How strong is a Cleat Hitch?

[estarzinger]

Originally Posted by danielamartindm

how much does a cleat hitch reduce the breaking strength of its line compared to, say, a bowline?

To the basic op question . . . . (excluding the discussion of the strength of the dock) it is all about bend radius around the base of the cleat - if that is sharp/tight it will weaken the line quite a bit (per the usual bend radius/strength graph). So, fundamentally it depends on the design and sizing of the cleat (in relation to the line). Properly sized and designed and cleated, it 'should be' stronger than a bowline but weaker than a splice.

I actually did some cleated break tests, but the results were relatively uninteresting, and I never published them.

[danielamartindm]

Originally Posted by estarzinger

To the basic op question . . . . (excluding the discussion of the strength of the dock) it is all about bend radius around the base of the cleat - if that is sharp/tight it will weaken the line quite a bit (per the usual bend radius/strength graph). So, fundamentally it depends on the design and sizing of the cleat (in relation to the line). Properly sized and designed and cleated, it 'should be' stronger than a bowline but weaker than a splice.

I actually did some cleated break tests, but the results were relatively uninteresting, and I never published them.

Thank you, Evans, your reply went to the heart of my question. It's the curvature of the line that weakens it, and as the line IS curved rounding its first turn on the cleat, it has to weaken the line there. When an eye splice does give way, which part usually breaks, the splicing or the loop? I would think the loop, and as the loop's curvature has a greater bend radius than the tightly wound U-shaped bend on a cleat hitch, it would make sense that the eye splice would be stronger?

[estarzinger]

Originally Posted by danielamartindm

When an eye splice does give way, which part usually breaks, the splicing or the loop?

Where an eye spliced loop breaks is interesting and somewhat counter intuitive.

There are three different possible failure modes for a spliced eye loop.

Before we get to the cases we need to establish the key point(s) to understand the loads . . . . . which are that are that the load on the rope inside the loop is only 1/2 the load on the standing part, because there are two legs (eg the left side of the loop and the right side) inside the loop carrying the load. So, the strength of the eye loop section is (a bit less than) 200% the strength of the standing part of the rope, and the absolute weakest part of the system is (generally) right at the start of the splice where there is often a stress riser (if it is not done perfectly)

Now the three failure modes are:

#1 If that bend inside the loop (bend radius to rope diameter) is too small, less than about 1.2: 1, then it will (usually) break at the bend

#2 There is another very interesting failure mode with spliced eye loops, which is where the emphasis generally is for commercial applications - when the aspect ratio (pin size to loop size) is 'too large' (pin size relative to the size of the loop note: NOT the diameter of the rope). Eg if the cleat or pin the loop is sitting on is so big that it forces the neck of the loop to be at a very wide angle, then there is strain created. If this ratio is too big, and the angle at the neck too large, then the splice will tear somewhere in the loop, often right at the Y point of the splice (but also often right at the 'top' of the loop).

#3 if both the bend ratio and aspect ratio are in the correct ranges, then the loop will usually break at the beginning of the splice (eg outside the loop).

[estarzinger]

^^ note with respect to typical cleats and failure mode #2 above . . . . the base of most cleats is long and narrow - so aspect ratio will depends on what angle the loop/line takes from the cleat. If it is 'in line' with the cleat the aspect ratio will be small (eg good), but if it is 90 degrees to the cleat horns the aspect ratio (generally) will be much greater (worse)

[estarzinger]

^^ and finally, that all is a bit complex and the exact answer is 'it depends' . . . . but a properly done splice on a properly sized and designed cleat will be strongest, a proper cleated line will be second and a bowline will be third.

Which may be initially counter intuitive (because you have 'loops' first and third) but the bowline (pretty much any knot) has unavoidable tight bends - whereas they can be avoided in a spliced eye loop and a cleated line.

