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      A Few Simple Rules   05/22/2017

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estarzinger

Rope/knot/splice load testing

1,771 posts in this topic

I am starting a series of tests.

 

Today I ran what I had expected to be some simple calibration tests to see how repeatable the results were.

 

I made up 10 samples, Samson LS Yacht braid 1/4", with a bowline on one end and a figure 8 loop on the other.

 

I had expected them all to break at the bowline, at about 50% of line strength, in a relatively tight grouping of breaking loads.

 

5 of the samples broke at the bowline at 83% of the rated line strength, with a 5% standard deviation

 

And 5 broke at the figure 8 at 84% of the line strength, with 3% standard deviation

 

It is really too small a sample for any sort of statistical calculation, but the test results were relatively tightly grouped, so I draw two conclusions (a) the breaking loads were higher than I expected, ( b ) there was no significant difference between the bowline and figure 8 in this line

 

post-8534-0-17933400-1388438385_thumb.jpg

 

 

 

 

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It looks like the 2nd from the right failed in the middle, not adjacent the knots. Is that right?

 

Is there a way to do a straight pull to test the actual line strength versus "rated" line strength to establish a baseline for how much a knot decreases the strength?

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I think if you pull on a line that has an eye splice at each end you will find it breaking in the middle. The 2nd from the right looks like it failed at the figure 8 but there is a long tail that makes it hard to tell.

 

Knots fail where there is a line under load that has a tight bend. A fishermans knot has lots of bends but they are not under load so it tends to be strong. The figure 8 does as well so it does seem strange that the bowline was just as strong. Perhaps these bowlines were tied in a special way :-)

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The 'rated strength' is 'average with two splices' according to samson. I can and will (a bit later) replicate that test to check the rated strengths because I want them comparable between mfgs.

 

None of those lines broke in the middle ( in the above or below test). They all broke near the knot exits. On some of the breaks it was 'clean' and on others it was progressive, with a core tail that broke last.

 

Second test:

 

Samson XLS yacht braid 1/4"

 

Again 50% broke with the bowline at 83% rated strength, 3% standard deviation

 

And 50% broke at the figure 8 with 79% rated strength, 2% standard deviation

 

Conclusions . . results similar to test 1 but a bit tighter grouped. Bowline = figure 8, Dacron double braid with both knots about 80% of rated average splice strength.

 

post-8534-0-22380800-1388443026_thumb.jpg

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What do you make of the bowlines reliably breaking at ~80% versus "accepted wisdom" that a bowline would fail at 50%?

 

Are you having fun yet?

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I notice that your bowlines are pulled tight. If it would not be much trouble, can you test a bowline where the loop is not snugged up. That may be closer to the way they were tested when the 60% to 66% numbers was observed.

 

I have a couple of useful articles referenced on my "Rope Reference Articles" page.

 

Another thing to consider is that some of the testing done in the literature is on climbing rope. That rope has a lot of stretch and that may be different.

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Stupid spread sheet error in test 2 (test 1 still correct).

 

Correct test 2 results are a little lower, but still higher than expected:

 

50% broke with the bowline at 71% rated strength, 3% standard deviation
50% broke at the figure 8 with 69% rated strength, 2% standard deviation
I just did the double end splice test (5 with each line) to check rated strength. They are very close (statistically equal to) to Samson's ratings.
XLS 98% of rated with 1% Stdev
And
LS 99% with 4% Stdev.
These were sewn splices - I did that because they are more repeatable (at least for me) than class 1 DB splices. All broke in the middle of the line, or near the first stitch (nearest the middle of the line).
I have some nylon line to test but I need to increase (about double) my hydraulic travel. Right now I can just handle the stretch of Dacron, and I will be perfectly fine with dyneema, but nylon will stretch and not break with my current travel. I have a longer ram ordered. I have it in my plan to test less dressed knots, including not pulled tight bowlines . . .but right now I am trying for the highest repeat-ability possible.
Not yet sure what to make of the higher than expected bowline results in dacron double braid. It is still early days in testing.

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The test I found had bowlines at 66% of line and that is pretty close to what you are getting although it listed the figure 8 at 80%. However, these were tested by different people. The dressing of the figure 8 probably matters as well. I think the important thing would be that both strands grip the line as it comes into the knot, if that makes sense.

 

I broke a lot of bowlines in spectra when I was developing the double soft shackle. I found that the bowline was weaker than a fisherman's knot but did not have a calibrated setup. I did calibrated testing at NE Ropes with Brion Toss but by then I was not using a traditional bowline and they broke in the diamond knot in the stopper loop. The diamond knot is very weak compared to what you are doing.

 

Allen

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Someone asked about my test bench set-up. I have twin 10ton hydraulic puller rams (standard auto body shop gear) and a calibrated Dillon load cell.

