I have some examples of two different brands of race/slalom fins, both from well respected manufacturers with proven performance records. One of these brands is typically thinner than the other at about 3/4 to 2/3 the thickness (this is thickness when viewed from ahead, not chord thickness).
My question is what effect thickness has in well designed high-performance fins? If thinner were always faster then they'd all be the same thickness wouldn't they? Could a thick fin perform better than a thin one?
I think there's several factors involved here, and you can't give an absolute answer.
It it's a weedy, then the stiffer it is the better it will perform, going thin increases the risk of too much flex.
For the same foil profile, a thicker fin will work better at higher angles of attack, so you can get away with a smaller fin without spinning out.
It's a very complex equation, personally I prefer fins with 8% to 9% thickness to chord ratio. But I haven't exceed 40kts, when you approach 50kts then cavitation starts to rear it's ugly head, and the thinner fins with a very smooth foil cavitate later than thicker foils.
So speed is also a factor.
So then thickness isn't an issue until you're really hitting high speeds and in fact may be an advantage of sorts in the lower speed range?
What about perceived (felt) drag at speeds say around 30 knots for instance. Is there likely to be any detectable difference? Or will a thin fin always beat a thick fin?
It's all about the lift to drag ratio, and although thin fins may have a lower drag, they're not capable of as much lift, (for the same sized fin with same foil).
So you can use a smaller thicker fin to get similar lift to drag ratio as a bigger thinner fin.
But if you have 2 fins the same apart from their thickness, the thick one will go better upwind the thinner one faster downwind.
No worries, but it's only my perception, I wouldn't bet sheep stations on it.
Just for instance though as an example. In our heavy weed induced smooth water, I feel I'm better off with a short fat wide fin, to lessen the depth of weed impeding the fin. But in weed free choppy waters I'm better off with a deeper, narrower, thinner fin, to help cope with the chop, although both fins could have the same lift/drag numbers.
