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Bottom Sanding- what grit and direction?

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Old 03-11-2007, 06:11 PM
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Default Bottom Sanding- what grit and direction?

Have heard from several racers to sand back third of hull for 1-4mph speed increases. I understand how this will increase speeds by allowing water to venturi off the hull, plus you can feel the stickiness of the smooth gel coat versus a sanded finish. most guys said to use 80-150 grit in a 45 degree angle. does anyone know the best application.
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Old 03-11-2007, 06:24 PM
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I have heard to use 220 grit. Start @ a point approx. 9 feet forward from transom on the keel and sand area from that point in a triangle to the back corners. It is easiest to tape it off first.
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Old 03-11-2007, 06:55 PM
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Don't waiste your time IMO. You will have a pain in the azz of a time keeping the bottom clean. Whe used to do it on blow boats but now they do not do it any more. Watch the America's cup boats. They spend more on speed then ANY of us do on going fast and they have glass finished bottoms. I think you will se no change to be honest with you.

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Old 03-11-2007, 07:46 PM
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maybe I was given some bad information on bottom sanding
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Old 03-11-2007, 08:15 PM
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400 grit. front to back. a gain between 1-4 should be expected. will take some time, but will work. some cases even did the lower of the drive.

a good analogy is taking a floor tile and puting it down on a tile floor that is finished, finished side down while the foor is wet. try to pick up the tile. good luck. the water creates a suction because of the shiny surfaces. take the same tile and put it down unfinished side down. you can pick it rite up because of the tiny lines in the tile breaking the suction.

same principal applies to the bottom of your power boat that leaves and renters the water.

evr pour water onto a car that has just been wet sanded? the water flies rite off and the panel vertualy dries itself verses a waxed paint job .
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Old 03-11-2007, 08:58 PM
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What do you all think of the "speed coat" waxes or coatings that are on the market? Wouldn't that be cheaper than sanding in the long run?

John S.
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Old 03-11-2007, 09:32 PM
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On mine they did a 320 grit sanding then a graphite coat over it. They did it from the first step to the transom.
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Old 03-11-2007, 09:35 PM
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Read several posts saying that it does'nt work at all.sanding has to work, simple hydrodynamics and water resistance on a fiberglass surface. also would work on a drive lower.
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Old 03-11-2007, 09:40 PM
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i have been thinking about this same thing over the last few days. keep us posted
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Old 03-11-2007, 10:01 PM
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John, what did the sunsation guys say about it and do you think it helps your speed, see ya at loto
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