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Mast Inspection Opinions

4045 Views 36 Replies 10 Participants Last post by  GeorgeB
Got the mast down to inspect and repaint. The fitting shown in attached pic looks to be 316 SS and is riveted (heavy stainless rivets) and through bolted (at the tangs used for forward and aft lower shrouds). This fitting clam shells around the mast and is fit perfectly to the mast shape. If not sealed well, however, water and salt could work its way between the fitting and aluminum mast and corrode- if that happened the mast could break as this must be a high stress point- seeing the mast is very firmly connected with 4 lower shrouds and a baby fore stay- a total of 5 connection points at this fitting with the addition of the spreaders. Note the spreaders do not pass through the mast- the spreaders fit into sockets in this fitting and held by one stainless through bolt (as shown in pic).

So request opinion- does the fitting look ok to leave as is and assume no major corrosion (note I can get a fiber optic camera and inspect the inside of the mast at this location- to make sure no corrosion through the mast wall)? Or would you recommend to remove the fitting? I would like to remove the fitting- but afraid I might open a can of worms and not be able to get the fitting installed as well as it is now- fitting might spring open on removal.


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I wouldn't hesitate to pull it. Contact between aluminum and SS is obviously fertile ground for galvanic corrosion. I'd worry more about that, given the large area of dissimilar metal contact, than about having to wrestle with the fitting to get it back on.
And I doubt seriously you'd have to do that. The SS isn't likely to spring out of shape after having been held there since the Gerald Ford administration. The fastener holes will position it correctly, and some c-clamps padded with wood, or a similar device, should get it in place if you even need them. And I'll bet you won't.
You could always pull fasteners a few at a time on one side to see if there's any resulting movement or malformation.
The through-bolts might go through SS compression sleeves inside the mast. These tubes keep the bolts from deforming the aluminum when tightened. So when you pull the bolts, follow them out with a stiff wire, screwdriver or pin of some sort to keep the compression sleeves from falling out of position. An easy operation. There also will probably be some structure inside the mast to keep the spreaders from squeezing the mast walls out of shape.
I pulled all the SS fasteners from my mast, coated each one with Tef-gel and re-installed. The tef-gel provides some galvanic insulation between the 2 metals. Lanocote does also. Screws tend to freeze in place over time without that.
You can galvanically insulate the fitting from the mast by sandwiching a sheet of mylar under it.
But I'd definately pull it off. I know that's easy for me to say, but the guy who assembled it in '78 probably wasn't a lot more skilled than you are.
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If it sticks after you remove the fasteners, it could be the sealant or it could be corrosion. Either way, when you replace it, just a simple bead of polychloride sealant, like 3m 4200 around the top ought to seal it. If you just seal it around the top, any water that gets in can get out. Polyurethane sealants like 5200 are good only if you never plan to move the part again. I wouldn't spread sealant on the mast under the fitting, as that will also make future inspection difficult.
But you could also consider coating either side of the mylar with Lanocote, so moisture has no place to go, as long as you don't clean it off where you want the bead of sealant to stick. In fact, with a coat of Lanocote, the mylar might be redundant. But it's your mast, corrosion will stay hidden, so for what it's worth, I'd go with redundancy.
Good idea re running the bead of caulk after the mast is stepped, if you can get up there. If you can't, put a block under the mast at that fitting to minimize sag between the sawhorses. The amount of mast flex over an 8" length has to be negligible, and polysulfide sealant remains flexible. After all, any substrate on a boat is bound to flex.
Either way, don't leave it out. Water that can't dry will be your biggest enemy in that spot. Might as well keep out what you can.
So instead of re painting my entire mast, I could strip all paint, buff it and leave it as is? Where fitting contact the mast, I would use proper isolation between mast and fitting to reduce corrosion.
Just drill out the rivets, slide the fitting up (with a hammer and drift if it's stuck). clean off any corrosion, separate the dissimilar metals, slide it back, pop in some rivets, and get on with life. Should take an hour or 2 and last another 38 years or until you sell it and buy a condo someplace. Perfection is the enemy of the good.
My sense of things is that the fit between spreaders and their sockets tends to be fairly loose. Probably any water that gets in will find it's way out. Although, with only half the paint left in there and some surface corrosion, obviously something's happening.
Maybe a layer of mylar around the spreaders inside the sockets, if you don't mind more unsolicited advice? It's not just the water, it's the dissimilar metals in direct contact.
If you lower your mast every couple years or so, the spreaders will be easy to pull, check and renew whatever you put in the sockets. Either way, you're wise to be looking at this stuff.
I don't plan to take this mast down again for at least 10 years.
Then all bets are off. Good luck with it.
The corrosion seem to be located where pockets of water were collected and held by the silicon caulk.
I'd suggest not caulking the bottom edge as it's nearly inevitable that water will eventually find a way in and it will need a way to drain out.
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