Repairing Stress Cracks

Now we feel like we are really beginning to understand the properties of fiberglass boats. The gelcoat which is applied to the outer surface is not as flexible as the resin with fiber embedded in it is. So when the sterndrive caused the transom to flex, the gelcoat cracked under undue stress and left a series of cracks mostly near the bottom of the outdrive. These cracks were actually very easy to fix, but the color matching of faded paint is an art form in itself. Since these cracks were near the bottom of the outdrive, we didn't care to spend much time mixing colors to match. You can see the repair job in the final product, we feel it just gives the boat some character.

To repair the stress cracks, we had to first grind the cracks out with a rotary tool commonly referred to as a Dremel. The grinding took a while to do, be sure to use a hardened steel bit otherwise the fiberglass will tend to eat it up. Here is what it looked like just after we started.

We then mixed up the gelcoat and added some pigment. The "neutral gelcoat" we got from US Composites had a grey-ish tint to it. So even though our pigment matched the faded off-white color of the boat hull the resulting gelcoat we mixed was a bit darker than we really wanted. Here is what the first coat of gelcoat looked like.

Ok after that cured, it was time to do some more sanding and see if we needed another coat.

If you look closely in the right photo you can see some gaps or voids in the surface after we sanded it down with 220 grit sand paper.

To address the gaps we had to put on a second coat. As you can see, it is a lot like painting thick paint on. As it dries or begins to cure, it turns into a gel-like substance. This happens in about 15 minutes so you have to work quickly. We were able to use an old hair dryer to speed up the process.

Well after we sanded down the second coat, we filled all the gaps so that it was smooth to the touch. If it weren't for the color mismatch, the repair would have been flawless. Anyway, it was then time to mount the transom plate, gimbal ring and bell housing to the transom. In this shot you can see the result of the stress crack repair job (looks like the boat has a tatoo).

Next step is to put the engine back in the boat. Engine Back In