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Old 19-12-2013, 10:44   #16
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Re: suggestions for things to test with a load cell?

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Originally Posted by estarzinger View Post
My prior test suggested the ABYC tables were approximately 4x high at 30kts and 2x high at 60kts. HOWEVER, the ABYC tables have a note saying they have (somehow, I am not sure how) "included the effects of current and wave action". My testing was with small fetch (so very little waves) and zero current. I think they have just added a fudge safety factor in, which accounts for quite a bit of this difference.

I don't go looking for lousy anchorages with big fetch, but I do occasionally end up in one, and I will try to get measurements when I do. But what I think I can say from my prior testing is that just the wind load (in a small fetch harbor) is way lower than the ABYC table.



What you have here is considered completely acceptable. It sounds like you know this, and do it at the aft ends . . .but the 'best practice' way to do that pulpit attachment is have a thimble in a spliced loop in the dyneema lifeline, which stops about 3" from the pulpit tube. and then a lashing around the thimble and tube. This is slightly better for three reasons. (1) the lashing is of smaller diameter cord, and usually lower modulus, so is less sensitive to bend radius, and (2) if you need to get a MOB back on board, you can cut the lashing to drop the life line, and you have not destroyed the lifeline and re-lash it quickly, and (3) the lashing gives you a good tool for tensionning (and retensionning) the lifeline.

(1) and (2) are still good reasons to have the lashing at the front end, even if you have a lashing at the aft end to do (3).

This is not a perfect example, but shows the general principle:

Attachment 72403

You do want to avoid knots in the primary lifeline. They do weaken the dyneema significantly. (here is a climbing article that does some knot testing in dyneema and other materials) If you need something that opens, I would suggest a soft shackle rather than a knot. The better technical solution is to splice in a trigger shackle (like a tylaska) that hooks to a spliced in ring. That would be full strength and easily openable and closable even under decent tension. But it does add cost/complexity.
Thanks for the feedback. I took a swim once on a delivery when a pelican hook let go, hence my aversion.

I think I am getting some year-old hand-me-down halyards from a friend who manages a fairly well financed big boat racing program. Keeping my fingers crossed there will be some sweet Sparcraft shackles on them, so that might be an option I hadn't considered.

Interesting bit about the big boat program, they replace their halyards annually as a part of their risk management program along with the other PM stuff they do.

It's not worth losing a race to them, so they just replace it whether it needs it or not. Hardly cruising on a budget!
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Old 19-12-2013, 12:40   #17
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Re: suggestions for things to test with a load cell?

Evans, in one of your recent posts you mentioned that you had some make of clutch that worked on Dyneema. I'd be interested in measuring the holding power of various clutches on both bare Dyneema and various covered lines. I've often wondered about the manufacturers claims in general, and particularly how the nature of the cover and the diameter of the line affect the holding power of clutches.

Oh... would you be willing to tell us what make of clutch it is that works on Dyneema?

Thanks for the offer of testing things, BTW. A generous and useful thing to do!

Cheers,

Jim
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Old 19-12-2013, 13:33   #18
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Re: suggestions for things to test with a load cell?

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Originally Posted by Jim Cate View Post
I'd be interested in measuring the holding power of various clutches on both bare Dyneema and various covered lines.


Oh... would you be willing to tell us what make of clutch it is that works on Dyneema?
Well testing clutches could get expensive, unless someone provides them to me. I might well break them in the testing.

We use spinlock ZR and ZS jammers (yes, jammers not clutches, sorry) successfully with bare (but core bulked up) dyneema.

But what I was referring to in the post above were the new generation of Chinese finger clutches . . . .see in textile: CONSTRICTOR | Ronstan Sailboat Hardware US

Click image for larger version

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and . .. in metal . . . . Karver Systems : Accastillage spécialisé - Poulies et emmagasineurs

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Old 19-12-2013, 14:15   #19
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Re: Suggestions for things to Test with a Load Cell?

just picked up a 10 ton puller ram (already had the hydraulic pump).

