curve. And I happened to have a nice sheet of 5mm (quarter inch) ply that Alec Jordan used to protect the kit for the Bee he supplied last year and I still haven't got round to building yet. Alec kindly confirmed that the ply is exterior grade and OK for a boat - so every Jordan Boats kit comes with two 'single sheet' boats free outside!
Using thinner ply also allowed me to adopt a much simpler 'tape and glue' construction using duct tape to hold the bits together for gluing with epoxy.
The first step was to draw the cut lines on the ply, which took minutes, and cutting them out with a regular cross-cut saw - Hannu correctly points out that you have much more control with a handsaw than a powered jigsaw and the lines are much straighter as a result.
I then attached the hull sides together with epoxy and tape, separating them from each other and the work surfaces with builder's plastic sheeting. The joints were clamped down with a pair of decking screws through each end of a bit of scrap timber.
The epoxy was SP, mainly because it is the only brand available in local chandleries, and has a 5:1 mixing ratio. To get it correct, I prepared a measuring glass by putting a sticky label on a disposable drinking cup, filling it with exactly 100ml of water and clearly marking the level. To measure out the hardener I used one of those little 20ml measuring cups you get with cold cures, which are never thrown away in our household.
Construction ceased to allow the resin to cure. Tomorrow: going 3D.

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