How We Repaired Fiberglass Using Underwater Epoxy

A few weeks back, we shared an incident in Dotham Cut where the anchor wrapped around the prop. As a result, our Sailboat Cadence received some minor fiberglass damage on the shaft strut. With no haulouts or service facilities near our location in the Bahamas, we had to find a solution.

Thankfully, we had underwater epoxy. Actually, we had one epoxy, JB Weld’s Water Weld, and a friend loaned us another underwater epoxy – All Fix Underwater Epoxy.

One of these epoxies did the trick. The other did not.

The goal of this job was to seal up the exposed fiberglass. Exposed fiberglass would likely absorb salt water and that would lead to the deterioration of a small segment of our hull. That would NOT be good!

If the underwater epoxies didn’t work, it’d be an end to our cruising plans. We would need to find a haulout facility, and the nearest would probably be Nassau, Bahamas.

Two Underwater Epoxies for Sailboat Repairs

We used both the JB Weld epoxy and the All Fix. The JB Weld did not adhere to the fiberglass on our shaft strut. As soon as there was a current, the putty mixture fell right off.

The All Fix worked great! It came in two containers, Part A and Part B, and it only required grabbing equal parts and kneading for about 5 minutes. A couple of dives under the sailboat and all of the putty was applied. After about 15 hours, we motored around for 30 minutes at “high” RPMs to see if the epoxy would shake loose.

Nope. The All Fix epoxy stayed in place and fixed our problem!

Underwater Fiberglass Damage

In the picture below, you can see the propeller shaft (center-left) and the fiberglass shaft strut (black, right). The shaft enters the shaft strut through a polycarbonate cutlass bearing. The bearing is housed in a self-contained fiberglass cylinder. The cylinder received the majority of the damage from the incident when our anchor fell while underway in Dotham Cut.

Exposed Fiberglass and Sailboat Repairs Underwater Epoxy
Exposed Fiberglass

The picture above shows the exposed shaft, which is slightly discolored from years in saltwater. The shinier part of the shaft was previously covered by the fiberglass cylinder. The cutlass bearing is 6 inches long and was largely undamaged.

After ensuring that the shaft was not bent or loose, the exposed fiberglass was our primary problem to solve.

The cutlass bearing on the Catalina 387 is one of two bearings that support the shaft. This is a fairly robust construction approach, which can keep the shaft stable even after incidents like the one we encountered.

How Does Underwater Epoxy Work?

According to Duckworks:

On dry surfaces, the bond between the surface and the epoxy displaces the air, which is a fluid. The same is true underwater. As on dry surfaces, the polar bond attraction is strong enough to displace the fluid, in this case the water, and produce a strong bond even underwater.

We found that it was quite easy to use underwater epoxy. Here’s a video showing the kneading process.

Kneading Underwater Epoxy Putty

The key point for us was the adhesive quality. If the putty does not stick underwater, and can not take the force of the currents, it’s no good.

Here’s a picture of the All Fix putty after it cured on Cadence.

Cured Epoxy Putty

It’s not the prettiest repair, but it keeps us on the water. We can fix it properly at the next haulout and sail around knowing the fiberglass is solid and sealed.





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