Physics question - which line method is stronger?

[skyhawk]

https://youtu.be/M2w3NZzPwOM

 

[psneeld]

Pilings are not pulleys due to frictional forces....so they are not really turning blocks.

If sufficient radius, the bend is not severe enough to greatly weaken line strength like a choker can.

For more info..... Bollard Forces

 

[JWellington]

Right, a rope on a piling is NOT a pulley. And a fishing line hanging over something isnt either. There must be somebody out there that could perfprm my experiment.

 

[JWellington]

https://youtu.be/M2w3NZzPwOM

A line hanging over something isnt a pulley. Try my experiment proposal.

 

[rgano]

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 think you are correct. If I am a bit short on line to return to the boat, I use a clove hitch on the piling as the strongest way to moor with a single part.

 

[psneeld]

Right, a rope on a piling is NOT a pulley. And a fishing line hanging over something isnt either. There must be somebody out there that could perfprm my experiment.

Obviously you didn't read the link or chart I provided.

A few minutes of maritime work may pretty much explain why your theory is not totally incorrect, but mostly incorrect.

 

[KnotYet]

Im not sure thats right. On the opposite side of the piling there is only one piece of rope, that takes all the strengh. It would be easy to do an experiment on this , with say a fishing line that we know the breaking strengh of. Im on holiday so cant do it here. Lets say its a 20lb line, we wrap it over a pipe in the ceiling, mimiking the piling. Do you think we could put a 40 lb weight on it, on the bottom?

Yes, the line could support 40 lbs that way.
In your thought experiment you can substitute scales for the straight
sections of line and they will read 20 lbs each if evenly balanced.

In the real world the line load is spread out along the half circle of the pipe due to friction.

 

[psneeld]

I think you are correct. If I am a bit short on line to return to the boat, I use a clove hitch on the piling as the strongest way to moor with a single part.

I agree.....

 

[JWellington]

Obviously you didn't read the link or chart I provided.

A few minutes of maritime work may pretty much explain why your theory is not totally incorrect, but mostly incorrect.

I dod, and the video on pullies and agreed with you a line around a piling isnt a pully. My math is too rusty for your site.

 

[JWellington]

Yes, the line could support 40 lbs that way.
In your thought experiment you can substitute scales for the straight
sections of line and they will read 20 lbs each if evenly balanced.

In the real world the line load is spread out along the half circle of the pipe due to friction.

I meant 40lb on ONE section of the line...between whatever we're hanging it over, and the 40lb weight, that the one stand is trying to support. I didnt mean a 20lb weight on each strand.

 

[psneeld]

Sure a 40 lb weight on ONE section of 20 pound test line will break it.....of course.

But I don't believe that was the original question..

Picture on the left doesn't really alter breaking strength, it just divides the load in half possibly. While the picture on the right has specific points that reduce the breaking strength of the line in all likelihood.

So the turn around the piling is loosely defined as the stronger connection as I see it.

I used modifiers as there might be some situations that are not so cut and dry.

 

[JWellington]

Sure a 40 lb weight on ONE section of 20 pound test line will break it.....of course.

But I don't believe that was the original question..

Picture on the left doesn't really alter breaking strength, it just divides the load in half possibly. While the picture on the right has specific points that reduce the breaking strength of the line in all likelihood.

So the turn around the piling is loosely defined as the stronger connection as I see it.

8 used modifiers as there might be some situations that are not so cut and dry.

Re the original, I chose A too.

 

[psneeld]

Re the original, I chose A too.

Post #23?

 

[JWellington]

Post #23?

I mean the 0P, #1. I reject 23 after thinking more. Anyway, you dont see anybody using A or B, except for tiny boats.

 

[psneeld]

I mean the 0P, #1. I reject 23 after thinking more. Anyway, you dont see anybody using A or B, except for tiny boats.

I have been using A on my 40 trawler for years and many transient/permanent docking situations. Great for solo getaways.

Only took a full turn on the pilings for hurricane season.

Have seen more than a few cruisers out East that do the same.

Check Freedom's starboard stern line.

 

[Hippocampus]

Currently tied to pilings as we wait to go into a shed. Side tie only. Start at boat cleat, clove hitch done twice over piling, bitter end brought back to boat and cleated to form spring. Line on piling doesn’t move so no appreciable chafe. Angle between two arms of line going back to boat ~120 degrees so no movement and can place horizontal fenders to protect boat from pilings. Only ~1’ of tide so placed clove hitches to allow for tide. This is possible and necessary as we’re side tied to a non floating fixed pier.
Tying to pilings is more than just line strength. Although even a long or even short splice drops line strength less than any knot it does drop line strength a bit. As does an acute bend such as a loop under load. PS is totally correct in his earlier analysis. As a fresh water fly fisheman the biggest concern in choosing knots is the degree they lower strength. Very obvious when using 4x or thinner leaders.
PS is also correct pointing out common practice. Through out the east coast and in many places in the Caribbean tying as Freedom is shown to do is commonly done. Not due to strength issues but rather what’s practical entering and leaving. There’s nearly no chance you could retrieve the line if under load if it went through a loop.

