Tension measurement for synthetic fibre rigging

[patrik111]

All,

What is the general approach to achieving a controlled tension if synthetic fibre rigging is used?

I would like something that would allow loading of the stays to get some forestay tension, but not too much.

Kind regards
Patrik

[Kay9]

I hope this helps.

http://moonblink.info/synthrig.html

K9

[patrik111]

Kay 9,

Thanks, This was one of the documents being very helpful up till exactly the tension point. it is left as a cliffhanger in close to the end of the page.

Furhter ideas?

[Kay9]

Sorry. Ill have to admit its one area I know next to nothing about. I was hopeing that one site would be your answer.

Have you tried calling Sampson to see what they say?

http://www.samsonrope.com/

K9

[patrik111]

Might just need to resort to that, but I think I will see if I can make a crude measuring device, or at least draft for some peer review.

//Patrik

[Kay9]

I had at one time a device that kind of clamped on wire rigging. It was sold by Sampson as well. Now I dont know how or why it worked, but as you tensioned the stay a mechanical meter went up in pounds. Im betting that have something like this for synthetic as well.

K9

[Paul B]

Might just need to resort to that, but I think I will see if I can make a crude measuring device, or at least draft for some peer review.

//Patrik

If your synthetic rigging is PBO you can use the Harken Rigtune Pro to measure the static rig tension on each stay.

Of course it is a Harken item, so the cost is about $350.00 US.

[patrik111]

As I will have a end boom sheeting with curved traveller track at similar distance to the mastbase as the forestay, I belive that a very significant contributor to the forestay tension is how hard I sheet the main, I would like some input on what I could expect that a normal man would pull on a rope. Would you expect around 30kg? More? Less?

Input needed for jib design. Ordered yesterday.

[RHough]

As I will have a end boom sheeting with curved traveller track at similar distance to the mastbase as the forestay, I belive that a very significant contributor to the forestay tension is how hard I sheet the main, I would like some input on what I could expect that a normal man would pull on a rope. Would you expect around 30kg? More? Less?

Input needed for jib design. Ordered yesterday.

Harken has a formula for calculating mainsheet loads.

About 50 lbs / 24kg is a reasonable load at the human end.

Loading Formula (http://www.harken.com/charts/mainsheetsysloading.php)

[Paul B]

About 50 lbs / 24kg is a reasonable load at the human end.



I think it depends on how much of their core muscles the trimmer is able to use.

The action of pulling on the mainsheet is similar to a seated one armed cable row from the lower pulley, in most instances. Sometimes it is more similar to a curl action.

If you are steering and doing the mainsheet yourself 50 pounds might be at the athletic end of sailors abilities.

I know my mainsheet tail load is far less than that.

[RHough]

I think it depends on how much of their core muscles the trimmer is able to use.

The action of pulling on the mainsheet is similar to a seated one armed cable row from the lower pulley, in most instances. Sometimes it is more similar to a curl action.

If you are steering and doing the mainsheet yourself 50 pounds might be at the athletic end of sailors abilities.

I know my mainsheet tail load is far less than that.

True enough! Big difference between driving and trimming compared to just trimming.

My mainsheet system has to keep trimming loads below the load it takes to move the traveler. Not upsetting the windward sheeting traveler is a higher priority than actual mainsheet load. So a 4:1 <> 16:1 Gross/Fine system is needed ... even though the sheet loading does not require that much purchase.

[jfranta]

All,

What is the general approach to achieving a controlled tension if synthetic fibre rigging is used?

I would like something that would allow loading of the stays to get some forestay tension, but not too much.

Kind regards
Patrik

Hi Patrick, If you are using Dynex Dux we will soon have calibrations for a Loos gauge for various sizes. Stayed tuned to our website for this. I talked with the Harken guys in la Rochelle and they told me they are working on a digital gauge for synthetic line (greater than 5 mm) but don't know when it will be out. You can however use any gauge for relative loading side to side but no absolute numbers can be had.

John Franta, Colligo Marine.

[patrik111]

Indication for normal adult pulling force is from Harkens below page 23-27Kg.

http://www.harken.com/blocks/Harken_mechanicaladvantage.php

Well worth the read is
http://hem.bredband.net/b262106/Boat/Blockfriction.pdf


Kind regards

Patrik

[RHough]

Hi Patrick, If you are using Dynex Dux we will soon have calibrations for a Loos gauge for various sizes. Stayed tuned to our website for this. I talked with the Harken guys in la Rochelle and they told me they are working on a digital gauge for synthetic line (greater than 5 mm) but don't know when it will be out. You can however use any gauge for relative loading side to side but no absolute numbers can be had.

John Franta, Colligo Marine.

So you've been selling rigging for how long?

And you have NO way to measure the tension?

Any rigger knows that all you need is a sharpie and a measuring tape.

For each 5% of breaking load every rigger knows that 1x19 SS wire stretches 1mm over 2000mm, Dyform is .95mm over 2000mm and rod is .7mm over 2000mm.

A two meter stick and a set of calipers is all you need to set the tension.