 

I plan to look at the bunt line hitch today, but because I had some splices left over from yesterday I did some quick bends:

 

Samson LS (dacron double braid)
Sheet Bend: Slipped at 51% of rated strength
Double Sheet Bend: broke at 65%
Double Fisherman: Broke at 74%
Samson XLS (dacron double braid)
Sheet Bend: Slipped at 50% of rated strength
Double Sheet Bend: broke at 65%
Double Fisherman: Broke at 65%
Since the sheet bends slipped in both lines I think it will be worth looking at the other 'quick' bends like the ashley and zeppelin.
I have various dyneema on the way, but it has not arrived yet.

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gripper hitches

 

1/2" dyneema single braid main 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

 

Not sure if there is a statistical significant difference between prusik and Icicle (would have to do more pulls) but definite difference to the rolling hitch.

 

Note on the buntline tests . . . I did notice while doing them that I needed (and did put in) a bigger pin at one end, because the bend radius was just slightly too small and the bunt lines were all breaking at that end (I tossed those test results out). That was not happening with the bowline and figure 8, so the buntline is more sensitive to a small pin, probably because it tightens up around the pin.

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The diamond knot is very weak compared to what you are doing.

 

Allen

so, you are the soft shackle expert . . .

I just pulled one - 1/8" amsteel - spec sheet says 2500lbs average break strength (with splices).

 

I expected the soft shackle to break at about 2500lbs.

 

But I got 4220lbs! Are you surprised by that?

 

One leg broke at the diamond. The other leg was still intact but probably would have broken quite quickly.

 

Pull - I need to get an larger diam oval shackle for this:

 

post-8534-0-15137900-1388524674_thumb.jpg

 

Broken - the diamond knot came apart -

 

post-8534-0-96656000-1388524691_thumb.jpg

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The diamond knot is very weak compared to what you are doing.

 

Allen

so, you are the soft shackle expert . . .

I just pulled one - 1/8" amsteel - spec sheet says 2500lbs average break strength (with splices).

 

I expected the soft shackle to break at about 2500lbs.

 

But I got 4220lbs! Are you surprised by that?

 

One leg broke at the diamond. The other leg was still intact but probably would have broken quite quickly.

 

Pull - I need to get an larger diam oval shackle for this:

 

attachicon.gifpull.jpg

 

Broken - the diamond knot came apart -

 

attachicon.gifsoftshackle.jpg

I am the guy you are thinking of. An expert? That is a different discussion.

 

I had several soft shackles tested at New England Rope courtesy of Brion Toss. They were 3/16 Dyneema supplied by New England Rope, not Amsteel. They broke between 6000 and 7000 pounds. The testing I have done myself has always been a comparison of different lines. For a soft shackle, I would have a link of the same line with two eye splices and that test link would always break first so I would say that the soft shackle was stronger than the line it is made of. The New England Rope testing showed strengths from 103% to 116% of line strength so I stuck with my statement about it being stronger than the line it is made of. To tell you the truth, I expected them to be stronger than what NE Rope found.

 

The construction of a soft shackle is theoretically four times the strength of the line so what you did broke at 42% of its theoretical strength instead of the ~30% at NE. There was a lot of variability in the NE testing so you might want to run some more samples. To answer your question I would have to say I am pleasantly surprised but what you found is closer to my expectation than what I actually found at NE Rope, but how can I argue with them?

 

I have also broken a lot of soft shackles and they always break at the diamond knot right where the line enters the knot.

 

Allen

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Second one.

 

4380lbs

 

This one broke first at the diamond, and then immediately at the lock point.

 

post-8534-0-04162100-1388526319_thumb.jpg

 

Allen,

don't be shy . . you have done us all a service by innovating and explaining soft shackles . . .and I love your weather site also.

 

 

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Shackle 3:

 

4130lbs broke like the first one (one strand at the diamond . . .if we could get both strands truly evenly tensioned we could probably greatly increase the strength)

 

Yes, I will check the line strength tomorrow . . .but Samson's dacron line strengths were spot on so I trust the rated numbers.

 

post-8534-0-43880700-1388527027_thumb.jpg

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Interesting point. You may be getting higher strength because of the long tails you have leading to the diamond knot. Amsteel does stretch ( maybe 2% in your test) and that can even out the load.

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Amsteel line strength - Samsons rated load (2500lbs) look spot on again.

 

For 5 pieces with bury splices on each end: I got average 2428lbs or 97% (133 stdev), and I did not do really careful tapers at the end of the bury's.

 

Simple hand sewn sewn splices do not works as well with dyneema as with dacron. I got full strength with the dacron sewn splices while I got 81% (5 pull average) in dyneema.

 

allen, on 31 Dec 2013 - 17:11, said:
Interesting point. You may be getting higher strength because of the long tails you have leading to the diamond knot. Amsteel does stretch ( maybe 2% in your test) and that can even out the load.
That's a possibility. I also only hand tightened the diamond knots. So they may have tightened up more evenly with the slow hydraulic pull.

