Formula windsurfing is demanding two contradictory types of performance. On the one hand, a high upwind speed should be gained; on the other hand, the speed on a downwind track should also be very high. This means that the right choice of profile will be crucial.
As this type of fin is a rather long one, theoretical ideas will be useful for its construction. The distribution of the profile parameters mostly is not the same in all fin regions. So, the thickness/chord ratio may increase towards the tip and the distance of maximum thickness from the nose may decrease.
A straight leading edge is improving all-round performance, spectacular outlines have not proved to be successful.
The degree of hardness of the Formula fin in terms of twist and flex is of greatest importance. Practical experience and tests have shown that the twist should be rather hard or even very hard. Flex may be much softer depending on weight and sailing technique of the sailor.
The sailor will have to find out for himself whether he should prefer a slightly thicker fin with a bigger area or a rather thin fin with a smaller area. He will have to take into account his own weight, his body size, type of board, rig and wind force. In each competition, the choice of the right fin may be decisive for his success.
From my own point of view, a custom made moulded fin can best meet the needs of an ambitious sailor. It is of low weight and the individual wishes of the sailor can be taken into account.