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Mast Sealing Technique
http://www.hobie.com/au/en/forums/viewtopic.php?f=20&t=72314		 Page 1 of 1
Author:  warmshoe [ Tue Jun 23, 2026 3:22 pm ]
Post subject:  Mast Sealing Technique
I am replacing my H16 mast base and see a flexible (and leaking) rubber membrane inside the mast. The boat is 1981 and has rivets and screws securing the existing base to the mast, so I presume this has been replaced already.

Hoping this link works here...
Image
OK that didn't work apparently :(
Low tech: https://www.flickr.com/photos/199792123@N06/

Herein I found some advice to silicone and A/B foam. I wish to repair it as robustly as possible and propose the following, advice appreciated.

- drill/tap four holes in the the new mast base (holes exist in mast) and ensure a nice fit. Do not re-install rivets since the holes are blown out (presumably why the existing base was drilled and tapped)
- wire brush and soap/water scrub inside of mast
- alcohol wipe inside of mast
- push cardboard plug/disk about 6" into the mast
- mix and dump A/B foam into mast (tape off outside of mast to not make a mess)
- cut off excess foam
- install mast base with copious amounts silicone in the first inch of the inside of the mast
- Stainless SHCS screw base to mast
- Silicone outside of base/mast interface

Seems OK? Perhaps do the same at the top of the mast?

Any sound advice will be appreciated!
Author:  rattle 'n hum [ Thu Jun 25, 2026 2:52 pm ]
Post subject:  Re: Mast Sealing Technique
It's really not as complicated as laid out in your post...

First read my reply in this thread and proceed accordingly (it's in the H14 forum, but still applies): https://www.hobie.com/forums/viewtopic.php?f=17&t=35295&p=142875&hilit=corkscrew#p142875

The H16 foam plugs are P/N 20060000: https://westcoastsailing.net/hobie-16-foam-mast-plug/?srsltid=AfmBOoqxM3F_E-eDCFLyCFgCHqSvibAYAF6UZwAogwUDEk0Azp5eRfR7

Drill 3-4 new holes through the mast (if the old ones are enlarged) and new base, then install 3/16" SS rivets.

Repeat process for masthead if necessary.

No need to seal base and masthead if the plugs are in there correctly.
Author:  warmshoe [ Fri Jun 26, 2026 7:11 am ]
Post subject:  Re: Mast Sealing Technique
So easy!!!

Thank you :D
Author:  warmshoe [ Mon Jun 29, 2026 3:48 pm ]
Post subject:  Re: Mast Sealing Technique
Plot twist! When I removed the rubber membrane at the base of the mast, it exposed a foam plug.

You suggest the foam plug does the trick, I am curious why (presumably aftermarket) rubber seal was added? It seems that is a bad strategy, as I presume the foam permits weeping out of water taken above it.

I have a couple plugs in the mail. These plugs look fine (but maybe 45 years old!). Leave them be (ain't broke, don't fix it) or replace?
Author:  srm [ Tue Jun 30, 2026 8:39 am ]
Post subject:  Re: Mast Sealing Technique
There should be a foam plug, then on top of the foam plug is an aluminum plate which is glued/sealed into the mast with a bead of sealant. This is how they come/came from the factory.

The foam plug may do some sealing but I think its main purpose is to hold the aluminum plate square when its placed into the mast and give you something to press against when applying the sealant. Otherwise the plate would just fall over. The plate and sealant are what do the actual sealing.

Unless you have reason to believe that the original seal failed or need to access above the seal for some reason, I would leave all of that alone. There should be no need to mess with the seal when replacing the mast base or mast head.

sm
Author:  rattle 'n hum [ Thu Jul 02, 2026 9:10 am ]
Post subject:  Re: Mast Sealing Technique
Yes, the old post that I linked above mentions the metal plate, and srm has described the whole bit better than I. I recommended removal/refit of the plug because warmshoe's first post states that it's leaking. In that case I think it best to make sure there's not water and crap trapped in there.
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