HOw much do various knots weaken a line

[tudorsailor]

I read that a bowline reduces the breaking strain of a line by 40%. It is a good arguement to have a spliced loop instead on a mooring line.
I wonder if someone has tested lots of different knots and their effect on breaking strain?

TudorSailor

 

[chanelyacht]

It is generally reckoned that a knot will reduce a rope's strength by around 50%, depending on the makeup of the rope.
Haven't got any test data to hand, but UIAA (the body who certify a lot of climbing kit) and various other rescue bodies have conducted research. There may well be something definitive on either the BMC (British Mountaineering Council) or the USCG websites.

 

[Leighb]

[ QUOTE ]
I read that a bowline reduces the breaking strain of a line by 40%. It is a good arguement to have a spliced loop instead on a mooring line.


[/ QUOTE ]

Mmmm... but how much does a splice weaken the line, and is this in any way predictable given that splices can vary depending on the splicer /forums/images/graemlins/grin.gif

 

[tudorsailor]

According to the Yachting TV report from Marlow Rope factory, the spliced line is much stronger than the bowline. They show a test to breakage on a jig. The splice is done by a professional!

TudorSailor

 

[Woodlouse]

Apparently in spectra a bowline will weaken the line by about 56%. (Told to me by a rigger.) A cow hitch though will see hardly any loss of strength.

 

[sarabande]

lots of tabular info here

left over right over left

 

[Salty John]

Bowlines weaken lines by about 45%, hitches by about 35% and a well made eye splice by less than 5%. According to the experts.

 

[cliffordpope]

But they are not comparing like with like. An eye splice on a rope usually has a metal thimble, which spreads the point of load. A bowline does not - the load is concentrated at a single point where the strands are tightly crushed.

The true comparison would be with a thimble-less splice, or alternatively a bowline with a thimble, if that is possible.

 

[Wunja]

So where does the knotted rope break? In the knot or in the bight?

 

[bedouin]

It must be at the knot - nothing else makes sense

 

[LadyInBed]

"It is a good argument to have a spliced loop instead on a mooring line."

NO! If you reckon that the breaking strain of a mooring line is at least ten times greater than the load that will be applied to it, unless of course you moor using string!

 

[Evadne]

[ QUOTE ]
Apparently in spectra a bowline will weaken the line by about 56%. (Told to me by a rigger.)

[/ QUOTE ]

I would say that you should never knot kevlar or similar materials, unless you aren't worried about the actual strength of the line.

 

[cliffordpope]

Big ships do have spliced loops on mooring lines. They drop them over the bollards on the quay, then winch in from on board.

 

[Salty John]

I was referring to an eye splice in three-strand or double-braid - no thimble. I put a 10" eye in one end of all my mooring lines.

 

[AntarcticPilot]

In Ashley's book of Knots, there is a section where he tested various knots in what seems to be a rigorous and practical way. I don't have the results to hand, but they are very interesting reading! There's very little new under the sun, but of course, Ashley's work only applies to natural fibre cordage.

 

[Ariadne]

Its very unprofessional to not pass the eye of a mooring line ashore! A seamen always pass a spliced eye ashore and makes up the loose end on deck, not the other way round. Thats for MOBO's who know [--word removed--] all about ropes, knots and splices.

Bowlines are for boy scouts!!! Splices for seamen.

When was the last time you saw a bowline on a mooring line passed down from an MN or RN ship.

1 rope 1 job.

 

[misterg]

[ QUOTE ]
The true comparison would be with a thimble-less splice, or alternatively a bowline with a thimble, if that is possible.

[/ QUOTE ]

To all that are asking this sort of question, follow TudorSailor's advice and watch the latest episode on Yachting Tv here.

There is a video of a test of a spliced eye (no thimble) and a bowline. Very interesting, I thought. (And I was aware of the various strength reduction factors for different knots).

Andy

 

[Ruba]

I know this is an old post, but I was looking for some information about the knots impact on line strength and came across this post. Then I found this video on Youtube and thought that it puts some light on this topic. Maybe someone will land on this page and find it useful.

 

[Stemar]

IMO, leaving aside emergencies, if the amount a knot weakens a rope matters, you're doing something very wrong, or using the wrong rope.

 

[Wing Mark]

I know this is an old post, but I was looking for some information about the knots impact on line strength and came across this post. Then I found this video on Youtube and thought that it puts some light on this topic. Maybe someone will land on this page and find it useful.

A friend of mine once tested some knots in ropes to destruction.
On a proper calibrated machine

The answer is, it varies a lot.
If you are going to use a rope above 20% of its breaking load, you should think seriously about knots and splices. And the type of rope.
How many ropes on your boat carry such loads?
Most are sized for handling or stretch and/or have a big margin for when the rope is not new any more.

Another big issue with some combinations of rope and knots is, can you undo the knot after applying a big load?