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Back to dacron double braid for a minute - adding New England Ropes Stayset data.

 

Bowline still statistically equal to Figure 8

NER ropes breaking at lower % of rated strength, but that may be because they are using a different measure of rated strength. I have asked, and I will check with my own "full strength" breaks.

NER ropes appear to have lower stdev (perhaps higher quality consistency?)

The NER line is 2.33x times higher in (retail) price than the Samson LS

 

Bowline
Samson LS 1/4": 1582lbs, 83% of rated strength, 5% StDev
Samson XLS 1/4": 1582, 71% of rated strength, 3% StDev
New England Ropes StaySet 1/4": 1575lbs, 67% of rated strength, 1% stdev
Figure 8 loop
Samson LS 1/4": 1590lbs, 84% of rated strength, 3% StDev
Samson XLS 1/4": 1590lbs, 69% of rated strength, 2% StDev
New England Ropes StaySet 1/4": 1558lbs of rated strength, 66%, 1% StDev

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I must be a nerd but I find this interesting. Thanks for sharing. Soft shackles rule.

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I must be a nerd but I find this interesting. Thanks for sharing. Soft shackles rule.

Yea . . . I was just looking at the 1/4" soft shackles that I use, and if my 1/8" results scale up, the 1/4" ones will break around 15,000lbs! However, I am not quite ready to pull at that load yet.

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@Estar. You are doing significant and important work here. I would love it if you would consider writing it up for a feature article on L-36.com.

 

The testing at NE Rope included some 5/16 soft shackles and they broke at 14,500 pounds. It was with the NE Rope Endura-12 which was significantly different in feel than Amsteel. That rating was about 110% of line rating.

 

I don't know if you can test larger rope. I have test data on 3/16 Endura-12. It would be interesting to compare the same size line. Be careful though. When I used a hydraulic jack instead of my winch, the recoil when the line broke blew out the seal on the jack.

 

Allen

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^^ in theory I can test up to 10 tons (rams and load cell) but I can see already I am going to need to stiffen the bench to get there. That should not be too difficult but I will have to order some more I beam. I think I can go to 4 or 5 tons as the bench is now.

 

And yes, thanks for the warning on the recoil . . . Will have to think about it . . . Perhaps there is a clever way for me to soften it.

 

I am being careful slowly working up toward higher loads. So far, at 2.5 tons, it is all pretty mild and unexciting when it breaks, but at 4x that I think it may be a bit scary.

 

I have some endura12 in 1/8" size and will test it soon to see how it compares to the amsteel. The spec sheet says it will be stronger, but I think NER's breaking strengths are more optimistic than Samson's.

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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

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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

AKA54, Your own work is so elegant and organized, I wondered if you had done some load testing yourself?

 

Your above suggestion is in my plans, when I do the 'bend radius' tests.

 

Three Amsteel tests first thing this morning, and the bowline is a total FAIL on dyneema singlebraid.

 

Regular bowline slipped/slide at average 370lbs (15% of break strength)

Double bowline slipped/slid at average 750lbs (30% of break strength)

Double double* bowline slipped/slid at 950 lbs (38% of break strength).

 

* This is a bowline with two loops around 'the hole' and two loops around the standing part before the end goes in the hole.

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Still amsteel . . . Figure 8 loop does hold, breaks average 44% of line strength (1100lbs in this case) 4% stdev.

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Estar,this is great information.

 

Any pictures of your test bench? I have been thinking of building one. I have made many loops that we use all over our boat and would like to test one or two to make sure we are comfortable with the safe working loads.

 

Thanks.

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Jacrider . . .I will take a pic or two - its simple, and aluminum box beam (steel would be better but I wanted it to be light enough to move around the house) with two auto body shop puller rams mounted on it. The dillion load cell is the only expensive bit.

 

Still on Amsteel - here is a bit of a surprise to me - Buntline hitch - FAIL - all slipped 385lbs, 15% of breaking strength. I first did buntlines on both ends, and the first two both slipped around the same pin end (which has a smoother pin) at around 385lbs. I then tied a firgure 8 around that end and a bunline on the other end and those slipped around 500lbs.

 

I guess we knew this . . . but you really need to use splices with dyneema!

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photo of bench

 

base beam is 2" x 4" 1/4" aluminum beam. The end bits where the rams and load cells attach are 4"x 4" 1/4" aluminum they are both bonded and bolted to the main beam.

 

In this photo I was just using one ram, but there is a second identical one that mounts on the end with the load cell.

 

I am going to add a lexan safety shield, two smaller beams between the tops of the end bits to stiffen it more, and a ram with longer travel to handle nylon better.

