Pop-Rivet Selection for Mast Steps

[Steverhnm]

So I am going to make mast steps for my boat. I have read all the information on dissimilar metals, etc, but I was wondering if anyone had some real-life experience regarding rivets on an aluminum mast.

My steps will be made out of 6061-T6 aluminum, 1/8" thick, 1 to 1.5 inches wide, probably 1.5 inches wide. I will use pop-rivets to secure the steps to the mast to include Duralac as an insulation compound. There will be two at the top of the step and two below. I'm 300 Lbs, which is why I prefer steps but I need to be sure the rivets won't fail.

What would be the best rivet to use so I won't have a problem for at least 10-15 years (or longer), which is as long as I will own the boat. Aluminum (reduced electrolysis-corrosion but not as strong as SS), 316 Stainless (for strength, but could have corrosion issues - is there a way to mitigate this?) or Monel (supposed to be stronger than SS or aluminum, less susceptible to corrosion but it comes with a steel mandrel so it makes me wonder).

Anyone have real experience with rivet life in a mast?
Anybody pop-rivet their mast steps onto their mast?
Any idea what type of aluminum alloy was used on the Hunter masts in 1990?
Any idea how thick the mast walls are? Does thickness vary as you go up the mast?

Thanks in advance, I appreciate the feedback.

 

[CloudDiver]

Your mast is AL and your steps will be AL, the choice is easy; use AL rivets.
You will not have dissimilar metals so no corrosion, the Duralac isn't even needed.
Don't underestimate the strength of AL Rivets;
http://www.mcmaster.com/#97447a045/=13yx3jc
A 3/16" aluminum blind pop rivet has a shear strength of 310lbs and a tensile strength of 500lbs, this is the most common size I use on my boat to attach select hardware. My mast has a wall thickness of about 1/8" (.125) so the grip range is ideal.
Your mast will probably be thicker and I would suggest a 1/4" diameter AL Rivet with 1/2" grip range (what thickness AL stock are your steps made out of plus the thickness of your mast?).
http://www.mcmaster.com/#97447a651/=13yx62h
The 1/4" AL Rivet with 1/2" grip range has a sheer strength of 600lbs and tensile strength of 750 lbs (sheer is the one you need to worry about). Keep in mind the load or your body weight will be distributed across 4 of these rivets... I wouldn't feel uncomfortable with just two myself.

 

[CloudDiver]

BTW, I use a pneumatic rivet gun... One of the few tools from Harbor Freight that is worth every penny and doesn't break after a few uses. Comes with change out tips to accept all the most common sizes of pop-rivets. Shoots rivets in straight and strong with a quick blast of 90 psi, much faster than any hand pull rivet gun. About $40 if I recall correctly.

 

[Steverhnm]

Thanks CloudDiver, Yeah, I you got me looking at the structural rivets which have a 1300 Lbs shear strength, a couple more bucks but I would never have to worry about them again.... Just might use those.
http://www.mcmaster.com/#blind-rivets/=13yxw7f

Anyone else?

 

[kimelmore]

First of all I agree with everyone that aluminum 'pop' type rivets are plenty strong. Rivets are strongest in shear type loads which is the type of load you are applying to them. I would caution you about the corrosion issue however. Different types of aluminum have differing electrolytic potential which will eventually cause a corrosion cell to form. It is best to always use some sort of protective film between the rivet, the step, and the mast. Buy a quality rivet ( not something from auto bones home auto repair ) and you should be fine. Use a depth gage to determine the thickness of the mast to make sure you form an adequate shop head on the inside of the mast that won't pull thru. You can easily make one yourself from a paper clip if you don't have one. Bend a small bend in the end ...stick it in the hole ... pull it tight and measure. Voila' instant depth gage. Also make sure to deburr the hole so it won't dig into the step and accelerate a corrosion problem.

 

[Crazy Dave Condon]

All good responses

 

[Steverhnm]

Looks like all I need to do now is make the steps and get down to Mexico to install them. A long distance relationship with with a boat is tough. I thought I might do better, but 3x a year is tough. Pretty soon I will get a few months each year, which will be worth the wait and all the preparation. I miss my boat and all its neediness. I do quite a few projects here at home while earning the vacation time to get back down there. Alas, for all the effort you put in, it delivers amazing times out on the water in the Sea of Cortez.....