Fin Foil Convex outside AND Concave inside

General Discussion
1

A friend just called me today to help him choosing his next board and within the call he mentioned some new fins the shop owner wanted him to sell.

 

It’s a normal FCS tab rail fin, BUT the inner side isn’t flat as it’s normally seen, it’s concave.

The shop guy told him that this fin is significantly faster and he didn’t believe it till he used them the first time and it was amazing, blablabla. Like everyone who wants to sell “new and better” stuff and make money.

Didn’t find something in the search, just a guy from surfermag who says he prefers concave fins in small surf.

 

So hydrodynamica geniuses who can tell about pros and cons of having a concave instead of flat fin? My guess is if convex lets the water flow faster around the fin doesn’t concave slow it down a bit or create more swirl?

2

I can't believe no one has fielded this. FYI, this isn't anything ''new''. Google up some wing theory and you'll find that foil shape influences lift characteristics either through pressure differentials or coanda effect. Applications in surfboard (side) fins have been going on for at least ten years.

Short version of ''pros and cons'' is that flat insides work good in juice, concave inside foil goes better in smaller and/or slower waves.

3

Futures Vll foil works for my wakesurf boards and the flat inside fins are way slow, tried all the flats that futures have and no good for may application. Boat speed from 10 to 12 mph.