 

post-8534-0-52384300-1388590506_thumb.jpg

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Ciao Estar, i've always wished to do my own breaking test ,but so far , i 've never had the opportunity ,i m very envious of your new toy

i m looking forward to see the results of the''bent radius,, test and also if the position of the diamond knot relative to the pulling load directions is effecting the breaking strenght

Always regarding the softy it will be interisting to see the relaition between multiple pass of thin line VS one pass of bigger diam line havig the same breaking strenght.....may be i m going too far

 

Grazie for sharing the info with us

post-74863-0-67671700-1388589654_thumb.jpg

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So, for you "knot experts", are there any other loop knots worth testing in the dyneema? Is there a know that is easier to untie than the figure 8 but may not slip like the bowline? Or a knot that is less bulky than the figure 8 but will not slip like the buntline? Or do we just conclude "figure 8 or splice"?

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lways regarding the softy it will be interisting to see the relaition between multiple pass of thin line VS one pass of bigger diam line havig the same breaking strenght.....may be i m going too far

From looking at the failure modes . . .I would say there are two keys to greater strength; (1) reduce the load on the diamond knot, and (2) equalize the load on the multiple strands.

 

The easy way to do (1) would appear to be to use a longer lighter (eg smaller cord) soft shackle and then take it multiple passes between to the two load points (like a lashing) before closing the diamond knot/noose. That will definitely cut the load on the diamond by several factors. And not be too much clumsier.

 

I am not sure how we structurally might better equalize strand tension - but people making these soft shackles should be alerted this is something they need to take great care with when making them/tieing the diamond.

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@Estar. Test an Alpine Butterfly. I like it and its cousin the Strait Bend. I tested an Alpine Butterfly against a figure 8 knot and it broke at the figure 8. No slippage at all. This is Amsteel.

 

Allen

L-36.com

 

 

IMG_20140101_075919.jpg

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@Estar. Test an Alpine Butterfly.

Interesting. I have always thought of that as a loop in the middle of a line rather than at the end.

 

You are correct . . .it did not slip . . . 5 pulls gives an average of 1140lbs (45% of rated strength) statistically equal to the figure 8 (1102lbs, 44%)

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Another advantage of the Alpine Butterfly is that, even after pulling it to the point of breaking a figure 8 knot, I could untie it.

 

The other knot to try is a figure 9 knot.

 

Allen

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I just pulled a figure of 9 knot against an alpine butterfly. The line broke at the alpine butterfly. There was no slippage with either knot in the Amsteel I used.

 

Allen

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I will have to try the figure 9 . . .never heard of it before today. My limited experience so far is that you need to do about 5 - 10 pulls to really know which knot is stronger, or if they are basically equal. my guess is that the figure 8 and 9 will be very close/essentially equal, but I will test it.

 

Here is a summary chart of the knots. I could not get any of the bends to hold/ not slip on the dyneema single braid, surprised that even the double fisherman slipped. . .will have to try the triple fisherman. There may be some other fishing lines bends I should try . . .any suggestions?

 

post-8534-0-40512300-1388608583_thumb.jpg

 

I have a question into NER about their rated strengths. West marine shows completely different numbers than the NER spec sheets show. I have used the NER numbers, but unlike Samson they do not say exactly what they represent and I would like to understand them a bit better.

 

By the way, regarding your comment/question on an article, you are more that welcome to quote any of these results. I am going to wait a bit before trying to write any sort of article. I want to see (a) if the mfg's have anything to say/suggest, and ( b ) to see if they scale to different diameters of line. The results look both consistent and repeatable so far, but I am leery about drawing conclusions too soon.

 

.

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The figure of nine is a common climbing knot and is said to be stronger than a figure of eight. On the article, you are doing significant work and I would like to see it documented and put up for others to benefit from. I can write something from your results or you can. I just think it is good stuff.

 

By the way, a lot of the soft shackle users are hammock people and they love very small line. :-)

 

I made a soft shackle out of Lash-It once. You can easily make them out of the smallest Amsteel if you use the right kind of fid. I have been meaning to write that up but basically you take some rigging wire and fold it in half and pull the line through instead of pushing it with a fid or knitting needle. For the Lash-It, I used some very small gauge wire.

 

Allen

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Yes, someone suggested a "palomar knot" as a 'replacement' to the buntline, for tieing a dyneema line to a shackle.


Looks like a winner.


In endura12, breaking strength is 1510lbs (54% of rated strength) vs the figure 8 at 1144 (41%). That is a statistically significant gain.


That looks like a good 'replacement' for the buntline in tieing to shackles. It's only limitation is that you do need to be able to take the loop fully around the attachment - works for shackles but not for say installed padeyes. And of course a splice would be better. But for a quick tie to a shackle this is the best I have so far for dyneema.

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The figure of nine is a common climbing knot and is said to be stronger than a figure of eight.

