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 Boat Design Forums Synthetic rigging properties?

#1
09-02-2008, 01:27 PM
 Gashmore Junior Member Join Date: Feb 2008 Rep: 58 Posts: 52 Location: Macon, GA
Synthetic rigging properties?

Thanks to Yade's mast load speradsheet I have a much understanding of the loads on my rigging. Shrowd loads came out very close to the numbers I got using two other methods. Now I need to apply it to Dynex Dux and find that trying to get structural data on fiber is frustrating. For example a chart will show a creep of so many inches/year at 20% load but don't say how long the line was. A half inch of creep in a foot of rope is pretty poor but in a 65 foot cap shroud it is pretty good.

The factor I really need though is the Young's Modulus (E) to figure the elongation at a particular load and diameter. With 1x19 you would use an E of 107GPa. The Hampidjan brochure says "3% stretch" which I assume is the stretch at breaking strength ( A number I do not care to verify) and an elongation of "120 N/tex". Is that used the same as Young's Modulus?
#2
09-03-2008, 04:54 AM
 Omeron Senior Member Join Date: Feb 2007 Rep: 31 Posts: 163 Location: Istanbul
Thanks.
#3
09-03-2008, 06:40 AM
 Gashmore Junior Member Join Date: Feb 2008 Rep: 58 Posts: 52 Location: Macon, GA
Truly a work of Excel art. It is really intended to calculate mast loads on a triple spreader rig but along the way he calculates the shroud/stay loads and just about everything else.

I had previously used the formulas proposed by Larsson & Eliasson and Gutelle's "simplified" method and all three results come out comfortably within range of each other. The best part is you can change almost any variable and see what it does to individual members and graphically watch mast bend. If you poke around in the spreadsheet you can find the compression loads on the spreaders and lots of other details.

The only thing I would like to see added is the ability to choose other than Nitronic 50 or 1x19. As I said, I am seriously considering Dynex Dux and I believe the modulus is a little higher than 1x19 and lower than Nitronic 50 but I am not sure how to translate from the N/Tex that rope makers use to Young's Modulus that structural engineers use. There are only 4 sizes of Dynex that are of practical use in most standing rigging and I am a little concerned that a much higher modulus in a larger line like D1 might create a stress point in the mast bend.
#4
09-04-2008, 01:14 PM
 RHough Retro Dude Join Date: Nov 2005 Rep: 793 Posts: 1,792 Location: BC Summers / Nayarit Winters
Quote:
 Originally Posted by Gashmore The only thing I would like to see added is the ability to choose other than Nitronic 50 or 1x19. As I said, I am seriously considering Dynex Dux and I believe the modulus is a little higher than 1x19 and lower than Nitronic 50 but I am not sure how to translate from the N/Tex that rope makers use to Young's Modulus that structural engineers use. There are only 4 sizes of Dynex that are of practical use in most standing rigging and I am a little concerned that a much higher modulus in a larger line like D1 might create a stress point in the mast bend.
IMO braided line for standing rigging is a poor choice.

I don't know of a fiber manufacturer that states a safe working load more than 20% of rated breaking strength.

A equal diameter rope will stretch more than steel wire under the same load.

To get equal stretch at the same load, the rope diameter (and windage) will be higher than that of steel.

The new custom made PBO paralell filament rigging is the best choice I know of. It is lighter for the same stretch as steel. You just cannot buy a roll of it and build your own rig.

Of course the cost of PBO makes Spectra/Vectran/Dyneema look cheap. At to that a 3 year maximum service life before replacement and the PBO option is for serious racing with a large maintenance budget.

The idea of buying a bunch of rope and splicing up your own rigging is attractive. Just don't expect to get the same performance as a professionally built rig. If you really want to do it yourself, buy the wire and some mechanical end fittings and do it that way. (Only 3 times more expensive than having the wires built for you).
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#5
09-04-2008, 03:34 PM
 Gashmore Junior Member Join Date: Feb 2008 Rep: 58 Posts: 52 Location: Macon, GA
You need to look at this Dynex Dux. It is Dyneema SK75 12 strand coated with a UV protectant then pre-stretched and heat set to remove any construction creep. While at a 5:1 safety factor the diameters required are slightly larger than 1x19 at 2.5 -2.8 the up weight savings are fantastic. It has been in use for about 5 years now and seems to be very popular in Australia. All the users and riggers that are familiar with it that I have talked to have seen very little if any creep. It is also Lloyd's approved and even more important it is OK with my insurance company. :-)

According to Hampidjan's charts the dynamic stretch of Dynex Dux is actually less than a 1x19 with similar breaking strength under the same load. Given the higher safety factor dynamic stretch in actual use will be even less.

