So as part of my annual spring cleanup/upfit I decided to replace my diamond wires. My boat is a 1983 with a straight tube for a spreader. I have noticed that the tube/mast fit was generous and that water could certainly enter the mast at that point, but always assumed that the mast was sealed above and below the spreader to prevent the mast from filling up in the case of a capsize. I remove the spreader today and decided to check my assumption by sticking a piece of hose in the mast hoping to hit something indicating a plug. Well to my astonishment, there is no plug above or below the spreader!?!?!?!?!?

So, question is how to I seal the mast?



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Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
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Bed the washers using 3M 4000 and seal around the spreader pipe. At the same time seal the mast top fittings and rivets to be sure. Then you are good to go.

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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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That part of the mast shouldn’t get much water unless the mast is underwater, in which case you would be turtled already. I would care more about the stuff closer to the top, and in doubt put a mast float. I use a fender, much cheaper and looks a bit better. I had to add an eyestrap to attach it at two points though.

wolfman

Bed the washers using 3M 4000 and seal around the spreader pipe. At the same time seal the mast top fittings and rivets to be sure. Then you are good to go.

All great advice and I plan to do that. The boat is 35 years old and there's no telling if the mast head and base seals are still holding. I was thinking maybe some type of expanding foam injected through the hole would be the trick. My mind goes to the home window insulating type (in a can from the home stores), but that isn't really the type of foam you need for this application. Possibly a urethane foam?

Seems as though this is the last part of the boat I've not been through yet since I bought it as a basket case 3 years ago. I'm amazed at the amount of slop (at least 3/16") there is laterally in the spreader tube. Seems like they could have drilled the cotter pin holes a bit closer for a better fit.

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Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
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If some water gets in it should have a way out, that’s why most sailors don’t seal the base. Maybe you do a good job now but how long will it last?

(imho) Foam in a mast is a poor idea - it WILL get wet and heavier with time (condensation)

When my 6.0 was rebuilt in 2011, the head was removed and all the foam was toast and a huge PITA to get out


Some people tap a small screw into the bottom section that can be unscrewed in the event of a capsize/turtle to release the water

On my 5.2 with the same spreader setup I also have a drain hole for that worst case scenario at the base of the mast. I cover the hole with some aluminum foil tape like is used in HVAC duct work. It seems to be impervious to UV and the day I need to drain the mast it would be fairly easy to puncture and drain without any tools.

If the top end of the mast is well sealed you should never have to worry about the spreaders. When you seal rivets make sure to not only seal the hole for the mandrel, but also around the edge of the rivet and whatever the rivet is holding down (like the diamond tangs).

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dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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MN3

(imho) Foam in a mast is a poor idea - it WILL get wet and heavier with time (condensation)

When my 6.0 was rebuilt in 2011, the head was removed and all the foam was toast and a huge PITA to get out


Some people tap a small screw into the bottom section that can be unscrewed in the event of a capsize/turtle to release the water

Doing some research I found that all the consumer pourable expanding polyurethane foams ("Great Stuff" one part pressurized can and two part flotation from West Marine) do in fact absorb water over time. Thanks for that input and that option is off the list.

This is how Hobie does it with a plug and it works very well as the foam is closed cell and does not absorb water. I don't know what the polymer is. Having installed a few of them it looks and feels like the same foam pool noodles are made of. Unfortunately the plug is not an option here.

https://www.murrays.com/product/50-60060000/

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Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
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This is how Hobie does it with a plug and it works very well as the foam is closed cell and does not absorb water.

I am no foam expert but it is my understanding ALL foam can get waterlogged (probably due to condensation)
sitting in a humid hull, overtime it will get heavier with water

also abrasion can deteriorate the foam: allowing moisture in

"The problem with closed cell foam is that it will still allow water vapor to permeate into the closed cells. There it condenses and cannot come out except by vapor permeation."
https://www.thehulltruth.…ll-foam-waterlogged.html

This is true, however some foams break down in contact with moisture. Single part expanding foam will deteriorate when exposed to moisture. Pool noodle stuff is decent. PVC, as used in many hulls, is good to very good. XPS is probably in between those (the pink/blue stuff you can get at your local hardware store). Kelgicell, which is a structural PMI foam developed for use in fuel tanks on lightweight racing hulls and primarily aircraft, is wonderful. It is what I use when I can. They all rely on the use of a sealant to prevent the water from entering to begin with. The 3M 4000/5000 series caulks are much better than straight silicon.

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Pool noodle stuff is decent

pool noodles don't last 1 season here in fl - they get wet and deteriorate