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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 06-08-2011
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dimples on my bottom

I`m doing a bottom job on my 37 Morgan. The bottom has been peeled so I`m taking it to the glass. I started sanding with a DA and 40 grit and it was taking forever, so I tried using a 4 1/2 grinder with 40 grit flapper type sander. The grinder is definately the faster way to go but I`m getting demples all over. I tried going back over it with the DA and it takes it down real close to smooth and its still easier than using just the DA. My question would be, how important is a smooth bottom should I be conserned about the demples??
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Old 06-08-2011
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Hey some say the bottom of a woman should not have any pimples or dimples on it. As a boat is "female" she shouldn't have any dimples but I wouldn't be to concerned about it unless you are trying to win a beauty contest or race.
i.e. dimples will influence the flow of water (or your hands across her bottom) creating eddies, which in turn will slow your boat (or you) down.
To many of them might slow your boat by 0.001 knt or less, but for the same reason a certain amount might create a better flow (golf balls) you never know. I would say don't worry.
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Old 06-08-2011
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Are you really going down to the glass, i.e. taking the gelcoat off? If so, why? Blisters?
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Old 06-08-2011
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Originally Posted by JimsCAL View Post
Are you really going down to the glass, i.e. taking the gelcoat off? If so, why? Blisters?
The gelcoat had already been removed. The boat had been neglected for a while and after pressure washing the barnacles came off and had removed alot of the barrier coat. I have found quite a few blisters as well so I figured since I just got the boat and it was already in the yard i`d do it right.
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Old 06-08-2011
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Quote:
Originally Posted by EJO View Post
Hey some say the bottom of a woman should not have any pimples or dimples on it. As a boat is "female" she shouldn't have any dimples but I wouldn't be to concerned about it unless you are trying to win a beauty contest or race.
i.e. dimples will influence the flow of water (or your hands across her bottom) creating eddies, which in turn will slow your boat (or you) down.
To many of them might slow your boat by 0.001 knt or less, but for the same reason a certain amount might create a better flow (golf balls) you never know. I would say don't worry.
Thanks, kinda what I was thinking. Kinda like a womans bottom in the sence nobody will know as long as her bottom is not exposed!
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Old 06-08-2011
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How about sanding just enough to open the blisters, dry them out and re-barrier coat? If it's already been peeled I don't know if I would grind any deeper than absolutely necessary.

I removed the ostrich skin from my boat a couple years ago and it made a very big difference in light air performance. Also, bottom paint will last longer because it won't be rubbed off the high spots.
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The sanding will go much faster and you'll have better results using a 7" variable speed sander/polisher. 80g is a good prep for high build coatings such as barrier coat, primer or bottom paint, 36 to 60 is good for stripping. The 36 is for very heavy cutting.

I peeled my San Juan 34 with 36g in a day using medium-low speed. Too fast or too much pressure will melt the old coating.
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Old 06-08-2011
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Dimples? as in low spots from the disc? Since your taking it down to the core you will need to do fairing as well as epoxy encapsulation. There's a air powered straight line sander that would help but a long board would be the way to make things "fair" again. It's going to take many hours!
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Originally Posted by SJ34 View Post
How about sanding just enough to open the blisters, dry them out and re-barrier coat? If it's already been peeled I don't know if I would grind any deeper than absolutely necessary.

I removed the ostrich skin from my boat a couple years ago and it made a very big difference in light air performance. Also, bottom paint will last longer because it won't be rubbed off the high spots.
I`ve looked at a couple different barrier coat manufacturers recomendations and they both say you cant put the epoxy over old barrier with good results as far as adhesion. The blisters I`m finding werent "weeping" until I sanded past the barrier. I`ve never done this but it seems like the only way to find all the trouble spots, as well as barrier coat man. recomendations.
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Quote:
Originally Posted by deniseO30 View Post
Dimples? as in low spots from the disc? Since your taking it down to the core you will need to do fairing as well as epoxy encapsulation. There's a air powered straight line sander that would help but a long board would be the way to make things "fair" again. It's going to take many hours!
Completely fair is optimal I`m sure, but is a .0001 knot speed difference the only thing I`m looking at? I am going back over it with a 6 inch DA sander and its pretty darn close to perfect.
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