Right now I am more worried that with the higher elastic modulus the thicker line required for D1 might not stretch proportionately to all the other rigging members. That could cause an uneven mast bend and create a higher stress point.

Other than that the only worry is a crazed machete wielding Haitian. :-)
#6
09-04-2008, 09:52 PM
 RHough Retro Dude Join Date: Nov 2005 Rep: 793 Posts: 1,792 Location: BC Summers / Nayarit Winters
Quote:
 Originally Posted by Gashmore You need to look at this Dynex Dux. It is Dyneema SK75 12 strand coated with a UV protectant then pre-stretched and heat set to remove any construction creep. While at a 5:1 safety factor the diameters required are slightly larger than 1x19 at 2.5 -2.8 the up weight savings are fantastic. It has been in use for about 5 years now and seems to be very popular in Australia. All the users and riggers that are familiar with it that I have talked to have seen very little if any creep. It is also Lloyd's approved and even more important it is OK with my insurance company. :-) According to Hampidjan's charts the dynamic stretch of Dynex Dux is actually less than a 1x19 with similar breaking strength under the same load. Given the higher safety factor dynamic stretch in actual use will be even less. Right now I am more worried that with the higher elastic modulus the thicker line required for D1 might not stretch proportionately to all the other rigging members. That could cause an uneven mast bend and create a higher stress point. Other than that the only worry is a crazed machete wielding Haitian. :-)
Construction elongation is one factor.
Recoverable elastic stretch is one factor.
Non recoverable stretch is one factor.
Creep is one factor.

Construction elongation is not stretch.
Recoverable elastic stretch is what the E factor is how this is predicted.
Non recoverable stretch is is due to a structural change after the material is stressed past the elastic limit.
Creep is a physical property of the material.

Dyneema creeps, it creeps due to it's physical properties. It does not matter what you do to it, it creeps.

What you (and most people) miss is not the breaking strength to weight ratio, but the stretch to weight ratio. No laid or braided construction will have the resistance to stretch that a single element has. At a given load, the material stretches as a percentage of length. The elements in laid wire rope (1x19) are longer than an equal weight of rod the same finished length. For the same cross sectional area the laid cable will stretch more since the element are longer than the rod.

The best laid rope (Zylon/PBO) stretches about 2% of it's length at 20% of tensile and over 3% at 30% of tensile.

To make a comparison, you must calculate the actual stretch of the rigging element. A 40 foot shroud in 302 alloy SS 1x19 stretches 1 inch at 20% of tensile. If the 1640 # you use 1/4" dia wire. That is 0.2% of its length.

If we assume that Dynex Dux has half the stretch that Zylon has you still have a rubber band for rigging compared to steel.

To limit the physical stretch to that of 1x19 wire, you have to load the line to something like 1% of tensile. For your 1640 pound load, you need a 164,000 pound tensile line. I can almost guarantee you that *for the same stretch* the high modulus fibre will weigh as much or more than the steel, and have much greater diameter.

That is day one when the rigging is brand new. The physical nature of the high modulus fibres is that they rely on long molecular chains for their strength. Just the internal chafe due to braided or laid construction starts breaking those long chains into short chains. The line gets weaker every time the tension changes. A 20% loss in tensile in 3-5 years is as good as it gets. Steel does not have this problem.

As a rigger, I have to go through this several times a year ... sometimes several times a day during boat shows.

It is my opinion that steel is the best solution for standing rigging and most halyards. I can prove it. Only if you are willing to allow more stretch for the same load can you save weight aloft ... it changes everything ... if you replace a steel rig gang or halyard with line *of the same tensile strength* you will wonder why the rig went soft. You won't like the result.

I just spent 30 minutes at the Hampidjan site:

Quote:
 The Dynex Dux 75 is a new generation of ultra high performance ropes. It is far stronger than the Dynex 75 or by some 20% up to 43% in the smaller diameters. The rope is very firm and compact with smooth surface. Elongation is very low or about 3%. The base material is Ultra High Molecular Weight Polyethelene, refined by DSM in the Netherlands and marketed as Dyneema. Well known for some years now, it is sold to rope makers, sail makers, fabric makers world-wide. The fiber is also known as Spectra, Plasma, UHMWPE etc... Hampidjan adds a secondary heating/tensioning treatment, UV protective and abraision resistance coating, 12 braids, and markets it as Dynex 75. However, the achilles heel of of the High Density Polyethelene seems to be cold creep: permanent deformation from a continuous load, measured over time (months and years) at a given temperature. Hampidjan has test data showing that a rope put under a load of 50% of its minimum breaking strength at 20C will creep past 10% (recommended elongation limit) after 7 months ; not a very useful length of time for holding up a mast. However when the sustained loads are at 20% of the minimum breaking strength at 20C (74F) for a year, 0.5% creep is encountered. A drop in temperature 10C (50F) will improve the time by a factor of 3 to 4. Easing shroud tension when not in use for extended periods can also help.
It's the same as Spectra, it elongates 3% (under an unspecified load), and it creeps. .5% creep is huge! 2.4 inches every year on a 40 foot shroud? A steel shroud won't strech 2.4 inches in it's entire life.

