The cheap solution would be the Silva-85 mounted on top of the deck in front of the mast, just behind the V of the breakwater.
One step up is the Silva-103 mounted on a mast bracket. The latter is also available in a racing versions (103PE). A racing compass makes it easy to recognize headers or lulls and it gives a prediction of the new course to steer after the tack.
Finally there is the pinnacle of compasses, every racer’s wet dream, the ‘Tacktick’ digital compass, mounted on a bracket on the mast. It gives perfect header/lull information, has audible indications, has a start timer and lots and lots more goodies. A real wanna-have. It just shouldn’t be that bloody expensive!