My new Select S10 & S11 fins arrived the other day and I am waiting for some wind to put them through their paces. The S11 is promoted as a more powerful and upwind orientated fin when compared to the S10. It is my inderstanding that the smaller S11's(Slam 25-39) are very similar in shape to the S07 and the Larger S11's (Race 41-61) are a completely new shape. The chord mid-line rake of the S10 & 11 are very similar and since the S11 has a larger area in the tip the leading edge is slightly more vertical.
The fins pictured are a 37cm S10 and 41cm S11.
The most noticeable differences in the plan view is obviously the tip area but when you look at the thickness the S11 is MUCH thicker in the tip. I will get the verniers out when I get the chance and compare the thickness ratios down each fin. Looking at the fin selector charts it looks like you can use a size smaller in S11 compared to S10 for the same drive amount of drive. It will be interesting to see how the different sizes compare across and downwind.
Similar mid-chord rake.
Tip area - S10 front, S11 back.
I took a few measurements of the fins at the base and tip(before the sweep on the leading edge).
Base - Chord 103.7 - Thickness 9.8 - Thickness/Chord 9.5%
Tip - Chord 53.6 - Thickness 5.3 - Thickness/Chord 9.9%
Base - Chord 108.4 - Thickness 9.3 - Thickness/Chord 8.6%
Tip - Chord 61.3 - Thickness 6.9 - Thickness/Chord 11.3%!!!
So both fins have a Thickness/Cord ratio that increases towards the tip but the S11increases by 2.7% compared to the S10's 0.4%!. This gives me the impression the fin will generate more lift from increased flex at the base and blocked twist at the tip with the thicker section.