Just a quick test, 5 pulls each, in 80lb test dyneema fishing line, figure 9 was 30% stronger (statistically significant) than figure 8. May be the right solution palomar can't be used (because you can bring a loop over the attachment point). I will have to do some further tests in the amsteel.

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Figure 9 in amsteel . . . 1184lbs average vs 1144lbs for figure 8 . . . but the variability was twice as much 79lbs stdev vs 30lbs . . . .so i believe if you dressed the figure 9 very carefully you could get 1240lbs (the average of the three highest pulls) which is statistically higher.

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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

post-8534-0-12887400-1388621125_thumb.jpg

 

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

post-8534-0-12867600-1388621143_thumb.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.

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Splice to splice test:

 

Before: two pieces, each with two splices, joined loop to loop, with 1:1 bend radius

 

post-8534-0-42317200-1388624351_thumb.jpg

 

After: broke at the end of the taper of one of the splices and not the 1:1 radius. Broke at 98% of rated strength (rated average strength with two splices).

 

post-8534-0-13429500-1388624378_thumb.jpg

 

Surprising . . .tentative conclusion . . .1:1 bend radius is just fine and anything bigger is gravy.

 

 

 

 

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If you do not have a smooth taper on the splice, that is where the line will fail. However, on your eyes and your 1:1 turning radius, the load on the line there is 1/2 the load on the line itself. We already know from the knot testing that a tight bend radius with constricting force on the line gives about a 50% loss so there is just no way you will get that kind of stress in the eye given that there are two strands carrying the load. Said another way, the theoretical strength of the splice itself is twice line strength. The taper is a stress point so that can be less than line strength and of course you will never get the entire system to be more than line strength. The bend radius is not enough to dump 50% of the strength so the line will fail somewhere else.

 

Allen

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^^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.

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It really depends on what the configuration is. If you have a line going through an end fitting and it is carrying 100% of the load then the bend radius will matter. But in the eye of a splice, probably not so much. Some of Colligio's fittings have a line going through them multiple times and each line has 100% of its share of the load so in that case, radius will matter. I have done some tests on friction over bends and there bend radius matters a little but not as much as just having a smooth bend. In other words, a circular cross section is noticeably better than a flat with radiused edges. Of course, with friction a larger bend radius also has more contact area so there is a compromise. It all depends on the application.

 

If you want to test bend radius you need to have a line with two eye splices with both of them on the same side of the pull and a bend radius on the other end of the pull. You will have to pull twice as hard to break it though.

 

As another obvious point, if you are using a knot, then the bend radius is truly insignificant because you have lost so much strength in the knot.

 

Allen

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If you want to test bend radius you need to have a line with two eye splices with both of them on the same side of the pull and a bend radius on the other end of the pull. You will have to pull twice as hard to break it though.

Not sure I understand what you are saying. In my last photos above I created two pieces, each with two splices. So, I had two pieces exactly as you say above "a line with two splices with both of them on the same side of the pull'. And exactly as you say the bend radius was 'on the other end' - eg it was a 1:1 bend radius created by the two joined splices. So, I think/thought I was doing exactly what you are suggesting here. Are you suggesting something different . . . if so please explain.

 

edit: perhaps what you are suggesting is that I could use the same two pieces, but instead of interlocking the end splices, I interlock the middle part, with the two splices (on one piece) both pulling from one end and similarly for the other piece. That would halve the loads on the splices (or double it on the 1:1 junction). That's more like the question of bend radius in a working sheave - than what I was trying to get at - bend under a stationary loop.

 

If you have a line going through an end fitting and it is carrying 100% of the load then the bend radius will matter. But in the eye of a splice, probably not so much.

That quote from Colligio is re life lines and I am quite sure was intended to apply at the bend radius for the 'main' line spliced around the outside of the fitting/thimble. They go on to say "Our pull testing has

shown that, with a proper splice, the Dyneema line breaks at the bend" . . . . note that's specifically a stationary splice. My test results seem to directly contradict this statement.

 

Looking at samson's literature . . . it is a little ambiguous . . . but suggests more like what you say and my testing shows . . . 3 or 4:1 for a 100% loaded working line (like a mooring bollard), and for a stationary splice loop they are concerned with the angle at the throat of the splice (so the ratio of splice length to hardware width) rather than the bend radius. . . . except they do say this "The diameter on fixed pin terminations should be at least 3 times the rope diameter (i.e. the bending radius for 1/2" ropes should be 1-1/2")." and I am wondering by "fixed pin termination" they mean in effect a spliced loop.

 

But it could be that some people have mis-interpreted the industrial bend radius guidance to apply to fixed spliced loops when it was not intended to.

 

 

As another obvious point, if you are using a knot, then the bend radius is truly insignificant because you have lost so much strength in the knot.

 

Allen

 

Yes, of course

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Here is a really crappy sketch of what I mean by testing bend radius:

Untitled.png

Pull on both ends toward the left and have the radius under test stationary, likely a shackle attached to the other end of your test fixture.

