I would like to build a new centerboard for my fish and am wondering if Oak will be as strong as mahogany? I realize that you need to buy a class legal board for racing, but this will not be for racing. Any woodworkers that can share some insight??
Mahogany is a little stronger in compressive strength than oak, but their bending strenght is about the same. Mahogany does have better weathering qualities than oak. The proper finishing method and care should be able to make up for that.
Central American (Honduran, etc), or "genuine" mahogany is preferred, Asian (Philippine) mahogany is an excellent, and less expensive second choice. Most of the tropical hardwoods would work well for marine - look at how much teak is used on boats.
Oak would make a fine board, although a little heavy. Very strong, but a little more prone to checking or cracking. Mahogany has a better strength-to-weight ratio (due to its interlocking grain), and is very durable for what a daggerboard can be expected to bump up against. Also, if you like showing off your woodworking, a well-finished mahogany piece has more of the ooh...ahhh... factor, IMHO.
I'm told Al Court, who frequents this board, makes a very good board for a decent price. There may be others as well. If you make your own, there are lots of previous posts with tips. If I could give one suggestion, it would be to dowel the handles instead of screwing them. Years of clanking down on the deck will make them break off.