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Old 09-01-2017, 14:54   #1
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Mast base corrosion: Repair or shorten?

Just dropped the mast on my Albin Vega this weekend, the corrosion at the base is ugly. My initial plan was to repair it by wrapping the base in aluminum sheet and affixing it with rivets (and maybe some 5200). I am not considering welding due to HAZ.

Questions:
  1. Should I repair this or shorten the mast?
  2. If repair, what grade/thickness aluminum should be used?
  3. Is epoxy the proper isolator between mast (aluminum) and mast foot (stainless steel)?

NOTES:
  • Max visible corrosion height = 1-1/16"
  • My rigging is made from Hi-MOD compression fittings by Hayne, so it would be possible to shorten the stays without replacement.
  • Albin Vega mast height ~ 30'
  • Additional weight items: Radar dome, VHF antenna, anchor light, oversized rigging, solent stay, Boomkicker rigid boom vang, T-track on boom, extra sail track for storm trysail

Photo 1 (aft = left):


Photo 2 (fore = right):


Thanks in advance for any wisdom.
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Old 09-01-2017, 15:25   #2
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Re: Mast base corrosion: Repair or shorten?

Your initial plan is no good

I would shorten the mast by the amount of corrosion then raise the step with something like g-10 by the amount the mast was shortened.
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Old 09-01-2017, 15:29   #3
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Re: Mast base corrosion: Repair or shorten?

I also have the same problem not quite as bad and have decided to sleeve the inside with 1/4" aluminum bent to the ID shape. I will then use a bunch FH stainless bolts fair and paint, I don't like the thought of shortening all my rigging, if I shortened the mast it. The sheer strength of the bolts will easily handle the compression are my thoughts.
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Old 09-01-2017, 15:36   #4
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Re: Mast base corrosion: Repair or shorten?

I would probably elect to grind off the base of the mast to a point where I had a uniform "healthy" metal surface. The rest of the answer may depend more on the structure of the mast step. From the appearance of the corrosion, my guess is that the step is a male plug that fits inside the mast, but maybe you have a female step that forms a collar around the mast. Either type of mast step will stabilize the base of the mast and the tension of the shrouds and stays will keep it in position. The height of the male plug or female collar of the step may allow you to place a shim under the mast that is a barrier between the different metals as will as a wrap inside or outside the base of the mast to isolate it. Epoxy may be suitable, but I would favor isolation with a fiberglass tabbing tape if you have room to fit. There may also be an opportunity to raise the step to match the loss of material at the mast. This is probably a good time to look at the structure under the step. You might find it easy to place an added secure plate under the base of the step.
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Old 09-01-2017, 15:52   #5
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Re: Mast base corrosion: Repair or shorten?

-Make the step taller and cut the mast back? (is this under the floor or deck?)
-Your plan for putting on a doubler is fine also. Rigging companies do this on racing masts sometimes. They make a lose fitting doubler and using structural epoxy they rivet the doubler to the mast.
-At the base of the mast absolutely no problem with welding either. It's all in compression there ....even soft aluminum is fine. (Think of it this way: aluminum boats are welded all over the place.)


-DO Not use big stainless bolts to hold anything on down there, you are just asking for bad corrosion. Multiple high strength aluminum rivets are better.


When done I would coat the end of the mast internal and external for a couple inches with lanolin.
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Old 09-01-2017, 18:04   #6
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Re: Mast base corrosion: Repair or shorten?

Quote:
Originally Posted by Sailmonkey View Post
Your initial plan is no good

I would shorten the mast by the amount of corrosion then raise the step with something like g-10 by the amount the mast was shortened.
Thank you for your advice, it will be taken into consideration.

Quote:
Originally Posted by djsaxton View Post
I also have the same problem not quite as bad and have decided to sleeve the inside with 1/4" aluminum bent to the ID shape. I will then use a bunch FH stainless bolts fair and paint, I don't like the thought of shortening all my rigging, if I shortened the mast it. The sheer strength of the bolts will easily handle the compression are my thoughts.
I am also not enthusiastic about shortening and would prefer to avoid it unless there's a consensus that it's necessary. Thank you for sharing your plans, in order to inhibit corrosion you may consider using aluminum rivets + an adequate adhesive rather than SS hardware. Unless the sleeve extends beyond what's left of the mast base, the rivets won't be left to bear the load alone.

Quote:
Originally Posted by Hudson Force View Post
I would probably elect to grind off the base of the mast to a point where I had a uniform "healthy" metal surface. The rest of the answer may depend more on the structure of the mast step. From the appearance of the corrosion, my guess is that the step is a male plug that fits inside the mast, but maybe you have a female step that forms a collar around the mast. Either type of mast step will stabilize the base of the mast and the tension of the shrouds and stays will keep it in position. The height of the male plug or female collar of the step may allow you to place a shim under the mast that is a barrier between the different metals as will as a wrap inside or outside the base of the mast to isolate it. Epoxy may be suitable, but I would favor isolation with a fiberglass tabbing tape if you have room to fit. There may also be an opportunity to raise the step to match the loss of material at the mast. This is probably a good time to look at the structure under the step. You might find it easy to place an added secure plate under the base of the step.
Your initial deduction was correct, I have an inner 'plug' that contacts the mast fore and aft.

