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Alex,
Thanks kiddo. Got it this time.
Cheers

A
 

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From the web, Young's Modulus for 1x19 wire rope is 107.5 kN/mm^2.

Using the table of breaking loads for different diameters of AISI-316 wire rope as given in the book "Principles of Yacht Design" I got the following table for wire stretch for a 2000mm wire loaded to 5% of breaking load:

diameter(mm)____breaking strength(kN)___delta L(mm)

3_______________7.7__________________1.01
4______________13.8__________________1.02
5______________21.6__________________1.02
6______________30.o__________________0.99
7______________40.9__________________0.99
8______________53.5__________________0.99
10_____________69.1__________________0.82
11_____________83.5__________________0.82
12____________120.2__________________0.99
14____________160.1__________________0.97

This practically confirms what Alex is saying.

regards
Right; I said the same thing. If the shroud length is constant; the amount of stretch required is the same. But you can't apply this universally to all shrouds because different boats have different lengths of rigging wire. If you plug in 4000 mm for your base length; the delta L will double to get the proper tension. Since that's true you can't use the 1mm/5% rule to get exact tension. If I tighten an intermediate 1/4" shroud using that rule the tension will likely be ~40-50% of breaking load because the shroud lenth is much shorter than the upper shroud; which goes from the masthead to the deck.

Giu-

I'll get back to you with the data; I am aboard my boat tonight using a different computer. I should still have the spreadsheat I was doing the calc's on; but if not I will make up a new one. I was just using the modulus for 316 stainless and an approximate breaking strength for each size. Please don't use those numbers I posted as "actual"; I was only trying to make the point that stretch is also dependent on wire length (and this is independent of the max strength of each wire diameter).
 

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Right; I said the same thing. If the shroud length is constant; the amount of stretch required is the same. But you can't apply this universally to all shrouds because different boats have different lengths of rigging wire. If you plug in 4000 mm for your base length; the delta L will double to get the proper tension. Since that's true you can't use the 1mm/5% rule to get exact tension. If I tighten an intermediate 1/4" shroud using that rule the tension will likely be ~40-50% of breaking load because the shroud lenth is much shorter than the upper shroud; which goes from the masthead to the deck.

Keel,

As I understand it, if you mark off 2m of a shroud 6m long and then tension it to 10% of its breaking strength you should find that the marks that you made are now 2.002m apart.

If you mark off another 2m of a shroud that is 10m long and you tension this shroud to the same amount your 2 marks will again measure in at 2.002m apart.

this sound logical to me but hey...I am no expert, I could be wrong.

regards
 

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Hello Xuraax, Since u r in Malta and sail u r doing the Marzamemi race next weekend! Good luck with your rig tuning and d race if you are doing it.

Regards

Mike
 

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Don't know yet, I crew for Willy on Bordeaux 3, But I have to be in Brussels on Sunday so I will probably have to miss it. Which boat r u on?

Mike
 

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OK; here is the way to solve for stretch at 15% breaking strength. It's a simple derivation; it really only uses two well known engineering equations to solve it.

Strain is defined using the greek symbol epsillon; I'm using E

Strain is defined as:

E = dL / Lo

Change in length is dL; Lo is the Original Length.

For elastic conditions; we can use the definition of Young's Modulus to determine how much extension (strain) exists in a length of wire for a given amount of force applied.

Young's Modulus - E = Applied Stress / Strain = S/E = S/(dL/Lo)

Young's Modulus is a material specific constant measured by a testing applied force vs extension.

For type 316 Stainless; E = 28,000 kPSI

We can solve this for the change in length; dL

dL = Lo * (S/E)

The only real "variable" in this equation is Lo. For all wire diameters we want the same amount of stress (15% of breaking) so we can say that S is a constant.

Let's calculate S for some different wire diameters to prove it's relatively constant:

S = (F/Ao) - "F" is the tension force in the wire; Ao is the original cross sectional area of the wire.