Harken and Loos sell tension gauges at nose bleed prices to people that can't use a simple stick and calipers.

If you had any engineering data for the rope you sell as rigging, you could publish the simple numbers so your DIY riggers could save the price of a tension gauge. What an amateur! Instead of having elongation for % MBL ... you have NOTHING?

You are selling rigging that if the tension is wrong by 5% it goes into unrecoverable creep and you have NO way to measure the tension?

Seems to me that ABSOLUTE numbers are MORE important for your Dynex Dux than for any creep free rigging like SS wire or rod or PBO and you expect people to what? Guess?

Good job.


NOT

[Gashmore]

"For each 5% of breaking load every rigger knows that 1x19 SS wire stretches 1mm over 2000mm."

Well, not exactly. From the Navtec specs 1x19 it would range from .93mm in 3/32" to .69mm in 3/4". While it can get you within 8 or 9% up to 1/4" but could be as much as a 20% high in larger diameters.

[RHough]

"For each 5% of breaking load every rigger knows that 1x19 SS wire stretches 1mm over 2000mm."

Well, not exactly. From the Navtec specs 1x19 it would range from .93mm in 3/32" to .69mm in 3/4". While it can get you within 8 or 9% up to 1/4" but could be as much as a 20% high in larger diameters.

There you go. There is an engineering spec and a simple way to measure. Since you are going to fine tune under sail, putting 15% tension in using a rule and calipers as a starting point is pretty easy.

Isn't this the information that you were trying to get for DDux over a year ago? You had to do your own tests didn't you?

Did you find that DDux has linear stretch over the 5-20% MBL range?

I think you can make the DDux work, you are able and willing to do research that few others are. My impression is that the maker of the rope and the retailers could not or would not answer your basic questions. If this is not correct and there is proper data available now I'll be more than happy to retract some of my statements about the rope.

[Gashmore]

At least over my test range up to 40% MBL the elongation is linear. Not only that but the elongation is directly related to the weight of the rope.

I think what happened is that the recreational market sort of snuck up on Hampidjan. Their primary business is supplying the commercial fishing industry. They had all the data but in a format that a trawler skipper wants to see. Even worse, it was for European skippers who had some idea how to use Newtons/tex. It took some time to get it published in a form that we could use but even now it takes some time to convert it to a format that I as a structural engineer am used to working with.

Taking the standard engineering results from my testing and working backwards correlates within 1 or 2% with the charts on John's page.

I do see a strong need for an accurate means of measuring tension in Dux however. Probably more so than wire. The elongation rate is so low that one turn of a turn buckle has a very large effect on tension.

[RHough]

At least over my test range up to 40% MBL the elongation is linear. Not only that but the elongation is directly related to the weight of the rope.

Taking the standard engineering results from my testing and working backwards correlates within 1 or 2% with the charts on John's page.

I do see a strong need for an accurate means of measuring tension in Dux however. Probably more so than wire. The elongation rate is so low that one turn of a turn buckle has a very large effect on tension.

This weight/elongation relationship is similar to SS wire then? :)

Turnbuckle thread pitch and length of the stay are related. Once the total length of the stay is known. The turnbuckle becomes a dead accurate tensioning device. :)

[Gashmore]

What I mean is that both elongation and ultimate strength are directly related to the weight of the rope. In fiber the weight per given length is used rather than cross sectional area because regardless of how tightly spun there is always some void. Unless you know the diameter of each fiber and have the patience to count a few million of them it is impossible to know the exact cross sectional area.

A given piece of Dynex Dux that weighs X per foot will have twice the MBL and half the stretch of one that weighs 1/2X per foot. I believe this is because, at least in the diameters up to 20mm, the angle of the fiber to the load doesn't change and the opposing braid eliminates any tendency to rotate. In contrast as wire rope increases in size the geometry of the wind changes slightly so the rate of elongation goes down as diameter goes up.

The last thing I have to work on to complete all the required data in an engineering format is the formula for creep. I have developed an exponential equation that describes the creep curve in my testing of 9mm. I applied it to 11mm and compared it to the curves on John's site. It works well up to about 10% MBL then goes crazy so I am doing something wrong.

Hampidjan gives the constants for the Baily-Norton creep formula but I can't figure out how to apply it to the finished rope.

[Joakim]

Turnbuckle thread pitch and length of the stay are related. Once the total length of the stay is known. The turnbuckle becomes a dead accurate tensioning device. :)

You can not measure stretch with the turnbuckle. I guess the problem is that DUX streches very little at the creep limit. According to this: http://www.colligomarine.com/Colligo-Synthetic-Systems/Dynex-Dux.htm
DUX stretches only about 0,05% at the creep limit. This is so small, that it can not be measured with a ruler.

I would think, that measuring the tension with a decent accuracy should be quite easy by measuring the force needed to deflect the rope to a defined angle.

[RHough]

You can not measure stretch with the turnbuckle. I guess the problem is that DUX streches very little at the creep limit. According to this: http://www.colligomarine.com/Colligo-Synthetic-Systems/Dynex-Dux.htm
DUX stretches only about 0,05% at the creep limit. This is so small, that it can not be measured with a ruler.

