Where Lines Break

[Warren Milberg]

Over the years, there has been a lot of discussion here about which knots, hitches, and splices are strongest. In over 35 years of boat ownership, I have never had an otherwise "healthy" line break at the knot, hitch, or splice regardless of the type. Yet I have had a few breaks over the years at the bite or loop of the line where it is effectively doubled back on itself by 180-degrees, like passing through the cringle of a headsail, where it is then either knotted, hitched or spliced. What has been your experience with this?

 

[GeorgiaBII]

Pretty much the same as yours. Usually where it holds whatever is where the most stress is concentrated.

Not been sailing nearly as long as you, but as a boy scout and then later as a leader I've seen many many ropes fail.

 

[Rob2435]

rigging manuals will tell you how much each knot will weaken the overall strength of a line.

 

[Joe]

I concur...... but attribute that to the greater likelhood of chafe damage in areas where a line is bent around a static piece, such as a reef cringle or a cleat.

Docklines are perfect examples. Where do they always fail? At the cleat, or where the line passes over the edge of the gunnel, so we place chafe gear there to extend the life of the line.

That's another good reason not to use one long headsail sheet cowhitched to the clew. Separate sheets, attached with bowlines, will last longer because you're more apt to change them end for end and side to side. At the knot end the chafe point is rarely the same with the bowline like it is with a cowhitch.

 

[Ross]

I can't recall any modern line failures. Chafe is the most likely demon and service applied well will control that. I have a couple of half inch laid nylon lines that I use for rough hauling and the bowlines in one end have drawn up so tight as to defy a marline spike for loosening.

 

[thinwater]

It's just a matter of time before someone joins the thread talking-up slicing....

Yup, unless a thimble is installed or the radius is long and fair, any difference is theoretical. Most often I chose a knot according to fit rather than strength. Likewise, I only splice when there is some matter of fit or handling where a knot would be bothersome. Very often a splice is more bothersome and (gasp) less reliable.

That should get em' going.

 

[Ross]

A knot is temporary and a splice is forever. They have different functions and can no more be compared than apple and oranges.

 

[higgs]

I have 40 years of a lot of cruising under my belt and have never had a line fail because of a knot. I had an old, mildewed halyard part once and that is my only failure. I was once at a dock with homeade cleats that were square rather than rounded. That cleat did eat through one strand of my 3 strand dock line. I have never experienced a failure even with knotted lines. I think the issue of knots weakening a line is way over rated. Not to say knots don't weaken a line, but for most of us, it is not an issue.

 

[Ross]

I believe that it may have been a greater concern with natural fiber than with synthetic fiber. To break cotton string is easy by forming a half hitch on your hand and pulliing across itself. But joining two lines with bowlines is considered secure?

 

[thinwater]

I believe that it may have been a greater concern with natural fiber than with synthetic fiber. To break cotton string is easy by forming a half hitch on your hand and pulliing across itself. But joining two lines with bowlines is considered secure?

Hee-hee!

I knew that would do it! Splicing chatter that is completely off the point. The question is, does the knot fail or the short-radius attachment point cut the line... or some other sharp spot?

The answer is that for most applications, ropes are sized for grip or stretch and won't fail in a knot or splice. In applications where they are truly stressed to the limit--very rare and generally not good design--with the help of a thimble, a splice can help. Additionally, a thimble can be fitted in a splice but generally not in a knot, and that can be a very important distinction, that goes right back to the original question.

 

[RichH]

The use of knots as used for marine purposes is essentially stale, harking back to WWI era and based on 'hemp', etc. materials.
If you want more secure, longer lasting 'knots', take a good look at what the mountain climbers and 'vertical rescue' folks are using ... as thats where 'modern technology knots', etc. now is seemingly found.
Youll almost never see a 'bowline' etc. used on a mountain, rather 'safer' knots such as a doubled fig. 8 for 'terminal loops' ... and if the knot is 'critical' (for rescue, etc.), you'll find 'rescue jumpers' across the 'knot' so that if the knot does fail there will be a 'backup'. So too in mountain rope craft youll hardly find a 'single turn' through an 'eye' but rather 3-4 'turns' around/though an 'eye', etc. to more evenly distribute any possibility of impact load.
Mountain rope craft has followed more closely the usage of 'synthetic' rope and its 'optimization' ... much more than 'marine' applications.

