I just finished repainting my boat, 1982 vintage fiberglass. The transom and part of both sides were painted with black imron about seven years ago. The rest was white gel coat. The heat absorbed by the black portions of the boat made small cracks in the paint--only in the black areas. So I ground it off. The cracks persisted into the gel coat. So I ground it off. They continued almost 1/8 inch into the glass. So I laid up new glass over everything and called it a day. I also had a small dock
ding on the white gel coat. The stress marks in the glass looked just like the heat-caused cracks in the black areas of the hull
. I started to wonder if I had substandard gel coat, so I poked around the boat yard and examined all the dark colored hulls I could find. I looked at everything from production sea rays to chris crafts to 100ft plus yachts. Almost without exception, I observed similar cracking on all dark hulls over five years old. In fact, there was a dark green yacht of about 85 ft, 2003 vintage. It's entire hull
looked horrible. The guy wanted to sell it, but had absolutely no luck. While this anecdotal tale applies only to fiberglass construction, it clearly points to the heat stresses placed on whatever material you use under a dark paint
. My boat is now entirely white.