My experience is that if you get rid of anhedral, the foil rolls much better.
The trade off with using an aft/bottom loaded section is that they do have more negative pitch moment and so might need a slightly bigger stabilizer to offset it. The picture of the Armstrong above is an example of an aft loaded section; the concave in the back 1/3rd of the bottom surface is the telltale.
I would agree with KDW that 600-800 is fine. I used to build sailboats and foils (rudders/daggerboards mostly but also some hydrofoils) for top racers and we would only sand to 600. Anything above that was a pretty small incremental gain. Though I do recall the sailors in super competitive classes would sand the hull of their boat with 1500 or 3000 gritā¦ Itās probably worthwhile if you are looking for that last tenth of a knot in a race
As for fences, some foiling sailboats such as Hydroptere with surface piercing foils used fences. That boat was developed and modified over decades so they likely work. The latest IMOCA foilers also have surface piercing foils and some use fences and some do not. Some at least seem to use aft loaded type sections as far as I can tell from pictures.
After blowing it on very many breaches on the HPS today and then catching the odd one, I had the thought that breaches are like losing traction in a car. I want to be warned through feedback that it is about to happen, and when it happens I want it to happen gradually and somewhat linearly so that I can anticipate and react to it (loss of lift on the foil and loss of traction in the car).
I think as this applies to foiling, the foils that handle breaches well, actually breach softer and āearlierā (through the various designs) than others, giving you a warning that the breach is happening, and progressively lose lift.
Foils that breach badly, lose lift nearly instantly, across the whole span, giving you next to no warning and no gentle initiation of the breach. Like a car with a big turbo and bad manners - when it goes, its gone (here is where skill comes into play).
The tradeoff is like grip in the car, maximum grip but no warning when you get to the end of the grip, vs something a bit mushier on the extreme, making it possible to better manage the grip near the limit.
This now makes sense. Once breached, you want the lift to return to the foil, much like the car, you donāt want it snapping back to 100% lift/grip, you need it to return gradually otherwise youāll overcorrect and start again, leading to another breach.
I donāt quite understand this, but I can imagine you donāt want too much tip loading as then when you lose that you lose a greater % of the total lift.
I know most of the foils Iāve ridden if I get the wing tip out like this them Iām going down down - but then Iām no Adam Bennets Enjoyed seeing this from his insta
F-one eagle with the winglets coming into effect
Enjoyed seeing this from his insta