Depends what they are sailing.

If they are sailing topper type boats (Rotomoulded and almost indescructable) you can play some "contact" cames lime tag, if not then you have to be much more carefull.

We've played shinning up the mast on lasers and the like - aim it to get to the top of them mast before you hit the water.

Sailing backwards races

Sailing with out rudders