Foil Building/shaping (rudders and centerboards)

I am after some advice on the best way to shape rudders and centreboards by hand from a timber or foam blank. Any info would be good.

[BrettM]

Try a router with a template/jig.

[Chris Krumm]

If you're building a board with lumber core and composite skins and/or spar caps, the core should be glued up with quartersawn strips for stability (the quartersawn portions make up the faces of the board; glue joints on the plain sawn edges. A laminated board like this will be more stable than one big plank.

If you build it this way, you can rip bevels on opposite quartersawn edges that will be tangent to your foil section. Your board blank should be a long, straight blank when glued up that is a faceted version of your desired final board. Careful planing and sanding , checked with a template, can yield a pretty nice board prior to laminating on spar caps or skins.

But if that's not tight enough tolerances for you, Brett's right - make a router jig and fly cut the board with templates at each end of the board.

One option for foam boards I've seen used, but have not done myself, is to create a female mould of sheet metal or thin hardboard bonded to female foil-shaped ribs. The board skins are bagged up in the mould, followed by layers of foam until the foam is higher than the 1/2 chord thickness in the center. This blank is routed flat as it sits in the mould. Another half is made in the same way, then the two halves are bonded along the center with glass cloth or just fiber reinforced epoxy. Battens can be fastened to the mould leading and edge to create a recess in the board to accomadate taping over the joint if desired.

thanks for the advice. The lumber I am using is laminated (with the grain running opposite directions) to give it stability.
I ended up running saw cuts at the correct depth down each side of the board to give me a guide to plane to. As the board isn't tapered this seemed to be an easy way to do it.
When I make a foam board I will try by gluing together 2mm veneers of foam cut to the correct contour outline and then sand/fair each half and glass them before joining the two halves. Foil making seems to be a very long process.

[Chris Krumm]

Yep -making a nice board is tedious, just like fairing and finishing a hull. Depends on your definition of good enough. For a one off (board, boat, whatever) seems like you're usually choosing between spending time filling, sanding, polishing over a male core or prepping a female mould you may never use again. The methods I mentioned work well for constant chord or straight-tapered foils, but you're into a lot of hand work for any curved planforms. Have fun.

Chris Krumm