I would think, that measuring the tension with a decent accuracy should be quite easy by measuring the force needed to deflect the rope to a defined angle.

If I read that chart correctly 11mm DD has .000468" stretch per inch per 1000 pounds of load?

40 foot shroud = 480 inches = 0.22464" stretch per 1000 pound load?
11mm DD is rated at 40480 pounds, 10% is 4048 pounds?
So round numbers at 10% load that 40 foot shroud will stretch 4 times .22464"? or 0.89856"?

I'm pretty sure I can measure .9 inch. :cool:

A rigging screw with 18 TPI moves .1111" per turn (double the thread pitch), so It would seem I have a 8 full turn range between 0 and 10% load?

Am I reading the chart wrong?

Take that 40 foot shroud in SS 1x19 using the 1mm over 2000mm = 5% rule of thumb. 10% load stretches the wire .48" ... about 50% of DD?

[Joakim]

If I read that chart correctly 11mm DD has .000468" stretch per inch per 1000 pounds of load?

I'm pretty sure I can measure .9 inch. :cool:

A rigging screw with 18 TPI moves .1111" per turn (double the thread pitch), so It would seem I have a 8 full turn range between 0 and 10% load?

Am I reading the chart wrong?

Take that 40 foot shroud in SS 1x19 using the 1mm over 2000mm = 5% rule of thumb. 10% load stretches the wire .48" ... about 50% of DD?

Why on earth are you making the calculations in mixed units instead of SI?

It seems that there is something badly wrong in the table. It shows a larger strecth for 1000 lbs than 1000 kg while 1000 lbs = 454 kg. Actually the 1000 kg stretch = 0.454 * 1000 lbs stretch while it should be divided by 0.454.

Looks like the 1000 lbs value is more reasonable and strecth is very close to 1x19 at target tension (10%MBL for DUX 20%MBL for SS).

When you tension the rope using a turnbuckle there is much more happening than just streching of that rope. Other ropes stretch as well, the hull changes shape, mast compresses and changes chape etc. Thus you can not calculate tension from the turnbuckle. You need to fix the ruler to the rope.

[RHough]

Why on earth are you making the calculations in mixed units instead of SI?

It seems that there is something badly wrong in the table. It shows a larger strecth for 1000 lbs than 1000 kg while 1000 lbs = 454 kg. Actually the 1000 kg stretch = 0.454 * 1000 lbs stretch while it should be divided by 0.454.

Looks like the 1000 lbs value is more reasonable and strecth is very close to 1x19 at target tension (10%MBL for DUX 20%MBL for SS).

When you tension the rope using a turnbuckle there is much more happening than just streching of that rope. Other ropes stretch as well, the hull changes shape, mast compresses and changes chape etc. Thus you can not calculate tension from the turnbuckle. You need to fix the ruler to the rope.


Sorry ... I grew up with Imperial so I "think" in those units. :) Riggers working in NA use Imperial sized rigging except for the wire supplied with Seldon/Furlex units.

That table is very confusing. That the table was created by the retailer of the rope so it is the only data to work with? Why not relate stretch to rated strength? If you conclude that the rope has the same stretch at target tension and the target is tension is 50%, then the rope stretches 50% less for the same load?

If we agree that the tension transfers from the unloaded side to the loaded side, then at the design load with 50% pretension, the leeward shroud is slack and the windward shroud carries 100% of the load. The mast moves some distance to leeward under those conditions correct? That distance should be 50% for the stiffer rope correct?

Cycle the rig between 50 and 100% of design load at a given frequency. One rig moves twice as far as the other in the same time. The means the accelerations are double for the stiffer rig correct? This doubles the cyclic load on the fittings does it not?

Now combine a stiff rigging material with a slack rig ... what happens to the loadings on the fittings? The soft rig treats its fittings more gently than the stiff rig. Has anyone taken this into consideration when they replace rigging with a rope has has only 50% of the shock absorption of the material it replaces? I spent about an hour rolling about in swell with very little wind during a race yesterday. As the boat rolled though 20 degrees I thought about what would happen if the rig was slack. Instead of a smooth transfer of load from one side to the other in the rig there would be a violent shock with each roll. Even with proper tension the fittings are subject to accelerations that place large shear loads on them. Fittings like tangs and clevis pins (if properly designed) will show zero deformation after 100's of thousands of load cycles, double the acceleration loads and how soon will you see elongated holes in tangs and clevis pins that show signs of shear stress?

Many boats built in the 1970's had 3/8" pins on 1/4" wire ... I used to keep a handful of damaged pins and a few tangs with oval holes to show my customers when I suggested that they use 1/2" pins and replace chainplates and tangs when they replaced rigging ... Has anyone done a cyclic loading test on fittings designed for SS wire when subjected to stiff synthetic rope instead? After a year rolling about on the mooring with a slack DDux rig, how much damage will there be?

Yes, you fix the ruler to the rope or wire so you measure the elongation of the rigging. Fixing a 2 meter measure to the rigging and measuring the change is a simple method that riggers have used for years.