Say you are going to replacse you rigging gang every 3 years.
Say you use the 20% load and 3% stretch (reasonable numbers for Dyneema/Spectra) Just to set the intial rig tension, you need 14.4 inches of adjustment. Then the rig gets 2.4 inches longer each year due to creep. After 3 years that is 7.2 inches (on a 40 foot shroud), add the adjustment range you need to pre-tension the rig and you get dead eyes 22 inches off the deck.

Are you convinced yet?

Spectra for standing rigging is a very poor choice. I've set all the fibers up under tension on a rig bench. By the time you get that 1 inch of stretch that your 302 alloy SS wire gives you, you need nearly an equal weight of spectra.

The only way to save rigging wieght with Spectra/Dyneema is to put up with more stretch ... every gust streches the rigging first ... then drives the boat ... stretch in standing or running rigging is a performance thief.

Bottom line, if it stretches more than 1x19 ss wire ... it is a bad choicefor standing rigging.
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#7
09-13-2008, 11:36 AM
 jfranta Junior Member Join Date: Sep 2008 Rep: 52 Posts: 16 Location: Mesa AZ
Quote:
Dynex Dux is not the same as spectra. Dux is made from SK-75, the same base material as spectra but it is stretched at load in a steam autoclave which results in 2 basic changes from sk-75:

1. The Constructional stretch is virtually eliminated for lower loads as a percentage of breaking strength as the braided strands are compacted.

2. The polymer is work hardened that results in a significant increase in strength and toughness. Dux is the toughest braided line yet. In fact the hardest part of splicing it, is cutting it. It is not like any UHMWPE line you have seen, spectra, dyneema, etc. It is so stiff that when you splice it you can push the bury portion of the line thru instead of using a fid to pull it thru (a 72x diameter bury!). In fact. the stiffness of the line reqiures (Hampidjan requirement) a 5/1 dia/dia ratio of thimbles/line which is why we designed our line of hardware.

So, constructional stretch is close to zero for our load conditions. The Elastic (material) stretch is slightly less than that of 1x19 stainless wire, size for size. Please see our stretch chart on our website for line sizes appropriate for sailing vessels. The elastic stretch number that Hampidjan gives on their site is a breaking strength.

We have a partner in Alaska (commercial fisherman) that started using Dux for his net towlines to replace wire rope and started cracking winches because of the low stretch.

I agree with your above statment, "if it stretches more than 1x19 wire it is a bad choice for standing rigging", Dynex Dux Does not stretch more than 1x19 stainless.

The main design limitation of Dux for standing rigging is Creep. But if used correctly you can design around it. An understanding of static loads is required. We use an experimentally determined equation for creep, please see the reference on this at our website. Also the curves for 7,9,11,13 mm Dynex Dux Creep are shown for a 50 ft shroud, load versus creep per year. If you study the chart you will see that creep is certainly a manageable property. The example we always give is on the Flying Tiger 1 design boat, they currently use 1x19 stainless shrouds tensioned to 1200 lbs-f. If you replace them with 7 mm Dynex Dux at 15,000 lbs-f breaking strength (3,000 SWL) you will experience about 0.5 inches of creep per year. If you replaced the shrouds with 9 mm Dynex Dux you will get about 0.1 inches per year of creep (1 inch in 10 years!). Keep in mind that 1200 lbs-f static loading is considerable and most boats of this size will not have near that static load.

Many sailors and even riggers get Creep confused with Constructional stretch (some call this Set), stating there experience with amsteel or spectra that immediately started creeping and did not quit. what they have been experiencing is constructional stretch, creep happens over time (load dependent).

Another design consideraton for Dux is UV resistance. Intitial information and experience on sk-75 is that it has the best UV resistance of any uncovered synthetic line. The Univ of Aukland completed a study showing some initial, external, UV damage is experienced but then the outer shell becomes somewhot opaque to UV, slowing down the damage considerable. We are conducting some testing in Mexico and will soon have some numbers (up to 1.5 years exposure now) but UV happens over time also and I have not been able to find reliable accelerated UV test procedures for Polymers. Most will say you should have at least 5 years now. You can also cover Dynex Dux which will obviously extend the UV life of it.

We have also seen inexperienced people splice Dux and not reset the braid after splicing and claim they have experienced Creep. Splicing upsets the braid and it needs to be pre- stretched before use if no elongation is expected.

