Rope/knot/splice load testing

allene222

Super Anarchist
3,961
58
SF Bay
I'd also like to see the Halyard hitch as this is currently the knot holding up New Morning's mainsail. Splicing an older line is pretty challenging, but so is replacing a 200' 12mm vectran halyard. When a chafe problem caused some worry, I swapped the halyard end for end and used a halyard hitch to attach to the shackle. I'm curious to know how much weaker that is than a splice.
I would also be interested in this knot as it is of a class that clamps the line before the line bends so should be relatively strong. Of somewhat more interest for my boat would be does it slip in Amsteel and I will test that later today.

That all said, I don't think for a halyard anyone is going to get close to having to worry about the strength of either the line or the knot. Halyards are sized for stretch so the loads are way under breaking strength.

Allen

 

mrgnstrn

Super Anarchist
1,375
4
Herring Bay, MD
Starting to think about bend radius.

I am a bit surprised the below broke at the figure 8 rather than at the 1:1 bend.

Before - two loops (figure 8 and figure 9), joined just simple loop to loop with 1:1 bend radius at join

attachicon.gif
bend1s.jpg

After - broke at figure 8, at 44% of line strength, which is consistent with what I found in the figure 8 test series

attachicon.gif
bend2s.jpg

And I just did one with a figure 9 loop and a spliced loop . . .broke at the figure 9 . . .so seems pretty much any knot is weaker than a 1:1 bend radius.
Estar,

Dumb question time, and I hope I'm not insulting your intelligence with it, but it's the kind of thing I'd screw up.

Your picture above shows that you have tied your loops as interlocking each other...but the "whole thing" is a big loop too.

so in reporting your breaking strength numbers, are you taking account for the load sharing by the portion of the loop on the "back side" of your picture?

i.e., are you reporting the load as 50% of what the load cell reads or as 100%?

-M

edit....the pictures aren't shown in my quote, so the picture i'm referring to is the one with the figure 8 loop tied to the figure 9 loop, and the whole thing is a big loop between your shackle and the head of the piston ram. hope that clears up confusion.

 
Last edited by a moderator:
That all said, I don't think for a halyard anyone is going to get close to having to worry about the strength of either the line or the knot. Halyards are sized for stretch so the loads are way under breaking strength.
Yes, that's definitely the case as I'm sure the sail would be ripped apart before the halyard would break under load.

I'm still curious because the long splice on the halyard takes the bury, and bulkier section of line, back onto the sheave while the knot sits well below the sheave. It may be a case where a knot is better than a splice.

 

bluelaser

Anarchist
604
0
How about a knot-on-knot like is used on some dinghys? Couple variations of it:

Either:

Passing the knot in the end of the halyard through the headboard then tying an overhand around the halyard

Or

Passing the halyard through the headboard as a loop, then sticking the tail of the halyard(with a figure 8 tied in the end) into that loop and pulling tight.

Really good information though.

 
Last edited by a moderator:

allene222

Super Anarchist
3,961
58
SF Bay
I tested it and the Buntline with the end tucked under the loop slips in Amsteel. The halyard hitch slips as well. Time to find a new knot.

I too would like a knot to use to tie a shackle to a halyard to avoid the added bulk of a splice in the sheaves. I have a way to do it now, but it is complicated and I can't expect crew to figure it out. It has no shackle, just a short dogbone. http://l-36.com/halyard_toggle.php

Allen

 

Ajax

Super Anarchist
14,767
3,046
Edgewater, MD
^^yes, I understand that logic, and that seems to be what my testing is showing . . .. . . . but there is a lot of rope industry literature saying absolute minimum bend radius is 4:1. And for instance Colligio says "3. All end fittings should have a minimum 5/1 bending ratio (minimum 80% break strength maintained at 5/1 but break strength drops off fast if the ratio is less)"

So, what's the deal, are they all wrong, or trying to sell more thimbles/end fittings, or is there something I am missing?

