Physics question - which line method is stronger?

[BruceK]

It is EXAXTLY the same as I can see and as described.

What are you seeing differently?

...

He(JW) seems to see most things differently to everyone else.

 

[Shrew]

I've never seen a line part at the knot or hitch itself. It parts at chafe points, like rub rails, chocks, another line, or a weak spot in the rope.

When I used to climb, it was a unheard of to step on a climbing rope. I see people stepping on dirty boat lines with shoes, flops, slides and boots. Dirt works its way into the line and the repeated cycles of stretching and relaxing create chafe from the inside. When placed under enough load, that weak point is the one that lets go first.

The least amount of slip would probably be a clove hitch with two half-hitches. A round and a half with two half hitches is also good.

Using the loop eye is fine, but if you're tying to a long term slip, I'd prefer to the have the loops ends on the boat and leave the lines behind when I go out. Using the loop eye can also cause the line to slide down the piling when it's not under tension.

Running the line out to the piling and back is great when you want to take off and take our lines with you. We'll sometimes do this in anticipation of leaving a transient dock. I don't like this for long term docking as the lines tends to slide down the piling.

 

[Alaskaflyer]

My two cents from years of rescue rigging: The strongest way to attach a line to a fixed object like a tree or piling is multiple, non-overlapping wraps without any splicing, knots, hitches or hardware. How many wraps to secure is a function of the diameter (and friction characteristics of the object’s surface) but for a usual piling I would say probably at least four to be safe. Finish the wrap with a simple hitch of some sort to mind the bitter end while leaving a bit of slack in that end as to not bind the system, or if you wish, run the bitter end back to your boat for a cleat. Line movement causing chafing is minimized if not entirely eliminated.

I recognize this might not be practical while maneuvering your boat to mooring but you can convert whatever simple loop (lasso? Lol) you might have used originally to this as a final tie.

 

[JWellington]

He(JW) seems to see most things differently to everyone else.

I described what I saw, and he confirmed that there was indeed a black, and a white line, but then said he was the only referring to the black one.

 

[psneeld]

I described what I saw, and he confirmed that there was indeed a black, and a white line, but then said he was the only referring to the black one.

And I called it a stern line not" lines" . Really?

 

[JWellington]

You ask if anyone has tested this to prove it right or wrong. Your misconception of this is very (very) common. I often demonstrate this in rope classes to correct the misconception.
In the example, pull on one end of a rope with 20# of effort. Result is that you can not do it. There has to be an equal resistance on the other end. Is it a pull at both ends? Or a pull at one end and resistance at the other? Think of it as resistance and it will be easier to wrap your mind around it. Doesn’t matter if the rope is straight, or redirected around a piling, or pulley. At no point in that rope does the strain on the rope exceed the pull on one end (because the other end is equal and opposite, just resisting the pull.)
If the rope is put around something large in diameter, like a piling, now you introduce a reduction of strain on the rope as shown in PSNeeld’s graph.
No! The force DOES NOT multiply behind the piling.
“A” has up to four times the strength of “B”. Up to, depending on what angle the load pulls off the eye. If the load line comes straight off the piling without being deflected more than a few degrees, then you have one line strength. If it deflect 180 degrees around the eye, you only have 50% line strength because you are putting effectively 2 times the load into the line that the eye is spliced into. Line end with the eye in it would break. (Not allowing for friction.)

My test proposal was different, a fishing line......stated above. In any case I chose A.

 

[Captain James]

Boats

I don’t like either of them.
I think boats should be untied and free.
Am I missing something?
Captain James

 

[pattormey]

A great video on tensile strength

If you're really concerned about strength (upcoming storm for example) then take 4 full wraps around the piling. That is considered full strength of the rope.

https://youtu.be/QPWQqN0dSXI

As soon as a line bends (like around a piling), the strength of the line is diminished.

Video is a great detailed explanation that you can use when selecting lines.

Additionally, check out Chapman’s recommendations on safe working loads for various line types.

 

[Circumnavigator]

There's a third way that is better -- tie a larger loop in the line and put the loop over the piling.


Also note that on all but the best boats, the cleat will probably pull out before you break a 3/4" line.


Jim

 

[Khays]

Line strength

Any line is weakest at stress point where it bends; the weakest point tying up is the cleat on the boat, probably the eye splice secured over the cleat. Method A distributes load to two weak points. That said if routinely tying to pilings a large eye splice to slip over piling is best.

 

[Shrew]

Any line is weakest at stress point where it bends; the weakest point tying up is the cleat on the boat, probably the eye splice secured over the cleat. Method A distributes load to two weak points. That said if routinely tying to pilings a large eye splice to slip over piling is best.

