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Old 05-05-2009, 00:57   #31
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jfantra, tested the same way as we do when we do tests for the Lloyds man here. We do a fair bit with Lloyds (ABS, GL and the rest) watching due to our superboat work.

Splices were what the 'average' seems to be around here, which is generally pretty good, and the difference between them and ours and/or manufacturers recommendations are next to nothing when talking loads.

Yes we also have previous test data showing differing loads, that's why this last lot has us a bit bamboozled also. The weird thing that really chucks the twist into it all was the other 2 heat-set 75's did a similar thing even if not quite as badly. One we expected to due to we know it is a knock-off of DSM's genuine dyneema fibre. But that one got better loads than the Dux, even if by bugger all. One other the others we 'suspect' maybe of the knock-off fibre as well but we don't know for sure. Read that para well and you may also start suspecting what we are currently but again, not confirmed in any manner.

The std 75's performed pretty much as expected and in line with previous data by us and others.

Ah, not sure why you think the Dux isn't a SK75 though. Never seen anything that would suggest otherwise, including from Hampidgan. It appears you know something we and at least 2 very significant and respected rope manufacturers don't.

Hpefully the next run of bustings will shed some light on what's up. We are going to change things to go for max load rather than what would be expected of a finished product. The differances shouldn't be that large or not for any reason we can see but we'll soon find out. Just waiting to make sure we get completely differing batches of the ropes..... just in case, to eliminate any that may have slipped passed below spec.

Therapy - My wife called me great also this afternoon.... err hang on it was 'you great {expletive deleted}' so probably she didn't mean quite the same as you

Have you read up on jfantra website? I haven't had a chance to have a big look but the little I have is good stuff. Combine that with Seacaps comments and all the others and you'll see reliable affordable fibre rigging for the average yachtie isn't far away at all.

Must run, I have a man in need of a personalised dingy painter. He's an idiot but does drive a big fizz nasty, so only to be expected
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Old 05-05-2009, 04:41   #32
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...Have you read up on jfantra website? I haven't had a chance to have a big look but the little I have is good stuff.
I see among other things on the web site there are terminations for synthetic lifelines which prompts me to ask when will synthetic lifelines be acceptable for Cat 1?

Must be stranded stainless steel in the current 2008/2009 ISAF Offshore Rule and the YNZ recook of that just says "wire" ???? and just recommends 316 ss - last time I asked a YNZ inspector about it (about 1 year ago I think it was) he stated that synthetic would be unlikely to be accepted even under the discretion allowance for a cruising yacht's offshore Cat 1 inspection for clearance here in NZ.

I want to replace mine, preferably with synthetic - is not urgent so am hoping to sit the situation out.

{Hope this is not too much thread drift but surely lifelines are part of Rigging too }
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Old 06-05-2009, 12:19   #33
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Ah, not sure why you think the Dux isn't a SK75 though. Never seen anything that would suggest otherwise, including from Hampidgan. It appears you know something we and at least 2 very significant and respected rope manufacturers don't.
Heat stretched UHMWPE line is work hardened material. This is analogous to work hardening metals like steel or aluminum. You can significantly change the material properties, ie. steel can be 50% stronger or more when work hardened, Forged, rolled, etc. Forged shackles are much stronger than cast, etc. It also becomes less flexible.

Polyethylene exhibits the same type of material property changes when worked. Take a plastic grocery bag and stretch it, it becomes stronger but it also becomes less flexible. Heat stretched line is the same, stronger but less flexible. In addition, if you bend UHMWPE line in too tight of a radius you put the interior strands into compression (they Buckle), which damages the now stiffer fibers, taking some of the strength.

Therefore if you are testing non-heat stretched sk-75 and heat stretched sk-75 (Dynex Dux) in the same manner, particularly around small diameter thimbles or line terminations, than you are not comparing apples to apples in your testing. The softer, more flexible line will take higher loads on the same small diameter line terminations.

However if you treat the heat stretched line a little differently, with large diameter thimbles/line terminations, at least 5/1 ratio, than you will see breaking strengths at over 90% of the rated breaking strengths with a proper splice. Lots of data already exists on this.

Also, the sitffer material make it more prone to improper splicing techniques. A long bury (72 times the diameter or more) and a proper taper are very important. A sharp end on the taper can produce a stress rieser in the material also.

Heat stretched dymeema SK-75 exhibits some very different material properties from non-heat stretched.

I look forward to the details of your testing.

John Franta, Colligo Marine
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Old 19-05-2009, 00:56   #34
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G'day again, been away and some sailing before the winter weather really kicks in.

John, The testing of the heatset 75's and the none were all done the same way. The ends were around standard sized thimbles, BS464's to be exact. Yes we know how to spice and test properly. That's why this ones so weird, we just havent had numbers that far off the mark before with any product, apart from ones that had been used/damaged and thing like that.

The weird thing was the Dux broke in the middle of no-where, not where ropes are normally expected to break. Not only in one run of tests, all of them. The Amsteel broke around the back of the thimble, again not a good spot, but we know why so no worries there. I don't know what's up really but on going investigations have raised a surprisingly large number of comments about Dux, most not that flattering to be honest.

And it's interesting to see most of the big rope companies all think heatseting the 75's is a bad move. Yes it does make it stronger but far more prone to flex fitigue. But in a stright line pull like yacht rigging I suppose that sholdn't be an issue and Dux was biuld for trawl wire replacement which is big straight line pulls.

They want to do another run of tests shortly but we are waiting for new shipments of the assorted ropes to arrive, just in case were had a dodgy lot last time/s. Busting at only 40% odd of publish loads means something is not right somewhere. We will do a series around the big drum which will eliminate any termination interference and give a pure rope load only.

75 time D bury? Woww that's big. We run 40 times and have never once seen any slippage. You wonder down marinas and see the massive (??) 10x, sometimes less, buries and think 'Oh, here we go' as well I'm constantly amazed at what some people do seem to get away with. Lucky for many 'ignorance is bliss' as they say but then most never get anywhere near break or even highish relative loads.
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