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Pa La O La 25-06-2005 13:22

Standing Rigging
 
Good day to all,

Looking for a bit of information. I have a 37 Prout Snow Goose and I am looking to find what would be the mean tension setting for the standing rigging. What Iím looking for is a ball park figure. I went on the hard to get the bottom painted but to pick me up I had to undue the back stays. I marked the turn buckles but I am unsatisfied with the tension. I gained access to a Loose tension gauge and found that not just my back stays were unevenly tensioned. I have 1-19 cable and it is metric (9mm) 5/16ish. Anyway I am trying to find what the recommended tensions are for the top bottom and back stay. The literature I have gives no starting point. I know Iíll need to test the tension on the lee side under sail but I am looking for a starting point.

Any advice?

Thanks for any comments or constructive help.

Gary - Shalimar, FL

delmarrey 25-06-2005 16:48

You state the word "backstays". Then you say "for the top bottom and back stay.

Not sure what you mean. I know some Cats have two backstays, p/s. But top and bottom? Are you talking about running backstays or shrouds or what? There are certain torque spec's for each wire size.

According to Loos Corp, manufacturers of rigging wire, guages, swaging machines, and tools, tension should be 1/10 of the breaking strength of the wire, for starters. For 1/4" wire that would be 820 lbs. for #302/304 stainless, and 640 pounds for #316 stainless. Strength for 302/304 wire is as follows:


3/16"...4700#
7/32"...6300#
1/4"....8200#
9/32"...10,300#
5/16"...12,500#
3/8"...17,500#


Strengths for type 316 wire are proportionally lower. Once tensioned, adjustments can be made for mast rake, etc as desired. Tighten lower shrouds first so as not to twist the mast. Most rigging problems, according to Loos, come from rigs that are too loose and allow the mast to "pump". Hope this is of help to one and all!

However, it is best to get your rigging tension specifications from the yacht manufacturer and to use a tension gauge to ensure they are correct. However if this is not possible you may like to proceed as follows.

The rigging tension has an important influence on both the durability and performance of the system. Contrary to popular thought a slack rig is more punishing to the cables, fittings, and hull than a properly adjusted tight rig, since it can subject the entire system to excessive movement and can cause misalignment, wear, shock loading, and fatigue. Similarly, the sailing performance is affected since the rigging tension determines the shape and deflection of the mast and the sag of the forestay. The expert skipper will benefit by maintaining consistent rigging tension while developing the optimum sail shape and sailing tactics.

This topic is divided into lateral bend, side lean, fore and aft bend and rake.

Masthead Rig - Lateral Bend

Since sails are designed to work with a mast that doesn't bend sideways it is obvious that any sideways bend needs to be eliminated. Sideways bend on a masthead rig is often caused by too loose or stretchy upper shrouds. This is not always easy to spot._ Check the_ angle of the upper windward shroud against the upper 6th of the mast and see if it has altered to a narrower gap as in the diagram below.
http://www.mckaymarine.com.au/images...le/Tunnin1.gif


As the bend increases the angle between the upper shroud and the mast narrows, increasing its leverage over the shroud. once the angle decreases to less than 11 degrees, the danger of ripping the shroud out of the mast or crumpling the spreader is acute. As well as this, side bend allows the head stay to sag excessively in a breeze, when it is most undesirable.

Talbot 25-06-2005 17:05

using monohull line tension is not a good idea on a cat. It is possible to overtension the hull and lead to boat failure, especially on the snowgoose where the rigging points for the lower shrouds (the ones connected to cabin roof) have a record of causing problems. If nobody else on this forum has the figures, then recommend that you ask Broadblue boats, as they have some of the old Prout people in the firm.

delmarrey 26-06-2005 04:58

Wire tention is wire tention weather is be mono or multi. If tightening the wire to it's spec's damages the hull. I would suggest down sizing. What's going to happen, when one is out in a gale or heavy seas, and that wire gets that tention of the larger wire while being tossed around. Something has to give, and it better be the rigging not the hull!

But like I stated earlier----- "However, it is best to get your rigging tension specifications FROM the YACHT MANUFACTURE and to use a tension gauge to ensure they are correct."

exposure 30-06-2005 03:11

Here's what little I know...

Certainly getting the specs from a manufacturer is best. But, if you cannot, the reccomendation I have seen is to tension the forestay to 15% of the breaking strength. This will in turn tension the backstays. The trick is to balance the mast rake by adjusting the stays and end up with the 15% load on the forestay.

Shrouds are should be adjusted to a starting point of about 10-12% of breaking strength and then observed when close hauled in a brisk wind to ensure that the leeward shrouds do not go slack. Of course you need to balance starboard and port and upper and lower so the mast is straight.

This is how my Prout was last done according to the previous owner. I too have a set of gauges and need to get out and check it for myself.

I'll just add that to the end of my project list! :rolleyes:

Woody

delmarrey 30-06-2005 17:46

Fore & aft stays
 
On racing vessels the F/A stays are adjusted to what ever condition, or sail is up. Like on mine I have a hydraulic back stay. And I'm constantly adusting pressure in relation to the direction and wind conditions.

So stating a specified F/A stay tension, in reality, is to feel. Experience will make the final dicission. Do start out with the 10 - 15% and go from there.

Also, in a rolling sea the F/A stays will increase and decrease as the vessel goes over each wave............................._/)

Pa La O La 28-07-2005 12:50

Hey,

Thanks all for the reply. I've been down in Key West, back home now. This will give me something to think about. Great sail down and back. Don't think I'll go the inside past the 1000 islands again. About got ate alive.


Again thanks

Gary


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