(Breaking strengths taken from loosco.com for 1x19 type 316 wire)

For 7/16 wire - S = 15% * (20,000#)/(Pi * (7/32")^2) = 15% * 133,040 PSI = 19,956 PSI

For 1/4" wire - S = 15% * (6900#)/(Pi * (1/8")^2) = 15% * 140,560 PSI = 21,084 PSI (within 5%)

For 5/16 wire - S = 15% * (10,600#)/(Pi * (5/32")^2) = 15% * 138,200 PSI = 20,730 PSI (within 4%)

Using Young's Modulus for type 316; the 15% breaking load equation becomes:

dL = Lo * (20,600 PSI) / (28,000 kPSI) = Lo * .000736.

Use inches or mm for the shroud length; multiply by .000736 and get the length you need to stretch the cable.

For a shroud 55' long: dL = 660" * .000736 = 0.485"

For a shroud 20' long: dL = 240" * .000736 = 0.177"

It's -fairly- independent of wire diameter; but clearly dependent on length! You could use this for type 316; (but of course the standard disclaimer applies); and it does not take into account deflection of the rig or hull when you tighten the shrouds. Again; you should use an appropriate tension gauge to determine the actual rig tension.
 

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THis is an outstanding thread, and I want to commend all who participated and especially Alex for a very, very good detailed explanation.

Super job!!

- CD
 

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For type 316 Stainless; E = 28,000 kPSI
Keel,

When I convert your number to metric I come up with 193KN/mm^2 which is a lot higher than the one I quoted (107.5). When I looked up E again on the web the numbers I come up with now are closer to the ones you give so I guess it is more proper to use the constant you gave. The equation for Delta L is of course the same (Phewww!! thank goodness for that)

For 7/16 wire - S = 15% * (20,000#)/(Pi * (7/32")^2) = 15% * 133,040 PSI = 19,956 PSI
I note that American's frequently use the # sign. Can you explain what it means?

Use inches or mm for the shroud length; multiply by .000736 and get the length you need to stretch the cable.

For a shroud 55' long: dL = 660" * .000736 = 0.485"

For a shroud 20' long: dL = 240" * .000736 = 0.177"

It's -fairly- independent of wire diameter; but clearly dependent on length! You could use this for type 316; (but of course the standard disclaimer applies); and it does not take into account deflection of the rig or hull when you tighten the shrouds. Again; you should use an appropriate tension gauge to determine the actual rig tension.
I can understand the apparatus needed to measure an extension of a few mm over a length of 2 m.

What would you use to measure the 0.485" (say) in the 55' shroud to ensure that you don't tension it more than 15% of breaking strength?

regards
 

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xuaraax,

The # sign can mean a few things

# ie lbs in this case lbs of force before it breaks,

or

I use it at work for "square unit"......unit typically being a foot of measure, meter, yards etc could also be used as the unit of measure.

My first option, ie lbs of breaking strength, could in some instances, be kilograms or equal force measure too, but lbs is most common.

Marty
 

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I went through this process recently and may be able to save someone some trouble.
The elongation method is a pain get the Loos gauge from the start.
This process requires patients. don't try to set the mast in column and lock it down at the dock. It wont work. The only way to get it right is to get the mast centered in the boat with the right rake and prebend and then do the rest undersail.
to do this right you can count on it taking forever. To get no wind and no wave action to get the mast in column at the dock is hard. then doing the real tuning under sail in the wind speed you want to tune for may require several outings and a lot of tacking.
Don't kid yourself that you can put the mast in collum and lock it down at the dock. the real tuning part can only be done under sail, with a load on the mast and stays. There is no short cut here!
I tuned my rig for twenty knots I figured that was good middle ground for us.
And did not exceed 15% on the lowers 20% on the caps.
I maybe the exception, Our boat was layed up for a long time when we bought it and I don't believe the rig was kept in tune pryer to that so i had a hard time getting things adjusted. I tried moving the mast with the stays at first and finally just loosened everything and started from scratch. And followed a procedure much like the the one Giu. posted.
Then after all the headache. and some help from Alex I finally got it right. I can drive with my finger tips on the wheel, my weather helm went down and the boat points higher and is faster.
A couple things that I found out were that ambient temperature has a big effect on tension and I have a hatch just aft of the mast. It was a lot easier to sight up the mast from the salon looking up through the hatch than trying to to do it at the base of the mast.
When the rig is right it makes sail trim and helm balance so much easier.
I look at it like this. if the foundation is crooked the house is crooked. There is no way you can get proper sail shape with the rig being out of wack.
If the center of the mast is falling off to leward then you cant flatten your main in heavier air. just when you want to depower the sail it's gettig powered up. The same as running loose back stays will add power to a jib.
It was an enjoyable process for me the results were well worth the effort.