If the same data was available for rope, the same method would work. I made up a spreadsheet using the standard cross sectional area of 1x19 to verfiy the 1mm per 2000mm stretch rule and satisfied myself that for the range of wire sizes I used to work with 1/8" to 1/2" diameter (3mm - 13mm) that the 1mm per 2000mm was a useful tool.

[Joakim]

If you conclude that the rope has the same stretch at target tension and the target is tension is 50%, then the rope stretches 50% less for the same load?

No, that was not the conclusion. The conclusion was, that the strecth is about the same.

Steel would be dimensioned to be tensioned to ~20%MBL and would then stretch about 0.2%.

If DUX would be dimensioned to ~10%MBL due to creep and would then strecth about the same 0.2%. Thus DUX would has twice the breaking load, but equal stretch at about the same diameter.

Maybe at 10%MBL DUX still has too much creep. Thus you may have to go even to 5%MBL. Then you would have about 50% less stretch and about 40% bigger diameter.

All the above was based on equal absolute tension in the rig.

[RHough]

No, that was not the conclusion. The conclusion was, that the strecth is about the same.

Steel would be dimensioned to be tensioned to ~20%MBL and would then stretch about 0.2%.

If DUX would be dimensioned to ~10%MBL due to creep and would then strecth about the same 0.2%. Thus DUX would has twice the breaking load, but equal stretch at about the same diameter.

Maybe at 10%MBL DUX still has too much creep. Thus you may have to go even to 5%MBL. Then you would have about 50% less stretch and about 40% bigger diameter.

All the above was based on equal absolute tension in the rig.

The data suggests that 20% is well into the creep zone.

If I understand correctly:
If Dux is working between 10% and 20% of MBL it will have about the same stretch as a Steel rig working between 20% and 40% of MBL at the same tensions?

That if the Dux must be limited to 10% MBL to eliminate creep that it will have 50% of the stretch of a Steel rig?

Do you agree that 50% of the stretch doubles the cyclic loads?

If you were rigging with DUX what sizes are direct replacements for Steel?

[Joakim]

The data suggests that 20% is well into the creep zone.

If I understand correctly:
If Dux is working between 10% and 20% of MBL it will have about the same stretch as a Steel rig working between 20% and 40% of MBL at the same tensions?

That if the Dux must be limited to 10% MBL to eliminate creep that it will have 50% of the stretch of a Steel rig?

Do you agree that 50% of the stretch doubles the cyclic loads?

If you were rigging with DUX what sizes are direct replacements for Steel?

I was referring all the time to static loads. I don't think creep is a problem during dynamic loads, which typically are very short compared to static ones.

A typical pretension is 20%MBL for steel. What happens at dynamic situations depends on many factors. The leeward shroud is never slack in my boat. In some other boats it is slack already at 15 degrees heel.

For DUX you can not use 20%MBL pretension, since it would creep like crazy. Even 10%MBL seems to creep about 0.25%/year, thus you would need to adjust the tension several times a year, if you like to keep the pretension constant. You can not use turnbuckles since they would run out of adjustment in 1-2 years.

At 5%MBL creep is less than 0.05%/year, thus pretension would be almost constant for a year and turnbuckles would be OK. Thus I would choose that.

All of the above is based on the charts and tables provided by Colligo Marine. I have no experience on synthetic standing rigging and I'm not considering to buy one.

I don't think that lack of stretch is a problem to rigging. Too much pretension might be.

[Gashmore]

RHough's calculation is correct but it also illustrates what I was saying about turnbuckle adjustment being very sensitive. In that 40' shroud if 8 turns creates an extension equalling 4,000 lb, one turn adds 500 pounds to the tension. When you are trying to add 200 pounds it gets pretty exacting.

BTW, The first rule for synthetics is to design for creep rather than load. If I designed for load my cap shroud would be 9mm Dynex or 3/8" wire but creep would be unacceptable so 11mm is the correct choice. I have run several simulations of creep based on the cap shroud of my boat projected over a year of relatively heavy use in the Caribbean.

Assumptions:
Shroud size = 11mm
Shroud length = 58'
Design load at RM30 = 4,150 lb (10% MBL)
Pretension = 2,000 lb (5% of MBL)
Average angle of heel 25 degrees.
Passage making hours (52 days @ 24 hours) = 1248
Day Sailing hours (5 hours on alternate non passage days) = 640
Total = 1888 hours (22% of the year and slightly higher than the SCCA survey results)

Results;
Creep in port = .16"
Creep under sail in windward shroud = .30"
Creep under sail reduced in leeward shroud = -.04"
Total creep = .42"

This does mean that the rigging will require some degree of attention. As the shroud creeps pretension will decrease so to maintain the correct pretension a 3/4" turnbuckle with a 16 tpi thread will need to be adjusted by an average of a little less than one turn every 3 months. A 3/4" turn buckle has an adjustment range of about 3" or 48 turns so at 4 turns a year that is about 12 years before it bottoms out. By that time I will be pushing 80 and probably driving a trawler. :-)

For those worried about the added windage I also ran the wind load calculations for the shrouds on my boat. At 27C, standard sea level pressure and 20 knots apparent at 30 degrees, the 11mm Dynex added 59 pounds of drag. That results in 51 pounds (cos(30)*59) opposite the driving force over 3/8" wire and 29 pounds (sin(30)*59) in the heeling direction. However, that has to be balanced against a weight saving aloft of about 90 pounds.

