Rig tension gauge

[haydude]

I was looking to purchase a rig tension gauge, but I was shocked at the price for the 10mm wire section model (Loos PT-3M), £200!

After all it is made of a not so accurate spring scale and a plate with pins and numbers.

Short of using the Selden folding tape method, which is good only when starting from scratch, is there a simple guide/formula to build and calibrate an accurate tension gauge?

I thought I could use a bar with pins and a scale that I could purchase anywhere, but how to calibrate the scale against the wire section and distance between the pins?

 

[john_morris_uk]

The cheapest way to measure tension if you are setting up from scratch is to use the 'how much has it stretched' method. Bit of tape on the wire a couple of metres appart and use a steel rule to measure how much the wire stretches as it is loaded up.

If you need to measure the tension actually in a loaded wire - I don't know of a cheaper alternative to the commercial tension gauges.

 

[SHUG]

Good idea.
If the top pin is the pivot then the force on the lower pin would be Tension times tangent of the angle that the rig is deflected through.If the distance between the pins is D and the distance from the top pin to the attachment point of the spring balance is L then the force at the spring balance will be T tan(angle).D/L. You could attach a bit of protractor to measure the angle or you could use a linear scale and use tan(angle)= deflection/L and carry a calculator.
Having said all that , it might be more practical to make some calibration measurements on an already calibrated rig. Another option is to use a torque wrench which is set to click at the correct loading and then you would just need a 1/2 inch drive at the end of the bar.
Interesting project. I'm not saying I have nailed the analysis but it will get the ball rolling!!

 

[Deleted member 36384]

Stretch Method Description Source

Illustrated Sail and Rig Tuning", Ivar Dedekam, Fernhurst Books, ISBN 1 898660 67 0

The above book describes tensioning your rig by the method described by John above. The method is independent of wire diameter and is quite accurate.

The book describes how length change increments between a tape mark 2m above the lower bottle screw directly represent tensile load. The initial load is hand tight. It also describes the correct tension settings and how to set up various rigs: fractional and masthead and associated order of adjustment of shrouds.

Its a very handy book for all sorts of sail trim tips as well. I have used the book to tension rigs but I am at work, abroad, so dont have access to the description.

 

[Csail]

If you know anyone in the raf or aviation game just borrow one.

 

[30boat]

The stretch method is the most accurate and also very free.As was said on a 2m long length of wire every milimeter of elongation equates to 5% of the breaking strength of the wire irrespective of diameter.This is good for 1by19.Other types are dscribed in the book .

 

[haydude]

The above book describes tensioning your rig by the method described by John above. The method is independent of wire diameter and is quite accurate.

Thank you, as I said I know the method, which is exactly what I did not want to use because it involves loosening the rig first, and it is useful only when installing the mast the first time. Not practical only to check once the mast is up and the rig needs just tuning.

 

[haydude]

Another option is to use a torque wrench which is set to click at the correct loading and then you would just need a 1/2 inch drive at the end of the bar.
Interesting project. I'm not saying I have nailed the analysis but it will get the ball rolling!!

I am not sure I understood the use of the torque wrench. Please could you illustrate with a drawing?

 

[Poignard]

How about using one of these:

http://www.mbbltd.co.uk/valve_keys.html

with one of these:

http://www.amazon.co.uk/Super-Samson-Spring-Balance-25kg/dp/B000IU3DTW

?

 

[john_morris_uk]

What exactly are you trying to do? Is there a problem with the rig? Are you racing? What sort of rig is it?

Getting the mast upright and straight is the first part - but if you give a clue as to what the problem is that you think you need a rig tension gauge for, then perhaps people will come up with some other alternative ideas?

 

[Lakesailor]

You don't say what sort of boat you have.

I use the tried and tested twang-the-shroud technique on the sub-20ft boats I've had.

 

[Deleted member 36384]

Calculating Rig Tension By Horizontal Deflection

Read this from the Beneteau Forum it describes what you want.

 

[Quandary]

Yep. just stand facing the mast, reach out at shoulder height to the shrouds and tug hard. I have been doing it this way for donkeys years without problems so far. Once you go sailing get her hard on the wind, tighten the lee shrouds if they LOOK slack. Tack, do the same plus a bit. Check again with sails down for plumb and straightness, lock off bottle screws, mark as starting point for next year.
Your arm is as sensitive as most rig gauges.

 

[Bosun Higgs]

Illustrated Sail and Rig Tuning", Ivar Dedekam, Fernhurst Books, ISBN 1 898660 67 0

The above book describes tensioning your rig by the method described by John above. The method is independent of wire diameter and is quite accurate.

.

Dont even bother. Just look on the Selden site and the info is there for free.

 

[Rigger Mortice]

I bought one of these
http://www.compass24.com/web/catalog/shop/technics_chandlery_rigging_screws/4858013

Work fine, but they are no use to OP as they don't go up to 10mm. He shouldn't have such a big boat.

Tensioning things properly makes a real difference. It always ends up much tighter than the "twang, that'll do" method. I notice the difference time and again when crossing boats when alongside.

 

[Lakesailor]

That's why I asked what size boat he has.
On small cruisers overtightening the rig will inevitably result in distortion of the coachroof or hull.
I've had to fit adjustable mast compression posts to two boats to overcome this.

On a much bigger boat the forces are so much higher that near enough is probably not good enough.

 

[Rigger Mortice]

As he is looking for something for 10mm wire his boat will be a bit bigger than yours or mine.

 

[haydude]

To clarify I was not looking for advice on a method to tune the rig, but rather trigonometry and physics formulae to build a device to measure loads on a 10mm wire.

That is because I know that £200 for such device is a RIP OFF! Looking at material and low-tech nature of it, it should not cost more than £50 to the consumer still leaving plenty of space to profit for the producer and reseller.

To build it the cost should be limited to a spring scale (£12?) an aluminium bar and two pins, plus the time to assemble and calibrate.

 

[Csail]

To clarify I was not looking for advice on a method to tune the rig, but rather trigonometry and physics formulae to build a device to measure loads on a 10mm wire.

That is because I know that £200 for such device is a RIP OFF! Looking at material and low-tech nature of it, it should not cost more than £50 to the consumer still leaving plenty of space to profit for the producer and reseller.

To build it the cost should be limited to a spring scale (£12?) an aluminium bar and two pins, plus the time to assemble and calibrate.

£12......i wouldn't get out of bed for that.

 

[P4Paul]

Where abouts in the UK are you?

You never know, someone may have a tuning gauge you could borrow to check your rig.....