So there we go. I finally finished the board a couple weeks ago. It was a lot more work than I thought, because I had to try lots of things I haven't done before. The split construction was new to me. So I studied glider wing construction, catamarans and a couple other constructions where light, strong and flexible is the call. I did some basic calculations to get an idea of the longitudinal forces I'm dealing with in the waves, and tripled the results to get a sturdy board. The construction looks fragile but is incredibly strong: the wooden construction in Paulownia is strong enough for the purpose. I added 2 layers of 4OZ E glass on top and bottom, with wrapped rails, to make a really strong board.
As the board is hollow, I had to insert a plug in either section to make sure it's not being damaged with changing temperatures. Left in the car, the board heats up easily to 80+º C in summer. That is a 60 to 70ºC difference to storing and to water temperature. 60ºC rise is equal a 25% pressure rise. That's enough to explode any board - 2.5N per square cm (0.25 bar or 3.6 psi) is a lot of internal pressure. I actually didn't like the pressure plugs on sale, because I believe 25 bucks for a plastic cap is an insult, be it IP 68 or not, and on top they are fugly. 2 plugs at 25 bucks each would have consumed half of my budget for this board
. So I made my own ones out of standard half inch brass water pipe material and a piece of gore tex cloth which I cut out of the inner pocket of an old sailing jacket. Again I had to test this stuff for water tightness, flux rate and so forth. Many working hours went into this kind of tinkering. But it was good fun to MacGuiver my own board. It's a hobby after all.
The fin is an old windsurf fin, a friend left me a couple fins he's not using anymore because he gave up on pole dancing.
My design is the attempt to make a compact yet stable board: the outline is taken from a starboard shape which gets good critics. the rocker however is a lot flatter along the center line making for a fast board, and I used a deep concave to achieve a much more pronounced rocker line along the outline of the board in order to have a good maneuverability in waves. On top, flat deck and deep concave give me a volume distribution with lots of volume in the rails. This makes for a laterally stable board, just like a catamaran, where all the volume is located at the outermost point on either side. My missus is a SUP rookie, and after all the board is for her.
Construction is as always simple: the inner frame is 5mm light ply wood; the rest is paulownia, cut into 2cm x 5mm strips for the deck and bottom, and to fit for the carrying inner construction of the split section. Simple does not mean easy though. As the board has rocker and deep concave, I had to build a rather complex 3D body with a very small error margin. Lots of measuring + cutting to size, which took extra hours' toll.
t.b.c.