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Old 05-20-2018, 10:44 AM   #1
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Fiberglass Delamination in Cabin Top

Just had a survey on a 34' Mainship Pilot. On the cabin top, pretty much center between the sides and front to back, it looks like the previous owner may have dropped an anchor or other heavy object. It dinged the gel coat and has a few spider cracks at point of impact. When tapping the top of the cabin, the surveyor determined that an area approximately 4' by 2' became delaminated due to the impact. Had a fiberglass guy give us an estimate of $500 to fix. He said all that was necessary was to drill a dozen or so small holes (I'm assuming 1/4" to 1/2" drill bit), and injecting resin. Apparently, the cabin top is cored. I'm trying to visualize what happened and how injecting the resin will fix it. Is the core material and resin so brittle below the gelcoat that a large sheet will separate from underside of the gelcoat due to the impact? Do you think injecting the resin is the proper fix? Will this affect the inside of the cabin top behind the headliner? Any insights are very much appreciated.
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Old 05-20-2018, 11:09 AM   #2
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I think it is unlikely that "dropping a heavy object" would cause such a large area to delaminate. More likely, there was water intrusion and you have a wet soggy void. Did the surveyor conduct moisture testing in that area? If just a dry delamination, moisture would be normal. We actually had repairs made to cored decks both by replacing sections of coring and replacing original FG deck surface, and by injecting resin. Both seemed similar in result. Lastly, is it possible, the original build left a void or inadequate adhesion between the deck and the sub structure? Your biggest issue is if there is extensive moisture.
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Old 05-20-2018, 11:15 AM   #3
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Yes, it's probably cored. You could drill a hole into it to see what the core is. If it's balsa or plywood, the multiple injections can/will work; you have to be sure whether you're trying to re-bond the top to the core or the bottom to the core and drill accordingly. If the core is foam it will be important to know whether the foam is still OK or whether it would rather be dust. If it's dust, or on the way to dust, you should be interested in how much of the boat is built that way. The foam failure will probably be correlated to sun exposure: flat, sun-facing surfaces would be more affected than vertical or shaded surfaces.

I owned a 1968 Flying Dutchman sailboat built by Newport Boats. I bought it in 1993 as a stripped, retired hull. The hull and deck structure was very good when new, but since weight is an issue, it had become non-competitive because of loss of stiffness. By the time I got the boat the urethane foam core was turning to dust so that the face skins would delaminate and fracture under my weight (or the time I hit a rock). I did the necessary localized repairs and kept the boat in use for about 5 years before I gave it away. The hull and deck were about 5/16" thick overall, including about 1/8"+ of foam core.
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