 

[JWellington]

I have been using A on my 40 trawler for years and many transient/permanent docking situations. Great for solo getaways.

Only took a full turn on the pilings for hurricane season.

Have seen more than a few cruisers out East that do the same.

Check Freedom's starboard stern line.

Not the same as A in the OP.

 

[FWT]

I think you are correct. If I am a bit short on line to return to the boat, I use a clove hitch on the piling as the strongest way to moor with a single part.

And equally strong is two round turns and a two half hitch.

Go round the pole twice as in a clove hitch, but then just finish off with a two half hitch.

That and a clove hitch rate identical.

 

[psneeld]

Not the same as A in the OP.

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

What are you seeing differently?

The stern line is the black line in the picture.

 

[psneeld]

And equally strong is two round turns and a two half hitch.

Go round the pole twice as in a clove hitch, but then just finish off with a two half hitch.

That and a clove hitch rate identical.

I too use the round turn and half hitches when not just a simple loop for storms or when a line is too short to just loop around the piling.

Clove hitches left seasonal through heavy tides and storms were sometimes just too hard to undo after constricting very tight and the cheaper lines getting a bit stiff.

 

[Bacchus]

I have been using A on my 40 trawler for years and many transient/permanent docking situations. Great for solo getaways.

Only took a full turn on the pilings for hurricane season.

Have seen more than a few cruisers out East that do the same.

Check Freedom's starboard stern line.

That is also my preferred method for a stern tie to shore when anchored and not wanting to swing.
The beauty is dingy can be stowed before preping to depart as releasing the stern is a simple quick maneuver that anyone in the crew can handle.
Especially helpful if wind is a factor in departing.

 

[JWellington]

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

What are you seeing differently?

The stern line is the black line in the picture.

In A, I see one line just going around the back of the piling. On your boat I see a white line and some sort of knot or mess at the piling, plus a black line, which you admit to.

 

[psneeld]

In A, I see one line just going around the back of the piling. On your boat I see a white line and some sort of knot or mess at the piling, plus a black line, which you admit to.

The black line is my stern line. It is Exactly what A describes and is EASILY seen as the STERN line in that picture.

If not, I will assumed you thought I am a liar as I said I use the method shown in A. Or too stupid to understand it.

Those mess of white lines are leftovers from previously unskilled boaters that took me forever to undo as they ran from the piling to the finger pier.

 

[Hippocampus]

PS same poster gave me agita not accepting form stability was not the only contribution to stability and has no beneficial contribution once you reach 90 degrees of incline. Boats he referenced could be expected to have machinery and other heavy weights as well as fluids below waterline so contributing to righting arm. Yet he focused on beam to the exclusion of other important factors. Same hyper focus here IMO so suggest move on with this otherwise informative thread.

 

[JWellington]

The black line is my stern line. It is Exactly what A describes and is EASILY seen as the STERN line in that picture.

If not, I will assumed you thought I am a liar as I said I use the method shown in A. Or too stupid to understand it.

Those mess of white lines are leftovers from previously unskilled boaters that took me forever to undo as they ran from the piling to the finger pier.

Ok not the white mess, just the black line.

 

[psneeld]

Ok not the white mess, just the black line.

So my boat is a tiny boat or other than tiny boats may use that method? And I have seen other cruisers using the same method when traveling...so don't think me a liar on this one....either.....

Referring to post #44.

 

[JWellington]

So my boat is a tiny boat or other than tiny boats may use that method? And I have seen other cruisers using the same method when traveling...so don't think me a liar on this one....either.....

Referring to post #44.

We have all seen everything out there.

 

[JWellington]

PS same poster gave me agita not accepting form stability was not the only contribution to stability and has no beneficial contribution once you reach 90 degrees of incline. Boats he referenced could be expected to have machinery and other heavy weights as well as fluids below waterline so contributing to righting arm. Yet he focused on beam to the exclusion of other important factors. Same hyper focus here IMO so suggest move on with this otherwise informative thread.

In that thread, I did NOT "exclude other important factors", but accounted for many variables, just as others did in that thread, including some who corroborated that stability issues can, and regularly are addressed when doing conversions.

 

[Greg S]

In Method A, it seems like there are two ropies attached to the piling. But at the back of it, where the force is concentrated, there is only one rope taking the force. So I dont think its any stronger..

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.)

 

[psneeld]

We have all seen everything out there.

You said "Anyway, you dont see anybody using A or B, except for tiny boats. "...I think it's just your own personal experience in boating.


And I think it shows in nearly every post you have been making to some degree.


It's OK to ask questions...but it's also important to figure out when you have been answered reasonably and that has been supported with references...which you typically don't.