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Old 15-01-2015, 19:18   #16
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Re: Mast corrosion

Ditto! You can locate high spots with a sheet of sand paper glued to a flat block. Lapping.

Sandpaper on a board. A very handy tool and one I find many uses for, including the mast base job.

I cut 1/2" off my mast the last time it was out. But I added a new cast mast step which was 5/16" higher then the old one. As well a I added a G10 shim to bring it back to specs and isolate the alum from the SS base plate. Check out my blog below.

I put a 1/4" thick sheet of 6061 aluminum under the mast. I used UHMWPE for the base. Didn't want any more Fe/Al interaction after the mess the last step made. Hopefully the polymer is up to the job. Any comments on my choice?

If you wrap a piece of wide shim stock around where you want to cut, that will create a perfect guide to scribe a line around to cut along and file to finish if need be.

You could add a decorative base plate, the same length as you cut off, under the step, made of a water resistant material, which would also get it out of the bilge and slowdown the erosion process dramatically. You just need to create a flow path for the water to run into the bilge again.

I cut four little mouse holes around the bottom of the mast and matching drain holes in the step.

Also, paint inside and out as a secondary preventive. And ditto on the aircraft paints if you want to go to that much trouble. My original base lasted 15 years before I got to it.

Paint is a good idea. I was so concerned about raising the step, keeping it dry and isolating the metals I sort of forgot about painting. Have some spare Al primer in the shop that will do the job just fine.

The water is always bluer on the other side of the ocean.
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Old 15-01-2015, 19:35   #17
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Re: Mast corrosion

I had a similar issue a few years back. Sanded that mast portion down to shiny aluminum and put on a few coats of automotive primer and covered by 3 coats of epoxy paint, both $4-5 cans from Walmart. My boatbuilder buddy traced the issue to my wet bilge (that's my next project, either restuffing or replacing the stuffing box) and interaction between the ss keel bolts of which I have 11, and the mast and the step (which is also aluminum and probably ready to be replaced soon). Since then I keep a bunch of old zincs in the bilge taken from the old zincs pale at the boat yard and the problem seems to be contained as I check that area often.

This is one of the few deficiencies I find with the builder/designer of an otherwise fine boat. I may even replace the existing alum mast step with G-10 box epoxied in, if I get handy enough to DIY. On the other hand a local rigger at the boat show quoted a few hundred bucks for the new aluminum step plus may be as much for the installation. And if it'll last another 35 years it just may be the most reasonable solution.

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Old 17-01-2015, 10:52   #18
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Re: Mast corrosion

I don't believe you'll have any problem with grinding that down,and then Heliarc, 1/8"plate aluminum. A welder can do this in the yard. At least 2 sections, on the sides of the mast. Or a really good fabricator can form a full round.
It's on the bottom of the mast, not in a lateral stressed area, than say mid mast.

One piece, or 2 sections on the inside or outside, 2 or 3" wide, clamped and tacked in, then closed, welding aluminum, is low temp, relatively speaking to other metals.
After, form and fill with epoxy, prep for awl grip.

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Old 17-01-2015, 14:43   #19
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Re: Mast corrosion

I would consider a small handheld abrasive blaster for removing the corrosion from the alloy. You can buy the hose in the bucket type for next to nothing and you will not need a large compressor for that small area.
If you use a dremel, you will remove some good material as well as the corrosion.


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