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Old 04-23-2009, 09:54 AM   #1
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A very good instructional article (with images) on tensioning a yacht's rigging is available as a .pdf download - HERE
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Old 04-23-2009, 12:41 PM   #2
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A first appreciation of pages 28/29 gives a simplistic method of measuring tension - is this a fair analysis? Is a more reliable piece of equipment required ?
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Old 04-23-2009, 05:21 PM   #3
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A first appreciation of pages 28/29 gives a simplistic method of measuring tension - is this a fair analysis? Is a more reliable piece of equipment required ?
I don't know a single rigger in San Diego with a real rig tension gauge....they all use "experience" or similar methods to that described.

No tools used by those pros. Nothing like the Loos gauge we're considering for our 3/8" dia wire rig...and we can't find that Loos PT3 gauge for under $170 anywhere in the US.

So, lets see...If I'm cruising and I don't want too much extra gear around and I already have everything needed to use the method of pages 28/29 aboard....will I spend the $170 and buy the specialized tool that's going to take up space on my boat? Or, will I take the time to learn and use the method described? Hummm.

I love having the right tool for the job, but in this case, even with a lots of wires to tune on a schooner rig, I'm shying away from the rig tension gauges.
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Old 04-24-2009, 12:52 PM   #4
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An accurate ruler - a vernier ( both could be said to be components of a measurement gauge - a device) How about the formula using 1 x 19 stainless (what grade of stainless ? 304 - 316 which??) 1 mm of stretch per 2 metres of 1x19 SS wire is equivalent to 5% of the breaking load.

Where is this formula proven ? It sounds like a thumb suck - no scientific evidence. Why not 1.257mm per 2m equivalent to 6.2% of breaking load in 3 year old 304 SS 1x19 wire?

How about the categorical statement that all 1x19 SS wire stretches under load BUT returns to its original length when the load is released ? Does this also apply to 304 SS Wire that has been on a boat for say 5 years ? Compared to new SS 316 wire newly installed ?

The point regarding cost is valid of course - whatever process is used to set up the rig so it stays up, depends in the end on experience and common sense; especially ensuring that the rig is balanced fore and aft and athwart ships that it is equally taught on both points of sail.
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Old 04-24-2009, 05:25 PM   #5
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MMNETSEA, in regards to your questions... I'd think a proper way to consider this method would be to get the specs on the wire from the vendor and use that information to calculate your 5% load vs x distance. Of course, most vendors don't have a clue about the wire they're selling you and you'd probably have to go back to the maker--for example in the USA Loos publishes a lot of info about their wire rope.

However, boats are "bendy"...tension a rig, go for a sail in a stiff breeze and watch everything change. I'm not sure that anyone needs exact measurement beyond what this .pdf document advocates if all they're doing is tensioning a rig that is already installed on the boat.

When initially putting up the rig, there is a tremendous amount of construction stretch that must be taken out of the wires (especially if a tall rig) and one really does need to know the specs on the particular wire in order to figure out how much of that stretch needs to come out before fine tuning a rig. For example, in the case of our mainmast, I'm told that the construction stretch on the 3/8" 1x19 wire should be more than an inch and 7x19 about 3 inches. I'll be tracking down that "about" for an exact number shortly.

I just noticed that Calder recommends the same 5% load/stretch method in his Mechanical and Electrical Manual. As many cruisers follow Calder as a good standard, I'd imagine many cruisers are using this exact method for rig tensioning.

