I share your questions, would be really nice if someone with more knowledge/experience could bring on more info.
My take for now is that canting is more useful at low speeds, when the heeling moment generated by the lateral force component is not enough to keep the board flat. In this case, the vertical component provided by canting helps in providing enough heeling moment.
I'm with ya and it still explains Paulo's explanation (whom I'm certain has experimented with this) that it keeps the board from sticking (by keeping the heelside from edging into the water at lower speeds)
Quick math - Rolling Moment about centerline of board.
all fin length = 40cm Assume Center of pressure < 20 cm
Board width = 70 cm
Cant = 5 degrees
Since the board width from the center line is roughly 2 x the center of pressure of the fin, adding cant gives you more than 2 x the moment arm for your force. Since there is going to be some foot pressure at low speeds that won't be manageable by fin lift, by adding cant you are doing what you can to preventing the board from edging and doing more of this with less fin , so this makes sense to me .
at a cant of 5 degrees 8.7% of your total lift is going to this heeling moment so these aren't insignificant angles. However, When I see videos of guys riding shadow fighting to keep a board flat at high speed it doesn't seem like it's being put to good use in that situation.
I would really like to experiment with fins (for example have 2 pairs of the exact same fin, one pair canted and the other not), but good fins are so expensive
Fin cost makes building my own raceboard economically not feasible. so I'm
currently working on molding my own fins and making them while I sleep for like 10 bucks worth of carbon. If I can get the process sorted where I can accurately mold out a 50+ cm foil, I can just cut them down and pot them at various cant angles, rake angles and lengths. To sort out the impacts of these variables.....
So far I've handmade a long length of reasonably accurate NACA 0010 foil by stepping the points every 1/16th of an inch on my router table out of foam and hand sanding the small steps smooth and glassing. I've got the plug smooth and shiny and ready to make a mold.
mold should be done in a week or so.
Won't be super high performance cause anything I can build has to have straight leading and trailing edges or it gets really complicated to make accurately but I should at least be good for testing things like rake, length and cant. and giving me an unlimited supply of fins for repairs.
Once I'm happy with the process, I can get a proper elliptical foil accurately CNC'd or buy an existing performance fin and copy it knowing I won't be throwing my money away.
If it works, I'll have a bunch of identical (albeit possibly shitty(ish)) fins at various degrees of cant laying around until my race board build is complete, if we still dont' get any anwers we can talk experiment at that point.