There are many websites that explain the use of the more modern and safer 'knots' used by climbers using synthetic (mostly braided 'kernmantel', etc.) 'ropes'. Mountain folk do NOT like 'splices', and with good reason.

 

[All U Get]

My question is what the preferred radius would be for different diameter lines. A knot or splice over a small radius piece of hardware or edge will chafe through quickly. If the radius is increased with a thimble, padding, etc., chafe is less likely. I had a topping lift fail because it was knotted around a pin at the end of the boom by the PO. Since then I spliced an eye with a thimble and there was no evidence of wear.
The chocks on my boat are a sore point with me having a sharp radius for bow and stern lines and during a strom can chafe the leather protection and into the dock lines. :cussing: This seems to be common with a lot of boats. So there must be a formula for a 3/4" dock line and the desired radius, lets say 2".

All U Get

 

[RichH]

Ideally the diameter of the 'turn' should be 4 times the diameter of the 'rope', if not then for a 'pin' of equal diameter of the rope there should be ~4 'turns' around the 'pin'.
All this has to do with 'point loading' where the rope 'bears' on the pin ... the more the turns the more the load is 'distributed' by greater rope surface area contact to the pin and where the pounds (force) per square inch - PSI loading of the surface of the rope is lower.

 

[Ron20324]

...So there must be a formula for a 3/4" dock line and the desired radius, lets say 2".... All U Get

My West catalog is out in the car from yesterdays flea market at Fawcetts, but i'm pretty sure there is mention of what the suggested size line for a certain size block diameter is.

 

[Maine Sail]

We broke a properly sized genny sheet, New England Rope brand IIRC, in a race on an Ericson 34. It failed about 8" behind where it passed through the clew of the sail.. I've yet to have one fail at a knot but I know it can happen...

When doing some load testing of wire crimps I tied the pull knot in the wire with a Bowline the wire failed at the knot before the crimp pulled out. Changed the knot and then the wire pulled out before the knot broke..

 

[Stu Jackson]

The chocks on my boat are a sore point with me having a sharp radius for bow and stern lines and during a strom can chafe the leather protection and into the dock lines.

Chocks are like saws on your docklines. I still don't understand them. I much prefer our simple cleats. If I had them on my boat, I'd remove them immediately and replace them with cleats. Just my preference.

 

[rardiH36]

Chocks are like saws on your docklines. I still don't understand them. I much prefer our simple cleats. If I had them on my boat, I'd remove them immediately and replace them with cleats. Just my preference.

Also my experience with my old and somewhat rough surfaced bow chocks. About a year after I purchased my boat, I really began to notice the beginnings of chafing damage on the almost new dock lines that the PO had delivered with the boat. So I've ignored the chocks since then ... instead just run the lines over the glass smooth toe rail crown. (pic below). Due to the really tight (virtually impossible) access from the inside at the bow, installing cleats up there would be a major challenge. The sampson post has been fine for both port and starboard duty.

 

[Stu Jackson]

rardi, you might want to consider putting in rub strakes under the lines to protect the fiberglass gunwhale. We, too, had only the big middle cleat on our boat. I installed a new port side cleat with some difficulty, but did it at anchor in Clipper Cove back when we first got the boat in 1998 and I was somewhat (? - a lot) more flexible!

 

[All U Get]

I looked for a picture and have this one while we were traveling last summer. We picked up a mooring at the Portsmouth YC in NH. I waited for slack to adjust the line since we had picked mid-tide to arrive. The floats were a PITA but they held the line off the edge inside the chock.
All U Get