Hey Curls......we agree.......our discussion on why 'whoever' designed the cut a ways into the Kyhoso board is purely speculative........

However......it is possible to 'prove' there effects.....

As I initially shared, they certainly will effect handling and aid in turning, even reducing surface area drag on the straights etc........

However - to debate your mentioned points on their self righting effects:

The Kyhoso board has a Step....a step is a step...reducing the running surface in its length, from one level to a lessor level
a Chine is a 'V' shaped type stringer in the hulls length that 'deflects' water back down from the hull surface, to the water surface, generating lift. If you had a Chine on a flat hull it would be near impossible to hope to lean it.

The actual calculated 'weight' of the cut a ways that you mention, is not the point at all - its the LESSOR BUOYANCY potential that the removed area has. The thinner the rail, the less weight it will require to submerge the rail. (like surfers who like 'thinner boards' for easier duck unders and ridding deeper in the wave) In the case of the Kyhoso the cut away seems to be as much as 25% of the overall thickness, which is substantial when calculating lessor buoyancy.

Comparing 'your boards' greater rail thickness, yet still self righting, would require comparing the 'minimum weight' the thinner plastic board would require to self right, which would be less, to realize the actual difference to prove the point.

It is NOT ONLY the weight and size of the surfer DUDE that rights the board......if you removed all the weight out of the board, it would 'not submerge' to its required Rotational Axis, therefore - it would simply float, lying on either of its rails, with the Dude floating on the surface of the water.......

One thing specific effect of the dude is 'if' the DUDE is WIDE - the Rotational Axis of the board will be shallower, requiring less weight in the board, but it will still need to reach the RA to self right.

So - to conclude....It can certainly be 'proven' that the cut a ways designed into the Kyhoso boards could benefit' surfing performance and self righting'......

Bro ********. ...
Share the STOKE !

After all that........I may have convinced myself to try them...........LOL