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1975 Newport 28
1986 Hunter 31
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Discussion Starter #1
While surveying my boat's plumbing, I've found that there's one old unused through hull and one old unused depth finding sensor. (At least that's what it looks like, though I don't know why someone would go to the trouble of making a new hole instead of replacing the existing sensor.)

Anyway, what's the process for glassing in an old through hull? I've never done any glass work ever, but is this something that a glass kit you'd buy from West Marine could take care of? Do you fill the hole with some kind of hardening putty, then just glass over the bottom, sand and repaint?

Or is this something best left to a pro if you've never done it before? Considering you need that hole to stay filled, I'd think "pro" in my case, but I'm still curious.
 

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jas use the west system guide for this its perfect for what you want. if you want some help doing it i can come down and help ya.

yes you have the basic idea, grind it out to a 12 to one taper then fill in layers with glass, fill then smooth and paint

edit if you have access to the inside you can also do the repair from the inside to have less to paint, but then the water pressure is pushing the patch in, not onto the whole. the best is do a couple of layers inside and more out side to form a sandwich
 

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Also if you get Don Casey- This Old Boat-chapter 6 on fiberglassing it is very helpfull if you have no idea.As scottyt says the west system guide is very good. Make sure you use epoxy.
 

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ASA and PSIA Instructor
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I think you have the right idea - this is the bottom of your boat, you can't afford a learning experience from making a mistake. Although the work is not technical or complicated, I'd have a pro do it. Find some other projects where you can learn how to use epoxy and fg where a mistake or two wouldn't carry such a downside.
 

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sailing fool you would have had a cow if you saw the side of my boat. at the water line it had a 10 by 18 inch area of the gelcoat scrubbed off. after grinding it back to good glass and further i had a 24 by 36 inch taper that was in the center 12 by 18 area was just the last layer of glass . i left the last layer to have something to lay the new glass on. the repair has held fine including when i had to beach the boat and it laid on that side on the repair.

its not hard to do, if you follow directions.

jas i even have some of the strong filler left to thicken the epoxy with, you wont need much, so let me know if you want to do the repair i can give some to you
 

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Glad I found Sailnet
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Is this true for large through-hulls too?
 

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bene this works for any hole. but if you go too big you need something to back it up to hold the cloth. a trick that works well is to lay some cloth on the hull right next to the hole on top of some saran wrap. when it gets like leather peel it off, mix a little more epoxy and spread it on the inside of hull around the hole, then put the leathery FG over the hole. work out the bulbs, and let it cure. this will give you a good back up for the repair. if the hole is say over 6 inches, just let the leathery piece cure till real stiff but still bendable. it should be flexible enough to match hull shape but be solid enough to hold its shape.

if the hole was over 6 inches i would feather out both sides first and use the leathery piece as the first layer on the inside.
 

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Glad I found Sailnet
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Thanks, I think my large through hulls are maybe 1 1/2 inches in size. This is a great thread. Thanks.
 

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1975 Newport 28
1986 Hunter 31
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Discussion Starter #9
What's a "12 to one taper"? Does that mean if the hole is 1 1/2 in diameter you grind an area 18" in diameter? Sounds kinda big. Do you fill the hole through the hull with anything?
 

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Sea Slacker
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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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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
 

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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.
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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Irrationally Exuberant
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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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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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Telstar 28
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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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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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Midwest Puddle Pirate
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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.

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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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:
Picasa Web Albums - ken - ariel
Picasa Web Albums - ken - ariel

Ken.
 

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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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