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Building my own kayak (3) – Compensating sloppy foam work & prototype preparations

August 26, 2013

I have noticed a twist in my plug that becomes even stronger towards the stern. Instead of starting with surface finish work this needed to be fixed first. In order to compensate the twist I had to remove about 2cm of foam (which has already been covered with glass and epoxy) at the right-hand side of the stern hull, and I had to add these 2cm at the left-hand side of the stern deck. I used an orbital sander for grinding off material and initially I have used polyester putty for the extension (only on top of the glass because the solvent contained in polyester resin eats styrodur). Due to its price and the complicated processing (hardens within 5-10 minutes), I have swapped to using plaster. I got a 5kg bag of plaster powder in a hardware store for less than 10 EUR, which just needed to be blended with water. The processing is very simple as one can almost arbitrarily refine the shape of the applied plaster. Up to now there are two shortcomings: my foam plug is now quite heavy – I guess I have added about 5kg. Also, the hardening process of the plaster takes ages due to its thickness (it is drying for three days now, and the thick spots are still wet). Also, I am a bit worried that the plug becomes brittle and might finally break, retrospectively I should have attached some small stripes of the original foam first, and then just do refinement using the plaster…
For recognising at what places to compensate for the twist and other major irregularities a water bubble and viewing from orthogonal angles (to the boat’s main axes) were the most important ingredients. Apart from some minor-ish surface irregularities I guess I have a somewhat smooth and symmetric boat. I expect to be able to fix these later on using thinned polyester putty. Up to now this has taken me around 14 hours – there is still some sanding to do after the plaster has completely dried.

Next, I will create a prototype directly from the foam plug. I will do this for mainly two reasons: Firstly, I am quite unsure whether I will actually fit in the boat and secondly, being my first boat to be built I have no clue whether the shape will actually work. So the plan is to roughly evaluate the current shape, do changes accordingly, finish the surface and then create a mould. For creating a prototype as cheap as possible I will just use some plastic wrap sticked to the plug using double-sided adhesive tape as separation between the plug and the glass work. I have in mind to use only 3 or 4 layers of 160g/sqm glass – there is no need to last more than one or two flat water sessions. If that’s not stiff enough I can still add some more layers after the first layers have cured.

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