 

I agree with your assessment on point 2. Colligio pretty much hates me but I have only nice things to say about them. They really do interesting work.

 

Allen

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Here is a graph from Hampidjan (makers of Dux) which suggests loss of 50% of strength at 1:1 bend radius for static bending. But I guess that means for a splice - a 1:1 bend gets the spliced part of the line back to 100%. That's logical and consistent with my test, but seems inconsistent with Colligo's statement.

 

post-8534-0-71323600-1388633463_thumb.jpg

 

edit . . .seeing your post above . . . ok I think we are in agreement here.

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Well, you can't go wrong using a larger radius but personally I just let the eye go around whatever shackle I have around. Typically my Ansteel applications care more about stretch than strength so there is some huge safety factor anyway. I think your understanding is correct.

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So, for you "knot experts", are there any other loop knots worth testing in the dyneema? Is there a know that is easier to untie than the figure 8 but may not slip like the bowline? Or a knot that is less bulky than the figure 8 but will not slip like the buntline? Or do we just conclude "figure 8 or splice"?

How about a double dragon knot and a zeppelin bend?

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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.

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Estar, regarding your post in the CA section, there are standards for accelerated UV testing available. I don't know details, but I think its based on calibrated UV lamps. May not be possible with a home setup

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Regarding the soft shackles, I was thinking about equalizing tension between the two strands and I went back and looked and all my samples first broke on the 'buried' strand rather than the cover strand. That makes some sense to me that the buried strand will be "straighter" and take higher tension than the cover. That would seem to suggest to me that the soft shackles constructions without any bury at all (Kohlhoff style?) might be potentially stronger, if the two strands are tied evenly into the diamond knot. And if you are going to use the buried style, to milk down the cover as hard as possible.

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I am not going to have time to break much today . . .but a quick one . . .

 

I was seeing whether I could get the double fishermen bend to stop slipping in the bare dyneema by adding a little resistance/friction with some (relatively light) sewing down the tails.

 

post-8534-0-69768800-1388670805_thumb.jpg

 

As you can see in the pic, the sewing just ripped out, and it did it very easily, so obviously near full load was being transmitted to the slipping tails.

 

That led me to do some quick stitch strength tests, which are interesting . . .

 

10 stitches of doubled V69 thread has a tensile of 212 lbes (10 x 2 x 10.6lbs), while loops stitched with 10 doubled V69 breaks (all the stitching breaks) at 440lbs = 2x tensile

 

15 doubled stitches have a tensile of 318, and the loop breaks at 620lbs = 2x tensile

 

5 stitches of single 80lbs test fishing line has a tensile of 400lbs, and the loop breaks at 600lbs = 1.5x tensile

 

So, there is a significant "clamping effect" increasing the stitching strength above the pure tensile, and using the tensile to determine the number of stitches would be 'safe/conservative'.

 

 

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On the Dux bending radius chart-- I would be curious to know how Dux differs from regular Amstel in this respect-- and if your tests duplicate the chart for Dux.

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I am not going to have time to break much today . . .but a quick one . . .

 

I was seeing whether I could get the double fishermen bend to stop slipping in the bare dyneema by adding a little resistance/friction with some (relatively light) sewing down the tails.

 

attachicon.gifsewing.JPG

 

As you can see in the pic, the sewing just ripped out, and it did it very easily, so obviously near full load was being transmitted to the slipping tails.

 

That led me to do some quick stitch strength tests, which are interesting . . .

 

10 stitches of doubled V69 thread has a tensile of 212 lbes (10 x 2 x 10.6lbs), while loops stitched with 10 doubled V69 breaks (all the stitching breaks) at 440lbs = 2x tensile

 

15 doubled stitches have a tensile of 318, and the loop breaks at 620lbs = 2x tensile

 

5 stitches of single 80lbs test fishing line has a tensile of 400lbs, and the loop breaks at 600lbs = 1.5x tensile

 

So, there is a significant "clamping effect" increasing the stitching strength above the pure tensile, and using the tensile to determine the number of stitches would be 'safe/conservative'.

 

This is interesting and good stuff. I use stitching to secure climbing tubular webbing and I have had a debate with a friend if the force was clamping or stitch strength. There is other testing that suggests it is stitch strength but there we are talking about hundreds of stitches so perhaps it converges to stitch where the maximum clamping force is less than the stitch strength.

 

A side note on stitching. You will notice on the Sampson site that they suggest using what I will call a snake stitch. It is one that is not locking like you would have with a sewing machine or a Lazy Stitcher, which is kind of a hand sewing machine. This is important and I would think you would want to stitch with a thread that has some stretch, not Lash-It. In my testing, if the stitching was too tight, it would break. Using a stitch like Samson recommends, the stitching does not break. I am talking about lock stitching a simple eye splice. You want the stitching to hold past the breaking point of the line. Too tight a stitch and the stitching will break first then the eye will not work under light loads if you do not break the line. The stitching is only there to hold the eye on light loads.

