Load Testing Results

[Paul Elliott]

Luggage Tag Slippage: I can personally verify that it slips. After sailing to and from Hawaii, mostly on starboard tack with the genoa (when we weren't flying a spinnaker) My luggage-tagged genoa sheets had slipped several inches. I forget the line we were using, but it was a braided cover with a non-dacron straight core (an upgrade from Sta-Set and Sta-Set X). For the next round trip, I did the luggage tag with a few stitches between the two halves, and the stitches eventually broke, with the line slipping several inches again. For the round trip after that I used what you might call a double luggage-tag (looped around the stainless clew ring twice, much like a Prusick), and it also slipped.

These weren't catastrophic failures, just a slow slip. An the end of each of these 4300 mile trips, one sheet was longer than the other by several inches.

A luggage tag around a sail's clew grommet might not slip, since there is fabric inside the knot and no doubt more friction than I had with just the stainless clew-ring.

On my last round-trip I tied bowlines (or buntline hotches -- I forget). No slippage there!

[Therapy]

Originally Posted by Paul Elliott

Luggage Tag Slippage: I can personally verify that it slips. After sailing to and from Hawaii, mostly on starboard tack with the genoa (when we weren't flying a spinnaker) My luggage-tagged genoa sheets had slipped several inches. I forget the line we were using, but it was a braided cover with a non-dacron straight core (an upgrade from Sta-Set and Sta-Set X). For the next round trip, I did the luggage tag with a few stitches between the two halves, and the stitches eventually broke, with the line slipping several inches again. For the round trip after that I used what you might call a double luggage-tag (looped around the stainless clew ring twice, much like a Prusick), and it also slipped.

These weren't catastrophic failures, just a slow slip. An the end of each of these 4300 mile trips, one sheet was longer than the other by several inches.

A luggage tag around a sail's clew grommet might not slip, since there is fabric inside the knot and no doubt more friction than I had with just the stainless clew-ring.

On my last round-trip I tied bowlines (or buntline hotches -- I forget). No slippage there!

After 4300 miles does a couple of inches mean anything when the sheets don't hang up on the spreaders nearly as much? I don't know. My (ex) Gemini had a forward stay where the sheets hung a lot with the bowlines.

[estarzinger]

Back to jib sheets for a moment . . .two points . . .

1. the ultimate slipping load does does not depend on the '2 line pull' setting load. The line will "self set" when pulled on one side. It will slip a bit at lower loads while setting but eventually it will tighten up and get to the same ultimate slipping load as if you initially set it at high load.

2. the luggage tag slips at about 40% while the clove hitch slips at about 60%.

[mikereed100]

Just a thought. If you take another turn around the clew ring you have turned the "luggage tag" into a Prussik which would be much less prone to slippage while retaining the benefits of the "luggage tag".

[estarzinger]

Originally Posted by mikereed100

Just a thought. If you take another turn around the clew ring you have turned the "luggage tag" into a Prussik which would be much less prone to slippage while retaining the benefits of the "luggage tag".

true . . .I will test the slippage with that extra turn.

on bends . . .

In my testing the sheet bend slips (very roughly) 50% of the time in brand new dacron line and breaks at about 59% of the rated line strength (which is low among the various good dacron knots).

I just tested the Zeppelin bend, an equally easy knot to tie, and it did not slip and breaks at 69% of rated line strength. It seems a better choice for 'everyday' use. Note: it does slip in bare dyneema.

Are there any other easy to tie bends that people have reason to believe are even better than the Zeppelin?

[estarzinger]

Following up the above suggestion . . .

Back to jib sheets . . . rather than using a luggage tag . . .taking another turn which essentially gives you a prusik

Before:

After . . did not slip, broke at bowline:

Not sure if this failure mode is preferred to slipping - higher strength but bigger bang.

[thinwater]

Originally Posted by Paul Elliott

Luggage Tag Slippage: I can personally verify that it slips....

And for me it never slipped (fuzzy polyester cover, Kevlar core, don't know the brand). Eventually the core failed (at the knot exit, not the ring, due to flexing while flogging I am certain), but the cover still held! Clearly, the PO massively over sized the line (5/8 Kevlar where 1/2 polyester was stock).

There is another variable; the clew ring. My example was on a very nice genoa by Quantum that has been used hard, but the sheet goes through a nicely leathered grommet, not a ring. A lot more friction and a much longer bend radius.



I'd be inclined to guess a larks head is safe on a grommet and not a ring.

A point of nomenclature, and a quick search did not resolve it. My understanding...

Girth hitch. Climbers refer to this as a closed sling wrapped around something, like a prusik knot with only 1 turn. Lugage tag should mean the same thing, since a "luggage tag" is a loop. Typically a luggage tag attaches a snap shackle to a halyard. Thus, the knot that slipped was not a luggage tag.

