Issues with synthetic rigging?

[jfranta]

Originally Posted by echidna

Hi Brion,

Well, I would say that my 0-30 Centigrade temperature range is quite reasonable, even conservative, for a boat left in the water year round (or hauled for winter rig-in) in New Jersey (where I used to sail), having on the one hand wilted in summer heat in the high 90's (Fahrenheit), and used my former boat as an ice breaker in the destination harbor (and near frozen to death) on a December trip to Mamaroneck, NY.

Regarding loads and creep, I just went to the Colligo site to refresh my memory on their creep data, and could not find the relevant information. It seems to have been removed - Google cache still has it though.

Assuming the old data was correct, a load 12% of breaking strength would cause creep of over 3" per year in 50ft at 22 deg C. I'm not sure that is acceptable.

The question now is, was that old Colligo data valid, and what happened to it? Insofar as creep is probably the dominant consideration in sizing Dyneema for stays, it's important to have good information on it.

I'd also like to raise another point related to temperature effects, and that is the temperature dependence of creep. Creep is typically strongly dependent on temperature, and the equation on the old Colligo graph would imply that the creep rate for a given load in Dyneema doubles with every 4 deg C temperature increase. So in discussing creep, it is surely essential to indicate the expected ambient temperature. Temperatures in the tropics could easily be 5-10 deg C higher than the 22 deg C reference point used in the old Colligo data. Probably a topic for another thread, really.

Due to many issues with understanding the creep data (or misunderstanding it), we are keeping it interrnal now. We can assist with sizing Colligo Dux Rigging with anyone who asks. For the time this is how we size the line in order of priority:

1. Stretch
2. Creep
3. Breaking strength.

We almost always have the line at much less than 10% of strength effiiciency, mostly based on stretch. Creep is figured at pretension and 0.1" per year is a maximum target. (@22C). This seems to be a good conservative number as we have many boats now rigged with normal travel turnbuckles that have not gotten into creep issues. One 65' monohull in the Carribean. For offshore boats we factor in long term dynamic loads as well. Keep in mind that creep happens over time, so average temperatures are what you need to look at, or time at temp if you have access to that kind of data.

A couple of comments on pretension: Since steel has such a low creep rate, sailors for years have been over tensioning with no short term consequences. This makes it easy to over tension at the dock and cover for any load conditions you may encounter. Some long term issues may result, stainless stress crack corrosion, Creep in the fiberglass at the chainplates, etc., but who cares about the long term stuff we are Americans!

If you oversize slightly you will be really surprised how little tension you need with Colligo Dux Rigging. I just installed/tensioned the diamonds on a F27 yesterday. We used 9 mm dux to replace the 1/4 inch wire, oversized for creep. The 1x19 1/4" wire was previously tensioned at around 2,000 lbs to get the required mast bend. With the 9 mm Colligo Dux we tensioned to around 400 lbs to get the same amount of mast bend! Yes, we have loos gauge calibrations for it now. For a 50 foot length of 9 mm UHMWPE line at 1200 lbs pretension you will get about 0.1 inches of creep per year. So this is 400 lbs and only about 20 feet long, so creep will be much less @ 22 degrees C and can tolerate much more temperature before you get into creep issues.

I don't have the time now to go thru the thermal expansion math again but suffice it to say that pretension seems to take care of it. You should expect to adjust some over long periods of environmental cycles. Fall to winter, etc will need some adjustment if pretension is critical. I can tell you I met a customer at the Oakland show this month that has a Catalina 36 (with turnbuckles) and Colligo Dux standing rigging in the Bay area, (pretty big daily temp cycles) and he was literally jumping up and down with joy about the performance of his boat. The pretension seemes to mask the linear expansion/contraction of his rigging and it still stays in the performance window for stretch.

We did have a boat (50 foot ketch) that sailed from Argentina to Greenland that used lashings initially but after getting into the cold north needed to change to turnbuckles. Lashings are somewhat limited in their ability to create pre-tension.

So bottom line as I always say, this is a new material, it is not steel and should not be sized like steel. Stretch and creep are its limiting parameters. Do not, and I repeat do not size it for breaking strength. We also like to think of it more as plastic than rope as rope carries with it certain paradigms that do not apply here either. Did I say do not size it for breaking strength???

Hope this helps. Would like to say more but no time. Please stay tuned to our website for Newsletters and our Facebook page for more and more examples of this rigging. The proof is in the pudding.

John Franta, Colligo Marine