Dynex Dux pull test- preliminary results

Just so there's no misunderstanding, I want to reiterate that I'm quite happy with the new rigging. I'm sure that what I'm seeing is the initial tightening of the braid. I think the rigger just didn't quite allow for enough initial adjustment. It's possible he didn't figure on the increased stability of a trimaran compared to a monohull of comparable size, or the quickness of the motion which adds more dynamic load to the rig.

One thing I like about the system is how easy it's been to adjust while sailing. I just go down to the leeward side to take up the slack if required, then so the same for the other tack. The line through the deadeyes is slippery enough to pull through, but it's not too hard to get a wrap around the bundle to tie it off before it slips back. If you need more grunt, take the tail around a cleat or winch and pull sideways on it. It just seems like less hassle than dealing with split pins, rigging tape, and tools to rotate a turnbuckle while holding the shroud from turning.

The message is, err on the short side when making up the stays so there's enough adjustment for the initial settling. It's not like there's a lot of weight associated with having the deadeyes a little farther apart in the end.

 

Thank you for the thread and data therein, most interesting... To reciprocate http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-25.html post #375 shows my built in chainplates, when deck is in position the whole boat will be as one piece... Over the next couple of weeks the chainplates to each bow (a 39 ft x 21 ft catamaran) and the 2 near the aft bulkheads will be built and the deck in place so bookmark the build as I will be posting as that is being done....

 

Downloaded the data loggers last night. Four loggers recording every 6 hours for 10 months results in a mountain of data. It will take me some time to make sense of it all but here are the basics:

I started the test at 2,000 lbf (8% of MBL) and for the first 2 months didn't see any creep at all so I boosted it to 4,000 lbf (15% of MBL) and saw about .025" over 2 months. Figured that was probably not valid because you really wouldn't design for that much static load. Dropped back to 10% MBL and the load varied between 2,600 lbf and 2,750 lbf from late march to now. Looks like the pump cycled about once a day.

November and December I had trouble keeping the temperature of the test rig steady. Solved that by adding a PID controller to the heating element in January. The test rig is heated but not cooled so the temperature was fairly steady at 65F through April then gradually rose through May and June and cycled between 80F and 95F in July and August.

The 24" test section elongated a total of .071". That would be about 1.77" in a 50' shroud but that is just the rough number. It will need to be adjusted for a couple of things..

I will try to find some time in the next few days to massage all these numbers in a spreadsheet. Definitely need to factor out the time it was at 15% MBL. May be able to get some figures on how the temperature effected the creep. During Foxy's Cat Fight at Jost Van Dyke last October I hung the sample in the rigging with a thermocouple and it never got above 80F even in direct noon sun so I may have to weigh the time when the rig got hotter than that.

 

Gashmore, so this is what gathering data is like huh? You set it up and wait and wait and wait.......

What diameter Dux were you measuring?

 

creep loads

Hey Gashmore glad to her this is still going on.

Doing some rudimentary research on common rig loads we found the flying tiger Sport boat tensioned their 1/4 inch shrouds to 1200 lbs-f. This is a very high static load for for standing rigging of this size (probably not too many boats set their pretension this high) so we would use 9mm Dux. We sue 12,00 lbs-f as an example for 7mm and 9mm usage comparisons. As you know Creep is exponentially related to load (see the creep tables on our site) so if the load goes up even slightly to 2,000 lbs static the creep will greatly increase.

Our calculations show for a 50 ft shroud in 9 mm dux, 4.000 lbs-f static load per year would result in over 10 inches of creep (per year). On the other hand 1,000 lbs-f per year would result in 0.05 inches per year for a 50 foot length in 9 mm. Point is choosing your load is critical and I think the 4,000 lbs-f load time period had a severe influence on your results. All of our creep data is from lab data generated at 22 degrees C.

John Franta, Colligo Marine.