Dyneema Thermal Expansion - Enough to Break Things?

[fourlyons]

Why can't you consult the load/elongation tables published by different manufacturers, say Marlow, and work backwards. For example a 9 mm sk99 core stretches 2 percent at 4000 kg, and 2.5 percent at 5000 kg. Now figure out what percent of your cap shroud, for example, is 1/2" of of the total length. 1/4" for the sk99 going one direction and 1/4" for the aluminum mast going the other direction. To make it easier lets convert to metric; let's say the shroud is 15 meters and the change in length is 12mm. 12 mm is a 0.08 percent change in elongation. In the table it took 1000kg to produce 0.5 percent increased elongation, so 0.08 is a little under 200kg. Pretty much what Colligo said, well more than 10 lbs, but still, not super significant for a rig with a design load of 30- 50,000 lbs.

What am I getting wrong here?

[s/v Jedi]

Originally Posted by fourlyons

Why can't you consult the load/elongation tables published by different manufacturers, say Marlow, and work backwards. For example a 9 mm sk99 core stretches 2 percent at 4000 kg, and 2.5 percent at 5000 kg. Now figure out what percent of your cap shroud, for example, is 1/2" of of the total length. 1/4" for the sk99 going one direction and 1/4" for the aluminum mast going the other direction. To make it easier lets convert to metric; let's say the shroud is 15 meters and the change in length is 12mm. 12 mm is a 0.08 percent change in elongation. In the table it took 1000kg to produce 0.5 percent increased elongation, so 0.08 is a little under 200kg. Pretty much what Colligo said, well more than 10 lbs, but still, not super significant for a rig with a design load of 30- 50,000 lbs.

What am I getting wrong here?

The thing is that the Dyneema is already pretensioned in the cold. I must admit that I know little of Dyneema rig tuning, but with stainless steel we pretension to 20% of breaking strength. From that point, when the Dyneema crimps and the mast expands, you can get to failure points quickly.

But yes, it must be relatively easy to calculate. How much does the mast expand, then with Pythagoras you can calculate how much longer the shroud should be. Then calculate how much the Dyneema crimps and add that up to the mast expansion number for total elongation of the Dyneema and see how close to breaking strength this puts you.

This leaves the chainplates as the big unknown factor. The bolts may pull through material, creating slots from the holes. This is where I expect problems first.

[Mark Johnson]

Originally Posted by scherzoja

I am considering re-rigging with Dyneema, but have a question about thermal expansion properties of Dyneema.

How much of an issue is thermal expansion with Dyneema standing rigging? I sail in an area where we get large temperature variations during the winter. As a cold front approaches, temps often rise to the mid 70s, then drop overnight into the low 40s / upper 30s when the front passes. Over the subsequent 3 or 4 days, the temp rises back to the 70s. Sometimes we'll get get a week or two of 40s at night / 60s in day. Then back to the 3 - 4 day freeze/thaw cycle.

This is a typical temperature cycle in the 2 or 3 winter months. During this type of temperature change, will Dyneema expand enough during the cold periods to cause too much slack in the rigging to cause issues with the tuning of the mast?

Fall/Spring temps are fairly stable and from June to about November, the temps rarely go below 80 degrees (90s in day, 80s at night). If I re-rig with Dyneema, will I have to retune the rig twice a year (summer vs winder temp ranges) or more?

Is there a temperature range within which the cold-expansion is not noticeable. Is the expansion linear across a temperature range or does it expand more at colder temps (< 40 degrees)?

I found this factor for cold-stretch: For every change of one degree Kelvin, one meter of Dyneema expands 0.000012 meters.

If my temp ranges from 70 degrees to 40 degrees (294.3K to 277.6K), that is a temperature change of 22.2K
With an upper shroud of 15 meters long, that means it will expand almost 3/16" (~4mm)

(22.2 K temp change * 0.000012 meters)*15 meters = .00405 meters, or 4.05 mm or .1597 inches


Is this calculation correct? How does the line diameter factor into thermal expansion?

Does "heat set" dymeema follow this thermal expansion formula?

