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Old 16-08-2010, 20:44   #1
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How Fair Is Your Bottom ?

Your BOAT'S bottom, that is. I have ground the loose ablative paint from the bottom of my Catalina 27, and sanded the loose dusty stuff everywhere I could reach, and I'm wondering how picky I need to get to have an efficient surface. If there are a few irregularities, will it drop my speed by a knot, a half-knot, a quarter-knot, or .00012 knots? Should I fill in the low spots with underwater Bondo? Should I just feather the edges of the ground out areas and repaint?

Keep in mind, this is a $1,500 boat, so I won't be getting a $500 ash-blasted hull.

Thanks for your advice. Picture attached.....

John
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Old 16-08-2010, 20:59   #2
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If you aren't putting a hard coat and you aren't racing I'd say you look pretty good there.

Definitely fill and fair the dings and major low spots and get the paint on.

Extra coats at the waterline and keel leading edge.
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Old 16-08-2010, 21:15   #3
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is there an epoxy barrier coat on the boat?? if you can afford one, do it, if not already done--will have to sand more , tho---otherwise, just go for the paint and add extra coat to leading edges and waterline

are the ground out areas filled with anything?? there should have been a filler in them. you may decide to sand off all the paint and barrier coat it so any more sloughing of patches wont spozedly occur. isnt a bad idea if there were blisters at one time, and especially after repair of same......
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Old 16-08-2010, 21:39   #4
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If you simply paint it, I doubt that it will affect your perfomance that much. I don't think you would notice any difference in speed if you spent a lot of money on making the bottom totally smooth.
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Old 16-08-2010, 21:45   #5
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Unless you are planning on racing at a very high level. It looks fine.
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Old 16-08-2010, 21:46   #6
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the pictured stuff will not affect speed or performance. if those were blisters that were not sealed just painted after grinding, then could be an issue. if that is the case, sand off all the paint and make sure is dry and seal it after filling the dings a bit. isnt for performance.
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Old 17-08-2010, 00:05   #7
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From what I see in the picture, you've knocked off several high spots, some appear to be down to the gel coat. Then again this could simply be using the wrong tool, like a DA sander, thinking you're fairing, when in fact you're just removing material and making the surface less fair.

The only way to fair a compound curve surface is with a long board. Every other type of sanding (palm or other jitter bug style, DA's and other orbitals, etc.) will smooth the surface, but do not have the "reach" to fair it.

Your boat came from the factory smooth, probably very smooth, but likely not very fair. Smooth is what you feel, when you rub a hand over the surface, but fair is what you see when reflections are cast on the surface.

Much like everyone else has mentioned, unless you're racing at a high level, where each 10th of knot counts, a good bottom paint job is all you need.

As to what you are doing with the sander, rather then using a pressure washer to the underside of you boat, well . . . Typically, you would pressure wash the bottom, repair and address any areas that need attention, then give the whole bottom a light scuffing, before applying more bottom paint.
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Old 17-08-2010, 07:22   #8
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Excellent replies!

Thanks to all who replied. I am pleased that I don't have to go all AR on the bottom and I'll finish the sanding/fairing this weekend. With 22' LWL, I don't want to be the last one at the bar.

John
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Old 17-08-2010, 14:28   #9
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I hope that you used wet sanding and not dry. Anti fouling paint is toxic - thats why it works!
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Old 17-08-2010, 20:03   #10
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Quote:
Originally Posted by Sailbad View Post
I hope that you used wet sanding and not dry. Anti fouling paint is toxic - thats why it works!
No, but I am covered up and wearing a mask, goggles, gloves, etc.
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