Cast Iron Swing Keel Restauration

In 2005 I had bought a small sailboat that had a cast iron swing keel. This keel, which could be lowered and raised with a hand operated winch, allowed the boat to be easily trailered and it was also possible to go into water as shallow as 12 inches. Of course, for sailing, it needed to be lowered.

The boat was over 20 years old and salt water had caused considerable amounts of rust and a form of corrosion known as scale. Movement of the keel had gotten so bad  that the previous owner had drilled a hole in the top of the keel box and used a piece of rebar and a heavy hammer to tap on the keel to convince it to go down. I intended to enjoy the boat so something needed to be done.

Here you can see the rust and scale that made it
almost impossible to move the keel.

The weight of the keel was about 350lbs. I took it out by removing the pivot bolt and lowering it while it was still attached to the winch cable. I wrestled it into the trunk of my car and took it to a automotive body shop that spent about 3 hours chiseling and sandblasting it. When I took it picked it up I knew I had to coat it quickly to prevent new corrosion.

The keel just after sandblasting

A detail of the surface after sandblasting. You can see how irregular and pitted it was, but there was no corrosion.

Interlux has a system to restore and protect underwater metals parts like this, with a number of different steps.First there is something that etches it - I think it's called Primewash and there is an initial coating to prevent it from immediate corrosion called Vinylux. This is the green material in the photo.

The keel with Vinylux on it.

After that you can coat it with an special waterproof coating they have that includes silica chips to provide armor against bumps and scratches and other hard objects hitting it. This coating is grey in the pics. Once there's a couple coats on it you can start fairing it. I used their underwater fairing compound, which is an epoxy mixed with a very waterproof filler to the right consistency for fairing.
After a number of cycles of fairing, sanding and coating again, you can have a good keel again. Before putting the keel back in the boat, I coated it with an ablative bottom paint.

The finished product ready to go back in the boat, faired, coated and with bottom paint

Reinstalling the keel in the boat required two people and some cursing. We used the winch to lift the keel up into the boat and then me under the boat trying to wrestle the keel around and a helper inside the boat trying to insert the keel bolt. It took a little while but got done.

I had the boat for eight years after that and always sailed it in salt water, in the Barnegat Bay and Atlantic Ocean in New Jersey and Florida and in British Columbia. The fix was permanent, the rust never returned.