corrosion hole in lower mast

I just bought an 82 18ft cat but it has corrosion hole at the lower diamond wire mount (???? forgive me I am a newbie learning). Can anyone tell me the specific kind of metal the mast is made of? Has anyone heard or seen of this kind of repair being done to a mast? Also I see that I have to drill out the rivets for the mount for the repair. What size rivets are these? Any and all help is greatly appreciated. As a Jeep owner who loves that community I have a good feeling I am going to love this community too.
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Have you ever sailed anything?
Nope, but lets give er a shot!!!

I'm super noob... that being said, I believe that plate that you are going to drill out is just used as a first kind of repair, the way that corrosion is coming out your looking for a rough fix.

I just installed those plates on my mast to reinforce my mast due to corrosion. The mast is aluminum.

Tom

The mast is extruded aluminum - 6061-T6 alloy/temper.

That "hole" is probably the result of galvanic corrosion with the reinforcing plate, which is stainless steel.

If the damage is confined to that area, probably the best way to repair it is to epoxy/rivet an oval aluminum reinforcing plate over the area. Welding is not recommended because 1) you'll have a tough time getting it clean enough to weld and 2) welding destroys the T6 temper (which gives the material about 30% of its strength)

Pieces from a scrap mast would make great reinforcing plates.

Ahhhh...that's what I needed to get my brain rolling. Working in aviation I have a lot of T-6 available to me. Plus I have access to a sheet metal roller to match the curve of the mast.
Hey MBounds, I noticed your from MI. I lived in Muskegon before the Army took me here, there, and everywhere. Thanks for the idea.

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Have you ever sailed anything?
Nope, but lets give er a shot!!!

I see lots of pitting and corrosion, but I don't see a hole in that pic. I would pull off the diamond reinforcement plates, clean up the area, and then decide what to do. In many cases, Hobie put black electrical tape between aluminum masts and stainless steel fittings to help prevent corrosion. If that tape isn't there, I would definintely add some prior to re-assembling. The plate is held in position with 3/16" diameter stainless steel pop rivets, about 1/2" to 3/4" long.

sm

Would it be possible to move the mast rotator anchor plate up/down 1 inch. It looks like the diamond wires could be tightened/loosened an inch without needing to cut them.

I have a spare mast with corrosion about 50% as bad as his, although who knows how bad his is under the plate.

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ALLEY CAT 1984 RED LINE HOBIE 18 MAGNUM
Sail # 10505 or 277

The hole is the dark spot in the bottom right in the middle of all that corrosion. I am going to coat my patch with zinc chromate and have my sheet metal shop "bake" it. A coat of paint and that should stop the dissimiliar metal reaction.

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Have you ever sailed anything?
Nope, but lets give er a shot!!!