Electrolysis / Keel stepped mast

[sailingdog]

What idiot bonded the mast plug to the thru hulls? The thru hulls were probably bonded to help prevent galvanic corrosion, and one of the things they should be bonded to is a large zinc. The mast step and mast should not be bonded to them for galvanic corrosion, as they aren't—at least on most boats I've seen, exposed to the ocean...

The mast and mast step should be bonded to the shrouds and chainplates, if you're bonding for electrical (lightning) protection. The thru hulls should not be bonded to the lightning protection bonding system, as if they are, they may blow out in an actual lightning strike.

[Faster]

Since you are likely to have to trim say, 1/2 " off the mast butt to clean it up, why not raise the mast step in the bilge by that 1/2" with a non-corrosive plate (solid glass, or maybe "Star board" if it will take the compression). This will keep the mast butt out of the bilge water for a bit, and more importantly, restore the original height of the rig so that your rigging will tension back up again like it did before.
With older standing rigging, that little drop in height might use up the free threads on some of the rigging screws.

[sailingdog]

Excellent suggestion. I don't think that Starboard can handle that kind of compression load. Solid glass is probably the way to go. The only problem I see with doing it is whether the mast step can be easily removed. In many cases the mast step will be very difficult to remove as the fasteners used to attach it will have severely corroded.

[Krogen38]

Yes, and disconnect the connection to the mast and you probably have lessened /removed some of your improtant lightning protection.

[sailingdog]

BTW, I wouldn't use Never Seez on a boat in something that might go in the bilge water... It contains copper, graphite, aluminum, and is probably a pretty good way to cause galvanic corrosion... graphite and copper are significantly higher than aluminum on the anodic scale.