rig tension

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jkim1

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I have been looking for a rig tension gauge, needless to say they are pound for dollar prices here. And most likely I will have to buy two as like most yachts, I have two different sizes of rigging. I was thinking about using a torque wrench the type that has two bars one of which bends according to torque and the other which moves a pointer on the scale. I wonder if anyone has done any work on this as to torque / deflection and rigging size. and the length of the plate and pins which would be used to deflect the rigging. For example pin distance 25 cm deflection 2,5 cm, torque 25 foot pounds. Rigging wire size 8mm.The connection of the torque wrench being in the middle of the two pins. Any mechanical engineers out there?

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Interesting concept which might work. I use a rigging gauge which handles 8 - 10mm but don't find it easy to use.

One method which is widely used is to slacken the rigging and then to measure the stretch over a length of (say) 2 m using a tape measure. This works regardless of rigging size as the stretch (in mm) is directly related to % tension.

There are load cells available which replace the pin and measure direct rigging tension. I intend to buy one of these for a project in the near future and will see if I can establish a relationship between torque/deflection and tension. I suspect the deflection will need to be measured accurately, but food for thought.

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Your idea will probably work but have you looked at the SureCheck rig tension gauges from <A target="_blank" HREF=http://www.jimmygreen.co.uk>http://www.jimmygreen.co.uk</A>.
Not as expensive as most (I added a small eye to get free carrage). The one I have covers 6, 7 and 8mm in the one instrument.
Perhaps that would cover your wire sizes.

Iain

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Thinking ....

A Riggers Tension meter ..... often is a split plate fitted to the wire and then pulled, the amount of deflection of the pointer giving an indication of tension. This pull acts on the meter and imparts to the wire as a whole.... as the meter lays along the wire.

The Torque wrench idea albeit good will actually act on a limited length of the wire as it effectively twists / deflects that section. WHY ? Assuming that we are pulling the arm down ..... the top of the 'jaw' will pull the wire out, while the bottom part will push it in ....

Just a thought ....... I am probably wrong - but maybe the torque wrench will show force to twist / deflection rather than tension.


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I came - cos they said was FREE Guinness !
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As stated, rig is tensioned almost regardless of boat. On main stays (backstay, forestay, caps) the rigging is set up to around 15 - 20% of breaking strain, somewhat less on lowers and babys etc.

There's a great little book from Fernhurst (a search would find it on this forum) which gives a well-illustrated introduction to rig tuning and sail trimming.

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Well that was fast, I didnt expect so many replies in such a short time. I will check out that rig tension gauge. Basically like most I have a fair idea of what the tension should be by pulling on the rigging, a sort of calibrated pull if you like! I am thinking though that a rig tension gauge would allow me to equalise the tension in the stays to a greater degree of accuracy than a calibrated pull. I have thought that a spring balance pulled on a defined length of shroud and the deflection measured would probably work. And this may be an easier way to go. As one reply suggests. As for load cells a very good idea if the facilities are available both to read and calibrate them. It may even be possible to pluck the stay and measure the frequency on an oscilloscope, if the tensions are the same and the lengths are the same then so should the frequency. In the meantime I will check that rig gauge out. Its been fun thinking about it anyway. Thanks

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Re Surecheck tension meters - 1 reason why they're relatively cheap - to put it simply - they're crap.

I have one & there is simply no consistency to the tension it measures - take a reading 1 minute, then take another 2 seconds later - get 2 different readings!

I have used ones by a company called LOOS (which you also see advertised in the UK), which seem much better. I'm sure there are other good ones as well.

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I havn't tried the gauge in anger so can'not make any judgement.
Just had all the standing rigging delivered yesterday. All 8mm with all the top fittings sweged on. So time will tell. The gauge looks ok to me.

Iain

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I was going to come in with the idea that tension can be gauged by monitoring the stretch of the wire, but Tome beat me to it.

Irrespective of the wire size a tension equal to 5% of the ultimate tensile strength (UTS) will stretch 2m of wire by 1mm so for a tension of 15% UTS 2m will be strechted by 6mm.

You monitor this by attaching a scale marked on a wooden batten to the rigging as you tighten it. BUt remember you only have to measure on side but tighten the screws on opposite sides by an equal number of turns.

The pecision is not great obviously but is a hell of a lot better than your (un)calibrated pull.

Tome's figure of 20% is a bit high IMHO but if he knows better then I bow to that. The tension should not exceed 25% UTS.

For the record the UTS of 5mm wire is 19kN, 6mm 27kN, 7mm 35kn, 8mm 45kN, 9mm 57kN, 10mm 71kN, 12mm 102kN. (I'll leave you to convert Newtons to pounds if you want but roughly a Newton is nearly 1/4 pound ie about the weight of an apple!)

My source of infomation is a "hints and advice" booklet published by, as then, Kemp Masts Ltd.

<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>
 
Don't you just tension it untill it feels right then sail a bit and see how she sails and alter things accordingly?

Or am I just being naive?

- Nick



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Re: sorry, bit of a misprunt

My figures went a bit adrift there. The stretch equivalent to 15% UTS should of course have been 3mm in 2m.

<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>
 
Should have said 'max of 20%'.

Most rigging is (according to riggers I've spoken to) set up too slack which allows mast pumping, fatigue, and snatching loads. Better to be tight than loose, as I discovered to my disadvantage in a lively channel crossing.

Regards
Tom

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Whilst there are rig issues with having the rig too slack, what about the other end of the equation - the hull?? If you have a very tight rig and leave it that way all the time, the hull/bulkhead/deck/maststep/kingpost whatever arrangement will deform over time.

When the first Whitbread in around 1970something finished I was living in Plymouth and went to see the boats in Millbay when they arrived. Overheard a conversation from GBII or III whichever it was in those days looking at marks on the deck. "That's where we got overenthusiastic with the backstay adjuster" - i.e. the boat had been bent somewhat.

Dinghy and cat sailors use high rig tensions, but they are always eased when not sailing for that reason. I used to tension my rig on the Tornado with the 7:1 mainsheet on a trapeze wire and substantial welly....

<hr width=100% size=1>Larry Botheras

Anderson 26 "Amber"
 
We run about 10,000 lbs (dependant on wind stringth, direction and sea state) on the backstay - but always ease it when not sailing, leaving just enough tension to stop the mast moving around.

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I like the spring balance idea!! At least you could ensure equal tension on all rigging of the same length.
I guess if you had it all set up 'proffesionally' you could record the spring balance tensions for future use. One up on tweaking by hand and rack of eye I guess??

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Its very simple really as another person posted...measure the stretch in the wire over 1 metre....3mm stretch represents the correct tension for rigging...e.g. 15% of the wire's breaking strain. I rig up a steel 1M rule and wrap a piece of masking tape around the the bottom and mark the start line...just tension till it has a 2-3mm gap...thats it. Just remember to tension the shrouds in pairs as one has a bearing on the other.


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