A piece of .030 thick metal plate (I like alumium) wiith a rounded leading edge and a sharp trailing edge (like a super thin airfoil) should be really good.

If you really want to get serious, find a college with a wind tunnel (or better yet, a flow tank) that has students needing a project to work on. You might even be able to rent tunnel time (schools need money = bargains available), or take a class that gets you access (repeat a class if you've already done one).

It always amazed me that college kids (seniors) need ideas for a senior project. I had a hard time norrowing down my list, let alone selecting just one! (I did a rigid sail (wing) for a landsailer).

> A skeg or rudder can increase efficiency. They can also add a
> lot of drag. You need a good foil shape to begin with. You should
> also steer with the rudder as little as possible.