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Building my own kayak (1)

July 27, 2013

I have decided to build my own squirt boat for various reasons: it is a lot of fun, I like making something that one can touch and I will learn a lot while doing this. Up to now I have noticed that it is less difficult than I actually expected, but let’s see how I think about that later on.

I have started by designing a 3d model using the great open-source software Blender (www.blender.org). Pierre Villecourt has given me a 3d model of his own squirt design, the Funk. This was very useful for seeing how particular features of a boat are modeled using 3d software. However, I decided to create my own model from scratch as I did not want to just copy his boat. Creating this design took me about 12 hours of work. Below you can see a few screenshots of  the result:

The main application of the boat will be flat water, thus I have kept it short (about 250cm) and I made sure that the volume distribution in the bow and stern is in equilibrium (see pictures above). As I have a lot of problems with numb feet in my other squirtboat I have focused on having a lot of foot room, which is additionally exactly at the place where I need it. For compensating the additional volume of relatively large foot bumps I have removed some volume in the hull that sits between the legs. The full version, i.e. unchopped, has approximately a total volume of 100l – rather a bit too much than too little. One can always take volume out along the seam between hull and deck.
The next step was the creation of cross-sectional templates of this model. For that I have coded a little programme that was able to do this extraction for me – as I am working with 3d medical imaging at my job I was able to reuse code that I have written earlier. This took me another 8 hours, I guess. The resulting templates look as follows:

Next, I printed out these templates on paper, cut them out, drew the outlines of the boat’s cross-section on cardboard and cut out these cardboard templates. Using a total of 25 templates I have cut 25 cross-sectional pieces out of 10cm thick styrodur foam. For cutting each of these cross-sectional foam slices I have attached two templates (one to the top and one to the bottom) to the foam using little pins. With that I have created a cardboard guide rail, whose path can easily be followed by a hot wire cutter. I have created a hot wire cutter by myself by attaching a guitar string between a wooden arc. Heating the string up is achieved by attaching both ends of the string to a computer power supply unit (using the 12V connectors let the string glow, so I attached it to the 5V connector, resulting in a slow but accurate cut). In order to compensate for the expansion of the string when hot, I have attached a spring (taken from a bike tyre pump) to one end.
Up to now, the cutting of these foam slices was most of the work, I guess it took around 20 hours in total.
Attaching all these foam slices together results in a rough original size model of the boat. Currently I am waiting for the glue to cure. Next, I will shape the cockpit rim and then an endless cycle of sanding will begin.

In the meanwhile I have started to create a little miniature plug of my 3d model – simply because I am not very familiar with composite work (have done two squirt boat reseaming jobs and a poor paddle blade repair) and I do not want to ruin a large amount of supplies. Thus I have decided to perform the entire procedure using a miniature boat to find out if the results are as expected. Here are a few pictures:

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