Loose Mast Baseplate

[Josh]

I was looking at the mast during lunch today and noticed that the base plate was a bit loose. It's just held on by rivots, and it looks like one of them might pull out before too long. Theres three rivots that I saw, one up front and one on each side of the mast holding the plate to the mast.My question is, how do I tighten this seeing as that it's held by rivots? How much stress is put on this? I mean, if the mast is just being pulled downward from the stays, the bit of slop in the plate that holds it there wouldn't matter. If there's side to side, or fore aft tension, I could see it being a problem.I'd almost prefer that it was bolted to the mast in place of the rivots, but how would I go about doing that? Hmm...or could the rivots be replaced by a pin of some type?Thanks for any help,Josh

 

[Don Evans]

Mast Baseplate Slop

My baseplate is held by 4 SS machine screws that have all but melted into the aluminum mast, due to dissimilar metal corrosion. From the reading I've done, rivots (aluminum of proper size), properly attached, are superior to screws because they are harder to backout due to vibration.I think your right that there would be little load on that plate, but "loose" anything inevitably means something letting go. If it was me, Josh, I'd knock out that rivot and replace it with the same size aluminum rivot.When I need to get my mast plate off I plan on drilling out my screws on my plate and replace with aluminum rivots.Don

 

[Josh]

Two metal problems caused by?

How does the disimiliar metal problem work? Is it because of salt water corrision? Or just because of two diffrent metals. Can't say I've had too much experience with two diffrent metals. Just used to the steel of autos! What about if I put a gasget or washer of some time in there? By the looks of it, I think the rivots are not aluminum. I might have to figure out a new way to put it on there. The rivots are pulling out of the aluminum, so the holes are probably slowlying enlarging.When I take it off (this weekend maybe) I'll let you know how it goes and what there is to mount it to. Hmm..do they make aluminum machine screws? The thing I'd like to do is get a screw in there with a nut on the back and two nice big washers.

 

[Don Evans]

Dissimilar Metal Corrosion

Hello Josh. Aluminum being less noble (or more positive) than stainless steel (more noble, more negative), assisted by salt water (the electolyte) sets up a nice little battery (flow of electrons) between them. You can minimize it by coating the SS screw. I think some form of lanolin is available for this. Washers will not work as the threads of the screw have to bite into the aluminum. Thats another reason why coatings fail here too. I can't see how you could add a nut to the inside of your mast once the plate is attached?? You could be right, that your rivots are not aluminum and the hole is enlarging due to corrosion. Thats why I want to use aluminum rivots on my aluminum mast next time.Here is a quote from a engineer on the problem..."A potential difference usually exists between two dissimilar metals when they are immersed in a corrosive or conductive solution. If these two metals are placed in contact (or otherwise electrically connected) this potential difference produces electron flow between them. Corrosion of the less corrosion-resistant metal in this type of condition is usually increased and attack of the more resistant metal is decreased as compared with the behavior of the two metals when they are not in contact. Because of the electrical currents and dissimilar metals involved, this form of corrosion is called galvanic or two metal corrosion and is a form of electrochemical corrosion."Don

 

[Josh]

No salt water, possible way to use a nut and bolt

I sail on the Great Lakes, so I don't have to worry about this type of corrision too much. I thought that it was because of the alkalide properties of the salt water, but wasn't certain.As far as using a nut and bolt inside the mast, theres a few possible ways. One is through the slot that runs the length of the mast through which to use a wrench of some type to hold a nut. A nut with a lip on it (self locking nut?) would allow you to keep it in the wrench better to position it to the bolt. It wouldn't get pushed out of the wrench. Or, you could mount the nut to the baseplate some how. You could also epoxy the nut in place. That should hold long enough to tighten the nut. A rivot is just kind of a half assed way to do it if you ask me. It can't be tightened! I'd wager somewhere you could get aluminum screws and nuts. I'll let you know how it goes when I actually do it.Josh