Foil behavior at top speed

Hello everyone,

The first generation of prone foils like the fone phantom, kujira v1,… where a bit thick and generating a lot of front foot pressure at max speed, that was the limitation.
The current foils tend to be really well balanced in regards to front/back foot pressure at their respective top speed, so it’s possible to spend more time there. However I find that some problems still occur.
I will take the example of the fone sk8 as this is the one I have been spending time on lately. The foil is nice and nimble, roll is free at cruising speed, but as it reaches its top speed, the roll becomes much more firm, it takes time to roll from one side to the other, you get stuck in turns and it takes a long arc to get out of the turn. Of course you can use a smaller size but…
Is this roll locking happening to every foil at top speed? Or is it a different problem occurring depending on the design? (foil becoming unstable, or too locked in, or front/back foot pressure changing, or other pb)


1 Like

Good question, hard to respond without more details. Foil size, actual speed, fuse, stab, mast, sounds like you’re wave riding? Wave size/power?

My current foil stays lively at all speeds that I’ve experienced so far in swell surfing:
Cloud IX fs900 10.1ar Catalyst stab, high mod 76cm mast. Haven’t felt it stiffen up at 19mph with a 195lbs rider.

Yes wave riding! Long period swell (hip to overhead) is where problems occur the most I would say, as the energy is high and top speed is crazy

Pretty standard problem across all foils I’d imagine. Only way to combat it is to have a larger speed range. You’re maxing your foil out and it’ll start to get tracky like you describe. Switch to a smaller foil. Or find a foil with a wider speed range (that typically means higher aspect).


If that’s happening - it’s time to go smaller.

Although - there comes the balance you mention on each kind of foil (latest gens handle this better) where the compromises of glide and stall speed are no longer big deal and the foil starts to handle better at higher speeds but depending also on wave power/size.
Right now I’m on SILK 650 and for my weight and size of waves I’m attacking (mostly shoulder to head high top) it’s carving ability at really high speeds it’s whats setting this foil appart from all the others I’ve tested, and still it’s able keep the nice balance of enough low end to be able to wing it or prone foil it.
There’s also the issue on the stabs - smaller stabs will defintely help on the control at higher speeds. The 650 it’s paired with an 135cm2 really small stab - so very loose still at some powered conditions.

Maybe try smaller stabs and see how that helps too.


What SK8 size are you on?

I have been on the 850 and 950. Now exploring the smaller sizes

1 Like

You can also tune the tail for more downforce and move the foil back to compensate for the increased lift. This will create more drag and keep the speed in check a little better in those conditions. It will also reduce turning sensitivity and make the foil more locked in. It will hurt your efficiency and pump some.

1 Like

You mean less locked in? By keeping the front wing from reaching its top speed with the tail setting

i mean that moving the foil back in the boxes in response to what your doing with the shim will reduce turning sensitivity and make the foil track more. For me, it feels less fun.

Its not a matter if “keeping the foil from reaching its top speed” its “keeping the foil from exceeding its top speed”. Foils misbehave when they go too fast.

edit: When i’m winging my prog 140 i like to shim for more lift(like above) for this reason, i feel like if i’m shimmed negative like i do for prone i get alot of this “bad behavior”. Now i wing strapped so i don’t do any track adjustment(i’m able to use the straps to hold it down and apply extra extra front pressure) so it still turns how i like it. I know the extra downforce adds drag and helps keep speed in check but i think the extra downforce in the tail might also combat some of that “nose diving at speed” on top of just controlling the speed, letting me hold down more. I’m not 100% sure on this i’d love an expert to weigh in. @Clifford can you weigh in?

1 Like

Front wing size is super important for high speed foiling.

Foils use asymmetric wings which can generate lift even at negative angles. If your front wing is too big for the required speed you will need to decrease angle of attack to counteract increasing lift.
Stabs are inverted, so as per every extra degree that you decrease front wing angle, you will increase (positive) stab angle.

This can take the stab away from its ideal working speed envelope, reducing inverted lift.
Past that point (you will feel a more unstable, forward pitching foil). Worst case scenario you can stall the stab, and if that happens you will for sure nose dive.

Hope this helps!


I will try different tail setup maybe higher aspect tail and shim it to produce less downforce. Might behave better at the top end but may compromising low end a bit.

you have reached the limitation of that foil if you cant go any faster and its feeling locked in but like its going to explode as you cant keep the nose down
yes foils do become harder to turn the faster they go , thats a given , even more so on HA foils
moving your foil back a bit and using a shim to increase stab angle to keep front foot pressure will help with stability , but this is easily overdone .
as mentioned , the solution is a smaller wing for sure


Thanks! Good to know that’s it’s where the limit is at