Dyneema Thermal Expansion - Enough to Break Things?

[OneBoatman]

The Modulus of elasticity quoted in the literature varies with both alloy and Dyneema in the literature vary over a broader range than sometimes quoted some have the difference as 170 GPa vs 110 GPa where others are closer to your numbers. The Op I believe was talking bout the risk of conversion which may lead to failure. So if you tuned your rigging at high temperature and it dropped 50 Deg F the Dyneema gets longer and an aluminum mast gets shorter, so the net change in tension is less than the example in the OP. In that case your are not at risk of breakage but one may still wish to re-adjust.

[s/v Jedi]

Dyneema rigging isn’t sized for strength so don’t compare it like that (diameter would go down for Dyneema). Instead it is sized for creep.

Colligo Marine has tables for conversion.

[markxengineerin]

Since changing to the synthetic rig, I've sailed up and down the east coast USA, from Maine to Florida. When I left Maine last November w/ the brand new dyneema rig, it was -3C. A few months later, Florida was in the high 20s (C). I think having to adjust the rig is pretty annoying, and not planned for when I made the regrettable decision to go synthetic. I've always had to tighten, never loosen, which indicates creep being more of an issue than thermal expansion, although it might have to do with when I happened to make measurements. Example: rig is set cold, rig gets hot, tension goes up, creep happens, temperature goes back down, rig is measured again, it's loose from creep, needs to be tightened. I did not record the daily temperatures in between measurements, although maybe I could figure that out from where I was. I will organize my notes and make a better post on this when I have more time.

My nominal tuning target for the rig is based on a % of the breaking strength of the wire I replaced (15-17%, copied from the previous owner's notes, results of professional rig tuning and in line with other references I've found), nothing to do with the breaking strength of Dyneema, which is way too high to use in this way. The result is 1500 to 1800 pounds for the uppers, and backstay. Aiming any higher than a boat was originally designed for is a bad idea without more specific analysis, on an individual basis. Things you might not think of can happen- for example- my toe rail leaks have been getting worse, right near the chainplates. Coincidence? Stuff you don't have to wonder about with a wire rig.

I like the idea of an insert under the mast step, to compensate for the mismatch in thermal expansion. The book "Illustrated Sail and Rig Tuning" finally arrived to me today, and I hear it has a good explanation of the role of wire tensions. I plan to read up on that then think about the insert.

[scherzoja]

MarkX, thank you for working out that spreadsheet and detailing your experience moving from Maine to Florida. I it looks like swapping to Dyneema is not as straight-forward when I have large daily and seasonal temperature changes.

Thank you also to the rest of you who had input. Although I have spoken with John at Colligo (he thinks risk of breaking things due to thermal expansion is minimal), I want to understand it more completely and the discussion in this thread helps.

Regarding chain plates, I think they should be sufficient. They are external 3/8" bronze chain plates with five 1/2" bolts through 1/2" factory layup with an additional 1" epoxy/1708 layup that I did over a 12" wide area, per chain plate. In addition, the 1/4" backing plates are welded at 90 degrees to 1/4" plate that attaches to the original knees with five 1/2" bolts. The only unknown is the ability of the fiberglass hull (+ epoxy reinforcement) to resist distortion chain plate bolts ripping through.

https://www.cruisersforum.com/forums...es-254157.html

[markxengineerin]

Some more notes (disclaimers) on my experience
- I did not use the Colligo terminators, made my own, and they were ~1.5" diameter, round. I don't blame them for any of the tension changes I'm seeing, just noting that this was not a Colligo system. I did use their splicing instructions.

- My mast "hangers" (I have been forbidden to call them Cheeky Tangs by the Cruisersforum copyright police) failed, due to my own bad design, and damaged my mast. That all got repaired here
https://www.cruisersforum.com/forums...al-270891.html
and has been working great since. I note this because failure of the mast/mast termination fitting is another possibility if thermal effects are really as dramatic as the calculations are showing. I have studied shroud connection attachments as I walk around boatyards since then, and there are a lot of variations, some capable of high forces, some really anemic. Usually design looks proportional to the cost of the boat.

