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Old 06-01-2021, 08:57 PM   #1
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Glassing Over Through Hulls

I'm pulling the boat this weekend and was thinking of glassing over a couple old through hulls. I did a search for info but didn't come up with much. Can anyone point me in the right direction to research this? Thanks
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Old 06-01-2021, 09:05 PM   #2
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I have done about 8 or 9 pn our boat. Basically grind down halfway on the inside and halfway on the outside. Do about a 12:1 taper on each side. If 1/4Ē thick grind out 3Ē on each side. I put a piece of plastic on the outside flush with the middle and then lay in 1708 glass with epoxy. You will have progressively smaller circles of glass. Lay them in until it is built up flush. Then remove the plastic and do the other side. Most epoxies leave an amine blush that needs to be scrubbed off with water and a brush after they cure before doing any fairing.
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Old 06-01-2021, 10:56 PM   #3
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Do a YouTube search on Fiberglass Through hull. Many examples.
I'm a fan of anything by Boatworks.

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Old 06-02-2021, 08:27 AM   #4
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Iíve also removed many thru hulls and do it pretty much the same way Dave described except I use polyester resin and 1 1/2 ounce mat and start with small. circles and go larger as I build them up.
No more than 4 layers at a time and let them cure before adding more so the resin doesnít crack.
Then gelcoat after itís layed up and sanded smooth.
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Old 06-02-2021, 09:25 AM   #5
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I agree with Leonard in that 1708 will work fine but you might find it easier to wet out the 1 1/2 oz material. Although, I would warn against doing repairs with polyester resin. Epoxy resin will provide better adhesion to the cured fiberglas hull.
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Old 06-03-2021, 04:04 PM   #6
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I agree with Leonard in that 1708 will work fine but you might find it easier to wet out the 1 1/2 oz material. Although, I would warn against doing repairs with polyester resin. Epoxy resin will provide better adhesion to the cured fiberglas hull.
I donít like to mix materials if I donít have to and never had an adhesion problem. My repairs are stronger than the hull.
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Old 06-03-2021, 05:00 PM   #7
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I donít have a hard time wetting out 1708 with epoxy. But I always am looking for the best and strongest and I donít mind paying a bit more. But it is probably overkill...
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Old 06-03-2021, 05:07 PM   #8
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At some point even the pros I know suggest using similar materias to prevent stresses developing from uneven forces.
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Old 06-03-2021, 06:29 PM   #9
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I donít like to mix materials if I donít have to and never had an adhesion problem. My repairs are stronger than the hull.
By "mixing materials," are you referring to using epoxy resin in a repair on a boat originally laminated with polyester resin? And then saying you therefore prefer to use polyester?

I don't share that thought. The reason I say that is that once the polyester resin is past the chemical bond stage (which would have been around the day after it was laid up), then you aren't bonding like to like. The primary bond/chemical bond stage is long over, and anything applied is a secondary/mechanical bond. So at that point (now) it's about what will adhere the best to cured polyester resin (and of course have other desirable properties) in a secondary/mechanical bond situation.

I believe epoxy makes a stronger bond in this case. Obviously polyester can work (yards often prefer it because a job can be completed faster due to quicker cure - which is understandable when time is being billed by the minute). But I think epoxy bonds better, and working on my own boat it's not as important to avoid billing an extra hour.

Either way, prep is king. De-wax, sand, fillets for gradual transitions, etc.
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Old 06-03-2021, 07:25 PM   #10
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At some point even the pros I know suggest using similar materias to prevent stresses developing from uneven forces.
So it's important to know what was used to construct the hull?
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Old 06-03-2021, 08:12 PM   #11
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One of the reasons that pro yards use polyester or vinylester is that gel coat will adhere well to it where it won't adhere well over epoxy. When doing a repair on a late model boat, it is best to stick with gel coat finish to match and appear factory. This doesn't mater as much below the waterline on a boat with bottom paint because you aren't trying to match the finish like a topside, deck or house repair. Most gel coat is polyester based and therefore just as prone to absorb water as polyester so there really is no sense in applying gel coat under bottom paint, you may as well go straight to barrier coat or bottom paint.

