This guide explains what leads to a hydrofoil stall,
and how to deal with it. If you’re foiling at low speeds, then you notice
your foil stops moving forwards and sinks instead, you may have experienced a hydrofoil stall.
Stalling is an understandable and instinctive mistake for new foilers.
Let’s see where the misunderstanding comes from:
The faster your foil moves through the water the more lift it generates.
You then shift more weight to the front foot to lower the pitch of your foil and reduce lift.
The slower your foil moves through the water the less lift it generates.
You then shift some weight to the back foot, raising the pitch of the foil
very slightly to increase lift, with only a small increase in drag.
If speed continues to drop therefore, new foilers,
naturally assume that they should keep shifting more weight to the back foot to retain lift.
However, as you slow towards stall speed, this is no longer the case.
At a certain point, excessive back foot pressure will not create
any more lift but it will sharply increase drag.
This drag causes a further drop in speed, of course,
then you loose lift and sink, stalling your hydrofoil.
That’s how back-foot pressure can result in a loss of lift when close to stall speed.
When reaching stall point it’s far more effective to shift some weight to the front foot instead.
When you shift to the front foot, you will still descend,
of course, but, as you descend, you’ll keep moving forwards and even regain speed.
By shifting to the front foot you’ve pitched the foil down,
which means it aligns with your descending trajectory for a low angle of attack.
This means you minimise drag.
With minimal drag, you then only need a little force from your wing to accelerate again.
Then once you pick up speed, the foil can lift you easily,
using just a low angle of attack and minimal drag.
Another way to think about this is to accept that when you reach stall speed you have to descend.
If you’re descending with the front wing pitched down that will help your foil glide forwards.
If you’re descending with the front wing pitched up,
that will encourage your foil to stop or glide backwards.
In this demonstration, stall speed was reached by raising the wing too high
and not pulling much with the back hand, reducing the forwards drive from the wing.
Simply lowering the wing and pulling a little more
with the back hand would have prevented this drop in speed.
In practice, you’re most likely to encounter stall speed,
either during a lull in the wind, or while doing a turn where the wing is depowered.
The way you handle stall point remains the same, however.
Pressuring the back foot as you get close to stall speed will make you stall rapidly.
Whereas shifting to the front foot as you reach stall speed,
will keep you moving for a while, avoids stalling, and gives the best chance of riding away.
Thanks for watching and I hope this helps you improve your foiling.