Nacra 5.7 mast corrosion :: Catamaran Sailboats at TheBeachcats.com

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Nacra 5.7 mast corrosion

SquamCat

Rank: Lubber

Registered: Sep 10, 2009

Last visit: Sep 17, 2021

Posts: 49
Posted: May 11, 2021 - 10:17 AM

Back in December the top of my Nacra 5.7 mast was broken by a tree and I picked up a used mast from Stuart (nofearofflying) on Fire Island, New York and hauled it back to New Hampshire. I just drilled out the mast base rivets and blocks to get a closer look at the corrosion.

Any recommendations on repairing / strengthening the base of the mast? I guess I could bend some aluminum sheet metal to line the inside and rivet / epoxy together.

Thanks,
Eric
MN3

Rank: Master Chief

Registered: Jun 20, 2006

Last visit: Dec 04, 2024

Posts: 7090
Posted: May 11, 2021 - 12:26 PM

finding a quality spar fabricator / welder would be optimal
epoxy/rivets or bolts would be better than nothing
tominpa

Rank: Mate

Registered: Jul 29, 2015

Last visit: Dec 12, 2024

Posts: 594
Posted: May 11, 2021 - 12:33 PM

That boat was used in salt water and there is some galvanic corrosion where the mast base was attached. Hard to tell from an image, but I would guess when the base is inserted in there, the mast will remain quite strong, and that is not an area normally under high stress during sailing. There are many ways to cosmetically fix the corrosion, but I don't see a structural issue where that is located.

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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SquamCat

Rank: Lubber

Registered: Sep 10, 2009

Last visit: Sep 17, 2021

Posts: 49
Posted: May 11, 2021 - 04:57 PM

Ok thanks for the replies. Here is a photo of the mast base, it covers up the bottom area mostly.

I talked to an aluminum welder about fixing the mast and he is willing to work on it, but doesn't know much about catamaran masts, certainly not a spar fabricator. I also have the original mast which is broken about a foot above the shroud connection, maybe 6' from the top. Is it worth thinking about welding a section of the other mast on to this one?

There is also some corrosion behind the bottom spreader wire mount. Should I drill these out, clean up and re-rivet them back on?

I want this mast to be safe to sail with 2-3 people in 20 knots of wind.

Thanks,
Eric

Edited by SquamCat on May 11, 2021 - 05:57 PM.
tominpa

Rank: Mate

Registered: Jul 29, 2015

Last visit: Dec 12, 2024

Posts: 594
Posted: May 12, 2021 - 09:07 AM

That stay chainplate is actually a bigger corrosion risk because the aluminum gives up electrons to the stainless in a salt environment. You can drill out the rivets and inspect the surface. If it is still strong, then I think you should coat it with a galvanic protection coating before fastening the new rivets. The stainless will clean up just fine. There was a thread by Andonista a while back that discussed some options for a corroded bow foil where I suggested CRC Marine Corrosion Inhibitor in the repair, and several other ideas were also put forward.
https://www.amazon.com/CR…-Inhibitor/dp/B0000AXYA0
https://www.thebeachcats.…ms/viewtopic/topic/18343

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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tominpa

Rank: Mate

Registered: Jul 29, 2015

Last visit: Dec 12, 2024

Posts: 594
Posted: May 12, 2021 - 09:31 AM

I'll add I don't think the mast structure is compromised, but it must hold the rivets at the attachment points. If the metal has thinned too much, you may have to relocate the fixtures slightly fore or aft on the mast and refill and cosmetically treat the existing penetrations or use a type of rivet that spreads the load over a larger area. A split rivet does this without a washer, and I used these on my trampoline track when conventional rivets used to pull out.

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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