Peter_Frank wrote: ↑
Fri Sep 08, 2017 7:10 pm
I dont know of poor design being able to create ventilation...
But "cavitation" yes, if a poorly designed profile at high speeds, but that is cavitation because of locally very low pressure points so the water will boil.
Got nothing to do with ventilation, which is when air from the surface is sucked down to the wing and you will lose a lot or all lift
Gunnar mentioned in his foil review of the new Spotz Shark that the Banga foil ventilates the strut in certain circumstances, seemingly without warning, while going fast.
I also heard a buddy say the Sword RS ventilates the strut a bit during normal riding. So this has nothing to do with a lifting surface leaving the water, just in normal riding conditions sometimes the forces that the mast creates will suck air down and create problems.
So all said, there are really 3 issues:
1) Breaching - wings come out of water and air is less dense than water so you lose lift and crash
2) Ventilation - air gets sucked in along a lifting surface (maybe because you breached the wing tip, but sometimes it just happens on the strut)
3) Cavitation - the shape of the lifting surface creates too much of a negative pressure zone which causes the water to "boil" and create air pockets
All 3 cause crashes for the same reason - a hydrofoil cannot create sufficient lift to carry a rider when pushing against air instead of water. The physical principles behind these three phenomena are very different.
As a side note, some lifting surfaces under water create wingtip vortices which can induce ventilation as well, so it's not always the strut, if you were riding with the wings close enough to the surface of the water, they might ventilate through their vortices anyway (unless there are winglets designed to disrupt these vortices).