Seal Leaking Mast

Sealing a Leaking Mast
A Pre-season Project                                                     ..Return to DSC hobie LIBRARY Page
By Chris VanEpps

To test your mast for leaks, remove it and drop in water. This water can be in a lake, pool, or even a long tube. If it floats, its sealed. If it sinks, it leaks. 

Another test method is to drill out the rivets in the base cap (the end that sits on the crossbar) and remove the bottom cap. Insert the hose of a shop-vac, set to blow into the bottom of the mast. DO NOT seal the hose in with a towel or anything. You don't need that high a pressure. With the shop-vac running, brush a soapy water solution over all the fittings, anywhere rivets are located and all around the top mast/cap joint. Anywhere you see bubbling is a leak. If the leak is directly up through a rivet you can try to clean it really well with a solvent, then dab some clear marine- grade silicone adhesive sealant around the rivet and retest when cured. If this doesn't work you'll have to drill the rivet out and replace. Original rivets are usually a material called MONEL, or Stainless Steel. Aluminum is cheaper, but I recommend against them. They aren't as strong. On the plus side, if you sail in salt water Aluminum rivets on Aluminum mast and fittings won't suffer from electrolytic corrosion. Its a trade-off. I usually use MONEL on end caps and stainless on fittings taking any load (Mast Hound, cleats, cams, etc.). Anyway, be very careful drilling out the old rivets. You don't want to enlarge the holes at all, or a weaker joint will result. Holding the head of a new rivet up to the old one is a good way to gauge the rivet size. Rivets are sized in a dia x depth/reach format (i.e.. a 3/16"x1/4" rivet is 3/16" dia by 1/4" reach. The drill you use to drill out the old one, or drill a hole for the new one is 3/16". simple.) Also, use the proper sized rivet sleeve, which covers and seals the mandrel hole. Gob some clear marine-grade silicone adhesive sealant on the bottom of the new rivet sleeve. Insert the sleeve, then the rivet, and "pop" it in. Wipe off the excess that squeezes out and use it to dab on the head of the rivet to seal the shaft. Run a bead of the sealant around the mating surfaces of the top cap (If you removed it) and reinstall with new rivets. You should see a little excess squeeze out, all the way around. Wipe it of. When the mast passes retest, reinstall the mast bottom cap the same as the top. If you do just one fitting or part at a time, you won't need to worry about remembering where everything goes. 

Remember: If testing your mast with a shop-vac to use as little air pressure from the vac as possible. You need to see air leaks with the bubbles, but you don't want to blow apart a perfectly good seal either. This is a great spring pre-season project that can be tackled by the average do-it yourselfer with a hand drill, a shop-vac, a rivet gun and some assorted rivets(the more the marrier). 

I plan to do this to my own H16 this spring. I'm sick of heaving like a rented mule to pull my baby back over when I flip and, if you're like me, "If you ain't flippin' a '16, you ain't sailin' her!" 

You may direct any questions to me at the email address below. I work part-time, when not at my day job, as the used-boat reconditioner/repairer for a local sailboat dealer. 

Cheers and happy sailing, 

Chris VanEpps 

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