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Internal mast seal


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Depends. Normally a mast plug can be used just above deck level, and with a drain hole in the side. But then cables must be in a conduit, and sometimes when it rains really hard a little water still gets by. It can be really hard to stop completely. Retro fit with mast in is almost impossible! Maybe a drain in the bottom to the shower or main bilges?

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If there is an existing seal, then provided all the cables are in a conduit, a SMALL amount of liquid expanding foam can fix it. Just sufficient to put say a 1cm thick layer on the existing one. Bloody hard to remove though...

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Find the lowest halyard or whatever hole in the mast that gives you some access inside. Find a ballon, put it in the mast and inflate, tie off balloon. Get a smooth tipped stick and push it down a bit, try to get it down at least 100mm from the hole you are working through.

Squirt in some foam on top of balloon. If you don't squirt in too much foam it will seal up to the access hole and all will be well with the world, too much and there could be a clean up pending.

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If using pourable silicone, first check there are no old rivet holes or other gaps in the mast wiring conduit that the silicone can flow into. Otherwise you’ll fill up the conduit and not be able to replace or draw new wires through it!

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I did as suggested by Steve Ashley and removed a halyard sheave box near deck level. If you don't have a hole there I imagine cutting one around 50-60-70mm dia should be ok - check with a mast fabricator

Next shaped some flexible foam to approx mast shape and pushed it in through the hole and down say 15mm below sheave hole.

(Flexible foam - might have used the stuff Burnsco sell for seating - not sure.)

Then spread flexible sealant from Sika on top of foam and left to set. This was a few years back so can't remember the name of the sealant but it was not silicone. As Steve mentioned it was thicker than what Sika used to produce so dificult to push around back of cable tube so we still had a slight leak.

Next mod was put in a layer of slightly thickened epoxy on top. Voila no leaks and been there at least 5 years.

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