Is there any reason not to use them on lightly loaded things? I need to mount a couple of cheek blocks on my front beam for positive mast rotation. I have SS, but I'm cheap and I'd think corrosion would be less of an issue with using like metals. I always coat rivets in duralac, but that's no guarantee.

no reason at all...I use aluminum rivets where ever possible to avoid the dissimilar metal corrosion issue....unfortunately, there aren't many areas they will hold up on the boat. I suppose they're adequate for the rotation controls (and if not, you've only lost $1 and a little time).

I've used aluminum rivets on some light load applications.

For reference, a 3/16" SS rivet has shear strength of about 950LBS and tensile strength of about 1200 LBS. For a aluminum rivet you're looking at about 350 LBS shear, 500 LBS tensile. I would use that as the the basis for deciding which fastener is better. The corrosion of the base component will be virtually eliminated when using an aluminum rivet (assuming it's an aluminum component).

sm

You can and I prefer to when possible but know your limits.

First, unless your blocks are plastic or alloy, it doesn't really buy you much.

Second, don't use no name, no spec rivets. Industrial or Aerospace Rivets are built to a spec. No Name could be recycled beer cans. The ones you buy at a Marine Store normally come from a distributor like Hanson. Hanson has specs on their website.

Know what strength you need.

The per rivet rated tensile/shear strengths for 3/16 pop rivets installed per instructions are:

100/100 Lbs no name this was from an email warning you to beware of counterfeit parts
700/500 lbs normal rivets, the mandrel has a ball on the end
1090/540 lbs High Strength This is from Cherry rivets wire draw

2150/1500 lbs this is a normal SS/SS normal rivet just for reference

I normally derate the numbers above by 2-3 to account for fixing something on the beach after drinking.

So, a WAG on positive mast rotation is 250 lbs. It's a 2:1 from the block to the mast so 125 lbs to the block. The block has 2 rivets in shear. Normal rivets should hold 160 lbs each or 320 lbs.

If you can't guess what your load is, at least meet the rating of your block. It's also a good idea to put a little loop of line that will break at 300-400 lbs and protect your mast when you forget to release before you gybe.

NEVER NEVER NEVER put Aluminum Rivets in Carbon.but, if you do please publish the pictures

couple related questions:
1. I know there are many different types of alum. I think most cat spars are built with 6061. Are alum rivits the same grade? and if not, would they have corrosion due to dissimilar metals?

2. I have seen how amazingly well Tef-gel works.. is duralac the same type of product (PTFE) and is it any better than tef-gel?

When the mast flops over will the cheek blocks ever be shock loaded? If so the aluminum will fail and if they rip out you'll probably wind up with a elongated hole in your beam and then you'll be using 1/4' rivets or screws/w nuts. I would first try drilling and tapping for a #10 fine and if that wears out go to the SS rivets.

Sometimes it's costly being cheap.

The intent of the OP was not only to save cost but also minimize galvanic corrosion. If the rivet were to fail, it would be the rivet that broke (head sheared off) not elongating the hole in the beam as you describe. I think there' very little risk to damaging the beam with this approach and there is likely to be a significant reduction in galvanic corrosion. A failure of the rivet could potentially ruin a race however. A better option may be to use a stainless rivet and simply rinse the boat really well after sailing in salt water as this will also greatly reduce galvanic corrosion but provide a much stronger overall connection.

sm

I didn't factor in getting quality rivets, not something I had honestly considered, but makes perfect sense. I think I'll just toss some SS ones in there. Hasn't failed me yet.


I don't know how you saltwater guys do it. I can see the effects right away. I don't see much saltwater fortunately, just slimy alge filled acidic lakes.

That why you attach the blocks to the rotation arm with wimpy line that breaks first. The line acts like a fuse, in an electrical line.

I bought one of Goran Marstrom's personal boats. I noticed there were about 10 pieces of 1 ft long ~1.5 mm line tied to the front crossbeam. I discovered all the blocks in the rotation system were attached with that kind of line. If I screw up, the line breaks. I have spares on the boast and you can replace them on the water.

Tieing the blocks to the jib track works just as well as putting cheek blocks on the beam. The fewer holes you have to drill in the beam, the better.

True. And I've got a butt load of Viadana H404 copies laying around.

I still have to screw two Harken micro cleats on.

I'll F with it on Friday.

I use Tefgel. The metal soaks it up and insulates the dissimilar metals. It really does work and it stays where you put it.

I would never use an aluminum rivet on any load bearing part.

I generally don't use rivets at all in load-bearing locations. I lost a mast and two sails once and I suspect it started when two rivets broke.

That said, aluminum rivets are perfectly appropriate in other locations. The Isotope mast base casting is attached to the mast extrusion with aluminum rivets. Should I accidentally drop the mast while stepping or unstepping, the rivets shear and the casting breaks free without damaging the extrusion. If stainless steel rivets or screws were used, they'd tear out and cause far more damage than 4 broken rivets.

Regards,
Eric