A thickness distribution of about 30 to 33 % in combination with a proportionate thickness will permit an excellent upwind performance. If the thickness/chord ratio is not too high the all-round properties will be extremely good.
If a special emphasis is placed on speed, the maximum thickness of the fin can be pushed further to the rear, even up to 50 % or more. This type of profile is called laminar profile as the transition of laminar flow to turbulent flow is delayed. For this purpose a very small nose radius is necessary which on the other hand reduces the possible lift. Therefore, a laminar profile is good for speed fins with a reduced upwind performance.
Figure 13: Types of profile
Standard profile: the T/S ratio lies between 30 to 35 % or a little less. It offers good all-round qualities, lift and speed potential are depending on the thickness.
Laminar profile: the T/S ratio starts at about 40 % and may increase beyond 50 %. The laminar flow pattern is maintained over a longer distance on the profile as the transition is delayed. This profile is suited well for high speed but, it delivers much smaller lift forces.