# Aluminum vs. Stainless cleats



## bwindrope (Feb 25, 2007)

I've been doing some research on whether my current aluminum deck cleats are sufficiently strong or whether I should swap them out for stainless. I've read a few references in Pardey and Leonard but nothing definitive. I've scanned online but it's a needle in a haystack. 

My current aluminum cleats are original to Aeolus and are in great shape. They are adequately sized with good backing plates and I've removed and rebedded them all over the past year. As I walk the docks in Friday Harbor I see many, if not most, sailboats have aluminum cleats. However, I know many standard products and installs are crap, so I don't trust that too much. 

Although used essentially for dock lines right now, they are also used for my 3 strand anchor snubber line at the bow and for towing dinghies in calm waters and such. 

I'm interested in hearing from someone who is knowledgeable about cleat failure or metallurgy of these two options. Has anyone had any experiences with the cleat itself breaking? I know people pull them out of decks due to poor installation, but that's not my concern. 

I appreciate any wisdom on this subject.  

Also just finished the removal and complete servicing and re-installation of my Edson steering system. Oh joy. Know it inside and out now, and that she is solid.


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## sailingdog (Mar 19, 2006)

While metallurgy isn't my area of expertise, I do know that aluminum is far more prone to fatigue related failure than stainless steel... so that would be one serious point in favor of stainless steel. Aluminum is also much weaker, which is a second point. Third, aluminum is more susceptible to corrosion.


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## bwindrope (Feb 25, 2007)

Thanks sailingdog, that all makes sense and is good info. I'm not too surprised there have been few responses to this question because it is a bit esoteric. Not many people have experience with failing cleats or conditions that would stress them enough to break. 

Part of my interest in this is just this question. On boats, as elsewhere, there is always a stronger way to do something, but that is not always the best way. It is an easy trap to seek strength at all costs, given the rational fear of calamity, and yet we don't use 1 inch wire on our rigging because you can't tension it properly. We don't build hulls that are 2 inch thick solid glass in all places. We make trade offs with weight and expense that will stand up to what is asked of them. 

This is the heart of my question about aluminum cleats. I've never seen or heard of one failing, though there is no doubt that stainless has superior qualities. Is it situation where they are used extensively on production boats because they are plenty strong enough and lighter, or for some other reason. Cost-wise they are about the same as stainless, so that doesn't seem to be the driver here. 

Remain curious on this point, and may just have to live with it!!


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## pdqaltair (Nov 14, 2008)

*A greater concern is size.*



bwindrope said:


> Thanks sailingdog, that all makes sense and is good info. I'm not too surprised there have been few responses to this question because it is a bit esoteric. Not many people have experience with failing cleats or conditions that would stress them enough to break.
> 
> Part of my interest in this is just this question. On boats, as elsewhere, there is always a stronger way to do something, but that is not always the best way. It is an easy trap to seek strength at all costs, given the rational fear of calamity, and yet we don't use 1 inch wire on our rigging because you can't tension it properly. We don't build hulls that are 2 inch thick solid glass in all places. We make trade offs with weight and expense that will stand up to what is asked of them.
> 
> ...


(with an opener like that someone will take this of-topic)

What I see is cleats that are too small for the line. We all see huge dock lines instead of good chafing gear, the rope stuffed around the cleat the best it can be stuffed. The same for over-sized snubbers and bridles. All of the load, really, should be down low on the first 2 passes, and so for the cleat to fail, either the mounting was poor or it was so undersized the load was on the horns. There really should be no loads on the horns, and so breakage is very rare.

The same thing happens when 2 lines are placed on the same cleat.

I might go bigger rather than SS. However, I don't know what you have.


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## sailingdog (Mar 19, 2006)

BTW, Cleats should be sized so they are about 16x the diameter of the normal docklines used on them in length. If you use 1/2" docklines, the cleats should be 8" at a minimum.


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## jrd22 (Nov 14, 2000)

bwind- like you I have not seen aluminum cleats fail in normal use. Most all are an alloy, and therefore much stronger than "aluminum". Unless the cleats on your boat are way undersized, or severely corroded, I would seriously doubt that changing to ss would accomplish much more than emptying your wallet (just my 2 cents). 
If you get by Blakely stop in and say hi.


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## brak (Jan 5, 2007)

My boat has aluminium cleats that are original to her - i.e. 37 years old. I had them all rebedded and reinstalled, and as part of that process - inspected. Of the 6 that are there, one failed - a side of fastener hole had a microscopic crack in it and I was able to break it off. Essentially if the integrity of metal is breached, it will admit water, go through a freeze-thaw cycle and fail completely. If not - it seems to do fine. 

So, personally, I inspected the cleats then and keep re-inspecting them occasionally so that if I find another crack - it's time to replace. 

Incidentally a new cleat I used as a replacement is aluminum too. 

One thing to consider is how the cleats are installed. For example, mine have a hole pattern that does not match anything currently sold. So, if I were to replace them - I'd have to balance potential improvements of new cleats with the weakening of the deck (due to more holes drilled in same general area). I went for less holes


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## bubb2 (Nov 9, 2002)

Ditto for the above. I seen far more cleats ripped out than broken. Of the broken cleats I have seen 90% of those were the galvanized dock cleats and not boat cleats.


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## NCC320 (Dec 23, 2008)

Several years ago, the boat that was across the pier from me had an aluminum bow cleat fail in a hurricane (storm was down to 70-80 mph when it hit us.). The boat dropped down onto a piling and was out of commission almost a year having the hull and deck repaired. I should note too that the cleat seemed a bit small to me. But on the basis of this one incident, I wouldn't take too much concern. I've seen lots of other boats with what look like large cast aluminum alloy cleats that held up well. If I had them and they were ample size, I wouldn't run out and exchange them for stainless without a good reason...like evidence of cracks. But I would prefer stainless steel if I had my choice up front.