On the other hand, Brion Toss's Rigger's Apprentice gives a bit more detail which you might like. In a section on wire options he gives us a discussion of Elasticity and Elastic Limit. Here we learn that rigs are generally designed with the tightest wires tuned to at most 25% of the wire's strength. Now, the Rigger's Apprentice takes the reader through a discussion of rig design including spars/masts and allows one to use the expected loading on the particular boat and the rig design to figure out which wire rope is right for the job. If we follow this section a bit further, we learn (on page 146) that elastic stretch is a function of local load and wire rope diameter relative to the inherent elastic properties of the metal used in making the rig. A formula is given for the approximate percentage of stretch for a given length of wire rope:

e=[P/D^2] x F, where

e= elastic stretch as percentage of length

P = load on wire rope in pounds

D= nominal wire rope diameter in inches

F= the reciprocal of (A x E x 100)

Th info that goes into F= 1/[A x E x100] is that A is the cross sectional area of the wire rope in square inches, E is the modulus of elasticity (which tells you how much a substance stretches per pound of tension applied) Carbon steel, for example has a lower E than stainless steel. In this particular book, there are a couple nice little graphics showing us inches of stretch per 50 ft of wire at 25% load for an example stay configuration.

I hope that you find this information somewhat useful and that other cruisers will as well. In several places I've advocated the book, Rigger's Apprentice, as one that should be in a cruiser's library. Its the only place I've seen that a layman could read about rig and spar design and actually re-engineer their own rig on their own boat (unless they've got a really exotic 4 spreader set up with wires galore...).

Oh, I must make a disclaimer here....though I said I was shying away from rig tension gauges....we just bought the Loos PT3 gauge. That's what you get when two engineers are married--the curiosity just takes over I'll probably be verifying the 5% method with the gauge and I'll let you know how it goes.

Regards,

Brenda
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Old 04-24-2009, 11:42 PM   #6
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Hi Brenda,

Thanks for adding additional references.

As another curious person I wonder what effect the heat of the sun has in expanding 1 x 19 SS or 7 x 7 Galvanized . An analogy (albeit a poor one) is the lengthening of rail track. Wonder if boats rigged in the tropics should be re-tuned when entering colder climes? And, vice versa

of course.

Richard
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Old 04-25-2009, 12:47 AM   #7
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Hi Brenda,

Thanks for adding additional references.

As another curious person I wonder what effect the heat of the sun has in expanding 1 x 19 SS or 7 x 7 Galvanized . An analogy (albeit a poor one) is the lengthening of rail track. Wonder if boats rigged in the tropics should be re-tuned when entering colder climes? And, vice versa

of course.

Richard
Remember when I said boats are bendy? I think that the average cruiser has enough hull and spar flex that this would not matter to them. On rod rigging a high performance boat, it would likely make a difference, though. JMHO.
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Old 04-25-2009, 01:11 AM   #8
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Last boat I tuned was constructed of corten steel - no bend. Still curious to know how much 1 x 19 SS wire lengthens by 3.30 pm in the tropics?

Is there a time of day when best to tune the rig ?
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Old 04-25-2009, 01:44 AM   #9
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Last boat I tuned was constructed of corten steel - no bend. Still curious to know how much 1 x 19 SS wire lengthens by 3.30 pm in the tropics?

Is there a time of day when best to tune the rig ?
I'm beginning to think you're messing with me I bet you're grinning along about now...

However, you're right that a steel hull would have no bend as vs GRP or wood. Someone with a materials handbook could tell you the difference in elastic behavior under load with temperature--however, I cannot at this time give you a good reference on that.

Warm regards,

Brenda
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Old 05-28-2009, 01:34 AM   #10
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I have a NEW LOOS & CO. Professional Tension Guage, model PT-3 for cable sizes; 9/32, 1/4", 5/16, 3/8". I paid $239.00. Asking $125. OBO 781-837-1329 (I have pics available)
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Old 11-24-2010, 09:02 AM   #11
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this link goes to nowhere? can anyone help me ?
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Old 11-24-2010, 10:07 AM   #12
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No link posted - just a contact number.
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Old 11-24-2010, 02:12 PM   #13
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this link goes to nowhere? can anyone help me ?
The phone number is for this member selling a gage. You can PM him about it.
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Old 11-24-2010, 09:11 PM   #14
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A very good instructional article (with images) on tensioning a yacht's rigging is available as a .pdf download - HERE
This link to dowload PDF

yeah I already PMed him
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