 

Allen

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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.

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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

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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.gifbend1s.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.gifbend2s.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.

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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.

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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.

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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

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^^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.

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^^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.

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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.

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I've always wondered why line manufacturers don't publish stress/strain curves for their lines. It can be pretty difficult deciphering their marketing jumbo for good engineering.

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^^ 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?

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The one that Dogbark previously posted is good: Halyard Hitch

 

I've used this for about 10,000nm and the halyard is showing less chafe than after 5,000nm with a splice.



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

 

Yes.

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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?

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By the way, Estar, thank you! This is good info.

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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.

 

post-8534-0-99563000-1388696486_thumb.jpg

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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

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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.

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^^ 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).

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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

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^^ 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).

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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.

 

Which begs the question, "Is there a difference in stretch between a knot and a splice?"

 

I don't see any reason why there would be, although one could easily imagine the splice yielding more than a knot (more line is involved), but it would sure be nice to have some data to back that up.

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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.

 

Which begs the question, "Is there a difference in stretch between a knot and a splice?"

 

I don't see any reason why there would be, although one could easily imagine the splice yielding more than a knot (more line is involved), but it would sure be nice to have some data to back that up.

I can tell you that you will not notice the difference in stretch on a foot of line on an 100 foot halyard. But you might get some construction stretch out of the knot that you would not get out of the knot. You can eliminate that with a little pre-stretch.

 

Allen

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^^ 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).

I used to say they were 200% strength based on some other web data but then Brion Toss challenged me on it and offered to arrange the testing. We settled on stronger than the line they are made of. He gives a seminar at boat shows where he teaches my soft shackle (gives credit too) and says that they are stronger than the line they are made of. It seems like a safe number to go around saying and easy to remember. You made some stronger. My testing is always relative and what I was able to show is that they are not twice as strong as the line they are made of but they are stronger than the line they are made of. It is easy to test both the 1x and 2x cases but the 1.5x case is more difficult. You have a load cell so can get that data but are limited to small diameter line because you don't want to kill yourself. The professional setups have a cage around the equipment. They also don't use hydraulics but rather screws. I still worry you will blow the seals out if you go to higher loads. I don't think they are made to go from 6000 pounds to 0 instantly. The bottom line is you don't want to tell people they are stronger than they might be and you don't know how careful they were in making them. The find that milking the cover a lot, perhaps even under some load, makes for a stronger finished shackle is a nice find. Again, you are doing significant work.

 

Allen

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Estar, that wasn't what I was trying to describe but I like your variation. It appears to do the same thing perhaps even better. This photo what I was trying to put into words, but is not dyneema and not pulled tight.

 

post-23187-0-03019300-1388712475_thumb.jpg

 

 

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Estar, that wasn't what I was trying to describe but I like your variation. It appears to do the same thing perhaps even better. This photo what I was trying to put into words, but is not dyneema and not pulled tight.

 

attachicon.gif00.jpg

That is what I tested and it slips in Amsteel.

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This is a bit harder to do accurately than I expected. But the bottom line is that Stayset is slightly lower stretch than the Samson double braids.

 

post-8534-0-32056900-1388713070_thumb.jpg

 

Allen, I guess you have some history with Colligo . . I have some history with Brian Toss. He 'tech reviewed' an article I wrote and told the magazine I did not have a clue what I was talking about . . to even suggesting I must not know how long my own halyard was (I was using a 2:1 halyard which he did not know). I told the magazine that Brian was full of shit and we should have a ''real engineer' review the article. They got a Harken engineer to arbitrate, and he completely agreed with me on everything. He's a very nice guy, but does not carry much weight with me in anything at all technical.

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Estar, that wasn't what I was trying to describe but I like your variation. It appears to do the same thing perhaps even better. This photo what I was trying to put into words, but is not dyneema and not pulled tight.

 

attachicon.gif00.jpg

That is what I tested and it slips in Amsteel.

Agree with Allen, I just pulled it in endura braid and it slipped at 34% of rated load. My 'modified buntline' is nicer :) but we can credit to you and Stan because I made it based on your description.

 

So, you guys may know . . .on say a volvo 70, what % of rated load does the halyard sit at? I presume its lowish because its sized to stretch, but does anyone know actual the ballpark %? Is it above or below 35%?

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Estar, that wasn't what I was trying to describe but I like your variation. It appears to do the same thing perhaps even better. This photo what I was trying to put into words, but is not dyneema and not pulled tight.

 

attachicon.gif00.jpg

That is what I tested and it slips in Amsteel.

Agree with Allen, I just pulled it in endura braid and it slipped at 34% of rated load. My 'modified buntline' is nicer :) but we can credit to you and Stan because I made it based on your description.

