stepped or dimpled hull

Has anyone ever experimented with a stepped hull (similar to powerboats) or a dimpled hull to reduce drag? Just wondering if they had and what kind of results they saw.
Dave

This is fairly common on whitewater boats, but I doubt it would be of benefit on a ski. The speed where you have to reach before you can use dimples or a step to cavitate the water is higher than what most paddlers see on an average paddle. At lower speeds, those dimples or steps would cause quite a bit of drag and would make reaching a speed where they would benefit difficult to reach. If they were ever to be used, I would guess that they would only be useful on skis used for fairly big water- high speed surfing where the speeds never really slow down. Again, the problem with that, is that if you are surfing, you are already going the speed of the wave, and having less drag really isn't going to speed you up enough to make up for the extra drag that will slow you down in the flats.

The whitewater boats that I have paddled that use something similar are pigs unless they are moving fast, and then they get somewhat difficult to control once on a plane because they are so loose in the water. I actually designed and built one of the first whitewater kayaks to use a step, about 15 years ago or so. The design I used was for surfing in ocean waves, and the purpose was to make the boat more "loose" in the water lengthwise making is easy to perform 360 type moves, never really to make it faster in a straight line.

These type of tricks are used on plaining hulls like some whitewater kayaks, and fast powerboats. The simple fact that our surfskis are displacement hulls make the idea not as feasible. The one surfski that might benefit from this is the new Think Legend that has a flat hull and is made to be more of a plaining design, but it still spends most of its time in the water as a displacement hull that would suffer from the extra drag.

As far as I know, the only proven route so far is the 600 grit treatment that sailing boat racers use on their underwater surfaces to reduce surface drag. It seems that the average ski user (me included) is too vain to mess up their gelcoat to go this route though.

Shaun wrote:

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The one surfski that might benefit from this is the new Think Legend that has a flat hull and is made to be more of a plaining design, but it still spends most of its time in the water as a displacement hull that would suffer from the extra drag.

Just to clarify, the hull of the Legend isn't perfectly flat, the chines give it that visual impression.


The V10 actually has a flatter spot in it's hull, but due to it's more traditional hull shape, you don't see it when comparing to the Legend.


Chined hulls are used extensively in white water play boats, slalom boats etc. Why? Because they want to surf, fast and in control.


It's the same idea behind the Legend hull. Some explaining of vortexes is probably required here to understand that there isn't a trade off in flat water speed.



Regarding finish on hulls. Talking to guys who do the Sydney Hobart, they wax their hulls, some sailing people sand their hulls. I'm not sure what is more effective, but wax certainly looks nice on a flash new ski!!