Dynex Dux does have its limitations like any other material but if those limitations are understood, it is a great material for standing rigging. The ease of installation, lightweight, lack of corrosion, UV resistance, and low cost compared to the Parrallel Synthetics are very attractive and should be considered by all riggers and designers.

We have been rigging a lot of boats with this stuff. A partner in Sydney, Strongrope has rigged a boat with Dux using traditional, low travel, turnbuckles, over 1.5 years now and no stretch or creep problems. See it at http://strongrope.com/fibre-rigging.htm.

I was just informed that Marlow is now using the same process on their brand of SK-75 also as I am sure they see the advantages of a low stretch single braid Synthetic.

We have a booth again this year at the Annapolis show if anyone is interested in seeing Dynex Dux. Also, let me know if you have any questions.

If anyone wants a sample of Dux, let me know.

jfranta@colligomarine.com
#8
09-13-2008, 03:16 PM
 RHough Retro Dude Join Date: Nov 2005 Rep: 793 Posts: 1,792 Location: BC Summers / Nayarit Winters
Quote:
 Originally Posted by jfranta Dynex Dux is not the same as spectra. Dux is made from SK-75, the same base material as spectra but it is stretched at load in a steam autoclave which results in 2 basic changes from sk-75:
It does not change the basic chemistry of the material, or it would be a new fibre.

Quote:
 We have a partner in Alaska (commercial fisherman) that started using Dux for his net towlines to replace wire rope and started cracking winches because of the low stretch
So the same lack of elasticity will shatter mast fittings?

Quote:
 I agree with your above statment, "if it stretches more than 1x19 wire it is a bad choice for standing rigging", Dynex Dux Does not stretch more than 1x19 stainless.
You have not proved that.

Quote:
Thanks for posting a well thought out response.

May I ask a few questions?

What is the load limit of elastic stretch? 50% of breaking? Yield strength is much more important number than what the textile industry calls tensile or breaking strength.

The FT uses 1/4" 1x19 SS wire. A 1200# static load is about 15% of tensile. The wire is elastic to 55-65% of tensile, at least 4000# load. This exceeds the SWL of 7mm Dynex Dux, so you cannot compare 7mm DD to 1/4" SS 1x19 you must use 9mm.

If 4000# exceeds the elastic limit of the rope, the rig will not hold it's tune as well as SS. Static tuning loads are only one factor, never exceeding the elastic limit of the material is another.

These things cannot be considered in isolation.

Every rigger has seen SS shrouds stretched to deformity, and rigs that are no longer tunable. Can you provide data that shows the yield characteristics of Dynex? Why is safe working load 20% and not the 55-65% of steel?

Of course you can just use bigger rope and still save weight right? What about windage?

A 50' x .354" (9mm) shroud has just over 40% more projected area than a 50' x .250" shroud. The 9mm rigging will have over 40% more aerodynamic drag than the 1/4" rigging. When you add 1mm of chafe and UV protection to the 9mm Dynex, you have a shroud that is 11mm in diameter (.433") ... now you have more than 70% more aero drag.

There are a good number of cruising boats that can barely sail to weather as it is, they will be that much worse with Dynex.

I think recommending DD as a replacement for SS wire without sharing all the facts is misleading.

No insult intended to Gashmore, but I don't think he/she is an experienced rig designer.

I see you do qualify some of the claims here: Link

SS wire you chose is 316 alloy, not 302 ... so you picked the weaker (15%) wire for the chart ... oh ... and you used a single strand of SK-75 for your estimates ... and you assume no constructional stretch ... and you claim Dynex Dux is 20% stronger than "non-post processed" SK-75.

Single strand? That means the data was collected on unbraided SK-75?
No constructional stretch? What you call constructional stretch is post-assembly stretch. You are quite right, assembly stretch can be removed by pre-tensioning the line. True construction stretch comes from how the fibres or strands are laid or braided. Any laid or braided construction has more stretch than a single filament. That is one reason the *same weight* of rod, stretches less than wire rope.

I see you use a Mobius Brummel splice. How many have you had tested to failure? The last time I was at the testing facility at Samson, we proved that any brummel weakens the rope unacceptably. The rope ALWAYS fails at the intersection. The only thing to recommend that splice is that it does not need to be locked. Testing to failure shows that a simple tuck and bury splice is much stronger (it must be lock stitched however). The strongest splice was a total 63 x diameter bury, with the first 21 diameters untapered. These samples fail at random points, not always at the intersection of the bury.

I'd love to see some new data that shows the conclusions I have come too are wrong. One thing I'm pretty sure of, an unbiased comparison is not likely to be had from someone that is trying to sell rope so people can build 'Do It Yourself' rigging.

For very high performance boats, with carbon spars and every other trick to save weight aloft, the trade off between higher drag and less weight aloft seems to favour less weight. Decreasing pitch and roll might overcome the very real drag penalty.

