88l Armstrong wingSUP. 85A+ mast. Can gybe, 85kg 185lb.
Using 1550V2 with 232 stab and 2 red shims. Just got HA195 and worked up to1 red shim (add blue next).
Sometimes in choppy, turbulent sea I get a sudden loss of lift. It's not a wobble from the Armstrong flexible mast, but a sudden nose dive. If I react quickly enough I can apply back foot pressure, or if windy (as it usually is when very choppy) pull on the wing to lighten my feet, and am quickly back to level flight. I'm guessing it's something to do with stab, maybe air getting down the mast in chop, or front foil loses lisft?

I think of these incidents as "unforced errors." Unfortunately, the Armie rigs tend to do this from time to time. You are doing well in controlling it. The new mast has completely removed this phenomenon in my experience.

I saw an interesting video by a racer (not sure if wind or wing foiling) who had experienced a number of stalls at speed and sanded his foil's mast to prevent the issue of water ventilating and stalling the foil. He gave a clear demo of dribbling water down the mast and it pooling or flowing off. I can't find the video now but someone else may have see it.

patronus said..
88l Armstrong wingSUP. 85A+ mast. Can gybe, 85kg 185lb.
Using 1550V2 with 232 stab and 2 red shims. Just got HA195 and worked up to1 red shim (add blue next).
Sometimes in choppy, turbulent sea I get a sudden loss of lift. It's not a wobble from the Armstrong flexible mast, but a sudden nose dive. If I react quickly enough I can apply back foot pressure, or if windy (as it usually is when very choppy) pull on the wing to lighten my feet, and am quickly back to level flight. I'm guessing it's something to do with stab, maybe air getting down the mast in chop, or front foil loses lisft?

Foil-mast ventilation is only an issue when the mast is going through the water at a yaw angle. For winging, this usually means when going upwind with a lot of windward heel angle. It's worse if the mast foil surface has defects, of the foil section design is poor, or if we suddenly yaw turn the board+foils. I doubt you're describing mast ventilation. See

When your board/foil dives pitch down, that has to be a sudden loss in front foil lift. Turbulent water or not, some front foil designs are much worse at this than others. eg. foils that pump well, are always pitch unstable at their higher speed range, and they will want to dive faster when you put them into a little dive. But race foils don't dive easily, they just go with little effort from the rider (but they don't pump well).

In your case, I guess that: 1. You've removed a lot of stability from the rear foil (choice and angle). 2. The 1550v2 foil has a design which suddenly loses a lot of lift upon small dive angles. 3. Maybe you have some defects on the surface of your front foil which are making the problem a lot worse.

jaume said..
I was told by a foil designer that big front wings at high speeds can produce big turbulences/ventilation that go all the way back to the stabilizator and it looses all the sustentation so the foil suddenly drops down/dive as the stabilizator function fails.

Could be something like that, though I only do around 12 knots when it happens though it is turbulent.