Just need to make up a steel I beam base, with the ram at one end and the load cell at the other and I will be ready start some serious breaking.
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Old 19-12-2013, 14:35   #20
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Re: Suggestions for things to Test with a Load Cell?

Hi Evans

I'ld be curious as to how much an eye splice on 3 strand nylon weakens the rode. I mention that since my anchor system uses a combination of chain (3/8 BBB) and line(5/8-3 strand) The splice I use is the eye splice rather than the typical anchor splices thru the chain length. A comparison of the different splices could be made.
(That eye splice is attached directly to the last chain length with 7 or 8+ tucks.)
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Old 19-12-2013, 16:10   #21
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Re: suggestions for things to test with a load cell?

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Just an FYI, I think it was Practical Boat Owner, the UK mag, that did breaking strength tests on a number of common marine knots this year. I probably should have bought that issue...
Quote:
Originally Posted by gordwedman View Post
Just an FYI, I think it was Practical Boat Owner, the UK mag, that did breaking strength tests on a number of common marine knots this year. I probably should have bought that issue...
That data, unless done for every combination of line size, construction, and brand, is worth exactly squat. Recently I decide to break some thing as part of a potential article and I learned:
  1. Variation between brands is ~ 25-30%.
  2. Some knots are extremely variable. Even when dressed the same, when they pull up under extreme load the results vary.
  3. The extent of #2 depends on the brand and type!
OK, I exaggerated. There are trends, but sometimes the rank-ordering even changes. Complicated.
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Old 19-12-2013, 16:43   #22
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Re: suggestions for things to test with a load cell?

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That data, unless done for every combination of line size, construction, and brand, is worth exactly squat. Recently I decide to break some thing as part of a potential article and I learned:
  1. Variation between brands is ~ 25-30%.
  2. Some knots are extremely variable. Even when dressed the same, when they pull up under extreme load the results vary.
  3. The extent of #2 depends on the brand and type!
OK, I exaggerated. There are trends, but sometimes the rank-ordering even changes. Complicated.
Interesting.

But when I think about it, perhaps not so surprising, if say there are two (or more) physical reasons for knot failures (say tension in fibers on the outside of a bend and crushing on the inside of a bend) then different rope constructions might well have have different internal failure modes, changing the rank order. I would not have guessed that, but I can see the logical possibility.

Regarding your #2, I would gave guessed there was a big difference between a load coming on slowly (like it will with a hydraulic ram) vs coming on fast (like with a drop test). Did you see (or test) that?
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Old 19-12-2013, 16:44   #23
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Re: Suggestions for things to Test with a Load Cell?

Sampson posted a nice study of Amsteel breaking around various radius pins, down to D/d=1. They also cover cow hitches and other variations. Why guess?

http://www.samsonrope.com/Documents/..._March2011.pdf

Regarding failure at D/d=1 for eyes.

"D/d = 1 did not show significant strength loss, however break occurred at the back of the eye (on the pin)."

Eye-to-eye is also efficient (90%)

Other configurations (loop) required a longer radius, but the reality is that the head of an eye splice is not highly loaded (2 legs = 50%). This is easy to overlook.

They also cover knots in several material. Good paper.

-------

The testing I did was specifically targeted at something I could NOT search data for (hand stitching and seizings). There is a LOT of good data on the net.
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Old 19-12-2013, 16:58   #24
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Re: suggestions for things to test with a load cell?

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... Regarding your #2, I would gave guessed there was a big difference between a load coming on slowly (like it will with a hydraulic ram) vs coming on fast (like with a drop test). Did you see (or test) that?
Yes, I think your intuition is dead-on.

I've never drop-tested anything other than dynamic climbing ropes, tubular webbing, and spectra webbing (bad). What I did notice was the effect was minor with conventional double braids and MUCH worse with slippery ropes; they often drew up in a different manner than which they were dressed and pre-tightened. They sort of slide where they like, sometimes staying well formed, sometimes not. However, they wer egenerally materials that should be spliced, anyway (low knot efficiency).