Just once, I'd like to see someone with something to sell show a fair comparison on their website.

At least compare the weight of the entire rig (everything above the deck) when you make the weight savings claims.
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#9
09-13-2008, 04:11 PM
 masalai masalai Join Date: Oct 2007 Rep: 1882 Posts: 6,847 Location: cruising, Australia
Thanks Mr "Retro Dude", jfranta, and for the thread Gashmore, for a most interesting discussion. I appreciate it very much....
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#10
09-13-2008, 05:21 PM
 Gashmore Junior Member Join Date: Feb 2008 Rep: 58 Posts: 52 Location: Macon, GA
I am not an experienced rigger but I am a licensed structural engineer. I need hard numbers to make a reasonable judgment which is the reason for my original post. Hampidjan is primarily in the commercial marine business where stretch is not as important as it is in rigging so getting numbers I can work with is hard to do. I did find that the "3% stretch" is at breaking load. OTOH, I have found the stretch rate of 11mm Dynex Dux to be .001205mm/mm/1000kg (.00055in/in/1000lb). I have also found that weight per diameter rather than cross sectional area is a valid means of estimating the stretch rate of high modulus ropes. From those two pieces of information I calculated the stretch rates for the sizes I might need and the 1x19 (from Navtec data) with the closest stretch . (in/in/1000lb)
7mm = .00134 ~ 1/4" @ .001306
9mm = .00084 ~ 5/16" @ .000833
11mm = .00055 ~ 3/8" @ .000580
13mm = .00040 ~ 7/16 @ .0004255

It appears that the primary consideration in designing for Dynex Dux is creep. Creep is geometrically related to the static load as a percentage of MBL. If a factor of 6 times the design maximum load is used the static load will be under 8% to 10% and creep will be extremely low. Using a safety factor of 6 for Dynex Dux and 2.8 for 1x18 (from the Navtec data and ignoring the metric sizes) the equivalent sizes at similar design loads are:
7mm (2735 lb) ~ 1/4" (2536 lb)
9mm (4421 lb) ~ 5/16" (3,679 lb)
11mm (6,744 lb) ~ 7/16" ( 6,907 lb)
13mm (8,992 lb ~ 1/2" (9171 lb)
(10 and 12mm 1x19 are actually a better match for 11 and 13mm Dux)

At the design load of 1x19 these pairs should have a total stretch within 4/10" of each other in 50 feet.

I also looked at windage based on these pairings. The greatest difference in diameters is 1.06mm. About 25 square inches increase in windage in 50' for 9mm over 5/16 but a weight savings of 6.7 lb. or about 170 pounds of righting moment.

I don't se how the yield point is particularly useful as designing at a 6:1 safety factor it is very hard to develop a scenario where the stresses would ever be anywhere close. Possibly if the boat were capsized with the sails up and got tee boned by a freighter?

I must caution that these figures are based on a number that I have not personally verified. However, I have ordered a length of Dynex Dux and will pull it on our test bench for a few months. With the economy in the state it is in it looks like the bench will not be in great demand for a while.
#11
09-13-2008, 08:14 PM
 RHough Retro Dude Join Date: Nov 2005 Rep: 793 Posts: 1,792 Location: BC Summers / Nayarit Winters
Gashmore,

Good idea asking about your rig on Spartalk. I'll follow that thread too. I am more than willing to be convinced that a 12 strand braid can replace SS 1x19.

Beware that people trying to sell their services read and post there also.

What seals the deal for me is that the NavTec sells both fibre and rod rigging. AFAIK, they have never used braided rope. Both their Kevlar and PBO systems are unidirectional fibres. If they could get the performance of their rod systems with rope, I think they would have used it.
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I have not failed. I've just found 10,000 ways that won't work.
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#12
09-13-2008, 09:17 PM
 Gashmore Junior Member Join Date: Feb 2008 Rep: 58 Posts: 52 Location: Macon, GA
I am still troubled by the lack of basic engineering data and also aware of the data on PBO (and the cost) but the potential advantages of a synthetic competitively priced against wire rope or rod has definitely peaked my interest. Yes, a lot of what I am hearing sounds like a sales pitch but the claims are not out of reason. I just don't think it can be rejected out of hand. Colligo, Precourt and Hampidjan really need to publish some hard numbers if they want to penetrate the US yacht rigging market. You guys are true skeptics. However, curiosity is my weak point so I am about to invest what would probably work out to \$10K+ of billable time if I were doing it on company time. (Assuming there was someone to bill that is. )

