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Old 05-07-2006, 15:06   #1
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Getting rid of thru-hulls (in GRP)

Maybe I'm a bit "anal", but I have a thing about holes in the hull...the fewer the better is my attitude.

I am taking Insatiable out of the water tomorrow. One of the jobs on the list to be done while she is on the hard is to get rid of some of the current (superfluous) thru-hulls. For example, she has a total of 4 thru-hull fittings for instruments: 2 depth sounders and 2 speed/logs. I plan on reducing this to 1 for the speed log and will fit the new sounder without a thru-hull.

The question is; do any of you wise people have any tips, hints, tricks of the trade or caveats for removing thru-hulls and re-glassing?
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Old 05-07-2006, 19:51   #2

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If they were installed "right"....they may have been bedded with something like 5200 which can last forever on GRP. You may have to chew them out. Once they are out, you bevel the glass out to a 1:12 slope (or 1:18 if you're really conservative) on both sides, and start laying in new material in overlapping layers to fill the hole. Oh, and if you want perfection, of course you'll be vacuum-bagging those.<G>

Tedious, but that will bring the patch/plug up to full strength with the hull (with or without the vacuum bagging!)

Sometimes using a hacksaw or Sawzall to cut the fitting in two (insert blade in hull and slice outwards) and then collapsing the fitting is the easiest way to do it. Sometimes, with a long crowbar or pipe extension, you can actually unscrew them and pop them out. But not if they were bedded with 5200.<G>

A sea chest is a nice idea, but considering all the work...I think I'd rather install a more robust bilge pump/alarm and buy a pack of damage control plugs.
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Old 05-07-2006, 22:42   #3
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What hellosailor is suggesting about patching the holes is more then right but I'd say a little over kill. Sailboats are not as fragile as spaceships and a typical GRP plug would be sufficient.

One can be made by rolling FG strips saturated in polyester resin until it's big enough around. Or flat laminates stacked up to the proper thickness. Either way you'll have a GRP plug. After it cures it can be machined or ground to the proper size to fit just loose enough to get in the hole.

Once that's done it can be secured in with polyester resin. Once that cures you can grind a slight dimple on both sides about twice the size of the hole, and then lay in glass and resin to fill the dimple. Once it's flush in the middle with the rest of the hull it can be ground flush trough out.

Then you'll need to put on a finish coat of polyester resin with a sealer (wax) so it cures properly.

Sand and paint, you'll never even know there was a hole. You could beat on it with a hammer and it'd never move.

I've done more then my share this way and nary a one ever showed back up, to my knowledge. The boats probably died or rotted away before the plug ever came out.

And if you have a cored hull, your sounder will have to go thru.

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