Charlie,
Poke around on the web. The question you're asking comes up frequently. Below is one reply.
His method of using a tape measure seems crude. I've got 1" inch travel dial indicators. Once you decide your wire size and amount of tension, I'd be happy to give you a hand.
OTOH, if you're selling the boat, a knowledgeable buyer might want to know the job had been professionally done. Ask some local boatyards what they'd charge to do a tension check once you had re-stepped the mast and re-wired the stays. Once you find a buyer, then have the work done, or give them a credit.
Charlie
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"Optimum tension is generally considered to be about 15% of the wire’s breaking strain for the cap shrouds; less for the lowers; and about 20% of breaking strain for the backstay on a masthead sloop. Fine, all you need now is a method of testing.
"You can buy rig tension gauges. They’re quite costly, and usually only fit a small range of wire sizes. And you may need to know the breaking strain of the wire first.
"There’s another method which costs nothing and is easy to do. It also works regardless of wire size, and you don’t need to know what the wire’s breaking strain is. It relies on the fact that a 2-metre length of wire stretches by 1mm when 5% of its breaking strain is applied (and 3mm for 15% and 4mm for 20%). It’s easier to explain with a diagram, but as we’re restricted to words, here goes...
"Assuming your mast is up and more or less in the right position, slacken off the shroud rigging screws (by equal amounts on port and starboard) and the backstay rigging screw. Take an ordinary DIY steel metric tape measure. Pull out just over 2 metres of tape. Fix the end of the tape measure to one of the cap shrouds, above head height, using sticky tape, so that the 2 metre mark on the tape measure is hanging a little way above the top of the rigging screw. Put a bit of string loosely around the tape measure and the shroud at the lower end, to hold the tape measure against the wire. Wrap a piece of masking tape around the shroud, in line with the 2 metre mark on the tape, and put a pen mark on the masking tape exactly at the 2 metre mark. Now, as you tension the rigging, you can see at a glance how much the 2 metre length of wire has stretched.
"Tighten the rigging screws (by equal amounts on port and starboard) until the pen mark on the masking tape shows a 3mm stretch (which equals 15% of the breaking strain of the wire). You only need to measure the stretch on one side of the boat, because the other side will be equally tensioned. Then tighten the lowers so they feel a bit looser than the cap shrouds, keeping an eye on the mast alignment. Then put the tape measure on the backstay and repeat the operation, using 4mm stretch to indicate 20% of the breaking strain.
"That’s your starting point. Watch the lee shrouds when you’re sailing. If they go slack, you need more tension. Purists may scoff (and probably will) but at least this method is something you can do yourself, easily and without incurring expense. My big worry is that it’s so simple it might be considered too close to the "Blue Peter" school of marine engineering!"
Finally, the age of your yacht makes no difference. Some hard-used boats start to bend (hog) if the rigging is done up fully, but that shouldn't be a problem with a Westerly.http://www.ybw.com/forums/showthread.php?19654-How-tight-should-the-standing-rigging-be
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