Climbing ropes are optimized for knotability; the required drop tests include a figure-8. Small wonder they have high knot efficiency.
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Old 19-12-2013, 18:00   #25
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Re: Suggestions for things to Test with a Load Cell?

Can a thimble weaken the eye? Yes, I think that is the case, based upon Sampson data and based upon some tests I ran. Protection from chafe, but not always greater strength.

The problem is overly broad (sailmaker's?) thimbles; they spread the throat and it rips there.

Read the report, consider the trig, and run some tests!
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Old 19-12-2013, 18:18   #26
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Quote:
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My prior test suggested the ABYC tables were approximately 4x high at 30kts and 2x high at 60kts. HOWEVER, the ABYC tables have a note saying they have (somehow, I am not sure how) "included the effects of current and wave action". My testing was with small fetch (so very little waves) and zero current. I think they have just added a fudge safety factor in, which accounts for quite a bit of this difference.

I don't go looking for lousy anchorages with big fetch, but I do occasionally end up in one, and I will try to get measurements when I do. But what I think I can say from my prior testing is that just the wind load (in a small fetch harbor) is way lower than the ABYC table.
...
Interesting, Ive always thought their numbers seemed high. A saftey factor is not a bad idea, but 4x is a bit much.
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Old 19-12-2013, 18:29   #27
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Re: Suggestions for things to Test with a Load Cell?

Last spring in another thread

Setting the anchor

we argued a bit about the tension in the anchor rode when operating in reverse and setting the anchor. The question was whether the bollard pull formula would give a reasonable estimate of the static thrust developed in reverse.

How about checking the tension your anchor rode when operating in reverse at several different engine rpm.

I bought a 0-2000 lb dynometer, and with my 2 blade 17x10 prop turned by a Yanmar 3HM35F with a 2.50 ratio in reverse gave 110lb@2000rpm, 170lb@2500rpm, 240lb@3000rpm, and 300lb@3500rpm.

It is my contention that I can not properly set and test (for a storm load) my anchor with my engine operating in reverse.

Bill Murdoch
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Old 19-12-2013, 19:44   #28
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Re: Suggestions for things to Test with a Load Cell?

^^ yup, bollard pull is definitely on the list. . . very easy to do. I really have almost no idea what my pull will be . . . but have to say I am surprised by how low your numbers are. Based on my previous (very limited for your size vessel) testing your 3500rpm number might be equal to about the 25kt wind load.
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Old 19-12-2013, 20:00   #29
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Re: Suggestions for things to Test with a Load Cell?

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The testing I did was specifically targeted at something I could NOT search data for (hand stitching and seizings). There is a LOT of good data on the net.
Have you tried doing machine stitching?

I am told that I can do 6mm line easily with the zigzag on my machine, and 8mm if I play with the foot. I have seen some photos that look pretty good, but I have not tried it yet. Small lines (except single braid) can be hard to splice so the machine stitching is interesting.

I had always assumed that machine stitching would be much stronger than hand stitching (because of more uniform tension), but your hand results were really good.
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Old 19-12-2013, 20:57   #30
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Re: Suggestions for things to Test with a Load Cell?

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Have you tried doing machine stitching?

I am told that I can do 6mm line easily with the zigzag on my machine, and 8mm if I play with the foot. I have seen some photos that look pretty good, but I have not tried it yet. Small lines (except single braid) can be hard to splice so the machine stitching is interesting.

I had always assumed that machine stitching would be much stronger than hand stitching (because of more uniform tension), but your hand results were really good.
No, only hand. Dozens of repeats. When the tension comes on there is enough give in the lin to equilize; different than fabric sewing.

Thrust data point: Yamaha 9.9 high thrust gives 250# forward and 180# reverse (several owner data points, all close).
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