If the rigging is tuned for 40 degrees and each week the temp rises to 70 degrees, then falls back to 40 or below, will this cycling cause enough fatigue in the metal parts connected to the standing rigging to be an issue? The metal parts are the chain plates, toggles, turnbuckles, mast tangs, mast tang fasteners (#10 machine screws in aluminum mast as well as 1/2" through bolt through mast)?

Another way to look at this with the temp change over a 24 hour period. Regardless of the absolute temp or time of year, the typical temperature change from day to night is between 20 and 30 degrees (higher range in low humidity condition). Late summer, this range shrinks to 10 or 15 degrees (humidity is very high during August and September).

With a 30 degree change, a 50' shroud will expand/contract by 4.05mm (almost 3/16")
With a 20 degree change, a 50' shroud will expand/contract by 3.05mm (almost 1/8")

How fast does the cold-expansion occur. For example, in the summer, a squall line will pass through and drop the temp by 20 degrees over a 30 minute period while we get 25 or 45 knots. Winds will get light again and temp will rise 10 or 15 degrees for the rest of the day. Twenty degrees is about 1/8" elongation, but how long will it take to shrink that much? 15 minutes, 10 hours, days?

How much of a difference in sailing performance will 1/8" make to sail shape and/or rig stability?
I don't race, I used to. Now I just sail, but I don't like scallops or incorrectly trimmed sails.



Thanks

The issue is whether or not you have a tune sensitive rig. Dyneema does not expand or contract like SS wire does. It does so, but FAR less.
If your Dyneema rig is tuned perfectly for 90°F+, then on a 50° day, it will be slack, because the aluminum mast contracts far more than the rigging.

With SS wire rigging, the wire and mast are contracting or expanding at a somewhat similar rate, so this is not an issue.

Some folks use SS on diamond stays to stay perfectly tuned, then a triangular Dyneema stayed mast, allowing it to vary.

[parkstone bay]

If the string elongates in warm weather, and shrinks in cooler weather (which I'm not arguing about), surely the same question would apply to people with steel rigging? Possibly even more because steel will expand/contract per degree of temperature change more than string - (I think). So, I suggest that if steel rigging people don't find an issue with temperature changes- or at least cope with it - so can you.

[Knotical]

Originally Posted by parkstone bay

If the string elongates in warm weather, and shrinks in cooler weather

If by string you mean Dyneema it will shrink in warm weather and stretch in cold weather.

[parkstone bay]

Originally Posted by Knotical

If by string you mean Dyneema it will shrink in warm weather and stretch in cold weather.

OK if it works differently from most other other materials that the Great Navigator ever made in that it shrinks in heat, and expands in cold, it doesn't negate my point. Those who have standing rigging of metal (which DOES expand with heat, contract with cold) have solved the issue. In fact, IS there an issue?
The OP was concerned that normal daily temperature changes would affect his rigging, and, specifically, its "infrastructure" (chain plates, turnbuckles, etc).
I SUGGEST (though I'm very willing to be corrected), that the thermal expansion of steel is more than that of Dyneema. On this basis, my point was that the OP may in fact be worried over a negligible point.

[s/v Jedi]

Originally Posted by parkstone bay

OK if it works differently from most other other materials that the Great Navigator ever made in that it shrinks in heat, and expands in cold, it doesn't negate my point. Those who have standing rigging of metal (which DOES expand with heat, contract with cold) have solved the issue. In fact, IS there an issue?
The OP was concerned that normal daily temperature changes would affect his rigging, and, specifically, its "infrastructure" (chain plates, turnbuckles, etc).
I SUGGEST (though I'm very willing to be corrected), that the thermal expansion of steel is more than that of Dyneema. On this basis, my point was that the OP may in fact be worried over a negligible point.

You don’t get it. When an aluminium mast expands in the heat, the steel stays and shrouds also expand and everything is okay. But Dyneema shrinks, so not only is there the mast expanding and requiring longer stays and shrouds… but those stays and shrouds become shorter. This is the big problem.

When you have a Carbon fiber mast, it’s thermal expansion goes the same way as Dyneema and everything is okay again.

[opusnz]

I am surprised how things always seem to get so complicated on these boards. I have dyneema rigging. As others have said, the aluminum mast expands more in the heat than the dyneema.

