SpeedCoat Lubri-bondA

[ZUL8TR]

Golf ball dimples

This is why a golf ball is dimpled.

Well actully golf balls dimples are there for a different effect created by this increased surface roughness. The effect is somewhat unique to round objects and was first experimented in the 1890's by Gustive Eiffel (France Eiffel Tower). He determined a reduced drag on spheres over a relatively small velocity range and pondered over the reason. It is presently understood that while the dimples increase the surface roughness and thus skin friction drag and thereby more quickly promoting turbulant flow on the ball the dimples ultimately result in a reduction of the size of the dead air region behind the ball thus reducing total drag on the ball. A result that at first is counter intuitive but none the less factual.

Here is a plot of sphere drag coefficient, Cd vs Nr, Reynolds number with V= velocity, D = diameter. Note the dramitic reduction in the sphere drag coefficient in the curve at about Nr = 2 x 10^5. Golf ball dimple designers strive for this low drag sweet spot based on driven ball speed:

http://www.me.utexas.edu/~dsclab/lab...re/Cd_v_NR.jpg

The effect of dimples on a flat bottom high speed hull would not have the same result that they have on a sphere (golf ball) in air. But maybe another effect is at hand with a water air mix?

[sam]

As long as Wart has the most speed records I think his example is the leading example to follow and the others are proven by his example to be snake oil.

Mr 400 grit holds about 110 speed records ... how many are held by these other techniques? Please list them

[Dave M]

Wikkipedia

I think Zult8tr is a wlaking encyclopedia ! hehehehe.

Sam, Nobody else goes for the Kilos like Wart does either. Kilos are Warts thing. He does not hold very many titles in ovals does he ? Not saying what he has done is not great, just that I don't think anyone else has ever attemped hundreds of kilos, let alone set them. So he kind of has the market cornered on it I would say.

Kilos are not that important to me anyway, just my opinion. I like oval races. I can go test locally and go fast in a straight line. Different strokes for different folks is all. I don't know of any top notch 850CCMH's that couldn't get at or over a 100 MPH in a straight line in a kilo if set up right. But I do know I don't want to do it in a race boat designed for oval races on shorter courses.... Good way to hurt yourself.

[Arcticracer]

Secret Powell Bottom Treatment

Really interesting thread, and I see there are still different ways to prepare a bottom. We used to mix powdered graphite with Turtle Wax, and rub it into a bottom that had been made completely smooth using a big foam glass block, then 400 sandpaper. I don't know where those foam blocks came from but they stink like rotten eggs or fa*ts. There was enough resin used to build up the bottom a little, like 1/8" at the rear to leave something to work with. Runabouts only. Hydros got the black goop only.

[RandY Aveline]

Kevin & Larry MaCafee could add some good info on the dimples i have seen them on their runabouts in days gone by and they also had a lower unit with the dimples as well .. i never did ask em how well it worked tho

Hmmm i know for a fact that the stink block will work a bottom in to shape real fast .. providing you have enough west system on it to remove the high spots, to even out the surface then apply another coat of west system and when dry use 400 wet dry in a front to back direction going with the grain and it will definitely be good for at least 1 MPH we proved it to our selves back in the early 1980's.
the wax usually slowed us down, to much smooth surface like a glass smooth surface actually makes more Drag and surface contact..

there was some stuff called "Fast glass" back in the 80's never used it but it was said it was good for 2 MPH for the first 2 laps then slow after that , it applied just like wax rub on , let dry and rub off

i saw it but never tried it all kinds of apps the 1 that worked for me was stink block then recoat and finish with 400 wet sand job worked well

GL HF
Randy

[tim king]

A hull with a golf ball dimple pattern would create drag due to the fact that each dimple would need to displace more water as opposed to a flat surface.

A golf ball needs the dimple pattern to stay airborn longer because once the ball is struck,there is no further propulsion and gravity will inevitibly play it's part.

On the other hand,a boat's hull has continuous propulsion and the smoother the surface it has,the less resistance it will have moving through the water.

[Kev43V]

A hull with a golf ball dimple pattern would create drag due to the fact that each dimple would need to displace more water as opposed to a flat surface.

A golf ball needs the dimple pattern to stay airborn longer because once the ball is struck,there is no further propulsion and gravity will inevitibly play it's part.

On the other hand,a boat's hull has continuous propulsion and the smoother the surface it has,the less resistance it will have moving through the water.

sigh I was going to keep my mouth shut.... but we all know how hard that is for me to do.
So, I will just say check out Myth busters and the segment they did on dimples on a car. they did wind and water tunnels with dimples and a car plus mileage test on a real car. there is a lot of applicable info

[RandY Aveline]

Tim
That all sounds good !
How many races have you competed in ?
How many times have you tried any of the above applications ?

I am not speaking to hear myself talk i am talking of actual applications and results !!

the McAfees actually have used the golf ball set up on hydro and runabout when i asked them they claim they saw no difference !! i might add have won many races In the AOF & NBRA a lot of which were nationals

as for myself i raced a lot from 1967 off and on thru 1990 winning or placing in several nationals and the 400 wet sand job was definitely1- 2 mph faster than a Glass smooth finished racing surface !
good luck have fun

A hull with a golf ball dimple pattern would create drag due to the fact that each dimple would need to displace more water as opposed to a flat surface.

A golf ball needs the dimple pattern to stay airborn longer because once the ball is struck,there is no further propulsion and gravity will inevitibly play it's part.

On the other hand,a boat's hull has continuous propulsion and the smoother the surface it has,the less resistance it will have moving through the water.

[tim king]

Your right I don't know a **** thing about a golf ball. I copy and pasted that it just sounded good. However I have raced a lot of boats. I'm going to race this year also. Here's what I think. All the above will probably work just fine, or you could just get a good start, and not worry about the bottom of the boat.

[pav225]

Your right I don't know a **** thing about a golf ball. I copy and pasted that it just sounded good. However I have raced a lot of boats. I'm going to race this year also. Here's what I think. All the above will probably work just fine, or you could just get a good start, and not worry about the bottom of the boat.

Hey didn't you crash me at DePue on the straight in front of the judges stand in OSY400???

- Mike

[tim king]

LOL Boy were you ever pissed. I could here you yelling at me over my motor. Sry.
PS. My driving skills have improved sence then.

[Trihedral_1]

While we're all sanding and waxing and doing the voodoo speed secrets with the bottoms don't forget the Buckeye Speedie polish for your props and lower units!!!
Ever wonder what to buff out the lower unit with? It's got the most drag of anything on the boat. These are gold bar sized blocks pictured.

Jimi O. (305-R)

[mercguy]

trivia question.........

since Jimi mentioned "drag"...............what parts of the boat DO NOT create drag??? Could be suprising answers here!!!!!!

[CSR4C]

I just finish the bottoms of my boats with a "stink stone" Check the record books for the results.
Darrell Sorensen