I am applying a slowly increasing load. Are the dynamics of a snatch/shock load different than a steady load, different enough to fundamentally move the breaking point? I had figured the piece would break in the same place with either type of load.

Or does this 'conventional wisdom' about 4:1 and 5:1 come from huge industrial ropes, and does not apply to our little yachting ropes?

I was actually pretty pleased with the splices at 98% of rated strength, as I in fact did not do all that careful a job with the bury tapers . . . I just snipped off the last inch at a sloppy 45 degree angle.
I think it may be.

I've read that synthetic fibers that are subjected to strong enough shock loads can in that instant, generate heat, melt, and part.

Specifically, I've read about this happening in automotive seatbelts where the drivers had accidentally buckled up with twists in the belt, and the belts parted during collisions. Obviously, they were shock-loaded in a sub-optimal way, having twists in them.

 

allene222

Super Anarchist
3,961
58
SF Bay
^^yes, I understand that logic, and that seems to be what my testing is showing . . .. . . . but there is a lot of rope industry literature saying absolute minimum bend radius is 4:1. And for instance Colligio says "3. All end fittings should have a minimum 5/1 bending ratio (minimum 80% break strength maintained at 5/1 but break strength drops off fast if the ratio is less)"

So, what's the deal, are they all wrong, or trying to sell more thimbles/end fittings, or is there something I am missing?

I am applying a slowly increasing load. Are the dynamics of a snatch/shock load different than a steady load, different enough to fundamentally move the breaking point? I had figured the piece would break in the same place with either type of load.

Or does this 'conventional wisdom' about 4:1 and 5:1 come from huge industrial ropes, and does not apply to our little yachting ropes?

I was actually pretty pleased with the splices at 98% of rated strength, as I in fact did not do all that careful a job with the bury tapers . . . I just snipped off the last inch at a sloppy 45 degree angle.
I think it may be.

I've read that synthetic fibers that are subjected to strong enough shock loads can in that instant, generate heat, melt, and part.

Specifically, I've read about this happening in automotive seatbelts where the drivers had accidentally buckled up with twists in the belt, and the belts parted during collisions. Obviously, they were shock-loaded in a sub-optimal way, having twists in them.
You cannot get away from the fact that loading is 1/2 in a splice eye compared to the load in the line itself. Using the data from one in the other application is just wrong. The two applications have to use different data.

 

estarzinger

Super Anarchist
7,622
1,003
I have tried to summarize what I have learned here :load tests I would be interested in any feedback, on what I wrote and on what you a have found interesting/new in the testing.

As to posts above . . . yes, I will test the halyard hitch and some others like it . . . I want to get some dacron covered dyneema to do it with (so they will not just slip), so I am waiting for that.

For dyneema around a shackle, the best I have tested so far is the Palomar Knot - does not slip and about 55% of line strength.


And yes, when I tested a 'tied loop', I did cut the reported breaking strength for the knot in half.

I did manage to do some nylon testing today, but there were no new 'surprises' - just like in dacron, the knots rated higher than I would have expected before this testing.

 
Last edited by a moderator:

estarzinger

Super Anarchist
7,622
1,003
^^ I am going to do some stress/strain/energy absorption measurements. I just (this morning) got my calipers off the boat so I can make accurate stretch measurements. But I have been trying to work thru and complete the very basic breaking strength data set before moving on to that.

Russ, is this the haylard hitch you are thinking of? - looks like a buntline with an extra turn?

 
Last edited by a moderator:

Training Wheels

Anarchist
865
52
On my boat
Here's one I've been wondering about. How about a appropriately sized dyneema loup on a dyneema line with a prussick. Will it slip? Where does it break and at what load?