I will report my stretch results soon after I get my sample. The creep figures will take a few months. The creep figures I have are at 20C but I live in Georgia. I need to build an insulated box for the bench so I can keep it at 30C to see how the line will do in temperatures where my blood still flows.
#13
09-13-2008, 10:51 PM
 RHough Retro Dude Join Date: Nov 2005 Rep: 793 Posts: 1,792 Location: BC Summers / Nayarit Winters
Quote:
 Originally Posted by Gashmore I am not an experienced rigger but I am a licensed structural engineer. I need hard numbers to make a reasonable judgment which is the reason for my original post. Hampidjan is primarily in the commercial marine business where stretch is not as important as it is in rigging so getting numbers I can work with is hard to do. I did find that the "3% stretch" is at breaking load. OTOH, I have found the stretch rate of 11mm Dynex Dux to be .001205mm/mm/1000kg (.00055in/in/1000lb). I have also found that weight per diameter rather than cross sectional area is a valid means of estimating the stretch rate of high modulus ropes. From those two pieces of information I calculated the stretch rates for the sizes I might need and the 1x19 (from Navtec data) with the closest stretch . (in/in/1000lb) 7mm = .00134 ~ 1/4" @ .001306 9mm = .00084 ~ 5/16" @ .000833 11mm = .00055 ~ 3/8" @ .000580 13mm = .00040 ~ 7/16 @ .0004255 It appears that the primary consideration in designing for Dynex Dux is creep. Creep is geometrically related to the static load as a percentage of MBL. If a factor of 6 times the design maximum load is used the static load will be under 8% to 10% and creep will be extremely low. Using a safety factor of 6 for Dynex Dux and 2.8 for 1x18 (from the Navtec data and ignoring the metric sizes) the equivalent sizes at similar design loads are: 7mm (2735 lb) ~ 1/4" (2536 lb) 9mm (4421 lb) ~ 5/16" (3,679 lb) 11mm (6,744 lb) ~ 7/16" ( 6,907 lb) 13mm (8,992 lb ~ 1/2" (9171 lb) (10 and 12mm 1x19 are actually a better match for 11 and 13mm Dux) At the design load of 1x19 these pairs should have a total stretch within 4/10" of each other in 50 feet. I also looked at windage based on these pairings. The greatest difference in diameters is 1.06mm. About 25 square inches increase in windage in 50' for 9mm over 5/16 but a weight savings of 6.7 lb. or about 170 pounds of righting moment. I don't se how the yield point is particularly useful as designing at a 6:1 safety factor it is very hard to develop a scenario where the stresses would ever be anywhere close. Possibly if the boat were capsized with the sails up and got tee boned by a freighter? I must caution that these figures are based on a number that I have not personally verified. However, I have ordered a length of Dynex Dux and will pull it on our test bench for a few months. With the economy in the state it is in it looks like the bench will not be in great demand for a while.
I thank you for sharing this. I hope, as you learn more you will continue to keep us 'in the loop'. I used to work in one of few rig shops that has a portable cold heading machine, so I've done more than my share of rod rigging, I hate the stuff ... until it is done and I go sailing ... then I think it's the cats ***.

When you consider your rigging, remember that you are comparing uncovered braid to 1x19 wire. When the fibre is covered, you will add at least 2mm to the diameter. To be fair to yourself you have to add the wet weight of the cover to your total rig weight.

There is internal chafe going on in laid or braided rope. The fibres move and try to cut each other as they do. Kevlar is very bad for this. If the rope gets dirty this internal wear is accelerated. Now you need a weatherproof cover on the rope to remove that unknown.

Marlow says that their rope looses 20% of its tensile strength in 3 years.

They do not say under what service conditions. So who really knows?

I've never seen any decent estimate of service life for textile rope. NavTac Says 40,000 sailing miles to major *inspection* for Nitronic50 Rod.

And for their PBO:

Quote:
 If working Load is less than 25% of the PBO cable rated strength, we recommend changing the cable following 26,000-30,000 miles, with a thorough inspection following 3 years of usage if the mileage has not been obtained during that time. - If working Load is more than 25% (but less than 35%) of the PBO cable rated strength, we recommend changing the cable following 17,000-20,000 miles, with a thorough inspection following 2 years of usage if the mileage has not been obtained during that time.
NavTec PBO is parallel fibres with a weatherproof cover. It is not braided rope. The best fibre rigging in the world has less than 50% of the service life of rod.

You have it right, weight per unit length gives a good idea of material density ... but ... rope is not pure fibre, the yarns are coated during the construction process ... no one gives out data on how much of what they use to allow the 1920's rope machines to braid or lay up the rope. Your strength estimates are based on each fibre having equal tension ... this is is a variable from machine to machine and from lot to lot. Some manufacturers make rope that has continuous fibres, others stop the machine and splice in new strands ... yet another unknown variable.

On the other hand, if you buy Loos 316 alloy wire, every strand is polished and the rope is wonderfully consistent. The same cannot be said for the wire that comes from Asia.

www.tensiontech.com has a bunch of information that I'm sure you will enjoy, it is a bit over my head.

