Creep in Dynex Dux

[echidna]

Hi,

Let me begin by saying I am quite interested in the possibilities of utilizing Dynex Dux rigging on my boat (11 year old Hallberg Rassy 53), which I expect to re-rig in a few years before going long-term cruising. So I am endeavoring to educate myself about the possibilities.


For certain parts of the rigging, the choice of Dynex Dux is not too difficult:

For example:

the running backstays (maybe not Dynex Dux, but certainly some high-modulus synthetic rope);

the removable inner forestay, which is used with hanked-on sails;

the backstay (hydraulically tensioned), given a way of providing an SSB antenna.

These lines are easily adjusted, adjusted frequently when sailing, and generally left under reduced tension when at dock/anchor.

However, changing the shrouds to Dynex Dux appears to me to be much more problematic. Thermal expansion (see separate thread "Issues with synthetic rigging?") and creep seem to be two key issues.

Please excuse me if I play devil's advocate and seek to challenge the applicability of Dynex Dux for the shrouds. It's my way of seeking better information on this topic, and such information (especially of a quantitative nature) is surely thin on the ground at this time, at least as compared with conventional rigging.

As a physicist with an engineering bent, I like to see quantitative analysis, and to make that analysis, one needs data on materials. This is the approach taken by Glenn Ashmore who a few years ago posted extensively on the topic of rigging with Dynex Dux, and I for one second his approach.


So with that preamble, let me begin on creep by quoting from the thread on thermal expansion. Apologies for pulling this out of context for the sake of brevity - the full context is available in that other thread.

From post by me ("echidna"):

"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.... 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"

From reply by "jfranta":

"Due to many issues with understanding the creep data (or misunderstanding it), we are keeping it internal 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."


I must say I am puzzled that issues with (mis)understanding would necessitate removal of the creep data. It seems to me that the right way to approach engineering is to have data, and adequately explain its application, where such additional explanation might be appropriate. I had no trouble understanding the creep data that was on the Colligo site, and I'm sure there are plenty of sailors/riggers/naval architects who also would understand it.

BTW, it seems to me that some additional worked examples (building on the example of the Flying Tiger design previously given on the Colligo site) would have helped clarify the application of creep data.


So let me ask my key questions, because any further analysis depends on this:

*** Is the graph of creep data for Dynex Dux rope previously posted on the Colligo site reasonably accurate?

*** Also, is the equation that was overlaid on that graph reasonably correct for Dynex Dux rope applied to rigging, insofar as it represents the creep rate as a function of load and temperature?

[jfranta]

So let me ask my key questions, because any further analysis depends on this:

*** Is the graph of creep data for Dynex Dux rope previously posted on the Colligo site reasonably accurate?

*** Also, is the equation that was overlaid on that graph reasonably correct for Dynex Dux rope applied to rigging, insofar as it represents the creep rate as a function of load and temperature?[/quote]

Yes, the graph of creep data that was previously posted on our site is correct and references were listed on the graph. I can supply these if requested. The stretch numbers are correct also being verified by external sources.

When I first started advocating Colligo Dux rigging my first approach was to have graphs and charts in my booth. As an engineer, I am a big advocate of data. I even had a large easel at the Annapolis show the first year with several big posters of data in chart and graph form. I still have this in my office here. 98% of the people that I tried to get to look at the data lasted about 30 seconds before their eyes glassed over, including most riggers and even some well known boat designers, who we consider our customers.

From experience, we have found that it is much safer to work with individual customers in their specific applications when working out the sizing.

In addition, we have found several repostings of our data in various places on the web where we were not referenced and our competition was even recommended so there is also a proprietary reason for not keeping all the information posted. We are in business to make money. I am sure all can understand that. Again, we are willing to work with all on an individual basis.

We, at Colligo, will do all that we can to get all the data out on our products and, I believe that when you compare us to the other synthetic rigging options that you will find much more information from us. Just try to get info on PBO rigging from the manufacturers.

The internet is also a good source for any info on Gell Spun Ultra High Molecular Weight Polyethylene (Dyneema or Spectra).

Best Regards,

John Franta, Colligo Marine