51 pounds is a very small percentage of the total driving force at 20 knots apparent so I am not terribly concerned about that but the question remains as to the relationship between the heeling force of the additional wind load and the increase in righting moment from the less weight aloft.

[Joakim]

For those worried about the added windage I also ran the wind load calculations for the shrouds on my boat. At 27C, standard sea level pressure and 20 knots apparent at 30 degrees, the 11mm Dynex added 59 pounds of drag.

There is something wrong here. 59 lbs would be a very high drag. I get something like 50 N = 11 lbs for total drag of standing rigging (assuming 4*18 m of rope and Cd=1). The difference to 9 mm would be about 10 N = 2 lbs.

I have no idea about your boat, but just based on the length of the shroud I guess it has a drag of 1000-2000 N (200-400 lbs) on beat.

[Gashmore]

Density was in kg/m^3 so the result is in kg. I converted to pounds.

Also should have stated that this was the wind load on 370' (including the back stay) of 11mm Dux vs 3/8" wire and used a Cd of 1 for wire and 1.2 for Dux to avoid any argument about the roughness of rope over wire. That probably overstates the difference by close to three times but I was trying to be very conservative. Double check my calculation:

I used (Cd*A*p*V^2)/2
Cd = 1 to 1.2
Area 3/8" = 9.5mm * 112.78m = 1.07m^2 and 11mm dux * 112.78m = 1.24m^2
Density (p) @ 27C = 1.176 kg/m^3
Velocity = 10.3m/s
For 3/8" drag is 66.7kg
For 11mm Dux at Cd of 1.2 drag is 92.6kg
At a Cd of 1 drag is 77.2kg
So the diffference is somewhere between 10 and 26 kg or 22 to 57 pounds.

[RHough]

RHough's calculation is correct but it also illustrates what I was saying about turnbuckle adjustment being very sensitive. In that 40' shroud if 8 turns creates an extension equalling 4,000 lb, one turn adds 500 pounds to the tension. When you are trying to add 200 pounds it gets pretty exacting.

BTW, The first rule for synthetics is to design for creep rather than load. If I designed for load my cap shroud would be 9mm Dynex or 3/8" wire but creep would be unacceptable so 11mm is the correct choice. I have run several simulations of creep based on the cap shroud of my boat projected over a year of relatively heavy use in the Caribbean.

Results;
Creep in port = .16"
Creep under sail in windward shroud = .30"
Creep under sail reduced in leeward shroud = -.04"
Total creep = .42"

This does mean that the rigging will require some degree of attention. As the shroud creeps pretension will decrease so to maintain the correct pretension a 3/4" turnbuckle with a 16 tpi thread will need to be adjusted by an average of a little less than one turn every 3 months.

Just for grins what is the next size up from 11mm? 13mm?

What does that do for your creep numbers, weight, windage?

Set the Pretension @ 10% and see what % you have under sailing loads. My concern (not for you) is that my experience has been that sailors don't check/adjust rigs more than once a year (if that) unless they are racers. The rig in 3/8" SS would get tuned once, checked once after a week or two then can be forgotten for years. I think you are talking about a level of care that I just have not seen on cruising boats. Okay for you, you are a geek (meant as a compliment), but for 95% of the boats I see, the tape on the turnbuckles as old as the rigging. Well designed and tuned rigs are set it and forget it ... if anything changes and a once taught shroud is slack, there IS a problem. If the habit is to wind it up a turn every 3 months, there is no reason to go up the mast and look to see why something changed.

[Gashmore]

In my experience significant number of boat owners pay no attention to the shroud tension at all. :p This stuff is definitely not for them.

It amazes me some of the people who buy big sailboats. I was talking to a salesman at the Annapolis show and remarked at the size of a galley and that there was no place for the cook to brace. He said the reason is that they sell to the wife, not the husband. He just wants a boat and will buy whatever she gives the OK on. He is definitely not a candidate for synthetic rigging. :p

[Joakim]

Density was in kg/m^3 so the result is in kg.

No the unit of force is N. Here on earth at sea level 1 kg = 9.81 N.

[Gashmore]

The density of dry air at sea level and 27C is ~1.176 kg/m^3 or 11.53 N/M^3 but because the kg is a unit of mass and the Newton of force the standard expression is in kg/M^3. You get the same result using either but the result will be in the units you started out with.

In a more practical way, consider that the total cross sectional area of the rigging is a bit over a square meter. The Cd of a flat plate perpendicular to the wind is 1.17. Think about holding a square meter of plywood up to a 20 knot wind. The force will be considerably more than a 11 pounds.