I was happy to see that NavTec agrees with me:

As you can see in the “Material Comparison to Nitronic 50” graph below, a slight windage penalty results in a significant weight savings and strength increase for a stretch equivalent application using NAVTEC PBO."

They show the windage of stretch equivalent PBO as about 140% of rod.

SK-75 has to be larger diameter for the same stretch as PBO, braid has to be bigger diameter than parallel core for the same stretch. I know of no cover material for braid, that will seal it properly ... you might be able to set it under its designed static tension, then parcel and serve it ...

When you get your Dynex Dux sample, you should try splicing one of the terminations using the Mobius splice they instruct you to use then test it ... See how long it takes before the eye you spliced is loose on the fitting ...

I hate to bust the guys chops, but he has a ways to go to convince me to use SK-75 braid for standing rigging ... I don't care that other riggers are doing it, I spent years fixing other rigger's mistakes.

As a engineer/detail guy you must find it even more frustrating than I did trying to work with textile to replace steel. Steel is good stuff.

I've used haylards of every fibre except PBO (Zylon) and Kevlar. I have never been able to build a stretch equal halyard significantly lighter than 7x19 SS wire. Also of note that when I went to Samson's "Rigger's University" (joke) they were working all out on a line of standing rigging ... 4 years later ... there is no product.

Again, I am truly interested in what you find out. It is my gut feeling that the people that are selling braided rope for SS wire rigging replacement won't be happy.
__________________
Proud supporter of The Far Kurnell Cat Racing Team

I have not failed. I've just found 10,000 ways that won't work.
- Thomas A. Edison
#14
09-14-2008, 11:45 PM
 jfranta Junior Member Join Date: Sep 2008 Rep: 52 Posts: 16 Location: Mesa AZ
Quote:
Mr Hough, PBO is damaged by water. I believe that is at least part of the reason why they recommend changing it so often.

This "guy" as you so adamantly put it, is not trying to convince anyone to use SK-75 for standing rigging. I am talking about Dynex Dux. So I hate to bust your chops but just as most metals can have very different mechanical properties due to working, heat treating, etc., UHMWPE can also. Dynex Dux does have different mechanical properties than SK-75. Check out Hampidjan's site for this.

If you do not understand this then please look up work hardening on wikipedia.

We have requested stretch and creep info from them but they are very focused on the commercail fishing industry and now the military and don't seem to have much time for the low volume sailboat industry.

Your statement about internal chafe is minimized in Dux (sk-75), along with constructional stretch and experience in the field has not shown any issues. kind of makes sense doesn't it. If the movement is minimized for our wokring loads the internal chafe would be also, right We are, however considering some cyclic load testing in the future.

Our product at Colligo is hardware so we would like to not have to sell the line ourselves but it is only available in a few places in this country. So we make it easy for people to get it. In turn putting money into testing someone elses products is not what we want to do.

We are also doing some stretch testing on 7,9,11,13 mm dux and will have that on our site.

You comment on our mobius splice is interesting. We do not recomend any splice over the other. In fact, the plain bury splice is the best way to go, unless you have a shroud or line that whips around then locking it with a mobius splice is a good idea. We have worked with Brion Toss on and agree with his claims of 90% beaking load on a brummel with a 72 times diameter bury. We only put the Modified Brummel on our site because of limited availability of instructions.

Our terminators are designed with a truncated apex to prevent the line pulling loosening on the terminator. As we are continually Prestretching 7,9,11mm Dux on our terminators I can tell you that it works. We pull 7mm to 3000 lbs-f, 9 mm to 4000 lbs-f, 11mm to 5000 lbs-f. It is not just our truncated apex at work here, it is also the stiffness of the Dux.

You really should look at this stuff for yourself so you don't mistakenly compare it to SK-75 anymore.

As I said before, there are some limitations with Dux, one is windage, but alot of sailors are willing to take the hit on windage for weight loss. Always compromises.

The facts are slowly getting out about Dynex Dux and we believe it is just the beginning of low stretch braided lines. They will probably never get to the low stretch numbers of the parallel fibers, or rod, but they are and will continue to be comparable to wire.
#15
09-15-2008, 03:51 AM
 RHough Retro Dude Join Date: Nov 2005 Rep: 793 Posts: 1,792 Location: BC Summers / Nayarit Winters
Quote:
 Originally Posted by jfranta Mr Hough, PBO is damaged by water. I believe that is at least part of the reason why they recommend changing it so often.
Not so, the PBO cable is sealed during manufacture. The replacement interval, is the classic, "lets test, and be very conservative" approach that has earned NavTec their reputation.