I have a feeling the effects are not as dramatic as the calculation, that there's something wrong with the assumptions. Maybe the effective modulus of dyneema is quite a bit lower than the number we're using. Maybe the hull can actually deflect a lot and not care. Maybe thermal expansion of dyneema # is wrong. Lots of possibilities. If I were Colligo, I would do some testing and provide more info for the more discerning customers who want to go beyond "tune it on a cold day and you're fine".

[s/v Jedi]

I’m trying to link a video concerning the pulling out of chainplates below. The interesting part starts at 1:20 minutes into the video and then at 16:30

https://www.youtube.com/watch?v=yvvyDdgUrrQ&t=80s

[Lee Jerry]

Originally Posted by markxengineerin

Since changing to the synthetic rig, I've sailed up and down the east coast USA, from Maine to Florida. When I left Maine last November w/ the brand new dyneema rig, it was -3C. A few months later, Florida was in the high 20s (C). I think having to adjust the rig is pretty annoying, and not planned for when I made the regrettable decision to go synthetic. I've always had to tighten, never loosen, which indicates creep being more of an issue than thermal expansion, although it might have to do with when I happened to make measurements. Example: rig is set cold, rig gets hot, tension goes up, creep happens, temperature goes back down, rig is measured again, it's loose from creep, needs to be tightened. I did not record the daily temperatures in between measurements, although maybe I could figure that out from where I was. I will organize my notes and make a better post on this when I have more time.

It's unfortunate you're having these issues, and as best I can tell it's also unusual. But I will reiterate that >25 degC is a pretty high range, so you may
just have to re-tune with these swings. SS rigging probably should be too, but since the change isn't as dramatic it goes unnoticed (and ignored). When your car moves between hot and cold the tire pressure should be adjusted. If / when you stayed in one climate more, that need should reduce (to maybe seasonal).

My nominal tuning target for the rig is based on a % of the breaking strength of the wire I replaced (15-17%, copied from the previous owner's notes, results of professional rig tuning and in line with other references I've found), nothing to do with the breaking strength of Dyneema, which is way too high to use in this way. The result is 1500 to 1800 pounds for the uppers, and backstay. Aiming any higher than a boat was originally designed for is a bad idea without more specific analysis, on an individual basis. Things you might not think of can happen- for example- my toe rail leaks have been getting worse, right near the chainplates. Coincidence? Stuff you don't have to wonder about with a wire rig.

That's what I'd expect (as a starting point). It's pretty low loading, though, for 11mm dyneema, like 5% of breaking. I know it's close to the creep limit that Colligo recommends. At that loading, the modulus may be even lower than the 66 GPa you derived (meaning the tension change is reduced).

But I don't see how rigging that is loaded the same as the previous could now be the cause of toe rail leaks.

I like the idea of an insert under the mast step, to compensate for the mismatch in thermal expansion. The book "Illustrated Sail and Rig Tuning" finally arrived to me today, and I hear it has a good explanation of the role of wire tensions. I plan to read up on that then think about the insert.

I don't see how that would work. At least not a passive insert. You'd need something with a higher negative coefficient than dyneema. But maybe I'm not seeing outside the box enough.

Originally Posted by markxengineerin

Some more notes (disclaimers) on my experience
- I did not use the Colligo terminators, made my own, and they were ~1.5" diameter, round. I don't blame them for any of the tension changes I'm seeing, just noting that this was not a Colligo system. I did use their splicing instructions.

- My mast "hangers" (I have been forbidden to call them Cheeky Tangs by the Cruisersforum copyright police) failed, due to my own bad design, and damaged my mast. That all got repaired here
https://www.cruisersforum.com/forums...al-270891.html
and has been working great since. I note this because failure of the mast/mast termination fitting is another possibility if thermal effects are really as dramatic as the calculations are showing. I have studied shroud connection attachments as I walk around boatyards since then, and there are a lot of variations, some capable of high forces, some really anemic. Usually design looks proportional to the cost of the boat.