[Joakim]

The density of dry air at sea level and 27C is ~1.176 kg/m^3 or 11.53 N/M^3 but because the kg is a unit of mass and the Newton of force the standard expression is in kg/M^3. You get the same result using either but the result will be in the units you started out with.

Density can only be mass/volume thus kg/m^3. When you use F=0.5*Cd*rho*A*V^2 formula you just put SI units in and get SI units out.

F = 0.5 * 1.0 * 1.176 kg/m^3 * 1.24 m^2 * (10.3 m/s)^2 = 77.35 kgm/s^2 = 77.35 N (by definition [N] = [kgm/s^2], remember F=m*a => [N]=[kg]*[m/s^2]).

Dividing that with gravity acceleration of 9.81 m/s^2 you get that 7.89 kg mass has the same gravity force. And then divide with 0.454 kg/lbs and get 17.4 lbs.

It so much easier with pure SI units....

[Joakim]

Think about holding a square meter of plywood up to a 20 knot wind. The force will be considerably more than a 11 pounds.

Haven't tried that, but no problems holding 6.5 m^2 sail of my windsurfer at 20 kn apparent. Even a 60 kg (132 lbs) surfer could do that. If the force was much more than her weight, the sail would make her fly.

I can also bicycle at 20 kn speed in calm for an hour. The surface area is somewhere between 0.5 and 1 m^2. I'm sure I can't output more than 200 W for a longer time. 200 W at 10.3 m/s => P = F * V => F = P/V = 200 W / 10.3 m/s = 20 Ws/m = 20 N. ([W] = [Nm/s]) 20 N = 4.5 lbs. That 20 N includes rolling resistance as well.

[Gashmore]

Well, you are right. In canceling units I forgot we squared the m/s. :-) All SI units but needing a different conversion. (I went to Tech in the slide rule, abacus and imperial era.)

So windage is a minor issue if it is an issue at all. Definitely out weighed by the improvement in righting moment.

[jfranta]

If you had any engineering data for the rope you sell as rigging, you could publish the simple numbers so your DIY riggers could save the price of a tension gauge. What an amateur! Instead of having elongation for % MBL ... you have NOTHING?

NOT
The Data has been on the website for over 2 years now in one form or another.

As for the incessant name calling, snake oil salesman, marketing BS, amateur. I do all the big shows, Annapolis, Chicago, Miami, Oakland, la Rochelle, Southampton, would be glad to buy you a beer and see how you respond to a person when he is in front of you. Let me know and I will get you on my schedule.

John Franta, Colligo Marine.

[jfranta]

There you go. There is an engineering spec and a simple way to measure. Since you are going to fine tune under sail, putting 15% tension in using a rule and calipers as a starting point is pretty easy.

Isn't this the information that you were trying to get for DDux over a year ago? You had to do your own tests didn't you?

Did you find that DDux has linear stretch over the 5-20% MBL range?

I think you can make the DDux work, you are able and willing to do research that few others are. My impression is that the maker of the rope and the retailers could not or would not answer your basic questions. If this is not correct and there is proper data available now I'll be more than happy to retract some of my statements about the rope.

No your statement is not correct. Gashmore has confirmed our stretch and creep data that has been posted on the website for over 2 years now. You need to retract your statements as any professional would do. FYI: If you can do it without any name calling it would add greatly to your credibility.

John Franta, Colligo Marine.

[RHough]

No your statement is not correct. Gashmore has confirmed our stretch and creep data that has been posted on the website for over 2 years now. You need to retract your statements as any professional would do. FYI: If you can do it without any name calling it would add greatly to your credibility.

John Franta, Colligo Marine.
As noted.

The data is available, not in a format that is generally used, but it is available. Gashmore asked for it in a standard engineering format so he could make comparisons and ended up with:

"Taking the standard engineering results from my testing and working backwards correlates within 1 or 2% with the charts on John's page."

and

"The last thing I have to work on to complete all the required data in an engineering format is the formula for creep. I have developed an exponential equation that describes the creep curve in my testing of 9mm. I applied it to 11mm and compared it to the curves on John's site. It works well up to about 10% MBL then goes crazy so I am doing something wrong.

Hampidjan gives the constants for the Baily-Norton creep formula but I can't figure out how to apply it to the finished rope."

Joakim says:
"It seems that there is something badly wrong in the table. It shows a larger strecth for 1000 lbs than 1000 kg while 1000 lbs = 454 kg. Actually the 1000 kg stretch = 0.454 * 1000 lbs stretch while it should be divided by 0.454."

So is some data available? Yes
Is it correct and usable by an engineer? No, Yes, Maybe?

Do I owe you a retraction? Has the data you provide changed in the time it had taken for Gashmore to run his own tests only to conclude that there is something wrong with either the formula or his application of it?

Have you provided the test to failure results of the rigging assembly's you sell as I asked for over a year ago? The ones that will show that your splicing method and end fittings do not seriously lower the MBL of the rope?

What is your response to this from Gashmore in post #31?
"In my experience significant number of boat owners pay no attention to the shroud tension at all. This stuff is definitely not for them."

