Foam Blanks

The last time (way back when), that I built a board, the sourcing of materials was dead easy. Basically you went polyurethane for the blank and e-glass/polyester for the shell and that was it. The task was also simplified because it was a short-board hence no centreboard, the mast base was fixed and consisted of a finbox and the blank was small enough to fit within the standard repertoire of a surfboard maker- and so was easy to purchase.

The longboard racer is a different ball game.

Not only has the choice of materials increased, but now it is necessary to deal with a sliding mast track system, a fully retracting centreboard and a board length beyond that of even a surfer's stand-up paddle board. The latter makes the purchase of a blank+stringer directly from a surfboard manufacturer more difficult. Additionally, it now appears that expanded polystyrene or extruded polystyrene are the materials of choice for the blank. A good introduction with respect to these materials can be found at Fibreglass Supply

After some searching, I've been able to source some blanks of a suitable size. Shapers Australia is a good possibility for people who live in Queensland Australia, not only having blanks, but also appearing to be a one-stop shop for most of the other materials required to build a board. Unfortunately I have not found a surfboard manufacturer in Victoria who can supply a blank with stringer of the required size. However, Polyfoam Australia have high density (24 g/l) EPS blocks of dimension 500cm x 120 cm x 60 cm which can be cut down to a suitable (rectangular) size. And, wonder-of-wonders- a sister company StyraPak P/L can supply computer cut blocks of EPS or the higher density XPS. The computer-cutting capability presumably means that they could cut a rocker into the block and potentially save heaps of elbow grease and some of the agonising during the shaping stage. I've just emailed StyraPak and am waiting to hear back. Stay tuned!

Working on the fundamentals

Thank-you rob134 for the encouraging comments and the 'Crownie' challenge. Thank-you Pat for the offer of help in the board design and the chance to contribute to a blog on LBWS. It's great to see that some Starboard Phantom 380s have made it to Australia.

The last couple of weeks has been spent working on some of the basic requirements of the board building project. This has included board design, coming up to speed with software for drafting the board design, and researching and sourcing the best materials for board construction. Although this is all very much work in progress, it's probably worthwhile getting these ideas out into the blogosphere.

Board Design
It seems to me that board design may be predicated on the following.

1. If the wind speed is light enough for pumping to dominate board speed- particularly upwind, then basically the fastest sailboarder will be the one with the highest strength to weight ratio and small variations in board shape are probably not significant.
   
   
2. For wind speeds above the 'pumping regime' and barring big variations in average board speed downwind due to wipe-outs, upwind board speed is probably the dominant factor in determining who it going to make it around a course in the shortest time. Of course in making this statement I'm thinking sailboat courses and equilateral triangles- not sausage courses!
   
   
3. My experience (from a few years back now so it may be a little out of date) is that you basically go for the biggest centreboard possible for maximum railing and pointing under marginal conditions. In stronger winds, you take advantage of the fact that the railing 'moment' is pretty sensitive to the centreboard angle of rake, and so it is possible to de-power the board as the wind speed increases by raking the centreboard back. This also has the advantage of enabling you to stand further back on the board.
   
   
4. Sharp straight rails in the forward half of the board would seem to be the way to go for optimal upwind performance. The compromise to avoid digging in and wiping out downwind is to have some rocker and softening of the rails towards the nose of the board.
   
   
5. Maximum board width sounds like a good idea for early planing, and perhaps for increased power going upwind. Here I'm thinking back to some limited experience in 14ft skiff sailing and the need to move away from the centreline to increase righting moment.
   
   
6. It seems a good idea to have a concave shape on the underside of the board, extending from the bow and terminating somewhere near the centreboard case (are single or double concaves better?). It is envisaged that a concave shape will minimise wetted area when railing upwind, and will provide additional lift when planing downwind. The downside is that there will be more wetted area in displacement conditions- but here it is expected that power-to-weight ratio will dominate anyway as discussed in (1).
   
   
7. Flat bottom with some rocker in the back half of the board and a nice big fin which doesn't cavitate for good downwind performance in planing conditions. The latter is to avoid those catastrophic wipe-outs downwind as mentioned in (2).
   
   
8. It would be nice to have a narrow tail for demonstrating that carve jibes are possible on a longboard- however a wider tail (i.e. Phantom 380) may be preferable for earlier planning in marginal conditions, and for planning at deeper angles downwind (Starboard promotes this design feature with the 380).
   

That's it on board design for now. Be interesting to get some feedback.

Google SketchUp
This is an example of a nice little package for constructing 3-D models. I think it's mainly promoted by Google as a package for constructing buildings and other objects for embedding into Google Earth (i.e. check out New York with the building layer enabled and you'll get the idea).

The package appears to easily have the capability to draft up a longboard design. This is demonstrated (at a very basic level) below where I've taken a plan view of the Exocet Warp-X and constructed a simple scale model using the line and arc drawing tools. Note that the intention is not to copy the design of the Warp-X, nor any other contemporary longboard design. At this stage I'm just using the Warp-X as a model to help build up the requisite skills with Sketchup.




















Construction Materials
I've been trawling through some of the surfboard manufacturers websites trying to come up to speed with surfboard construction techniques where they appear applicable to the construction of a sailboard. More on this in the next Post.