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Old 09-02-2010, 14:58   #1
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Strength of Rivets vs Screws, Aluminium vs Wood.

Hey!

This is mostly out of curiosity. We have wooden masts and everything is ofcourse screwed into it. I'm just curious, which is stronger, the rivets in an aluminium mast, or the screws in a wooden mast. Assuming they are both correctly dimensioned ofcourse and no rot or corrosion.

/Hampus
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Old 09-02-2010, 16:04   #2
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Rivets
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Old 09-02-2010, 16:33   #3
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Hahaha - RIVETS ???

Like why?

b.
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Old 09-02-2010, 16:39   #4
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Aluminum or steel? Aluminum with steel mandrals? Steel with Aluminum mandrals? or c'snk alum or c'snk steel? Button head Cherry Rivets or .... well you get the pic.
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Old 09-02-2010, 17:31   #5
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All of th4e above stronger than wood screws
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Old 09-02-2010, 18:01   #6
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Much depends on the forces applied the them, shear or pull. Where a rivit may take pull better, the same aplication may have a fitting that is designed for the fastener to take shear forces when screwed.
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Old 09-02-2010, 18:03   #7
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There are too many variables to make an accurate statement given the limited information.

What grade of aluminum rivet? How thick is the aluminum mast? Is it a sheer load or a pulling load? What material and grade of metal is the rivet? How many rivets are being used?

Is the screw a wood screw or a sheet metal screw? What grade is the metal? What type of wood? How far is the penetration? What is the diameter of the wood screw? How many screws are being used?
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Old 09-02-2010, 18:53   #8
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3/16" Aluminum rivet/aluminum mandrel: shear strength: 330 lbs; tensile strength: 515 lbs
3/16" Stainless steel rivet: shear: 1150 lbs; tensile 1300 lbs

These are breaking loads, i.e., no safety factor.
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Old 09-02-2010, 23:53   #9
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Aluminium Mast
1st Choice Monel Rivets
Diameter
.188" (3/16")
Length
.547"
Shear Strength
742 lbs.
Tensile Strength
844 lbs.
---------
2nd Choice High Strength Aluminium Rivets
Shear Strength Range
501 - 1000 lbs.
1001 lbs. or greater

Tensile Strength Range
251 - 500 lbs.
501 - 1000 lbs.
-----------------
Don't use Stainless Rivets on Aluminium Masts (unless you are desperate)

Also available are Aluminium Machine Screws which can be used provided the wall thickness of the Aluminum Mast allows at least 4 threads to be tapped.
-------------
Grooved Rivets can be used on wood - but not advisable for adding structural components to a Mast
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Old 10-02-2010, 06:11   #10
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Aluminium Mast
1st Choice Monel Rivets
....
Don't use Stainless Rivets on Aluminium Masts (unless you are desperate)
I'm surprised you would use monel rivets rather than stainless on aluminum, since monel is even further separated from aluminum on the galvanic scale:
Anodic index Monel: 0.3 V
18-8 stainless: 0.5 V
Aluminum alloys: ~0.9 V
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Old 10-02-2010, 07:24   #11
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Originally Posted by Hampus View Post
Hey!

This is mostly out of curiosity. We have wooden masts and everything is ofcourse screwed into it. I'm just curious, which is stronger, the rivets in an aluminium mast, or the screws in a wooden mast. Assuming they are both correctly dimensioned ofcourse and no rot or corrosion.

/Hampus
As usual the origional question is not being answered.
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Old 10-02-2010, 07:35   #12
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Quote:
Originally Posted by barnakiel View Post
Hahaha - RIVETS ???

Like why?

b.
I'm also not sure why rivets would be stronger. Let's simplyfy it and say one rivet vs one screw. 14.5mtr (49 ft) mast on a ketch. I wouldn't know the thickness of the aluminium mast but I'm sure someone does. Most commonly used rivets (ie. no titanium, cryptonite or gold plated super-space rivets are used).

The wooden mast is spruce, stainless steel wood screws, 6x60 mm.

Top shroud mounting plate.

/Hampus
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Old 10-02-2010, 09:30   #13
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Quote:
Originally Posted by Hampus View Post
I'm also not sure why rivets would be stronger. Let's simplyfy it and say one rivet vs one screw. 14.5mtr (49 ft) mast on a ketch. I wouldn't know the thickness of the aluminium mast but I'm sure someone does. Most commonly used rivets (ie. no titanium, cryptonite or gold plated super-space rivets are used).

The wooden mast is spruce, stainless steel wood screws, 6x60 mm.

Top shroud mounting plate.

/Hampus
IMHO if all things are equal, same material, thickness of screw body and rivet body the two factors that should weigh in the rivets favor are the strength of the aluminum mast vs wood, i.e. tensional forces against the wood will cause the wood fibers to compress and the fitting to ultimately pull out long before a rivet would shear from an aluminum mast.

Another factor that can't be understated is the rivet is secured from both sides of the mast where a screw is not, making for a much more secure fitting.

If simply screwing fittings to a mast where as strong from an engineering standpoint as "Pop riveting" wouldn't we still be screwing down the fittings that are now riveted?
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Old 10-02-2010, 09:35   #14
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But all things are not equal. Screws are thicker than rivets for the same size of mast. The thickness of the aluminium mast is a few millimeters where the wooden mast is approximately 5 centimeters (2"). What I wanted to compare was two mast of the same size but one aluminium and one wood. If you put a load on the shrouds, which mast will hold up the longest?

"Another factor that can't be understated is the rivet is secured from both sides of the mast where a screw is not, making for a much more secure fitting. "

How do you mean?

/Hampus
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Old 10-02-2010, 10:16   #15
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But all things are not equal. Screws are thicker than rivets for the same size of mast. The thickness of the aluminium mast is a few millimeters where the wooden mast is approximately 5 centimeters (2"). What I wanted to compare was two mast of the same size but one aluminium and one wood. If you put a load on the shrouds, which mast will hold up the longest?

"Another factor that can't be understated is the rivet is secured from both sides of the mast where a screw is not, making for a much more secure fitting. "

How do you mean?

/Hampus
I attempted to answer your question and that is clearly not what you asked in your first post: I'm just curious, which is stronger, the rivets in an aluminium mast, or the screws in a wooden mast. Assuming they are both correctly dimensioned ofcourse and no rot or corrosion.

So what is the question the strength of a wood mast vs. aluminum mast or the strength of a wood screw vs. a rivet? I would suggest that irespective of wether you are seeking an answer about rivets or masts it is critical that all the criteria are equal i.e. mast, screw and rivet diameters, loads, etc. otherwise the data you wish to make your assumptions on are inaccurate.

I would also suggest that one of the primary reasons that "Most" modern sailboats use aluminum, vs. wood for the mast is the strength to weight ratios of the aluminum is much higher.
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