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 .