How does that comment fit with your statements about 100's of cruising boats using DIY rigging?

Gashmore concludes that his rig will need adjustment every 3 months. How many SS rigs require that?

What does buying space at a boat show have to do with anything? Are you saying that boat shows screen renters to make sure that the claims they make are valid? I've done too many shows myself to believe that.

I have said time and time again that I would love to be convinced. So far I have your claims as the retailer and at least two people that seems to know something about rigging questioning the formulas you provide. The engineer that started asking questions, still has questions and has concluded that constant adjustment over the life of Dux rigging is acceptable.

When you compare two products they must be comparable. For a replacement of SS wire in rigging, that must include the ability to hold a tune. At a minimum customers should be advised of the increased maintenance requirement.

We can sell you Dux rigging. The benefits are: X,Y, and Z compared to your SS rigging. However, to take advantage of these benefits, you must do A,B, and C more often.

The reduced weight aloft comes at a price. Increased cost of the rigging itself if you consider the fittings and professional splicing and installation. Increased maintenance if you have to pay to keep it in tune.

What to you think when you hear claims that offer something for nothing? Less stretch, less weight and NO cost?

From what can be learned here:
Same stretch as SS but will creep and require frequent adjustment for reduced weight benefit.
Less stretch than SS at no creep sizes but higher cyclic loading and less weight reduction.

Does anyone get that from you? You claim direct replacement for SS with Dux, until your replacement recommendations result in rigs that are as low maintenance as SS (no frequent re-tuning needed), they are not really direct replacements are they?

Synthetic rigging has a future. Until you come clean and make people aware of the trade-offs, I'll keep holding your feet to the fire.

Fair enough?

[Gashmore]

Randy, this conversation definitely illustrates the validity of my great grandfather's dying words "'Tis the friction of minds that causes the spark of truth."

What I believe is the foundation of this problem is that Dynex Dux is a product originally intended for one market and unexpectedly adopted by another. Hampidjan serves the commercial fishing and heavy marine industries. They talk the language of hawsers and tow lines. It has taken them some time to learn the language of recreational sailing and even longer to understand the market. In fact, after talking to a couple of their engineers I am not sure they understand it fully even now. That said, there is a lot more detailed data available today than when I started this project two years ago and my testing indicates that the data is valid.

Today there are a number of vendors from Europe to Australia selling Dynex Dux for standing rigging and of them all John has made the most effort to discover and publicize the available data.

Are there compromises to be made? Certainly. A boat is one big compromise. From the material the hull is built from to the size of holding tank. Discovering and understanding the effects of these compromises is my primary goal in this effort and I have to say that your role as devil's advocate has been a great help in the process.

I believe I have enough information now to answer the questions presented here and on other forums and over the next few days will organize it all in a report that lays out the choices. I will put it on my web site and post a link here. Hopefully I can sell a simpler version to one of the sailing rags. After all, I have to buy a couple thousand bucks worth of rope soon. :D

[RHough]

Randy, this conversation definitely illustrates the validity of my great grandfather's dying words "'Tis the friction of minds that causes the spark of truth."

What I believe is the foundation of this problem is that Dynex Dux is a product originally intended for one market and unexpectedly adopted by another. Hampidjan serves the commercial fishing and heavy marine industries. They talk the language of hawsers and tow lines. It has taken them some time to learn the language of recreational sailing and even longer to understand the market. In fact, after talking to a couple of their engineers I am not sure they understand it fully even now. That said, there is a lot more detailed data available today than when I started this project two years ago and my testing indicates that the data is valid.

Today there are a number of vendors from Europe to Australia selling Dynex Dux for standing rigging and of them all John has made the most effort to discover and publicize the available data.

Are there compromises to be made? Certainly. A boat is one big compromise. From the material the hull is built from to the size of holding tank. Discovering and understanding the effects of these compromises is my primary goal in this effort and I have to say that your role as devil's advocate has been a great help in the process.

I believe I have enough information now to answer the questions presented here and on other forums and over the next few days will organize it all in a report that lays out the choices. I will put it on my web site and post a link here. Hopefully I can sell a simpler version to one of the sailing rags. After all, I have to buy a couple thousand bucks worth of rope soon. :D

If anyone follows your lead and goes in with eyes open as to the compromises and makes an intelligent (based on knowledge rather than sales claims) decision, then this forum has done it's job.

Your willingness to share information is a great example to others. IMO we have all learned something. I have decided to wait and see before I decide.

Until tension measurement in Dux is known and repeatable, you have to be very careful not to pretension too much. What I'm hearing is that 10% is a target to limit design load to 20% to limit creep. If you miss 20% on SS wire, there is no harm done, SS is elastic way past 40% MBL.

I'm hearing that static preload in Dux is more critical than in SS wire and there is no tool or procedure to measure the tension accurately.

All this makes Dux an experimental rigging product IMO. I don't feel it is ready for the prime time retail market. I'm willing to think that it could be, but it is not there yet. The attitude of the people selling it as DIY kits is not presenting a good case. So I call them out on it.

