Glassing over old through hull openings - Page 2 - SailNet Community
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post #11 of 24 Old 03-01-2009
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fwif I had on other boats (and have on this one) a few thru-hulls that are removed. I don't think there is any taper and no one seems to do the 12-1 thing with these. Consider that under normal conditions this thru-hull is a hole, and (in particular if using plastic thru-hull) it has nothing structural holding it.

Thru-hulls appear to be closed by glassing over them with cloth from inside and then filling with resin+filler and fairing. This has to (and clearly does) provide as much strength as a closed seacock (which would have been holding the water otherwise).

Personally, if I had to remove another thru-hull, I would do it that way again. Doing the taper arond thru-hull would appear to me to needlessly remove good glass and potentially weaken the area with unknown benefit. YMMV.
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post #12 of 24 Old 03-01-2009
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actually brak a thru does have structure holding, the lip in the mushroom head.
the way to not have to do as much painting is you do the tapering on the inside. the reason for the 12 to one taper is not for looks, there is a real reason.

the idea is the taper evens out the flex that happens, if you were to just plug a hole, then add a bunch of glass over it you would be adding a stronger spot in the hull, any flex that happens will now be concentrated on the edge of the patch, which can cause the glass to flex more right there and break the fibers. a way to show this is get a piece of paper and glue 3 2 inch circles of paper to it all in the center. now roll the paper up, yes this is and exaggeration of the flex but paper will roll up fiber glass will not. when rolled the paper will crease on the edge of the "patch"

the taper also evens out the stress on the now only mechanically bonded patch. yes epoxy only mechanically bonds to the hull. it would be like glueing a quarter to the piece of paper when you tried to roll it up the quarter would pop off. edit maybe a better example would be glueing the quarter to a thin sheet of aluminum, then roll the sheet up

the taper allows the patch to flex with the hull not against it, and it evens the flex between the stronger epoxy vrs the weaker polyester. it is very important in the long run

Last edited by scottyt; 03-01-2009 at 09:54 PM.
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post #13 of 24 Old 03-02-2009
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Quote:
Originally Posted by brak View Post
fwif I had on other boats (and have on this one) a few thru-hulls that are removed. I don't think there is any taper and no one seems to do the 12-1 thing with these. Consider that under normal conditions this thru-hull is a hole, and (in particular if using plastic thru-hull) it has nothing structural holding it.

Thru-hulls appear to be closed by glassing over them with cloth from inside and then filling with resin+filler and fairing. This has to (and clearly does) provide as much strength as a closed seacock (which would have been holding the water otherwise).

Personally, if I had to remove another thru-hull, I would do it that way again. Doing the taper arond thru-hull would appear to me to needlessly remove good glass and potentially weaken the area with unknown benefit. YMMV.
OMG.. your comments make my case that work like this should be done by a pro. No form of filler has a place in a hull bottom! (I am not a FG expert..subject to correction by an expert I believe this to be true). Hulls are subject to flex..epoxy fillers will not flex, they will crack if worked. Your dismissal of the need to use FG and to taper it properly MAKES THE CASE as to why DIY bottom repairs are risky...someone might do something dumb where it really matters.

If you put any filler into a bottom repair, other than cosmetic fairing, for the safety of your boat and person, I advise you to grind it out and start over. If you don't want a pro to do it, at least follow professional practices in DIY.

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post #14 of 24 Old 03-02-2009
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Of course, brak is assuming that if you get a professional to do the job they will do professional-quality work. I wouldn't make that assumption.

Yes, do it the right way. If you study up and are careful, many jobs such as this are doable by the boat owner. If you aren't comfortable doing it, you're still going to need to study up and be careful to find a good person for the job.

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post #15 of 24 Old 03-02-2009
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I agree with scot.. and arf.. good points! Hubby says if you want a job doing well do it yourself but after making sure it is done right. We have closed several holes under the waterline and luckily could do them from the inside so that cosmetics wasn't too much of an issue.The important part is to as said read up and study the best way to do anything.As ARF145 says pros dont always do it right.Read read read!!!
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post #16 of 24 Old 03-02-2009
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IMHO, you're better off repairing holes from both sides...since that will make a stronger repair generally. More work, but a better repair.