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## tager (Nov 21, 2008)

What's wrong with Nylon?


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## bacampbe (Mar 17, 2009)

I've seen a horn break on an aluminum cleat. The boat in question had its cleats installed on the topsides rather than deck. That is, they were mounted on a vertical surface. This caused the horns to carry almost the entire dock line load.

We figure the broken horn flew about 100 yards before hitting the water. We were extremely lucky that it didn't hit anyone.

I don't know if a stainless cleat would have done any better under the circumstances.


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## bwindrope (Feb 25, 2007)

*Aluminum vs. alloy*

Cleat size is surely a central issue. That's not a concern on Aeolus because my cleats are 8" and my dock lines appropriately sized. I've also seen that people beef up their dock lines on puny cleats which has the double whammy of stretching less and putting more force on the cleat.

That question of alloy vs. pure aluminum has me interested because I've long thought my cleats were some kind of alloy. The surface is not a normal oxidized aluminum surface like the mast, and yet they are not steel. I've never seen a source online that labels them as anything other than aluminum but I wouldn't be surprised if one of the gurus here said they were 2% zinc or molybendipendigorganium or something.

I hear the views that the cleats, if properly sized/installed with proper lines, are not the weak point in the system. Makes sense. My cleats are the type that have two holes down the center of the legs and stainless bolts go through. I've removed, rebedded, inspected and corrosion protected them all last year. The way they are rigged with the dock line loop fed through the middle and around the horns per usual, all the force is really right at the base of the cleat and not at the horns.

I appreciate the shared experiences and perspectives. I'm off to keep installing a new forward hatch to replace the old slider. Oh the fun never stops.


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## jtsailjt (Aug 1, 2013)

If the cleats are properly mounted, almost all the forces on the cleat will be parallel to the deck it’s mounted on so the cleat mostly serves serves as a buffer for the stainless fasteners that are holding it in place so most of the force on the cleat is in compression and almost all of the force on the fasteners are in shear. Most substances are MUCH stronger in shear and in compression than they are in tension. So, I think that what your cleats are made of is much less important than their size and the size of the fasteners that attach them to the deck. If the dock line is routed such that it is pulling the cleat outward from whatever surface it’s mounted on, that’s when an aluminum or fiber cleat is likely to fail. 

I think quite a few cruisers that were originally designed with being a “performance cruiser” in mind back in the days when any D/L ratio was considered racy, were equipped with undersized aluminum cleats so they wouldn’t be in the way of the anticipated racing crew, not to mention it helps keep production costs down. Then, 20 years later when the boat is firmly in the cruiser category, it’s owners wish for big cleats to put bigger mooring or multiple dock lines on. I ran into that issue on my 1985 vintage Nordic 44 and replaced its undersized aluminum cleats with larger SS ones. It was a pretty easy upgrade because I could reuse one of the two holes through the deck and the one I filled was not very visible because it was hidden by the cleat or line on the cleat. The hardest part was removing the 5200 to allow the new, larger backing plates to fit flush against the underside of the deck.


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## jtsailjt (Aug 1, 2013)

In the above post I meant to say "any D/L ratio under about 200" but didn't proofread well enough prior to posting...


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## Minnewaska (Feb 21, 2010)

jtsailjt said:


> In the above post I meant to say "any D/L ratio under about 200" but didn't proofread well enough prior to posting...


The three little dots on the top right of your post allow you to edit it.


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## JimInPB (Oct 5, 2020)

I see that this post is from 2009 & there are 3 responses from today, so it seems unlikely that the original poster is going to benefit from today's contributions, but I will post this anyway for the general benefit of anyone who may read this in the future.

The commercially available "aluminum" parts that I have seen on most boats were usually made out of a marine alloy like Marinium. That stuff is pretty darn different from plain old aluminum. It's a lot stronger. It's a lot more expensive. Most of the actual "aluminum" parts on boats are still an alloy, like 6061 "aircraft aluminum" which has fairly good corrosion resistance, or another alloy that has even better corrosion resistance. Most of the T-tops, Radar arches, etc., that I see on boats are made out of 6061 spec aluminum pipe. Looking up a common reference source for 6061, I find a tensile strength of 45ksi & a yield strength of 40ksi - ASM Material Data Sheet. That says that in this case, "pull" strength is actually a little higher than "shear" strength.

Stainless & aluminum both suffer from repeat stress cycle fatigue. I have seen plenty of 316 parts fail for that reason. In the marine industry it is often blamed on crevice corrosion, but I have also seen those failures occur in sanitary beverage manufacturing equipment, which is not subject to corrosive environments. Aluminum is not the only material that has a fatigue issue.

When I google up some spec's on 316, I find a tensile of 85ksi & a yield of 44ksi - 316/316L Prodec Stainless - Penn Stainless KSI is thousands of pounds per square inch. That means that with SS at 44ksi yield & 6061 Alum at 40ksi, aluminum is only 10% weaker in that regard if the parts have the same cross section dimension. When you consider that aluminum weighs far less than SS per cubic inch, it becomes apparent that aluminum is actually stronger on a per pound basis.

If I owned a boat with aluminum cleats that did not show signs of cracking or corrosion, I would not change them any faster than I would change a stainless cleat in the same condition. If I did change from aluminum to stainless, I would consider what materials are connected to the cleat. Aluminum might have been originally selected for a reason.


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