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Old 21-05-2022, 08:29   #1
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Underwater sealer for hull repair

This may be a long shot, but I thought I'd ask. I have a small crack in the fiberglass near the keel that is allowing a small amount of water to seep into the bilge. I know the fix is to haul and repair the fiberglass but is there a material (sealer/adhesive or tape) that can be applied to the hull crack as a temporary fix?
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Old 21-05-2022, 09:19   #2
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Re: Underwater sealer for hull repair

You have a bolted on cast lead keel. You're most likely getting that water around your keel bolts, suggesting the bedding compound is worn. Crevice corrosion is going to be a problem with those keel bolts, and of course you can't see what they look like and how badly corroded they are until you unbolt your keel and drop it. IMO this is too structurally important for a temporary fix. How old is the boat? Have the keel bolts ever been checked? How do you know it's a 'small crack'? Is the crack from a grounding or because the keel bolts are loose and the keel is not secure?
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Old 21-05-2022, 09:26   #3
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Re: Underwater sealer for hull repair

I know it's a small crack because I isolated where the water is intruding in the bilge and then dove the hull and found the 4" crack near the keel. Keel bolts are tight and keel/hull joint was sealed in November when hauled out. N water coming from bolts. Thanks for the insights though. Still interested if there's a temp fix to stop/slow the water through the crack.
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Old 21-05-2022, 09:38   #4
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Re: Underwater sealer for hull repair

You can use the epoxy putty that comes in sticks and you roll in your hands, it will stick and cure underwater. I've used that on scrapes in the gel coat and seen it hold until hauled out next. That will help slow your leak, but you're describing a pretty serious problem if you have a visible 4 inch crack that goes all the way through your hull. The real crack is probably much longer just not visible from the outside and not through the entire laminate.
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Old 21-05-2022, 09:50   #5
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Re: Underwater sealer for hull repair

There is underwater epoxy made for this. "Marine Tex" I have helped a young couple once do it to a 23 ft boat they had just crossed the gulf stream in. Apparently it worked, at least for some time. Lost track of them after a week...

Marine Tex has always been the go-to for this. I imagine other modern ones work too.
amazon.com/Marine-Tex-RM305K-White-oz/dp/B0014419V0/ref=asc_df_B0014419V0/?tag=hyprod-20&linkCode=df0&hvadid=312151579877&hvpos=&hvnetw= g&hvrand=14033956654876102609&hvpone=&hvptwo=&hvqm t=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033393&hv targid=pla-439323138692&psc=1
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Old 21-05-2022, 10:10   #6
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Re: Underwater sealer for hull repair

I have three different options for you. Your profile says Dominican Republic, so that may affect availability.

And yes, you should fix it properly out of the water, but the realities sometimes trump the “proper way”.

1. Underwater epoxy as mentioned above. Semi-permanent but not always great in very narrow cracks - may require enlarging the crack to get enough of a good bonding surface.

2. There are underwater silicone-like sealants and adhesives. Adiseal is one brand that makes a fully underwater curable sealant/adhesive. About the same cost as most caulk, applies with a caulking gun (or a finger). Works well, but availability in DR may be a question.

3. I know available in the DR - toilet wax ring seal (used to seal toilet to floor/pipe flange). These are a relatively soft wax. Easily applied underwater, I carry one on board exactly for this purpose. Temporary, harder to clean up when making the permanent repair, and can wash out depending on location, shape, boat speed, etc. But, cheap, easy to get and use.
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Old 21-05-2022, 17:01   #7
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Re: Underwater sealer for hull repair

Pettit Splash Zone 2-part epoxy is the industry standard for this kind of thing.
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Old 21-05-2022, 20:35   #8
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Re: Underwater sealer for hull repair

Milagroman I will be interested to see if anything sticks after a few hours of using the yacht? Just because there will be some slight hull flex.
Have you thought about using some JB then glassing on the inside of the hull once the leak stops? I am not talking permanent but I would feel a lot better if there was a fiberglass patch over the crack. A hot mix with polyester and chop strand would work until you could slip the yacht.
I have good results with JB Weld. We punched a hole in our fuel tank four wheel driving and managed to plug the hole successfully with a stick of JB.
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https://www.jbweld.com/product/waterweld-epoxy-putty
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Old 22-05-2022, 15:23   #9
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Re: Underwater sealer for hull repair

I had a 3" crack on the port side that leaked terribly while on a port tack but never otherwise. I used 2-part underwater epoxy on the outside and a 6" fiberglass patch on the inside. That was 10 years ago. No problems since.
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Old 22-05-2022, 21:56   #10
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Re: Underwater sealer for hull repair

Ferropre. It is a two pack water-based epoxy putty used by plumbers which is really strong and available at most trade hardware shops. Mix it up 50/50, and use polyurethane or rubber disposable gloves. Clean the area, and it is best to dive overboard and push it into the crack there first using a cake icing method, a plastic bag with a corner cut off, to keep the mixed putty dry until you are at the damage under the hull, and can push it in with a thumb starting at one end and working along the crack. Push it in GOOD. Then you can go inside, dry off the area and clean it, and add a bit more on the top side in the bilge. The bottom repair should hold, at least until the top sets but Ferropre sticks like the proverbial poo to a blanket--one should always have some aboard for emergency.
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Old 23-05-2022, 01:05   #11
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Re: Underwater sealer for hull repair

Seriously?
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Old 23-05-2022, 15:36   #12
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Re: Underwater sealer for hull repair

I have used plumbers epoxy putty and polyurethane sealants as emergency/stop-gap underwater repairs. They will both cure underwater but the challenge with both is to get them to adhere to the damaged area underwater long enough to cure. Antifouling paint and very smooth surfaces are the enemy as the epoxy or sealant will not stay in place or will slide or rips off later when underway. I successfully repaired a significant reef scrape on a fiberglass hull (almost but not quite right through!) by diving down with glove-fulls of fast cure polyurethane sealant (3M4200 I think) and working it into the torn fibres with a putty knife, taking care to smooth it off and not to overlap the antifouling. 4 months and a couple of thousand miles later we hauled out and the temporary repair was still perfect. I now always carry a couple of spare tubes on board for this kind of emergency.
Working the sealant in, in order to drive out the water and get initial adhesion is the trick. A small or hairline crack will probably require careful chamfering for this to be successful. If using the underwater epoxy it would really help to rig up a way to protect and physically hold the epoxy in the crack until it has cured.
Good luck!
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