Aluminum or stainless steel rivets?

Rick D · Mar 16, 2011

OK, I'm totally an idiot with this stuff, but having gone through the same scenario recently, I used aluminum since they had lasted well and since I don't want to push my luck. No doubt, smarter folks than me will weigh in!

FourPoints · Mar 16, 2011

I'm not an expert either, but I do know that one of your biggest causes of corrosion on a boat is when you have dissimilar metals in contact with each other, and salt water. So an aluminum mast and aluminum rivets should give the least risk of corrosion.

Paul Brinkley · Mar 16, 2011

Neal, corrosion usually occurs when you have different metals in contact. You should not have a problem with aluminum rivets in an aluminum mast. All of the rivets in my 21-year-old mast are aluminum and there is no evidence of corrosion. I have also not seen any evidence of corrosion between the aluminum rivets/aluminum mast/stainless steel tangs. -Paul

Bill Roosa · Mar 17, 2011

Two things Neal
you need a more robust rivet gun to do the SS rivets. most guns will just break when you try to use them.
you get to choose where the corrosion occures. If you ut SS rivets the mast will corrode, if you us aluminum rivets the Ss bracket will corrode.

My advice would be that SS is for those hight strength applications and it is easier to replace the corroded bracket than to fix the mast. Stick with aluminum rivets.

Scott T-Bird · Mar 17, 2011

I would go along with the aluminum rivets because it's not a high-strength application. My experience with taking apart mast components has been that everything SS more-or-less fuses with the aluminum. Speaking from a strictly non-technical standpoint, it's not so much that you get any degradation of the materials from SS to aluminum contact. It's more like the small amount of corrosion causes the metals to fuse together and it makes life a bitch to get them apart. I had to drill out SS screws to get them free from aluminum and, no, PB Blaster didn't help one bit (an impact driver does, if you can keep the heads from stripping and when they do strip at least you have a hole to start your bit - if it was phillips head). I even had a very stubborn SS sleeve (for a through bolt) which was unreasonably difficult to free.

At least a SS rivet, when it needs to be removed, is going to be drilled out, so better drilling out a rivet than a screw. I did use SS screws for some block attachments but I coated them to try to avoid future difficulty. Never use self-tapping screws with a spar if you are going to have anything inside the spar .... use machine screws just long enough to avoid long protrusions and tap the holes.

Don't use aluminum rivets for anything structural, like rigging or control blocks.

Rick Sylvester · Mar 17, 2011

Hey Neal

I'll be dropping our 26 year old Isomat mast tomorrow morning. I've already removed and disassembled the boom though so I'll share a couple observations.

I've drilled out over 20 rivets which were used by the manufacturer in both structural and non-structural situations. Not one was loose or compromised in any way. I'll be reinstalling the same.

A couple of small SS fittings had seriously degraded the areas of aluminum where there was contact. Major pitting.

I would seriously consider having an aluminum bracket fabricated for your VHF antennae.

Good luck with yours.

Rick Sylvester · Mar 17, 2011

I've done something similar to that.

It's a step in the right direction and would probably be fine, especially in that application. I've used plastic sheeting (think gallon milk container) with some success.

tommays · Mar 17, 2011

When i painted my mast i used UHMW tape on all the SS surfaces that made contact with the mast and never had anymore problems

It did not cause any issues with the rivets even in the high stress areas like the vang and boom mounts

monkeybars · Mar 17, 2011

purchase a quailty epoxy primer(two part) from any auto paint store.paint two coats on the stainless part where it will be in contact with aluminum or other dissimular metal.use good prep ,and let fully cure before installation and you will be corrosion free. you can also primer screw and rivet holes to prevent dissimular corrosion.

CarlN · Mar 17, 2011

Aluminum rivets are fine. No corrosion worry.

Never leave stainless touching an aluminum mast - especially a painted mast. The paint will bubble as galvanic corrosion between the stainless and aluminum pushes under the paint anywhere there's a fastener or tiny scratch. Very hard to stop once it get's going.

+1 on Tom's suggestion of UHMW tape. Also called Slick Tape. Just stick it to the back of the stainless bracket and trim. It breaks the electrical connection between the stainless and aluminum.

For any stainless screws or stuff that won't take the tape use Tef-gel.

The next owner of your boat will thank you.

And keep the left over tape and Tef-gel aboard. It's a great favor to to anyone you see working on a mast or boom.

Carl

Rich Stidger · Mar 17, 2011

Help me to understand the insulating issue with the fasteners. It seems to me that regardless if you insulate the bracket to the mast by whatever material or method you choose, as soon as you connect the two metals with a fastener you now have a connection between two metals.

If you use an aluminum rivet then the rivet and the stainless steel bracket are dissimilar, and if you use a stainless steel rivet then the rivet and the mast are dissimilar.

I fail to see how you can insulate the mast, bracket, and fasteners all from each other.

Rick Sylvester · Mar 17, 2011

What you say makes sense Rich

but I didn't see any corrosion of the aluminum rivets where they were in contact with the stainless pieces. Maybe they were pre-coated with something?

tommays · Mar 17, 2011

I drilled out some were in the range of 60 3/16 SS rivets out of my 1981 J24 mast/boom with ZERO corrision issues between the rivet and mast/boom

The stuff that was held on with 10-24 screws had the worst issues at deck level and almost no issues above the spreaders

The stuff somebody put on at some point with self taping #10 SS and #12 SS screws all came out in pretty good shape and was holding some fairly high load high use stuff like haylards

Being trained as a Marine Tech i have learned some fairly simple stuff like Mercruiser Pefect Seal will stop most issues between Outboard and Sterndrive lower unit SS bolts and Aluminum parts in HD saltwater use and seems to do well on masts

jibes138 · Mar 18, 2011

In aerospace applications they typically use steel screws in aluminum housings. The housings of course are anodized or at the very least conversion coated, your mast will already be prepared this way, but if you drill any holes or tap any holes you will need to provide protection for the aluminum by conversion coating the holes. We always used zinc chromate primer on the screws to provide some level of protection. I always doubted how well this works as the actual threads wonce torqued will squish out all the primer and end up with small contact area of metal to metal. Better than nothing I guess. I would use some of Mainsails Butyl Tape between the mast and the stainless bracket, he claims it lasts forever and will provide a wonderful barrier between the dissimilar materials as well as dampening from vibrations. The antenna will vibrate like crazy in the wind so the damping is a good thing.

Jon_E · Mar 19, 2011

Use aluminum rivets on the aluminum mast. I'm currently drilling out SS rivets out of a host of fittings on a mast. You should see the corrosion! The mast was painted, but the corrosion bubbled and blistered the mast from under the paint. The corrosion is the worst down low where salt water has sometimes touched both metals.

Added bonus: If you ever have to drill the rivets out again, aluminum will drill easier than SS.