[BlackHeron]

With a properly sized and installed thimble the eye splice is for all practical intents as strong as the rope itself. With a chain leader around the cleat this is the strongest and most durable way to attach the line to another object like a dock. But in practice, most of the time the weakest link will be the cleat attachments at the deck or dock, or a chafe point somewhere along the dock line where there is movement or deflection. If mooring lines are sized for sufficient stretch the loads should never get close to this or breaking the line or knots. It is the shock loads, or chafe where stretching lines are moving past other things which is why a mooring line will fail. If there are static wind loads that great on your boat there are other bigger problems like the dock itself failing.

[Hartleyg]

BlackHeron, I agree completely, which is why I built my "at home" docklines as my picture showed earlier. The chain and cleat will rub, but chafe is NOT an issue - compared to ANY properly stretchy dock line on a galvanized cleat (which is like sandpaper). Lines on a cleat that are loaded WILL chafe against the cleat - in my observation, this is the primary chafe point of docklines, as the boat cleats and chocks tend to be very smooth stainless, aluminum or bronze, not rough galvanized steel. Having more than one line on a single cleat isn't good, either - you DON'T want nylon rubbing on nylon.
The only failure I ever had in the system over 9 years was when one of the rubber snubbers failed and while this left that breast line a bit slack, the boat wasn't going anywhere. I was much more concerned with my dockmates who were using poly truck rope and the like


Hartley
S/V Atsa

[Steve Bean]

Not a failure of the line, but in1999 there was a fatal accident at Disneyland in California when an inadequately trained employee placed a bowline of a mooring line on a cast iron cleat on a moving boat. The line was fixed to the dock. The bolts holding the cleat on the boat failed and the stretch of the line threw the cleat, killing a guest and injuring his wife. One of the results was that the boat must come to a stop before the bowline is placed on the cleat.

[contrail]

Originally Posted by JPA Cate

Danielamartindm,

I saw that you have a catamaran there, and it may be lacking in backing plates for its cleats. If so, deal with that, too.

What you want is line that is strong enough to hold your boat safely, through the upcoming hurricane season, with chafing gear wherever line goes around a cleat. It does mean you have to carry a lot of line, because you will want to double them if you leave the boat for a named storm. We left our boat (12 tonnes, mono, not prepared for a cyclone) in a windy area for 7 months one time, and one of the dock lines, which did not have chafe protection, had chafed through 2 of its 3 strands on our return; and our friend who watched the boat for us had had to put a doubler on one of the stern lines, which he saw with only one strand chafed through. Those were 16 mm diameter, 3 strand nylon, and we had not doubled them. If your boat is going to be in a marina, you may be able to get permission to install a couple more dock cleats at your expense, so that you have more attachment points for your lines.

However you decide to do this (I can imagine using dyneema tails for the dock portion), having put an eye splice with an s/s thimble onto the nylon. Or, you could use stretchy line and dyneema soft shackle then to the cleats, get more lines on a cleat that way.... You will need to have stretchy line, or introduce something else in the tie up system for yield, because an un-stretchy line like dyneema will jerk the cleats out of your hull, or out of the dock.

Your boat might need heavier line than we use, because the windage will be more of a factor.

It wasn't part of the question, but consider larger fenders, too, and more of them. People's boats tend to pop the smaller ones in storms.

The cleat hitches themselves had no problems, tied with one full round turn, and two half hitches.

Ann

I agree with most of it, but would ask why the boat is more likely to have insubstantial backing plates, because "it's a catamaran"? I have seen good and bad on mono's and multi's.

I would also add that for hurricanes and such, it's much better to find some tires rather than fenders as it takes a whole lot more wind to lift them up, compared to fenders.

[Chas.7]

Thinwater,
It all comes down to a twisted line.

[danielamartindm]

Originally Posted by estarzinger

^^ and finally, that all is a bit complex and the exact answer is 'it depends' . . . . but a properly done splice on a properly sized and designed cleat will be strongest, a proper cleated line will be second and a bowline will be third.

Which may be initially counter intuitive (because you have 'loops' first and third) but the bowline (pretty much any knot) has unavoidable tight bends - whereas they can be avoided in a spliced eye loop and a cleated line.

Your last three replies are exactly what I wanted to know. Thank you, Evans, for taking the time.