The arch beneath the mast step which is in charge of supporting the load is reinforced very well with an SS plate and angle aluminum contoured along the arch, I don't envision it failing. Thanks for your advice.

Quote:
Originally Posted by Cheechako View Post
-Make the step taller and cut the mast back? (is this under the floor or deck?)
-Your plan for putting on a doubler is fine also. Rigging companies do this on racing masts sometimes. They make a lose fitting doubler and using structural epoxy they rivet the doubler to the mast.
-At the base of the mast absolutely no problem with welding either. It's all in compression there ....even soft aluminum is fine. (Think of it this way: aluminum boats are welded all over the place.)

When done I would coat the end of the mast internal and external for a couple inches with lanolin.
It's deck stepped. I would prefer not to raise the step if there aren't compelling reasons for choosing that option over the 'doubler' (a term which I was unfamiliar with). See below for an explanation.

Thank you for sharing your advice/knowledge
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Regarding my hesitation to raise the step/shorten the mast: I intend to begin a circumnavigation shortly (March 1) and would like to choose the repair which maintains structural integrity while not costing extra time/expense (there are other jobs which need doing).

Of course if one method was by and far the more structurally desirable then it would be easier for me to get on-board. But if instead the recommendation of one over the other is due to aesthetics then I'm inclined to choose economy.

The way I see it, adding a sleeve should increase the strength of the base when done properly, and would not require much time to complete. And on this note, I am not aware of instances of dismasting which were the result of the mast base failing (though we can assume it has happened).

I am open to having my mind changed, but for the time being I am of the understanding that both options are viable.
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Old 09-01-2017, 19:12   #7
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Re: Mast base corrosion: Repair or shorten?

Ahh... deck stepped. Boy that's a bunch of corrosion for a deck stepped mast. As mentioned, welding is not an issue there at the base. But finding a piece of that shape is likely quite difficult. (?) Is there currently enough boom clearance over the dodger etc for shortening?
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Old 09-01-2017, 19:15   #8
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Re: Mast base corrosion: Repair or shorten?

Been there, done that. And on a Vega no less.



The Vega didn't need anything else done to all fit back together. If I'd wanted, I could have stuck a pad of something like Tufnol underneath the mast base to restore the height. I've also cut 6 inches off the base of another mast after it crumpled as the result of a backstay failure. I made a pedestal out of stainless steel to go between the mast base and deck for that one. Little bit more complicated by the fact that a sheave had to be moved to the pedestal, too, but it all worked out well in the end.
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Old 09-01-2017, 22:41   #9
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Re: Mast base corrosion: Repair or shorten?

You're better off to just crop the bad section out of the bottom, & be done with it. Well, in addition to electrically isolating the spar from it's step.
Take the money saved by going this route instead of attempting to rebuild the tube, & put it to good use elsewhere. As trying to put 1" of height back onto the tube is a bit silly.
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Old 10-01-2017, 08:09   #10
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Re: Mast base corrosion: Repair or shorten?

That looks bad. Cut an inch off the bottom and raise the step. I don't know what your step looks like or sits on, but I just used 1/2" thick GPO3 and epoxy 2 layers of it under your current step plate to raise it. GPO3 is strong FRP plate and cheap, available from onlinemetals.com, $30 for 12"x14"X0.5"thk. Then there is no impact to rigging, etc.
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Old 10-01-2017, 08:17   #11
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Re: Mast base corrosion: Repair or shorten?

Vagrant, as others have suggested, cut the mast back to clean metal. A sleeve, although acceptable, simply hides the problem. Removal eliminates the problem. You also need to isolate the dissimilar metals with an anti-corrosive compound or a fiberglass pad mounted atop your tabernacle. I like to use a simple analogy: after taking a bath do you wear clean underwear before you dress or ones that are day old? Good luck and safe sailing.
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Old 10-01-2017, 08:24   #12
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Re: Mast base corrosion: Repair or shorten?

I had a similar issue last year. Solution was easy and clean: cut off the mast step until you are into "good" aluminum. Then have a "foot" fabricated from G10, a synthetic and very dense polymer. It will stand up well to compression and also serves to isolate the mast butt from any moisture. I had a rigger do the job for me with the mast out. I would recommend having the G10 fabricated in a rig shop or, at least, a knowledgeable machine shop. You will also have to redrill any exit holes for masthead lights etc. Good luck!
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Old 10-01-2017, 08:52   #13
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Re: Mast base corrosion: Repair or shorten?

Just cut the end off back to bare metal as others have suggested. Sleeving is just making work and adding potential problems in my view. If you can't get hold of dense polymer to regain your height (should you really feel it necessary), then a piece of teak or similar can be easily cut to size and will do the job.
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Old 10-01-2017, 10:02   #14
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Re: Mast base corrosion: Repair or shorten?

Looks like about an inch (?) or so. Just cut it. Add a shim of teak or delrin and be done with it. There's plenty of other stuff to overthink! Lol!!
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Old 10-01-2017, 11:44   #15
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Re: Mast base corrosion: Repair or shorten?

My mast was fine but the iron mast step was rusty, I had these guys build a new mast step out of massive aluminum.

dcproductsllc@yahoo.com

I sent them the old mast step and 2" of the mast that I cut off, had the new step powder coated and had it built with two "ears" so I could pin the mast to the step in case of a rollover.
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