So thank you for the kind words and for sharing your test findings. Your attitude is professional and much appreciated.

[Joakim]

Until tension measurement in Dux is known and repeatable, you have to be very careful not to pretension too much. What I'm hearing is that 10% is a target to limit design load to 20% to limit creep. If you miss 20% on SS wire, there is no harm done, SS is elastic way past 40% MBL.


Well this depends a lot on how you look at it and what is your goal.

If your goal is to have a well known pretension for the whole season, you are much better of with steel (or really over dimensioned DUX). E.g. if you are measuring your settings from turnbuckles like I do, creep is not a nice feature.

If you use too much pretension with steel, you are more likely going to have fatigue issues and eventually something will break. Going over 25%MBL pretension is not a good idea.

Due to creep DUX will in a way pretension automatically. If you put 20%MBL pretension, it will creep quite fast until it reaches a low creep pretension. Then you could measure the turnbuckles and set up the same pretension for the next season. Eventually you would reach a constant pretension, but it may not be the pretension that is optimum for your rig and sails.

[RHough]

Well this depends a lot on how you look at it and what is your goal.

If your goal is to have a well known pretension for the whole season, you are much better of with steel (or really over dimensioned DUX). E.g. if you are measuring your settings from turnbuckles like I do, creep is not a nice feature.

If you use too much pretension with steel, you are more likely going to have fatigue issues and eventually something will break. Going over 25%MBL pretension is not a good idea.

Due to creep DUX will in a way pretension automatically. If you put 20%MBL pretension, it will creep quite fast until it reaches a low creep pretension. Then you could measure the turnbuckles and set up the same pretension for the next season. Eventually you would reach a constant pretension, but it may not be the pretension that is optimum for your rig and sails.

That is a novel idea! Tension the rig, see if it creeps. Let it creep to reduce the tension. Once it is stable, see if it has enough pre-tension, if not go up a size and repeat the process!

I agree about not going over 25%MBL on SS rigging. Point was that if if you are close to 20% a small error of 5% does not damage the rig in most cases. 5% in SS wire is about 10% of the elastic range (IIRC the deformation load is about 50-55%?). For Dux, the no-creep range is 0-15%? so 5% is 33% of the target range? 10% of the working (no-creep) range is 1.5% for Dux, thus you need more accurate measuring tools?

Way back in this thread I suggested using a halyard to heel the boat to 20-25 degrees to get a ball park pretension. Centre mast, add some pretension, heel the boat and see what goes slack and adjust from there. The actual numbers are no so important if the rig is sized properly, just make sure nothing goes slack before 20-25deg of heel. A SS rig should hold this tune until the service life of the wire is reached. When it no longer holds tune, the wire is due for replacement, it has reached the point where the elastic range is lower than the normal sailing loads.

I have run into situations where a new wire will not hold its tune. The culprit has been a rig that was marginal with 302SS wire and a replacement with 316SS has made the normal sailing loads to high for the wire size. Production boats fro the 1970's are apt to see this when a NA owner wants to re-rig with "Tropical" 316 wire. I try to do the basic math on rig to make sure that a change to 316 will not reduce the safety factor too much if the owner requests 316.

I think what I find hard to accept is the concept of creep being manageable and acceptable. I equate Rig not holding tune = Problem I can fix. I just cannot see a customer that will choose Dux after hearing, "Your new rigging might creep and require re-tuning depending on how you sail the boat. This is normal. The rig tension must be checked every 3 months or so until we know how often you rig will need to be re-tensioned." I'm a rigger and I would not put up with that, I want my rig to be stable, even if it means using larger diameter Dux ... I'd have a better feeling about the sizing suggestions if they were "no creep" replacements. Then the only thing to check is the safety margins of fittings to handle the increased loads. The approach seems to be to size Dux just big enough to keep creep in the "managable" range ... for me that is zero.

[Joakim]

I agree about not going over 25%MBL on SS rigging. Point was that if if you are close to 20% a small error of 5% does not damage the rig in most cases. 5% in SS wire is about 10% of the elastic range (IIRC the deformation load is about 50-55%?). For Dux, the no-creep range is 0-15%? so 5% is 33% of the target range? 10% of the working (no-creep) range is 1.5% for Dux, thus you need more accurate measuring tools?


According to this the yield limit for steel rope is 70-85% MBL: http://www.fatzer.com/contento/LinkClick.aspx?link=Fatzer%2FDokumente%2FSBO+englisch_Drahtseiltechnik.pdf&tabid=241&mid=734

But I think fatigue is much more important limit than yield for steel in this case.

I don't think it is good to compare %-values here. For steel using only 10%MBL pretension is too little and 30%MBL is too much. Thus missing the target pretension by 50% leads to problems. I don't think many would accidently use 30%MBL since that would not be easy to achieve on most boats and many owners don't dare to use even 20%MBL.

For DUX your target may be 5%MBL. 10%MBL would be 100% error in pretension and an extremely tight rig equal to 40%MBL for steel. How many turnbuckles could handle that without ruining threads?