Gel coat cracks?

Gel coat cracks?

October 16th, 2010  |  by Marilyn  |  Published in Maintenance and Repairs  |  1 Comment

We just noticed that Rainshadow has a bunch of small cracks on the topsides near the toe rail. Yikes! There are a lot of them, maybe 20 per side. They are not evenly spaced (though they seem to come in pairs separated by a few inches). They are not uniformly positioned relative to the screws that hold the teak toe rail in place, so I doubt that’s the cause.

We know from drilling holes for the head vent thru-hulls that the just below the toe rail, there is the deck-to-hull joint and the hull is about 3/4” thick there. So these cracks won’t go through the hull, they must just be in the gel coat.

We’re wondering if they might have something to do with the dark colored hull and thermal expansion. It gets pretty hot when the sun is on it, even in our mild PNW climate. We checked, the cracks are on both the port and starboard sides. Rainshadow spent about 20 years in the same slip in the same orientation. Sun exposure seems to have been enough to make her have many small cosmetic blisters below the waterline on the slip’s ‘sunny side’ (port side faced south) and practically none on the ‘shady side” (starboard side faced north). Since these cracks are on both sides of the boat, maybe sun has nothing to do with it.

We’re also curious why we never noticed them before. It seems very doubtful that so many small cracks would form in the 11 months since we’ve had her, when she’s 36 years old now. Maybe the cracks were full of polishing compound when we first bought her last November. She definitely needs a polish now. The topsides were painted about 10 years ago, so maybe there were a bunch of repairs made and now they are failing?

I suspect we should do something about them, because it’s not good to let moisture get down inside the gel coat. The idea of repairing them all with new gelcoat, and then repainting the topsides, is daunting indeed!

I wonder if any other Nic 38 owners (or other fiberglass hull boat owners) have seen such cracks and have any suggestions?


  1. JG Nadeau says:

    October 17th, 2010at 11:01 am(#)

    I had a slew of these on Gosling. They were not limited to the toerail but several other places including around the windows where the screws held the frame. When I had the boat repainted last year i removed all the windows and had a closer look. They appeared to be only in the gelcoat so I dug out the gelcoat with a dremel to about a 1/4 in groove and refilled the gap with a good resin based filler.I also drilled a small hole at the end of the crack to dissipate any pressure that may have existed along that fissure. For the more damaged areas below the gelcoat I drilled them out to remove any broken material and made sure the first filler application was wet enough to permeate.
    The secret to preventing the problem when you replace the screws is to drill a hole larger than the screw that you place back in the hole. The backing material, whether wood or FG will retain it. I always dip the end of the screw in a good bedding compound (5200 in my case) to make sure of the seal.
    I also had a lot of these cracks along the stripe. You may be correct in assuming that heat and time have something to do with that. Again. we used the same techniques to repair those before the repaint.
    Cheers, J-G
    SV Gosling

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