Yet, out of all the lines that you've seen part.......have any parted on the cleat or a sharp bend in the knock or hitch?

I've never seen it.

 

[ScottC]

This is my first post in a long time. I've been "off line" from TF for awhile, mostly for reasons having to do with travel (and cruising!).

As discussed in other threads, the typical Mediterranean tie up is stern-to-pier and bow-to-anchor or buoy. Prior to my first travels in the Med, I had read about the surge which one often has to endure while moored in marinas. And I can now say, from experience, that it is most unpleasant.

I normally like to tie the stern as in the OP's "Method A". But if the discomfort of the surge (I call it the "Pushmi-Pullyu" effect) is really bad, I switch to single-line "Method B" to get a little better shock absorption. It does, indeed, make a noticeable difference.

In some situations, where there's surge and, for some reason, side-to-side motion as well, I've tied the stern as shown in the left diagram in the picture below. This is a variation on the OP's "Method A"...and it gives a bit longer line, overall...and therefore more stretch. The additional benefit is that it helps keep the stern shifting from side-to-side. I guess I would call this method: "Scott's Macrame" mooring. I'm not sure whether it's my invention - but I don't recall seeing anyone else do it.

The the little circles on the pier represent rings (or similar). I don't bother with any additional turns around the rings. So far, I am of the opinion that it would be unnecessary additional macrame.

 

[Khays]

Nope, neither double braid nor three strand.

 

[Leo Reise]

First thing that happens is the bowline knot reduced the the line strength By about 30%. Best solution for lines up to 5/8 is a hitch around a post with a diameter tear. greater than 4 inches. Larger posts for larger lines.

 

[ABfish]

You ask if anyone has tested this to prove it right or wrong. Your misconception of this is very (very) common. I often demonstrate this in rope classes to correct the misconception.
In the example, pull on one end of a rope with 20# of effort. Result is that you can not do it. There has to be an equal resistance on the other end. Is it a pull at both ends? Or a pull at one end and resistance at the other? Think of it as resistance and it will be easier to wrap your mind around it. Doesn’t matter if the rope is straight, or redirected around a piling, or pulley. At no point in that rope does the strain on the rope exceed the pull on one end (because the other end is equal and opposite, just resisting the pull.)
If the rope is put around something large in diameter, like a piling, now you introduce a reduction of strain on the rope as shown in PSNeeld’s graph.
No! The force DOES NOT multiply behind the piling.
“A” has up to four times the strength of “B”. Up to, depending on what angle the load pulls off the eye. If the load line comes straight off the piling without being deflected more than a few degrees, then you have one line strength. If it deflect 180 degrees around the eye, you only have 50% line strength because you are putting effectively 2 times the load into the line that the eye is spliced into. Line end with the eye in it would break. (Not allowing for friction.)

This was well established when I was enrolled in Engineering Statics 35 years ago.

 

[stow it]

The first thing I thought of would be chafe factor but I don't see any comments about that. The line on the left would constantly wear on the pile. What would be the point of having two points coming back to the boat if the line between the pints fails due to friction/chafe?

 

[Satch]

Knot relevant

No one has yet mentioned that the B configuration contains a knot. It is well established that knots reduce the breaking force on ropes. In Mountain Rescue, we use a rule of thumb that a knot in the system reduces it by 50%. On that basis alone, configuration A has the greatest breaking force.

 

[AquaDestiny]

I don’t like either of them.
I think boats should be untied and free.
Am I missing something?
Captain James

:lol:

 

[psneeld]

The first thing I thought of would be chafe factor but I don't see any comments about that. The line on the left would constantly wear on the pile. What would be the point of having two points coming back to the boat if the line between the pints fails due to friction/chafe?

One it doesn't constantly rub and it provides flexibility. The biggest is just release one side and you are free in bad conditions that may pulling to the piling difficult to dangerous.

 

[RustyPBucket]

All things being equal when tying to a piling which method provides the strongest lateral breaking strength:

Method A - line around piling and back to boat cleat (variation double wrap around piling), or

Method B - line through eye and back to boat cleat.

Attached is a crude drawing showing both methods.

If I remember correctly from my high school physics class Method A spreads the load along the back radius of the circle while Method B has the force concentrated at the eye. Is my thinking correct?

I have a loop of line with a half dozen or eight gill net floats on it. Two shackles at either end to make the loop. Twenty feet of line with a shackle to tie to a shackle on the loop. Loop just floats up and down the piling with the tide. Works good.