I have a feeling the effects are not as dramatic as the calculation, that there's something wrong with the assumptions. Maybe the effective modulus of dyneema is quite a bit lower than the number we're using. Maybe the hull can actually deflect a lot and not care. Maybe thermal expansion of dyneema # is wrong. Lots of possibilities. If I were Colligo, I would do some testing and provide more info for the more discerning customers who want to go beyond "tune it on a cold day and you're fine".

Did you re-set the splices after you put them in? If not, that could be some of the 'stretching' you're seeing. Colligo recommends 3000 lb for 11mm. This is nearly half of your tune load, so if not set could be slowly working it's way out. (I hope that might be your issue.)

[markxengineerin]

as best I can tell it's also unusual.

Has anyone else ever measured?

SS rigging probably should be too

Here are the calcs for a stainless rig at the same 26C swing, 2.6X less of an issue vs. dyneema.

But I don't see how rigging that is loaded the same as the previous could now be the cause of toe rail leaks.

It's not loaded the same- a higher load happens when the desired tension is set at anything other than the maximum temperature. The odds of installing/tuning the boat on the hottest day of the year are 1/365...

I don't see how that would work. At least not a passive insert.

An insert that somehow directly compensates for the difference in delta T's doesn't seem realistic, but what about just something with low modulus, like the rubber pad someone suggested? If the mast were made out plastic/rubber/anything really low modulus, this thermal stuff wouldn't be a problem, but it would obviously cause other problems. I wonder if there is a compromise that is an improvement over not using any insert.

Did you re-set the splices after you put them in?

Yes, I used 4,000 pounds, measured with a load cell. I found that to get consistent lengths matching my target, I had to pre-stretch the line for a period of time, unload it, wait another period of time while it shrinks, measure and make my marks, do the first splice, load it up again for a period of time, unload, wait again, mark again, make 2nd splice, load up, wait, unload, wait, then check and confirm length. I was getting +/- 0.5" center to center with this method. The lengths keep moving over time, so this is all a compromise between getting the work done at a reasonable rate and getting close enough to the right length. Someone who does it all the time can figure out a quicker system, but not a DIY'er on 1st try.

[Lee Jerry]

Originally Posted by markxengineerin

Has anyone else ever measured?

I'm not aware of anyone having the issues to the extent that you seem to be having. (Obviously, that doesn't mean they don't or haven't though.) I have heard stories, including here on CF, of people happy with their fiber rigging.

Here are the calcs for a stainless rig at the same 26C swing, 2.6X less of an issue vs. dyneema.

Still a 25% change, in case that is significant...

It's not loaded the same- a higher load happens when the desired tension is set at anything other than the maximum temperature. The odds of installing/tuning the boat on the hottest day of the year are 1/365...

Those are the odds only if you choose a day at random. If your intent is to pick the hottest day, even a modicum of thought can improve those odds considerably. For example, just picking the proper season will improve it by 4 - it's unlikely the hottest day will occur in the winter (even with climate change ). And then further improvement with weather forecasting. But I don't think you need to hit the hottest day.

You said you load it the same as the previous wire as tuned baseline. The chainplates, if properly designed, should be able to withstand the full rated load of the original wire (and then some), so a "small" increase above baseline (even as high as 2x) should not be a problem. IMHO, anyway. The loads while sailing are higher than tuned. So as I said before, I'd recommend tuning for a medium seasonal temp twice a year. That way the swings would be more like +/- 7 degC instead of a 26 degC change.

Further, if your rig has any pre-bend, then I think the tension changes will be lower than predicted and will manifest as changes in mast shape.

An insert that somehow directly compensates for the difference in delta T's doesn't seem realistic, but what about just something with low modulus, like the rubber pad someone suggested? If the mast were made out plastic/rubber/anything really low modulus, this thermal stuff wouldn't be a problem, but it would obviously cause other problems. I wonder if there is a compromise that is an improvement over not using any insert.

