Rigging tension methods

[Vara]

May well be reinventing the wheel here but;
Yesterday(and many times over the last year) there was a question about setting up rigging and getting the right tension,which I answered by directing to Selden Manual where they outline the method I have always used to measure the stretch in the shroud with sticky tape,tape measure and vernier gauge.(Very Blue Peter).

On thinking about it I think you could achieve the same result by calibrating your bottle screws either empirically by measuring the uptake of x revolutions of screw x2 (to account for double action) or by calculating using pitch of thread.By then calculating the stretch required over entire length of shroud you could then apply correct tension simply by whacking on the calculated number of turns on the bottle screw and thus eliminating any setting up or measurement once the initial calcs had been done.

Anybody see any problems with this?Or am I merely reinventing the wheel and loads of people have been doing this for years and not telling!

 

[tome]

Your method would work, but the Selden method measures the stretch over a fixed length of rigging (usually 1 or 2 metres). If using the bottlescrews, you would need to calculate the stretch for each screw based on the overall length of its individual stay.

When I use the 'Selden' method I measure the gap between the 2 screws in each bottle screw and note this for future adjustments.

 

[bruce]

better to get a LOOS gauge or other tension gauge and do it right, stays stretch and may not stretch the same on both sides...

 

[Vara]

You are of course absolutely right but a Loos gauge would cost me the equivalent of 62 pints of Guinness,a sacrifice I am not prepared to make.

Seriously I have used a Gauge and am not entirely convinced that they are as good as they say.But that maybe the fault of an inexperienced operator.

As to shrouds having different "stretch" characteristics surely this would affect reading of gauge as well as,in essence they are measuring the same thing.

What I am looking for is a quick relatively foolproof,and cheap way of getting the correct tension in shrouds

 

[bruce]

guess you could use a guitar tuner and pluck the stays and measure res.

 

[yachtie8]

Use pendliums from the masthead..and have a "feel for the rig" nad therefore your boat

 

[Graham_Wright]

Out of idle (worthless?) curiosity, just did a few sums to evaluate the effect of heat on the tensions.
With coefficients of 10.4 and 23 X 1/1000000 for stainless steel and ali respectively, a 38 foot mast and a temperature swing of -20 to +50 the differential expansion is around 9mm.

How's that for useless?

 

[Graham_Wright]

Out of idle (worthless?) curiosity, just did a few sums to evaluate the effect of heat on the tensions.
With coefficients of 10.4 and 23 X 1/1000000 for steel and ali respectively, a 38 foot mast and a temperature swing of -20 to +50 the differential expansion is around 9mm.

How's that for useless?

 

[Vara]

Sorry too complicated for me.
In simple terms does that mean that my mast will fall down when it's very hot or very cold?

 

[tome]

[ QUOTE ]
guess you could use a guitar tuner and pluck the stays and measure res.

[/ QUOTE ]

Feasible for relative measurements but colmce wants absolute tension and is suggesting an alternative method. I have a Loos gauge but it isn't quite the answer to a maidens prayer.

Provided he knows the length of each stay and is handy with a claculator, his method will work ok. Same could be said for measuring tuned resonance provided you knew the length of each stay. This would turn the observation from relative to absolute.

Better than your first reply!

 

[john_morris_uk]

Tyring to calibrate the bottle screws for tension would probably be a futile exercise. You will not be able to measure how much the hull has deformed versus the rigging tensioned and so any value would be meaningless.

Its very easy to measure the stretch in a 2m length of 1 by 19 Stainless wire and work out the tension from that...

 

[tome]

You're probably right, although the resonance idea would still work provided you knew the rig dimensions.

 

[oldsaltoz]

G'day Colin,

There is a simple way, we made our own tension meter, a small length of stainless flat bar with two pegs through it bent toward each other on the working side, later we replaced the pegs with old halyard sheaves; another flat bar at right angles to the pegs formed a lever with a 6 mm hole drilled close to the outer end; another length of flat bar was attached to the bottom of the plate with the pins, this bar had 'V' cuts in it so that it formed a curve like the lower part of the letter 'C'.

Place a sample length of stay between the pins and pull down the bar at right angles to the stay/pins till you get the required / specified stretch. Mark the curved bar, now put a simple fish scale into the 6 mm hole on the end and note the pressure required to achieve the required tention, then multiply by the length of each stay. Seemed to work ok, never dropped a mast or broke a stay.

This was all done 40 or more years ago so if I have missed a bit, I'm more than confident someone will correct me, or perhaps even agree.

Avagoodweekend.............

 

[Vara]

I am Baldrick to your Blackadder,that on reflection is a serious flaw in my otherwise cunning plan.Back to the sticky tape and gauge it is then.

 

[angelsson]

Could you do a sketch of your tension meter?
Thanks