Quote:
 This "guy" as you so adamantly put it, is not trying to convince anyone to use SK-75 for standing rigging. I am talking about Dynex Dux. So I hate to bust your chops but just as most metals can have very different mechanical properties due to working, heat treating, etc., UHMWPE can also. Dynex Dux does have different mechanical properties than SK-75. Check out Hampidjan's site for this.
I have, I read every word I could find, before I posted about it. But in case I missed something I'll read it all again ... looking for hard engineering numbers.

What happens to the pre-stretch when the rope is worked? How does torturing the fibre during the splicing operation effect the rope? Does this statement ring a bell?
Quote:
 The Brummel Splice will not pull out. You can expect about 2 inches of stretch for 7mm and 4 inches for 9 mm to reset the line braid.
Has the pre-stretch been destroyed? Are all the fibres still aligned? Have any high stress points been introduced? Is the rope as strong as it was before?

Here is another statement:
Quote:
 The taper is very important, without it the splice strength will only be about 50% of breaking strength.
Very true, because the untapered end of the bury creates a stress point, that is where the rope will fail. The Mobius Brummel does exactly that at the throat of the eye.

Quote:
 If you do not understand this then please look up work hardening on wikipedia.
Work hardening:
"This leads to an increase in the yield strength of the material and a subsequent decrease in ductility."
"Ductility is the ability of a material to undergo large plastic deformations before fracture."

Are you saying that work hardening makes SK-75 less ductile? That it cannot stretch without breaking? That it is brittle?

Quote:
 Your statement about internal chafe is minimized in Dux (sk-75), along with constructional stretch and experience in the field has not shown any issues. kind of makes sense doesn't it. If the movement is minimized for our wokring loads the internal chafe would be also, right We are, however considering some cyclic load testing in the future. Our product at Colligo is hardware so we would like to not have to sell the line ourselves but it is only available in a few places in this country. So we make it easy for people to get it. In turn putting money into testing someone elses products is not what we want to do.
Gosh, that makes me feel good. NavTec and Loos do the testing *before* they sell a rigging product. What you just said is that you have no idea how cyclic loads effects the rope, but you are selling parts to DIY boaters to rig their boats with it.

Quote:
 You comment on our mobius splice is interesting. We do not recomend any splice over the other. In fact, the plain bury splice is the best way to go, unless you have a shroud or line that whips around then locking it with a mobius splice is a good idea. We have worked with Brion Toss on and agree with his claims of 90% beaking load on a brummel with a 72 times diameter bury. We only put the Modified Brummel on our site because of limited availability of instructions.
Brion is a good guy, I don't know that he has a formal engineering degree. No doubt he is a good rigger. I've seen the splices fail. These are professional splices, not the ones that amateurs make. Ask Brion how many splices an apprentice needs to make before they are good enough to sell to a customer.

Quote:
 Our terminators are designed with a truncated apex to prevent the line pulling loosening on the terminator. As we are continually Prestretching 7,9,11mm Dux on our terminators I can tell you that it works. We pull 7mm to 3000 lbs-f, 9 mm to 4000 lbs-f, 11mm to 5000 lbs-f. It is not just our truncated apex at work here, it is also the stiffness of the Dux.
I give you full marks for doing your homework, the terminators look great! I can see using them for several applications.

Quote:
 You really should look at this stuff for yourself so you don't mistakenly compare it to SK-75 anymore. As I said before, there are some limitations with Dux, one is windage, but alot of sailors are willing to take the hit on windage for weight loss. Always compromises.
I say it again. I want to be convinced! It is just so easy to poke holes in the hype that I am very reluctant to take anything at face value. I think it would be wonderful to be able to go to a boat with a spool of rope, a bag of fittings, and a splicing kit and re-rig it. I much prefer working with rope over wire or rod.

Quote:
 The facts are slowly getting out about Dynex Dux and we believe it is just the beginning of low stretch braided lines. They will probably never get to the low stretch numbers of the parallel fibers, or rod, but they are and will continue to be comparable to wire.
I think you are dreaming. I don't think you understand the physical properties of UHMWPE.

One thing I know, you don't have enough engineering data on the rope to be able to recommend it for a mission critical application like standing rigging. When that engineering data *is* available, then we can see how suitable it might be for rigging.

I think it is borderline irresponsible to sell a product that was not designed to do a job without knowing how well it will work.

The fact is that rope and cable manufactures have engineered textile cables for standing rigging applications like guy wires for radio towers. Every one of those products I know of has a parallel core inside a weather-proof cover. That should tell you something.

Until you have numbers so people can engineer a rigging system properly, you should not be defending the product. Just wait until the first rig comes down and kills someone ... the answer from the rope maker will be, "We are not responsible, we did not make that product for that application."
__________________
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I have not failed. I've just found 10,000 ways that won't work.
- Thomas A. Edison

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