 

So, you guys may know . . .on say a volvo 70, what % of rated load does the halyard sit at? I presume its lowish because its sized to stretch, but does anyone know actual the ballpark %? Is it above or below 35%?

I am going with 0 stretch for a Volvo-70 because they use halyard locks.

 

Allen

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^^ not stretch . . . What % of rated load does the halyard max at? My question is really . . . Is Stan's modified buntlines in fact, in actual practice, ok because they don't pull it over 35%?

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Didn't someone say that Stan didn't use Dyneema? In that case, it would not slip.

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Didn't someone say that Stan didn't use Dyneema? In that case, it would not slip.

No, I believe the comment was that the demo photo was not of dyneema.

 

Actually I have talked with Stan directly about this knot (he helped me a bit when I was writing the USSailing dyneema life line article) . . . And he did mention it in reference to dyneema . . . . I think uncovered (stripped cover) but am not completely sure about that. I never asked him for any details about the knot or the line . . . He just brought in up in passing and said he himself did not know what the strength was, and he was curious about it. We were requiring splices for the life lines so I never followed up on it.

 

Anyway, my curiosity stands . . . Anyone know what percent of rated strength the halyards of a top ocean racers max's at?

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@Estar. Again, the top ocean racers don't let the halyard stretch matter because they use halyard locks so the main is locked at the masthead. But I understand your question and don't have an answer :-)

 

A very interesting thing happened here. The "above" knot is not listed in ABOK as far as I could tell. That makes it a new knot and one that does not slip (I confirm this) and that is a very desirable property. You have invented a useful knot. Congratulations. What are you going to name it?

 

Back to testing. Another knot that did not slip in my testing is the ABOK #1848 shown on this page http://l-36.com/abok.php?listed_page=&abok_page=310

 

The Portuguese Bowline (#1848) seems to have the added advantage that I was able to untie it after loading it up. The "above" knot, not so much.

 

Allen

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In my limited experience Stan's knot worked just fine on stripped dyneema. Based on your testing I would attribute it to the fact that the halyards in question were probably over sized and under loaded. Previous problems with splices wearing on the sides of the sheave boxes were eliminated and no further breakages have happened. I do not like to put things on the ultimate edge though so I cannot disagree with Allen's assertion about the slippage in an ultimate loading situation. I do like the Estar change though and will probably use it in the future. Thanks Estar for all your work on this, I really appreciate it.

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Allen - Estar is not talking about stretch - see his post.

 

He's asking what load they put on the halyard. Obviously if it's a halyard lock, then it's only the load when hoisting the sail.

 

Now I will show my ignorance because I don't know how halyard locks work when reefing, but a sail flogging in 30kts puts a load on the halyard. It's certainly not the same as when the sail is sheeted in, but it is a load.

 

Do the V70's use 4mm Amsteel, 14mm Vectran or something in between? And how loaded is the line when it's maxed out, however they use it?

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A pretty good way to know how maxed out the line might be is to know what size winch they use, but I don't know that either. I did see that a Swan-70 has 1848 sq ft of mainsail which is 6.5x what my 36 ft boat has. I use a 10x winch so most I could put is about 300 pounds. That would scale to about 2000 pounds, which would require a 50 power winch. The Volvo-70 has about the same mainsail area as a Swan-70 according to Wikipedia. This is just a way to ballpark it, not intended to be an answer.

 

Allen

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Do the VO70's lock off when they reef? They must have some loading data for reef 1/2/nuke.

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Good article, but still begs the question of how much load. Maybe they have a "cunningham" type down haul for each reef so they don't need to tension the halyard, they get all the luff tension from the downhaul with the head locked in place.

 

There must be a real V70 sailor here somewhere who knows the answer.

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Yes, they would get the tension by pulling down on the tack ring. Estar, why do you want to know?

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Just a thought, but how does the carrick bend hold up?

 

I can add that the formula for crane sheave diameters is based on the thickness of the cable it is to have on it. The codes demand that the thicker the cable, the bigger the sheave. This indicates the diameter of a rope is a factor in it's ability to withstand sharp changes of direction.

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I was going to test some halyard shackle knots in dyneema double braid (dacron cover so we would get breaking strength and not just slipping). . . . however . . . . the cover is just tearing at the knot and then the dyneema slipping.

 

Bowline at 51% of rated strength

Buntline at 42%

 

Bowline: post-8534-0-39166600-1388763133_thumb.jpg

Buntline: post-8534-0-61836700-1388763147_thumb.jpg

 

This is with FSE Robline. I have some warp speed coming and will try it, But basically this seems to be about cover strength, which is an interesting aspect of high mod cored ropes that I have not seen examined closely.

 

But I am a bit puzzled by this - why is the cover breaking? It should not be taking any/much load. Is it being 'crushed' into failure?

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