I've recently purchased a 2nd hand Nacra 5.8, haven't had the chance to get it wet yet, it's currently getting a once over and a couple of fix ups with the Nacra builder/shop. They've reported the mast has some corrosion in the lower section and they're repairing it, no worries. They've also stated the lower section (not sure how much) had been filled with expanding foam, but they're not sure why this would have been the case, they could understand someone putting it in the top of the mast for flotation but not the lower. This got me thinking:

- In an ideal situation, you want the mast fully sealed without leaks
- In the event of a capsize, if the mast did leak at the top, with the foam in the lower section. sealing the mast from any corrosion holes or leaks in rivets, prevent air escaping, therefor creating an air pocket
- If water did get in the mast, the foam would prevent water from leaking out the base, and cause corrosion ? but it's meant to be sealed anyway. If water did get in, you'd have to work it back out the entry point, or drill a rivet or something.

What's your opinion on this, good/bad/ugly?

Cheers,

Johno

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1335 XTSea Nacra 5.8 NA
605 Nacra 4.5
Cleveland Yacht Club
Brisbane, AU
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Johno,
Your scenarios are correct. To add to that, expanding foam "Great Stuff" is open cell foam which holds water and makes the mast heavier.
The tried and true way is your first scenario.

Open up the base, pour in some paint thinner, acetone, or anything similar to dissolve the foam and remove it. Let the mast vent well in the sun before sealing back up.
Disclaimer: I have been told these will dissolve Great Stuff. Try a sample before continuing. Be warned that poor ventilation will make the worlds largest pipe bomb. This may be a piss-poor suggestion. I do not know how these volatile chemicals will affect existing silicone sealant.

Depending on how far up the foam is you may be able to mechanically remove it.

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FYC, Nacra 5.2 "Chris's Flyer" & Nacra Playcat & Farrier Tramp
Previously owned: Trac 14, H14, H16, H18, N5.0, G-cat 5.0
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Quote

Be warned that poor ventilation will make the worlds largest pipe bomb. This may be a piss-poor suggestion. I do not know how these volatile chemicals will affect existing silicone sealant.

Adding fresh air (ventilation) won't change the toxic, flammable byproduct, but will reduce the chances the fumes will kill you. "caps" that would constrain the rapid expansion of sed byproduct is what will prevent it from being a bumb



(sealed) Masts / or anything with air in it will accumulate moisture with normal condensation. Foam in a mast will trap that.
Hot moist weather will exacerbate the quantity of trapped h20.


you can drill / tap a small screw near the bottom as a drain hole. I recommend you apply a coat of lanicote or tef gel around it (and all fittings).

my suggestion is to open the mast from the bottom (unless GOOD alum welder is avail - then do it from top and bottom)


use rebar or longer iron/steel rods. Heat them with a torch until pretty hot and use this to melt the foam out.



Edited by MN3 on May 12, 2021 - 09:20 AM.

A long electrician's auger might help.

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'82 Super Cat 15
Hull #315
Virginia
Previously owned: '70 H14, '79 H16, '68 Sailmaster 26, '85 H14T
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