Are you transfinbic?

LB , here is the contradiction . Cav is the result on any solid moving thru liquid and not only does it cause drag it does destroy impellers and the old days props . Ever surf a LB behind a boat ? At 5 mph going straight behind the wake its impossible to walk to the nose . Increase speed to 10 and u have the ability to hang ten . Not only do we reach those speeds , it also highlights suction. The slip profile , changes in speed , and surface all play into the equation . Your foil explanation is perfect on racing yachts . The fish with no cant in the fins creates substantially less cav but also feel faster due to the slip profile .

 

Guns I have with quads feel like chit on takeoff s in mushy big waves . 4 canted fins creating drag , they feel sticky and slow , put that on the rail and face its like the pedal to the the metal ! The cant elaborates the turn with directional change , creating huge drag . 1 canted fin flowing into the rear thruster produces forward drive .

 

Flat foiled fins also play into these theories.

 

Fin placement is more important than the fins themselves. Toe-In, Cant, Distance from rails, Dristance from tail and distance from one another all play a role. Also the shape of the tail and the hard down edge and how far up the hard edge goes up the rail. Personal opinion is that people focus too much on the fins themselves. If the other factors I've mentioned aren't right you'll be on a mission to find fins that make up for the board's shortcomings. If the factors I mentioned above are spot on just about any fin within reason will work.

 

The toe-in part is pretty mysterious to me, but the single foil/canted fin creating lift makes sense to me.

I have ridden fast twinnie fishes/simmons with stringer-parallel keel fins and double foiled. All of those boards were pretty much flat thought the middle, low entry and exit rocker, wide short boards with parallel rails, and carried a lot of width out the back. In other words, boards that have a lot of speed-generating attributes in the hull, and probably don't really need/benefit from any additional lift that you might get out of canted single foil fins.

 

Gonna go backwards here, so forgive me... and btw I appreciate the discussion!

Like a plane needs a minimum velocity to lift off, a fin needs a minimum velocity to create lift.

More fins equals more drag, yes... but also more lift and thrust, depending upon degrees of toe and cant. Increasing degrees of toe and cant increase lift until drag forces overcome lift and thrust... all relative to speed, of course. During turns, drag wants to become the dominant force... and it needs to be for the fin to work in terms of facilitating turns (directional change).

Fins do interact... with each other and with bottom contours, edges, etc. Obviously distance between the rail fin and trailing fin (or front fins and rears on a quad) has a huge impact how much or little they interact.

 

Cavitation as it relates to surfboard fins happens when the liquid around the fin vaporizes due to pressure differences. That only happens at super high speeds (kiteboard speeds, I'd guess... but don't really know for sure), or during turns, when the pressure differences are very large. This applies to surfboard fins, props, world cup racing boats... whatever.

Double foiled fins, with no toe and cant crate no lift, and very little drag. That's why they go so fast down the line. But put it on a rail and they not only resist directional change, but also stall and decelerate way faster than a single foiled fin that's toed.

What is slip profile? Does that refer to the boundary layer? I haven't heard that term.

 

There is only one fin setup that actually matters:

 

Slip profile is the variations of surface roughness in liquid , in hydro theory the slip is quantified by the Navier slip length .

 

LB , been LB ing a small e pulse the last few days fyi , looks like the wind will behave today too .