On hot days the rigging is slightly tighter than on cold days. Since the dyneema is so low stretch, once you are setup, it makes no difference when I am sailing. I wouldn't care a bit about it unless you are on an extreme, finely tuned race boat.

FWIW, aircraft control rigging has the same problem. They give a range of tension and have an allowance depending on temperature.

[Renoirpierre]

Originally Posted by scherzoja

Jedi,



Does anyone know if a formula exists that I can use to calculate the force exerted when dyneema shrinks? If we know the starting tension (1000 lbs) and dyneema shrinks 1/4" or 3/8", how many additional pounds are exerted on the end fittings? I suppose the same formula that calculates force when a turnbuckle is screwed down 1/4". I don't know that one either.



Thanks again y'all.

I think you will find that thermal stress is equal to

Stress=-E*a*dT

Here E is the modulus of elasticity of your material, a is the coefficient of thermal expansion, and dT is change in temp.

This is the part that I might screw up. You have 2 different materials acting together. I think I would use the difference between the two coefficients of thermal expansions as together they reflect a the total length-less growth component and then I would use the E of your mast. (I suggest mást as the cross sectional area (see next paragraph) of the rigging might be hard to determine)

Take the stress and multiply it by your cross sectional area of your mast and you should have your forces assuming nothing bends (like your boat).

If I got this wrong I’m sure the better engineers here will correct me.

Watch your units!!

BTW I’m an engineer that deals with people a lot more than numbers so I’m likely wrong somewhere.

[s/v Jedi]

Originally Posted by opusnz

I am surprised how things always seem to get so complicated on these boards. I have dyneema rigging. As others have said, the aluminum mast expands more in the heat than the dyneema.

On hot days the rigging is slightly tighter than on cold days. Since the dyneema is so low stretch, once you are setup, it makes no difference when I am sailing. I wouldn't care a bit about it unless you are on an extreme, finely tuned race boat.

FWIW, aircraft control rigging has the same problem. They give a range of tension and have an allowance depending on temperature.

No, Dyneema doesn’t “expand less than aluminium”: when Dyneema expands, aluminium shrinks and when Dyneema shrinks, aluminium expands. They go on opposite ways.

The reason that you are fine is that the temperature differences you experience are smaller.

[BjarneK]

As others have said above, these things can be calculated. Aluminium has a coefficient of thermal expansion of about 13 ppm / deg C and for dyneema it is about -12 ppm / deg C. Amsteel Blue SK-78 elastically stretches 0.46 % at 10 % of breaking load. For the sake of argument, let us assume that the mast and the dyneema is parallel and only thing to stretch or compress is the dyneema. Then the change in shroud tension with one deg C change in temperature is (13e-6 + 12e-6) / 0.0046 * 0.10 * BL = 5.43e-4 * BL, where BL is the breaking load.

This means that for 12 mm Amsteel Blue with a breaking load of 15,400 kg, one deg C change in temperature will change the shroud tension by 8.37 kg. On my boat, the shroud tensions are around 800 kg, so if I had 12 mm dyneema shrouds and I tuned them at 20 deg C, the tension should stay within 21 % of the desired value from 0 deg C to 40 deg C.

In reality, the mast might compress a bit, the hull might bend a bit, etc. This means that the change in tension will be less. The elasticity for Amsteel Blue is less at higher loads, so if a shroud is tensioned to 20 % of the breaking load of the dyneema, the calculated change in tension will be larger. The elastic stretch of Amsteel Blue between 10 % and 30 of breaking load is 0.25 % per 10 %, so the calculated change in tension for this range is about twice the above value.

Looking at the Dynice Dux page, it looks like the elastic stretch behavior is similar to Amsteel Blue:

https://hampidjan.com.au/product/rop...nice-dux-rope/

I guess the big difference to Amsteel Blue is in creep, not stretch. So the above calculations more or less also apply to Dynice Dux.

[s/v Jedi]

Originally Posted by BjarneK

As others have said above, these things can be calculated. Aluminium has a coefficient of thermal expansion of about 13 ppm / deg C and for dyneema it is about -12 ppm / deg C. Amsteel Blue SK-78 elastically stretches 0.46 % at 10 % of breaking load. For the sake of argument, let us assume that the mast and the dyneema is parallel and only thing to stretch or compress is the dyneema. Then the change in shroud tension with one deg C change in temperature is (13e-6 + 12e-6) / 0.0046 * 0.10 * BL = 5.43e-4 * BL, where BL is the breaking load.

