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How do I stop my mast from leaking?

2024 March 1

Dear Boat Doctor,

My new-to-me boat has a keel-stepped mast. I’m happy to have it, but I cannot get the mast-to-deck joint to stop leaking. Even in a gentle rain, I find water dripping into my saloon. I did a careful job with Spartite, but it still leaks. What am I doing wrong?

Chris Foster

San Diego, California

Dear Chris,

Congratulations on the new boat. I strongly prefer keel-stepped masts as the whole arrangement tends to be more stable, but you do have to deal with a big hole in your deck.

You made a good choice with Spartite. A keel-stepped mast must be supported at the deck, traditionally this is done with wooden wedges, but a poured continuous “wedge” such as Spartite does an excellent job. But, as you found, the seal is not always watertight.

You can approach the leak a few ways. If there is room, you can try to apply a bead of caulk between the Spartite and the mast deck collar and see if that works.

If not, you’ll have to add a layer of protection and tape the seam.

There are a few choices when it comes to mast boot tape. There are several self-amalgamating tapes out there, like CS Johnson Rubbaweld (www.csjohnson.com). Self-amalgamating tape isn’t sticky. As it stretches into place, the layers of tape join together, forming one solid piece of rubber. I have also had good luck with Windblown Products Mast Boot Tape. Windblown tape is a heavy rubber tape with an aggressive adhesive backing. Windblown tape isn’t widely distributed, but a number of online chandleries and fishing supply stores carry it.

Whatever type of tape you choose, apply it from the bottom up. Layering in this direction will lay the upper layers over the lower, layering like shingles on a roof.

Mast boot tape jobs aren’t always beautiful, so you may choose to invest in a fabric mast boot cover for a nicer look. The cover will clean things up and displace a little water on its own.

Good luck, I hope for a dry cabin for you. There is nothing worse than a persistent deck leak.