Underwater emergency hull repair kits for GRP - any experience?

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Trident

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My boat has a small fist sized hole in the hull and is currently patched with a steel patch. She's been leak free afloat on that for 7 months since Irma and is about to be put aboard a ship to come home to the UK for proper repair. My concern is that whilst a steel patch doesn't degrade underwater due to lack of oxygen, as soon as she's on a nice salty deck for 10 days it will rust like crazy.

So, before she is craned in to the water I want to apply a temporary repair but will have very little time between being allowed on to the ship and the boat being lifted in the water. A couple of hours perhaps. So if I bring a battery sander to clean growth and a repair kit I can hopefully get everything fixed up quickly. What I need though is recommendation for a product that will adhere well and cure either very quickly or still cure when it hits the water and then cope with 60NM up to the solent to lift out for proper repair.

Any recommendations please ?
 
My worry is that it will have actual holes in the patch after being on deck - I think an epoxy and fibreglass patch makes more sense. So far she has not had a drop of seawater ingress and I'm trying to keep it that way :)
 
Unlikely that steel would corrode in that time to result in perforation. You don't say how thick it is, nor how it is attached to the GRP.
 
Its like roofing tin - very thin and put on with self tapers and some sika behind. The boat was blown out of the water by Irma but a mangrove branch punched a small hole which the salvage company patched like that and re-floated her. They ran out of epoxy hot patches in the BVI in hours so resorted to more primitive means. I may be worrying over nothing but I want to be prepared before she hits the water just in case. She'll then go straight to a yard to haul out so I can properly glass the hull and start refitting
 
I can't see rust happening that quickly either.
But if needs be I'd cover the hole with a board and lots of mastic.
Is the damage in a relative flat section of hull?
Is there access to the inside to fasten the plate if needs be?
 
Trident said:
Its like roofing tin - very thin and put on with self tapers and some sika behind. The boat was blown out of the water by Irma but a mangrove branch punched a small hole which the salvage company patched like that and re-floated her. They ran out of epoxy hot patches in the BVI in hours so resorted to more primitive means. I may be worrying over nothing but I want to be prepared before she hits the water just in case. She'll then go straight to a yard to haul out so I can properly glass the hull and start refitting
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Maybe be prepared to repeat what they did.
Good Luck!
 
If you think that you’ll only have a couple of hours I wouldn’t risk removing the temporary repair. Better to simply clean it up and add a generous coating of primer or anything else to inhibit corrosion during the voyage.

Best of luck.
 
Trident said:
Its like roofing tin - very thin and put on with self tapers and some sika behind. The boat was blown out of the water by Irma but a mangrove branch punched a small hole which the salvage company patched like that and re-floated her. They ran out of epoxy hot patches in the BVI in hours so resorted to more primitive means. I may be worrying over nothing but I want to be prepared before she hits the water just in case. She'll then go straight to a yard to haul out so I can properly glass the hull and start refitting
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Try and get some thickish flexible plastic sheet (polypropylene?) over top of the existing with sealant and more self tappers if the tin sheet looks bad. I seem to remember that 1mm of rust uses 0.1mm of metal. CT1 seems good and if possible put some on the inside if possible.
 
Rust forming on steel can almost be regarded as a protective layer. Think about corrugated iron roofs. They go all rusty quite quickly once the galvanising has gone yet actually continue to provide a weatherproof roof for years thereafter. Your boat will be out of the water on board ship for a couple of weeks at most: rust will not penetrate far into even fairly thin steel in that time. Provided it's a quick dip on unloading and then into the yard, I'd not be worried about it. If you're still concerned, then slap a couple of coats of the nearest paint onto it once it's dry. Even if it doesn't adhere very well, you're only dealing with a few days before the patch is removed and replaced with a permanent repair.
 
I agree with Duncan above. Highly unlikely that even thin steel will perforate in that time. Will you have access after the boat is loaded? If so wash it down with fresh water to get rid of most of the salt. Even a bucket of fresh water sloshed over it will be effective for that time in keeping corrosion at bay. Before launching another fresh water wash then plaster Sikaflex all over the patch and put a another sheet of flexible material over the old one overlapping onto the undamaged hull around it. Steel sheet, galvanised steel, stainless, copper. Pretty much anything will do for the short journey unless you run into bad weather. If you have access to the damage inside maybe plug it with fast setting epoxy repair kit, the kind where you knead 2 sticks together.
Good luck and hope it works out OK
 
Pasarell said:
I agree with Duncan above. Highly unlikely that even thin steel will perforate in that time. Will you have access after the boat is loaded? If so wash it down with fresh water to get rid of most of the salt. Even a bucket of fresh water sloshed over it will be effective for that time in keeping corrosion at bay. Before launching another fresh water wash then plaster Sikaflex all over the patch and put a another sheet of flexible material over the old one overlapping onto the undamaged hull around it. Steel sheet, galvanised steel, stainless, copper. Pretty much anything will do for the short journey unless you run into bad weather. If you have access to the damage inside maybe plug it with fast setting epoxy repair kit, the kind where you knead 2 sticks together.
Good luck and hope it works out OK
Click to expand...
There the answer , repair it from the inside if you can then even if the patch falls off the boat will still be water tight.
At the repair stage , they can cut your repair out and do a proper job.
 
Thanks for all the replies, sadly I cannot get to the boat once loaded or else I would just wash and paint a primer on as others have suggested. I also can't get to the patch from inside as it is in an inaccessible place in the stub keel. I've found a 20 minute curing hot patch that I can stick over, on arrival at the boat to offload, which should be good I hope if there is any corrosion damage from the voyage. Its going from Southampton to Chichester which is not too long a journey but of course I may have to wait overnight depending on what time its craned off and I'll no doubt have to wait out tides to get in to Chichester so it may easily be in the water 18 hours before craning out. She went through two hurricanes with no damage to the rig and not a drop of sea water inside and I'm going to be very sure that she stays dry on the last little leg home!
 
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