This means that for 12 mm Amsteel Blue with a breaking load of 15,400 kg, one deg C change in temperature will change the shroud tension by 8.37 kg. On my boat, the shroud tensions are around 800 kg, so if I had 12 mm dyneema shrouds and I tuned them at 20 deg C, the tension should stay within 21 % of the desired value from 0 deg C to 40 deg C.

In reality, the mast might compress a bit, the hull might bend a bit, etc. This means that the change in tension will be less. The elasticity for Amsteel Blue is less at higher loads, so if a shroud is tensioned to 20 % of the breaking load of the dyneema, the calculated change in tension will be larger. The elastic stretch of Amsteel Blue between 10 % and 30 of breaking load is 0.25 % per 10 %, so the calculated change in tension for this range is about twice the above value.

Looking at the Dynice Dux page, it looks like the elastic stretch behavior is similar to Amsteel Blue:

https://hampidjan.com.au/product/rop...nice-dux-rope/

I guess the big difference to Amsteel Blue is in creep, not stretch. So the above calculations more or less also apply to Dynice Dux.

Agree. So for the OP with a wort case temperature swing of 20 degrees Celsius, when they tension during the cold to 800kg tension, it goes up to almost 1,000kg, well within safety limits of the Dyneema, so it all comes down to the chainplate bolts.

The Dyneema does well because it is sized for creep rather than strength, which means it’s always oversized.

How did you get to the 800kg pretension? Was this 20% of the old stainless steel breaking strength?

[BjarneK]

Originally Posted by s/v Jedi

How did you get to the 800kg pretension? Was this 20% of the old stainless steel breaking strength?

I still have stainless steel shrouds and stays, my numbers were just what I would do if I had dyneema instead to get the same tension as I currently have on my stainless wires.

I don't have a gauge, so I did approximate measurements of all my stays and shrouds (except forestays which have roller furling). The measurements were done one shroud or stay at time and the method was this: I brought it in vibration and filmed it while vibrating. I could then step the movie frame by frame to determine the frequency. Knowing the length and weight of each wire, I could calculate the tension according to this: Standing Waves on a String

Starboard and port tensions for the corresponding shroud or stay (I have two backstays) were quite similar, which was reassuring. To check the numbers further, I also did a 5 kg sideways pull on one shroud and measured the deflection. The numbers agreed nicely. The range is around 600 kg to 1,000 for the different shrouds and stays I have. The boat is aluminium, so high tension does not bend the hull much.

[s/v Jedi]

Originally Posted by BjarneK

I still have stainless steel shrouds and stays, my numbers were just what I would do if I had dyneema instead to get the same tension as I currently have on my stainless wires.

I don't have a gauge, so I did approximate measurements of all my stays and shrouds (except forestays which have roller furling). The measurements were done one shroud or stay at time and the method was this: I brought it in vibration and filmed it while vibrating. I could then step the movie frame by frame to determine the frequency. Knowing the length and weight of each wire, I could calculate the tension according to this: Standing Waves on a String

Starboard and port tensions for the corresponding shroud or stay (I have two backstays) were quite similar, which was reassuring. To check the numbers further, I also did a 5 kg sideways pull on one shroud and measured the deflection. The numbers agreed nicely. The range is around 600 kg to 1,000 for the different shrouds and stays I have. The boat is aluminium, so high tension does not bend the hull much.

Wow!

I measured how much a 2 meter length stretched and thought that was freaky hahaha

[OneBoatman]

The coefficients of thermal expansion for the materials you are discussing are pretty much of a similar magnitude. Dyneema, Aluminum, and Stainless steel all expand as temperature increases and contract as temperature decreases. They are not all dead equal, but they move similarly. Your rig will do it's job if tuned properly and not require re-tuning to prevent damage because your mast get shorter and so do the shrouds, change of less than .2 inches over a length of ~50 ft. is not enough to cause you a problem. You might want to re-check your tune if you are sailing from the Caribbean up through the Northwest Passage.