 

estarzinger

Super Anarchist
7,622
1,003
Happy new year

Estar, i really like the present Santa brought you....,said that i ll be interested if you could try a soft shackles breaking test putting the diamond knot just passed the SS shackles pin (not in the center) and using the 2 strong points(ss pin and ram pin) 2 x line diameter

grazie
I have just done two with the diamond at and right near the pin . . . They are very certainly not weaker. They are in fact the strongest two I have tested, but that may be due to better construction rather than the pin location - but I got two at 194% and 195% of rated line strength. I think this is very very close to the practical maximum strength of these with the diamond knot.

diamond.JPG

 

estarzinger

Super Anarchist
7,622
1,003
Here's one I've been wondering about. How about a appropriately sized dyneema loup on a dyneema line with a prussick. Will it slip? Where does it break and at what load?
Dyneema on dyneema will certainly slip. I don't even need to test that. I did test dacron prussick's, and some other gripper hitches, on a dyneema line and got the following:

Pulling on a 1/2" dyneema single braid line, with 3/16" Dacron double braid gripper line (Samson LS - rated at 1200lbs)

Rolling hitch slipped at 200lbs
Rolling hitch with 3 turns slipped at 370 lbs
Prusik slipped at 860 lbs
Icicle hitch did not slip, broke at 900lbs
 

estarzinger

Super Anarchist
7,622
1,003
Estar, if you get the opportunity can you try out both a halyard hitch http://www.animatedknots.com/halyard/index.php?Categ=typehitches&LogoImage=LogoGrog.jpg&Website=www.animatedknots.com and a buntline hitch with the non-standing end tucked back into the loop around the shackle in the opposite direction. The latter was supposedly tested by Stan Honey (according to the story told) on dyneema to nearly line strength. It does slip a little at first and cannot be untied after loading but is easy to tie to a pad eye, etc. I have used it successfully (meaning it didn't slip or break) but never had any means to test it. Thanks.
mmm . . . can you post a couple sequence photos of that buntline modification? I am quite skeptical it will hold to anything near line strength, as the best knot I have so far is 54% in single braid, but I am certainly willing/eager to test it. But I can't quite visualize what to do yet, and need some photos, drawings or more instruction.

 

estarzinger

Super Anarchist
7,622
1,003
^^ the above in dyneema single braid is not bad . . .does not slip, and breaks around 50% of line strength. The Palomar Knot is marginally better/stronger and very easy to tie to shackles (where you can take a loop around the shackle), but this one above is easier to tie to padeyes and such (where you could not take a loop around the hardware).

 

allene222

Super Anarchist
3,961
58
SF Bay
An interesting thing about both the Palomar knot and the "above" knot is that there are strands that need to slip past each other in opposing directions for the knot to slip. This gives a great deal more resistance to slipping than most knots where a strand needs to slip through one or more loops all of which can slip past each other in with little friction between the loops. The "above" know looks to be easier to dress than the Palomar.

As far as your summary page, it is great. I would still like to put it up on L-36.com but I would like to have more raw data on the write up.

I would hesitate to say that soft shackles are as strong as what you are saying based on my own testing, which was with bigger lines. I did not test smaller lines as I used the line that NE Rope supplied. That was part of the deal as they were not interested in testing Amsteel and Samson was not interested in working with me as they apparently had another soft shackle company they had worked with (even though I don't sell soft shackles and just give away how to make them). In any event, one soft shackle broke at 16,000 pounds which was 110% of line strength. I think the statement that they are between 100% and 200% of line strength is as fine as I would go for a summary statement.

Allen

 

estarzinger

Super Anarchist
7,622
1,003
^^ I am getting another box beam to stiffen my bench. It's noticably deflecting now around 6,000 lbs. I will test some bigger soft shackle when I get that additional beam bolted on. Should just be a couple days. You have way more experience than I do with these soft shackles, but i guess I am optimistic that "almost 200%" is achievable.

I don't know how obvious the link is, but there is a link on my web page to a spreadsheet with most all my test results (all except some of the single pull tests).

 




Top