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How do I stop leaks down the mast?

2022 January 1

Dear Boat Doctor, 

I just got my first big boat and I am facing a new problem. My boat has a keel-stepped mast and I am struggling to seal the mast to the deck. The boat came with a rubber strip but it’s in pretty bad shape. I am not sure where to start, all the boats I see on the dock seem to have a custom collar and I have no idea where to get one.

Bob Steiner

Chicago, Illinois

Dear Bob,

You’re not alone. Leaks down the mast have vexed boat owners for ages. 

Let’s start with the support of the mast.  The mast slides through the deck collar and there is room to spare. This space around the mast is traditionally taken up with wooden mast wedges or these days with a strip of hard rubber or plastic. The spacers center the mast in the deck and provide support.  

Spartite is a custom wedge that you form in place. First, you center the mast and create a damn on the underside of the deck, then pour in the Spartite material, which cures into a hard rubber wedge, custom fit to your boat. Regardless of how it’s formed, this wedge is purely to support the mast, but it will not stop leaks.

Sailing Specialties makes generic mast waterproofing boots that you can find online or in a well-stocked chandlery. Their product is a strip of UV-resistant vinyl that is held in place with large hose clamps. 

A better solution is self-amalgamating rubber tape. This tape bonds to itself and becomes one solid layer.  CS Johnson (www.csjohnson.com) makes Rubbaweld Tape, which is great for somewhat smaller boats. It is 4 inches wide and is designed to be layered in place.

Windblown Products’ Mastboot, available at Annapolis Rigging and other outlets, is great option for larger boats. This tough rubber tape  is 5 inches wide and designed to be installed in layers from the bottom up, like shingles.

Either tape product can look a little industrial once in place, and the tape itself is not terribly chafe resistant. A fabric mast boot is nice finishing touch.  Any canvas shop can help you out, or it’s a great DIY project to help you develop marine canvas skills.