Hope this helps
 

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I bought a PT2 Loos gauge the other day. I have 7/32 wire on everything but the mid upper shrouds. which I believe is either 5/32 or 1/8. This is not listed as to what I need to check with current gauge. Does any one know how to figure out what the smaller wire number should be with the bigger gauge. As I really do not want to go buy a 2nd gauge for the smaller shroud.

Guessing by how the three sizes go, I should be able to halve the numbers for the 3/16 which is the smallest size for the gauge I have and work pretty close for the next size down. any one care to say I am correct, not quite right.........

I may in the end, email loos and see if they have it figured out.

Marty
 

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LOL,

Actually got the same size, but the pro model vs your one level down. It was tempting to get the battery operated one tho!

You got crew for wed night racing yet? If not, we will be out, and I am sure with 15'ish boats out normally for summer racing, someone will want a hand.

Marty
 

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I note that American's frequently use the # sign. Can you explain what it means?

What would you use to measure the 0.485" (say) in the 55' shroud to ensure that you don't tension it more than 15% of breaking strength?
# for American "Engineering Notation" is Pounds. It can be either LBF or LBM; it's just a shrot-hand for Pounds because it's called the "pound" symbol.

To measure the 15% tension I'd just use a standard Loos Gauge. Although the calculation predicts 0.485" extension I would not bet my life on it. Young's Modulus is a theoretical constant for the material and it is calculated based on lab results under ideal conditions (perfect sample, solid section, etc.). If the theoretical is within 20% of the actual tension in LBF I'd call it a good comparison; but that's not as close as you would get with a Loos Gauge.

If you wanted to measure the extension I would put a pair of calipers on the open body turnbuckle and measure the distance between the threaded ends. That's a direct measure of the amount of elongation you are putting into the shroud.
 

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Disclaimers don't mean squat anymore (who's smart enough to understand them?), you'll probably be in the middle of a class action suit soon from all the unemployed riggers that your information put out of business:eek:.

Thanks Alex, timely info., I should be stepping the mast within a month and I'll have this printed out and with me when I do.

John
John, I don't think too many riggers will be put out of business or even resent the fact that there is good info available. :)

I posted the following awhile ago. While not nearly as in depth or comprehensive as Alex's perhaps it has it's place.

The first part speaks to inspections while the rest addresses tuning.



"While not intending to dismiss anyone's advice, I am going to try to simplify this whole process.
Cracked swages are really not too difficult to find. Clean the surface of the fitting with a scotch-brite (it helps if you spit on it before scrubbing), then take your magnifying glass and look very carefully over the whole thing. Don't neglect to inspect the clevis and cotter pins/rings.
I've even seen a fairly young marine eye with absolutely no swage cracks split above the clevis pin.
If you have swage cracks they will be visible, if not obvious.
If your rigging is more than ten years old and it has been in central Florida for all that time then you are likely to find a crack or two.
If you find a small crack in your starboard upper and you have reason to believe the rigging is all of the same vintage then you will probably find some more upon closer inspection.
If you only have one week off from work, (and it's next week), and you have been planning this trip to Honeymoon Island for months and you have sense enough to reef early, stay at anchor or motor if you think you are stressing the rig, then you can almost assuredly enjoy a nice vacation and then rerig when convienent. Certainly before you decide to do the thursday night beer can race at the yacht club.
I've seen, and continue to see neglected and poorly designed rigging stand up to amazing abuse.
That said, you never want to push it. If you have time to rerig before your trip, then do it. If you can't, then take it easy, be smart and have a nice trip.