My personal preference is vinylester, it is right between polyester and epoxy in terms of strength, cost and it is more predictable to work with than polyester. Unfortunately it is hard to come by, quality boat yards use it all the time and sometimes you can buy some off of them.
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Old 06-03-2021, 08:24 PM   #12
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Biggest problem with vinylester is shelf life. The venders I use tell me 6 months. And that is time from manufacturer not time since opened.
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Old 06-04-2021, 08:58 AM   #13
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Biggest problem with vinylester is shelf life. The venders I use tell me 6 months. And that is time from manufacturer not time since opened.
They all have a self life. I find if they are kept cool they last a long time. I've had polyester and vinylester last a couple of years at New England "basement temperatures" (approx 55 F)
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Old 06-04-2021, 09:10 AM   #14
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By "mixing materials," are you referring to using epoxy resin in a repair on a boat originally laminated with polyester resin? And then saying you therefore prefer to use polyester?
Yes that is my personal preference. I'm used to a "freeze/thaw" environment and I feel using like materials will keep internal stresses down a bit.
It has been successful for me in the past and I'll keep on doing it when possible.
There are lots of ways to do fiberglass work. I learned from a friend and from Legnos boat works in Groton, CT. Legnos sells all the supplies including epoxies. Polyester, vinylester, and bondo are all compatible and play well together and add something different to the party.
And I have used epoxies in the past and will still use them when I feel it's better.
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Old 06-14-2021, 12:45 PM   #15
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I have done about 8 or 9 pn our boat. Basically grind down halfway on the inside and halfway on the outside. Do about a 12:1 taper on each side. If 1/4Ē thick grind out 3Ē on each side. I put a piece of plastic on the outside flush with the middle and then lay in 1708 glass with epoxy. You will have progressively smaller circles of glass. Lay them in until it is built up flush. Then remove the plastic and do the other side. Most epoxies leave an amine blush that needs to be scrubbed off with water and a brush after they cure before doing any fairing.
I think you meant to say that you would have progressively larger circles as you work your way to the surface. You want each subsequent layer to have contact with the original hull material.
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Old 06-14-2021, 01:23 PM   #16
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Glassing through hulls.

Quote:
Originally Posted by Max Simmons View Post
I'm pulling the boat this weekend and was thinking of glassing over a couple old through hulls. I did a search for info but didn't come up with much. Can anyone point me in the right direction to research this? Thanks
Iíve had several done. Do what I do. Hire a professional fiberglass technician with an established business and good reputation. While heís at it, have him take care of your blisters.
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Old 06-14-2021, 05:16 PM   #17
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Spend some time watching Andy at Boatworks today on Youtube. The guy is like a fiberglass Bobb Ross. No, there is absolutely no reason to use epoxy for filling holes unless the hull is made with epoxy. Is epoxy stronger? Absolutely. Do you need it for a thru hull, not even close. I would not even spend the money on vinyl ester. Use an ISO ester. Biaxial 1708 glass makes it quick. And is easier to bridge the hole. Make sure u get a fin roller to work out bubbles with. Mertons fiberglass in Springfield is a great place to get the stuff. Way cheaper and very fresh
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Old 06-14-2021, 05:54 PM   #18
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I think you meant to say that you would have progressively larger circles as you work your way to the surface. You want each subsequent layer to have contact with the original hull material.
This is a debated topic, so I bet Comodave did mean he puts the largest patch on first (closest to the hull). This is also the way WEST System shows it. Here is one rationale: As you sand or fair, you may sand a bit into the top fiberglass patch layer. If that is your largest piece, you may break the continuity of this, your best most continuous piece.

If the largest piece is up against the hull, it's going to say full thickness and full contact.

This seemed counterintuitive to me many years ago when I first started, so I did it the opposite way at first, with the smallest piece first, then larger as I went outward. Seemed to "match" the shape of my dished out area.

After reading more I changed to the way WEST and Comodave specify. I have not tested either way to failure, but I tend to agree with the aforementioned reasoning so I do it largest first, then work my way to smallest. If my fairing process cuts slightly into the top layer no biggie, as it's not the full sized one.

As far as bond, I have never seen the upper layers fall off, so I don't see that each layer needs to touch the hull (for a small rim area). Probably the layers bond to each other is stronger anyway, as it is a chemical bond. The bond to the hull is a mechanical one.

As I mentioned above, I have seen people do it both ways, so what I'm saying is not gospel. But also I'd say Comodave's way is not wrong.

Here is a page from the WEST Systems manual appendix, on closing out a machined hole (seacock):
Attached Thumbnails
WEST seacock.png  
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Old 06-14-2021, 08:07 PM   #19
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I always have followed the West approach as Frosty noted. I like to start with a thin film of thickened epoxy (cabosil or milled fiber) on the dished out area. Next wet out and laminate your successively smaller patches on cardboard or a board. Really brush tap or squeegee out all the excess resin to get a tight laminate. Btw, putting a sharpie mark in the middle of each patch when you cut it will make centering them on each other much easier as 1708 distorts shape easily.

Smack that patch on the thickened epoxy and brush tap to stretch, smooth & squeegee the edges out. Provided there’s no air bubbles or dry spots, the less resin will be stronger and stick better, even upside down.

Depending on the curvature at the patch location, you may have to do a 2nd step, either with fairing compound or CSM to blend. Get that 1st patch bedded down nice & tight, even if it creates a flat spot.
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Old 06-14-2021, 08:24 PM   #20
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Boatworks, Onboard Lifestyle and Sail Life on Youtube all have great videos showing how to glass over through hulls.
Good luck,
Dave
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