I believe the power is used to control the wing (sail) and the foils. These boats don’t have a keel and instead rely on foils that they drive into the water. I think they’re adjusted constantly as they fly and they swap from side to side as they tack.
Here’s a clip that gives a bit of an idea.
https://youtu.be/VQUl_hf6yo8?si=T3kDqScMxsu0krQF