I would think a low modulus pad would just compress and not do much.

There are boats that use mast jacks, hydraulic or screw, that could be adjusted as required.

[RaymondR]

So the choice is between constant attention to the weather or mast jacks, hydraulic or screw and the simplest device devised (a spring) to maintain a constant tension?

[Lee Jerry]

Yeah, I didn't say any of that.

What I said was: tune twice a year, once for warmer weather and once for colder weather. (If you live in a seasonal area.) You can include the creep adjustment at this time. The daily and weekly changes to the rig tension are acceptable. If you live in a more consistent climate, such as the tropics, you should only need to adjust for creep once a year.

IMHO

YMMV

[markxengineerin]

It has been difficult for me to study the impact of temperature on my dyneema rig, because I've mostly been moving from warm climates to colder climates, where any reduction in tension could be blamed either on creep or temperature change, and because I have continued making small adjustments.
But today I have gotten a datapoint that I think is valid, with no rig adjustment in between.
Going from Feb 29th (74F in Gibraltar) to today (April 20, 84F in Caribbean), the average tension in the rig (measured backstay, uppers, and lowers on Pacific Seacraft 37) increased by ~250 pounds each. If I plug these temperatures into the (very over-simplified) excel calculator, it predicts a change of 260 pounds per shroud.
Since temperature was increasing and tension going up, any creep during the time interval would reduce the apparent effect of temperature, so I consider this a minimum sensitivity value.

This is only one measurement, and a lot more data is needed to draw any conclusions, but so far, to me, it does look like the temperature sensitivity of a dyneema rig is pretty extreme. It would be interesting to get some data from boats with stainless steel rigs as well, to try to separate what normal mast/hull contributions are vs. what's unique to dyneema.

[s/v Jedi]

Originally Posted by markxengineerin

It has been difficult for me to study the impact of temperature on my dyneema rig, because I've mostly been moving from warm climates to colder climates, where any reduction in tension could be blamed either on creep or temperature change, and because I have continued making small adjustments.
But today I have gotten a datapoint that I think is valid, with no rig adjustment in between.
Going from Feb 29th (74F in Gibraltar) to today (April 20, 84F in Caribbean), the average tension in the rig (measured backstay, uppers, and lowers on Pacific Seacraft 37) increased by ~250 pounds each. If I plug these temperatures into the (very over-simplified) excel calculator, it predicts a change of 260 pounds per shroud.
Since temperature was increasing and tension going up, any creep during the time interval would reduce the apparent effect of temperature, so I consider this a minimum sensitivity value.

This is only one measurement, and a lot more data is needed to draw any conclusions, but so far, to me, it does look like the temperature sensitivity of a dyneema rig is pretty extreme. It would be interesting to get some data from boats with stainless steel rigs as well, to try to separate what normal mast/hull contributions are vs. what's unique to dyneema.

It is about the temperature coefficient being the reverse between Dyneema and aluminum. It would be interesting to compare Dyneema rigging between aluminum, wooden and carbon fiber masts.

With steel rigging and aluminum mast, the temperature coefficients work the same way so the effect is drastically reduced but is probably worse with carbon fiber masts while wooden masts will be almost neutral I think.

[OneBoatman]

When we have thoroughly licked all of the obvious problems, we move as smoothly as we possibly can to the what ifs, done right and quite regularly it become second nature. So, it seems even though you have answered your own predicament before the rest of us chimed in, no disrespect to it having provoked much attention including my own in this forum. The thing that came to mind is: Is your rig rug? That is what I used to say to my buddy just before we got on our sailboards to enjoy the aftermath of a hurricane. As engineers we sometimes look to the God of righteous materials and hope that at least a couple of the plusses act in our favor to cancel a good measure of the minuses, but only when necessary, and actually not really. What we do hope is that no others burn up any more fuel than necessary on the launch pad. And what if I just went sailing and never decided to become engineer.