Larks head. The knot that slipped. A girth hitched tied on an open line.

Cow hitch. Same as larks head.

Prusik. Girth hitch with another turn. I wonder, however, if the typical ring has room for a prusik tied with full-size line. Mine would not.

Wiki shows all of these as the same (closed loop). That, to me, is no more true than saying a sheet bend and a bowline are the same knot because they share the same turns.

-------

So, which is which?

[estarzinger]

regarding bends . . someone suggested the Strait/butterfly bend . . .

In dacron, I get identical breaking strength numbers for the Strait and Zeppelin. and in dyneema single braid I get them both slipping. So it would seem to just depend on which geometry you find easier to tie.

I still have not found a simple bend that will hold in the bare dyneema.

[estarzinger]

regarding aging and UV . . . UV exposure damages all lines and fibers, but it particularily degrades the strength of single braids, as there is no cover to shield the load bearing core fibers. How much the line strength will be degraded depends on what sort of coatings are applied to the fibers and exactly what sort of braid is used. The following graph shows the high and low cases for UV damage to dyneema single braid lines. Most dyneema single braids will fall somewhere between these two lines.

[thinwater]

Since covered Dyneema is core-dependent, damage to the cover is much less important. Any single braid has the same challenge.



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However, the fiber itself does pretty well. Heck, even Dyneema at 10 years in the NM sun is pretty impressive; most ropes are only 50% at that point, depending on who's data you examine.

But the question is this: if cover failures are a big part of the failure equation, those cover-supported knots may not be much after just a few years. I have used knots with high-strength line, and cover failure at the knot is something I saw (I had a 2:1 Kevlar halyard with a knot at the top--I spliced it the first time, but it became easier to just re-tie the knot every few years when I was inspecting the rig.). Cover failure was not a big deal, because Kevlar does not slip.

What if (and this is ugly) you tied a triple fisherman stopper knot in the tail of your favorite knot, to prevent the tail creeping through? It could be tied around the standing part, for neatness, though this might reduce its effectiveness.

[estarzinger]

Back to nylon for a moment . . . load vs stretch . . .

As expected, nylon double braid is the least stretchy.* But the difference between good old 3 strand and Brait was not as big as expected, and at least with these particular lines (Yale 1/2" brait and Samson pro-set 1/2") and loads the 3 strand was marginally stretchier.

[estarzinger]

by the way . . .for any lurkers . . .if you want a summary of the thread conclusions and data without reading thru all the posts (that's a non-commercial site with no advertising)

[B-Baysailer]

Great job making the estar knot I was just wondering do you think it would be any stronger if you did 2 raps on the shackle before you make the knot up.I was looking in one of my fishing knot books and there is a collar and capstan knot and thought the capstan might work on your knot

[estarzinger]

Back to sewing a moment . . .here is data for three different stitch counts in three different materials (sorry I am posting ajpg of the table because I cant get the forum software to format a table). The number shown is the breaking load as a percent of the stitching tensile strength. There is a 'clamping/friction' effect in all tests, but as you can see it varies quite a bit.

My initial hypotheses is that the variance is primarily due to two factors: (1) the surface friction - dyneema less and dacron more & smaller diameter less and larger diameter more, and (b) the thread contact with the material - thin/small diameter less and thick/large diameter more.

Is there any sewing literature on all this? Do any of you expert sewers have any better explanations/observations about the cause of the differences?



*Note: the stitches in this test are just simple 'straight thru the middle' stitches.

[estarzinger]

Edited . . . small spreadsheet error

I was/am using few stitches because it is easier to count/be accurate, particularly with the machine. But I will do some stronger ones by "inches of stitching".

I am trying to test "across" and down" patterns separately, so that I know how they each contribute to a box pattern.

and some machine stitching . . . . a bit surprising . . . weaker than my hand stitching and zigzag weaker than straight stitch. But I am only doing 10 stitches (5 forward and then 5 back), so the end stitches may not be firmly locked. I will have to try more stitches.

10 straight stitches across webbing (V92 thread) 132% of thread tensile
10 straight stitches down webbing (V92 thread) 129% of thread tensile
10 zigzag stitches across webbing (V92 thread) 104% of thread tensile
10 zigzag stitches down webbing (V92 thread) 96% of thread tensile

50 Straight stitches down webbing (v92 thread) 78% - that is very puzzling!

For the 'theoretical tensile calculations, I am using 14lbs for the thread, 2 threads per stitch (that's right for a machine lock stitch - right?) and the number of stitches (perhaps I should not count the first and last, but that will not make much difference in the 50 stitch calculation). The rank order of the results is almost the opposite of what I expected.