Most rigging, made by a professional will be consistant. Meaning that your starboard upper shroud will be almost exactly the same length as the port upper. (+or- 1/8" to 1/4"). So, if your mast is standing, then adjust your upper shroud turnbuckes exactly the same by opening them to the same point while your mast is being held by the lowers,headstay and backstay (you may even want to open the turnbuckles up completely and make sure the stud and t-bolt, ie top and bottom are started evenly).
Then while tightening, count the turns and take up the exact same count on each side until hand tight. Now ease off the lowers one at a time and set them all hand tight.
Next ease and set to hand tight the backstay and headstay, (if ajustable or accessable depending on furling systems). Now stop and sight up the main sail track like a gunbarrel. You will be able to see any curve (side to side) or bow (Fore and Aft) right away.
If the mast is curving to starboard and bowing forward, then start to adjust it out by tightening the starboard forward lower and backstay. It's all pretty logical if you just remember that you want to keep the top of the mast in the middle of the boat. So move the middle of the mast.
I realize that one must assume that the last rigger made the rigging correctly.
That the builder put the hole or the mast step in the middle of the deck and the chainplates are the same length and in the same positions, but what the hell, you have to make some assumptions in life.
It's really pretty easy to see if a rig has been piece-mealed and as for the rest a tape measure will answer most questions if you are really worried.
Anyway, back to the tuning.
Now that you have the mast in column, It's time to go for tentioning. If you have a gauge the use it. Set the shouds at the same tension, somewhere around the middle of the scale.

The most important part is to do the same thing on each side. If you turn the starboard upper three full turns then turn the port upper the same. Port aft lower two turns, Stb aft lower two turns etc.

If you don't have a gauge then just feel them. Don't try to make them sound like a guitar string but just get them tight. Tighten the uppers more than the intermediates and the intermediates more than the lowers. This assumes that the uppers are of an equal or larger diameter that the intermediates and the intermediates are of an equal or larger diameter than the lowers.

I have never seen a mast bowed forward on purpose. Lots of masts bow aft, some even are designed that way. Unless you have a in-mast main furler you probably won't have to worry about a little aft bow.
As far a rake (how much the mast leans aft from vertical), that can also usually be determined by the adjustment of the turnbuckles, Furlers and backstay adjusters.
If you have turnbuckles on both the HS and BS then go for about 50% adjustment on both. Adjust that later depending on weather-helm or lee helm.
After you have successfully tightened all the shrouds and stays to a reasonable degree, the mast is in column side to side and you have the desired amount of bow then go sailing. In a moderate breeze, sailing a close reach your mast should still be in column and there should be no shrouds swinging in the breeze. Meaning that even the looward shrouds should still be under some, if smaller load. If not then adjust the loose shouds, counting the turns, come about and do the same thing on the other side.
Again, the same turns on each side. Keep it in column.

If your headstay deflects too much and you can't sail too well to winward then tighten up the headtstay or backstay depending on weather/lee helm (you might want to ask a knowledgeable friend or racer to go sailing with you for this)
After returning to the dock, eyeball up the mast again. If necessary, make whatever minor adjustments to make sure the mast is in column then install all the cotter rings/pins.
Congratulation,you're done
I have not made it a practice to go sailing on the boats that I tune. Don't have the time. Most riggers don't. As a sailor, it's a skill that one needs to aquire.
Good luck and happy sailing"
 
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