Rum_Pirate
Well-known member
How tight should standing rigging be on a 40'0" cedar strip and epoxy catamaran?
Shrouds ?
Back Stay ?
Forestay ?
Shrouds ?
Back Stay ?
Forestay ?
How tight should standing rigging be?
- Thread starter Rum_Pirate
- Start date
30boat
N/A
That's acomplicated one.How's the rigging attached to the hulls?
Poignard
Well-known member
Here's a link to the Loos tension gauge instructions. Maybe that will give you an answer.
http://www.loosnaples.com/how-to-use-pt-series-tension-gauges
http://www.loosnaples.com/how-to-use-pt-series-tension-gauges
pvb
Well-known member
The answer is probably "tighter than an owner would ever dare". Get a rigger to do it properly.
D
Deleted member 36384
Guest
Page 28 provides instructions for tensioning and gives a table of ultimate tensile strength for various wire sizes. You can work out what the tension will be from the instructions when rigged correctly. http://www.riggingandsails.com/pdf/selden-tuning.pdf The tension is 15% of the 'breaking load' (ultimate tensile strength). I assume this will be the same for your cat.
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Rum_Pirate
Well-known member
Rum_Pirate
Well-known member
Lakesailor
New member
Standing rigging is only a part of the mechanism. the hull and fixing points are just as important.
I had a wooden boat which, as you tightened the shrouds, you could see the gunwhales moving together.
I had a wooden boat which, as you tightened the shrouds, you could see the gunwhales moving together.
30boat
N/A
I was asking because in a muiltihull the angles are greater and the greater they are the less tension is needed.So it must be established what the shroud base is before tensions are decided on.
jwilson
Well-known member
Not always on some multihulls - you have the potential to stretch hulls/crossbeams rather than increase rig tension.
pvb
Well-known member
Which is why my full reply included the advice "Get a rigger to do it properly."
Graham_Wright
Well-known member
I have noticed a marked alteration in rig tension dependent upon ambient temperature.
Coefficients are stainless steel 10.4 aluminium 23.
Doing the sums for a 20 metre mast shows a length difference of 13mm for a 50°C rise in temperature.
(Takes courage to do sums when there are so many mathematical genii on the forum!).
On my boat, the difference is quite marked but the actual rigging and mast temperatures may be significantly higher than ambient du to radiant heating.
Coefficients are stainless steel 10.4 aluminium 23.
Doing the sums for a 20 metre mast shows a length difference of 13mm for a 50°C rise in temperature.
(Takes courage to do sums when there are so many mathematical genii on the forum!).
On my boat, the difference is quite marked but the actual rigging and mast temperatures may be significantly higher than ambient du to radiant heating.
pvb
Well-known member
I don't know where you found your coefficients. Most people consider that stainless steel (316) has a linear thermal coefficient of 16 to 17 per °C, not 10.4, so the length difference is much less than you've claimed.
Graham_Wright
Well-known member
Mt reference book is Kempe's Engineers Book volume 1 page 80A. Coefficient is 10.4 X 10 -6 (don't know how to do superscripts). Mild steel is 11.0. Maybe these are incorrect.
However, empirically, the change on my boat is most marked. (I haven't done the trigonometry on the rigging plan as that is a stage too far!).
vyv_cox
Well-known member
A 50 degree C rise in temperature would be something of note! Presumably most people set their rigging up in reasonable ambient temperatures, so at worst there might be a variation of +/- about 20 degrees in extreme cases.
Graham_Wright
Well-known member
I don't think the air temperature is what counts. Try grabbing a piece of stainless when it has been sun irradiated for a while!
30boat
N/A
I did ,yesterday.It hurt!
rogerthebodger
Well-known member
Not a much as walking on a steel deck in the middle of the day in summer or even winter where my boat is.
pvb
Well-known member
I think you may be looking at °F coefficient, rather than °C. 316 stainless has a coefficient of 16 to 17 x 10-6 per °C, see these references...
http://www.upmet.com/products/stainless-steel/316316l/physical
http://www.aksteel.com/pdf/markets_products/stainless/austenitic/316_316l_data_sheet.pdf
Graham_Wright
Well-known member
No - they are definitely °C. It gives the conversion to °F. I agree other references agree with you.
I've had these reference books since '69. Perhaps things have changed since then!
Anyway - the point remains. Rigging will tighten as the temperature increases assuming you have an aluminium mast and steel or stainless wire. Try it. It's quite marked.
