This project was done in concert with the replacement of the holding tank, since the mast had to be removed to provide the necessary access for that project. It is worth remembering that we were doing both of these projects at the same time.
When we took responsibility for Eolian, the butt of the mainmast showed evidence of corrosion, pretty severe in fact. Eventually, the mast was going to have to come out and have the butt repaired. Also, the remainder of the spar had evidence of galvanic corrosion as well, indicating that, like the mizzen, it was going to need to be repainted. Given that the mainmast is like 65 feet long, and about 2 feet in circumference, (that is, about twice as tall, and more than twice the circumference of the mizzen), and that it took most of the summer to repaint the mizzen in place, repainting the mainmast in place was something that just wasn't going to happen.
Pulling the mast out of the boat can only be done with a crane. It requires quite a bit of preparatory work (remove the sails, remove the wiring, remove much of the standing rigging, and finally, free up the remaining standing rigging so that when the crane is in place and the mast is supported, no time is required to loosen turnbuckles which have stood in place for 20 years in a salt water environment). We motored to the boatyard dock, at low tide, and the crew was ready at the crane.
The first problem we encountered was that the corrosion at the mast butt had the mast chemically welded to the mast step. When they first pulled on it, the entire boat rose up 3" in the water... that was a weird feeling. But the mast didn't come out. The yard crew, moving fast, solved this by driving a wedge under the step, distorting it and freeing the mast.
Of course there couldn't be just one problem. Next, at low tide, with the crane attached as low as possible on the mast (if you go too low, it will swap ends once free of the boat...), and with the crane two-blocked (all the way up), there was still about 6" of mast in the boat. After puzzling briefly (the tide was coming back in and the boat was rising...) we got it out by walking the boat forward, out from under the crane and mast. But this meant that putting it back in had to happen at a tide lower than +0.8 feet. Unfortunately, looking at the tide tables revealed that the next qualifying low tide in daylight hours was in January. More on this later. Unfortunately, I got no pictures during this operation - we were way too busy and rushed.
With the mast out in the light of day, the problem at the butt is obvious. The bottom 6 - 10" of the mast is rotten with corrosion.
Also, the entire mast shows evidence of galvanic or electrolytic corrosion. Galvanic corrosion could result if there were an electrical connection between the mast and the internal lead ballast. In this case, the mast would corrode to protect the lead (lead doesn't need protection, but the mast doesn't know that). Or the cause could be electrolytic, caused by, say, the mast being part of an electrical circuit (for example, by having a short in the mast wiring).
Both were possible - the mast step was screwed into the keel area with lag screws which may have connected with the ballast, and bad wiring was in place at the masthead lights. The cure for the latter is obvious. 
To isolate the mast from the keel, I obtained a piece of 1" thick nylon and cut it to fit as a spacer under the mast step. The nylon will lag bolted to the floor, and the new mast step will be bolted to the nylon, providing electrical isolation.Further, there was evidence that the tiny drain holes in the mast were not working. There was a high water mark inside the mast some 6-8 feet above the butt. And the drain holes were blocked with corrosion products. I drilled a 1-1/4" hole in the mast step, and routed a trench in the nylon under it, leading to the edge. No more tiny little drain holes.
We talked to LeFiell, the mast manufacturer, and obtained a new mast step and a splice kit* as well as 2 feet of new mast extrusion (at the time, there were only 20 feet of this section left, in the entire world). To make the splice, first the right amount of the mast had to be cut off. And the cut had to be clean and *square* - this part of the mast is very heavily loaded - an unsquare cut would make a kink in the mast.
Using a sheet of newspaper wrapped around the mast, pulled tight with the edges matching, I colored the edge of the paper with a magic marker. I cut to very near this line using a skill saw with an abrasive cut-off blade, and then did a little clean up with an angle grinder and finally, a file. This surprisingly simple method (which I discussed with a Boeing machinist beforehand) produced excellent results - it came out very good!
Next, 33 holes had to be drilled into the splice inserts above and below the splice, on both sides... totaling 132 holes. Each had to be laid out, drilled, over drilled in the mast, countersunk, and then the matching hole in the splice insert had to be tapped. The picture shows the process 1/4 done, with one splice insert attached at one end. It took an entire day, but when it was finished, the mast was whole again (but an inch shorter... to accommodate the thickness of the nylon isolator).While the mast was horizontal, it was an excellent time to replace the partially functional masthead light and the decaying VHF antenna. We also pulled some new wires, and left a pull string in the wiring conduit as insurance for the future.
Now, painting the mast. After a thorough scraping to break open all the corrosion "worms" under the paint, we gave it a heavy sanding with 150 grit sandpaper. Next a coat of zinc chromate corrosion protector, then a coat of epoxy primer. Sand again. Then 2 coats of 2-part polyurethane finish coat.Unfortunately, this was happening late in the year, it proved impossible to get the high gloss that this paint can deliver. Despite application as early as possible (10 am, just after the humidity had fallen below the dew point), and with a beautiful finish still in evidence by 19:30 in the evening, by the next morning the dew had severely blushed the finish.
We gave up and had the yard spray on a final coat; they kept the mast inside their heated building (it barely fit, on a diagonal) until the paint was fully cured. Looks pretty good, doesn't it!
And because we were not willing to wait until January for a daytime tide low enough for the yard crane to restep the mast, we rented a big crane from Ness (well, we shared the rental with two other boats who also needed it).
I got one picture of the pick and hoist. I can't give enough credit to Rolland and Harris, the Seaview West guys who managed the process. With 30 years in heavy industry, I think I am qualified to say that these guys and the Ness crane operator really know their stuff.
Finally, after hooking up the wiring in the newly painted bilge area (with that new holding tank in place), it looks great!* Splicing of mast extrusions is not uncommon, especially in the larger sections. An aluminum extrusion press is a batch machine - there is a maximum size to the slug of metal which can be placed into the press chamber before it is closed. Large mast sections use a lot of metal for every foot of length, and the largest presses cannot hold enough metal to create an extrusion long enough to make a seamless, long, large cross section, heavy wall mast.
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