I have a sunfish that I keep at a lake a couple hours a way. It is 20 some years old. I have had it for probably 7 years. Anyway, I live in Michigan and the weather has been fair to cool. I left the boat uncovered for a couple months this spring (april - July). I now have a bunch of areas with spider cracks. My uncle had moved the boat at one point. Did the sun cause this? Should I consider repairing it or just, clean, wax, cover and keep using? I know nothing about gel coat. I find it hard to believe a couple of months exposure to sun in the spring in Michigan caused this, but that is the only obvious thing.
Hi Jeff, Yes the Sun is the culprit however the age of the gel coat is at play here too. This would have happended years ago if she had been left to the sun. If the cracks are just inthe outer coat, then clean and wax her up and press on. Don't forget the cover though.
Gel coat is quite tolerant of UV. Spider cracks can be a couple of things, but are usually stress cracks. These are most often found around hardware, like cleats, mast steps, fairleads, etc., but also around tight radius areas, such as comings, corners and any change in angle in the laminate. These corner areas are where the gel coat is much thinner then the flatter areas, so they're the first to go.
Other places you might find these types of cracks is in areas that get regularly deformed during use, such as foot wells, seating areas, around the hole the mast goes through, etc. The cause for these is a little more complicated to explain, but they're treated the same way.
When gel coat gets cracks, it's one of two things happening. One is laminate failure under the gel coat. This can be from impact or repeated flexing (such as areas under your butt). The fibers in the mat have separated and some movement is occurring, which strains the grip the gel coat has on the surface. The other is gel coat thinning. This occurs naturally if left in the sun, but takes many years. I know boats that have lived in the same place in direct Florida sun for 20 years, but haven't cracked. If the gel coat is thick enough it'll hang tough for a long time. Buffing or polishing the gel coat repeatedly will thin it down, eventually wearing through so the laminate shows or cracks appear.
The SunFish was an inexpensive boat and built that way, particularly in the era yours is. Gel coat wasn't thick, laminates were minimal and the resin not especially strong. This means they "age".
Unfortunately, gel coat is the only part of a polyester laid up hull (like yours) that is water proof (and it's not totally water proof either). When the gel coat gets breached, from damage or age, then moisture gets into the laminate. In climates where you have freeze/thaw cycles (like your neck of the woods), the moisture expands when it freezes, then contracts when it thaws. This cycling within the laminate forces it to break apart, which can cause cracks at the very least and wholesale laminate failure in the worst cases.
So, my suggestion is to make a repair, to protect the laminate. I address these types of issues frequently on other discussion forums and in repair work all the time. It's not so bad, but your options are limited.
You can gouge out the cracks, fill with putty and re-gel coat, but this is next to imposable for a back yard repair to get a good color match. Even the pros have a difficult time matching gel coat. The other option is filling the gouged out cracks, then painting. This is the easiest and fastest way. It's probable your gel coat is plenty faded and weathered by now, so you needed an excuse to paint the old gal anyway, right?
Take a scratch awl and pick out the cracks of loose gel coat and look down in the crack for bare laminate (mat, which will look like a random arrangement of fibers). If you see mat, then use a sander and feather out the area. Apply some unthickened epoxy, let this gel then apply some thickened epoxy (micro fibers and silica in highly stressed areas, silica and micro balloons if just cosmetic). Sand flush, then paint.
If the gel coat isn't breached, just scratched, then use a high build primer, then block and sand until the scratch is filled, then top coat with paint.
Of course you want to work on freshly cleaned surfaces, especially inside the cracks, where epoxy or primer will have to stick best.
If the cracks come back, then the area needs more reinforcement. This is a more traditional repair, where you grind back to the mat, apply fabric, fill, smooth/fair and paint.
Greetings,
Every Sunfish I have ever seen has had spider cracks around the cockpit. They are very thin and sometimes form concentric rings around the corners of the cockpit
One of the guys here at the local sailing pond (Ken) is a serial Sunfish owner. He owns two right now. One to sail, one for parts. Every Sunfish Ken has ever seen has spider cracks around the cockpit.
The boats are inexpensive. The edge of the cockpit is unsupported. It's only a matter of time. Less time if you weigh more than 10 stones.
If you are worried about a yacht-grade finish on a Sunfish, then you are missing the whole point of owning a Sunfish. They frequently get dragged to the water, sailed hard, and put away wet.
Wax the boat and go sailing.