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post #17 of 24 Old 07-07-2009
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I’d like to give this thread a bump. I’ve read and re-read the West manual on fiberglass repair. Very useful! I have an old transducer thru-hull that is empty (boats out of the water). I’d rather fill it and install a shoot through the hull transducer since I’ll be buying something new anyways.

My question is:
In the manual it seems like they advise cutting the first piece of cloth (the largest) to lay in the tapered area and come just shy of the lip of the taper, so it’s in the shape of a bowl. Then the next smaller piece dose the same and so on and so forth until you use the final and smallest piece of cloth to go in the center. This one would be nearly flat.

The photos they have in the West manual seem to mimic this, showing the largest piece of cloth going in 1st. I was under the impression that you ground out to you 12:1 and then start with the smallest piece of cloth matching the hole in the boat, and then work your way to the larger pieces of cloth finishing with the largest, roughly the same size as your taper.

Is this not correct?


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post #18 of 24 Old 07-07-2009
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I used to think this way as well. In fact, I used to think this way because I read instructions showing this method. The problem with using the smallest first is that the glass fibers are shorter. The fiberglass layup gets it's strength from the glass fibers. You want the longer glass fibers to be in direct contact with the hull for the longest distance possible. This will give you the best strength. Grind a taper around the hole on the inside as well as the outside and do the layup with the biggest patch first. If you do the inside patch first, you will have something to adhere the outside patch to. You can use a small piece of wax paper and a lot of tape to make a backer for your inside patch, then the inside patch will be the backer for the outside.

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Originally Posted by WesterlyPageant View Post
Iíd like to give this thread a bump. Iíve read and re-read the West manual on fiberglass repair. Very useful! I have an old transducer thru-hull that is empty (boats out of the water). Iíd rather fill it and install a shoot through the hull transducer since Iíll be buying something new anyways.

My question is:
In the manual it seems like they advise cutting the first piece of cloth (the largest) to lay in the tapered area and come just shy of the lip of the taper, so itís in the shape of a bowl. Then the next smaller piece dose the same and so on and so forth until you use the final and smallest piece of cloth to go in the center. This one would be nearly flat.

The photos they have in the West manual seem to mimic this, showing the largest piece of cloth going in 1st. I was under the impression that you ground out to you 12:1 and then start with the smallest piece of cloth matching the hole in the boat, and then work your way to the larger pieces of cloth finishing with the largest, roughly the same size as your taper.

Is this not correct?


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post #19 of 24 Old 07-07-2009
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What Scotty says, it refers to the hull thickness. on thick hulls I prefer making repairs from both sides since it makes it easier to fair in and finish afterwards.

With larger holes I'll use a plug cut from a coffee can lid taped in place as a backer. It's stiff enough to provide support, and epoxy doesn't stick to it so it's easily removed. They also work for pre-wetting patches.

Just don't do a 'repair' like I found on my Ariel:
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post #20 of 24 Old 07-07-2009
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as merc and US27 said the largest piece makes the most contact with the old glass. it also makes it slightly stronger by building in a curve in to the glass structure. look at it like a mini blind, the curve they put on the slats ( assuming metal or plastic ) holds them straight, not floppy. any structure with a compound curve is stronger than just a flat plane.

also if you ask me putting the larger pieces on first is easier, it helps support the repair. what i mean is getting a piece of glass that measures 4 inches to stay in place over a 3 inch hole would be hard, but a 6 or 8 inch piece will "hold" better when not cured.

the biggest trick to make it look good and get the most strength is when all the glass is in place and still "wet" put a piece of plastic drop cloth, trash bag etc. then squeegee like mad until you cant get any more resin out, then let it cure and after cure pull the plastic
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