Mythbusters-dimple idea

[SkiTower]

Anybody see the Mythbusters (just saw a repeat) where they tested a dirty car vs. a clean car for mpg? The myth was that a dirty car got better mileage because it had a golf ball effect. They tested dirty vs clean and found the clean car 10% better. Then they dimpled a bowling ball and model cars and wind tunneled them and saw that the dimples reduced drag. Next they took it one step further and covered the car in smooth clay and tested and got the same as a clean car. Last they cut divots like a golf ball in the clay and got 10% better mileage than the clean car (20% better than std dirty car).

What does this have to do with boats you ask? Wonder if anybody has experimented to see what effect a dimpled hull would have on the ski wake.

[SquamInboards]

RE: Mythbusters-dimple idea

Was just talking about this tonight with some fiends while fairing a freshly milled hull. If you do some research into hydrodynamics, the critical idea behind hull speed and reduced friction is the laminar flow of water over the surface. Laminar flow is essentially a pad of water between your hull and the water "moving" below you. As the water flows further down your hull it becomes disrupted and creates very small eddies which pull at your hull, creating drag. Dimples would only increase this effect on a boat hull is what it boils down to. One of my old Connelly "Blade" skurfers had dimples which they claimed increased suction between the board and water, stabilizing the board. *cough* bullsh*t *cough*. Hopefully that helps, if I'm misinformed then chime on in.

[SquamInboards]

RE: Mythbusters-dimple idea

Just found this, it probably explains it better than I.

http://www.hydeoutdoors.com/boats/randd/
http://en.wikipedia.org/wiki/Laminar_flow

[SkiTower]

Re: RE: Mythbusters-dimple idea

As the water flows further down your hull it becomes disrupted and creates very small eddies which pull at your hull, creating drag. Dimples would only increase this effect on a boat hull is what it boils down to.

That's the theory. The laminar flow actually creates a pocket behind the car (and boat?) and the dimples reduce that pocket by increasing the turbulent flow.

[SkiTower]

Re: RE: Mythbusters-dimple idea

Just found this, it probably explains it better than I.

http://www.hydeoutdoors.com/boats/randd/

I have to admit, I've very impressed you found this. Only thing I would say is maybe this applies to drift boats and it still might, applied correctly, affect a ski wake. I'd love to see where someone tested it. This study says the ball rotation is the key, but Mythbusters did it with a car, ie. no rotation. However there was only a 10% improvement while the smooth to dimpled golfball test they did showed I believe a 30-40% improvement which may be explained by the rotation.

[2gofaster]

RE: Re: RE: Mythbusters-dimple idea

On the flat bottom v drive drag boats my dad and I used to build, we would spend hours blocking and sanding the running surface completely flat. Then we'd spray what was called speed laquer over the sanded gellcoat. The speed laquer had a rough satin finish but we'd then spend hours again bead blasting the coating with microbeads to get the textured finish that we wanted. Done correctly, we'd pick up 7-8mph from a gellcoat only bottom on a 125mph boat.

[robertsmcfarland]

I know when I take the jet ski out I can hit a higher mph when there is a slight ripple on the water as opposed to glass.