It looks similar to the aft fin on a Compass 28. The idea is to move the centre of lateral resistance aft and reduce weather helm. Alternatively it allows you to carry more mainsail in circumstances where you might want to reef the main to maintain balance.
BTW there are quite a few Top Hats with the P bracket propeller shaft. It is not so good for steerage but being clear of the deadwood it makes the prop a lot more efficient.