Galv rigging - accounting for the extra stretch

[Orchidius]

Hi there,

One more about galvanized rigging, last one, I promise!

So I've got most all of it figured out now, just about ready to put my order in. Then it hit me, I can't just take the old SS stays to the rigger and ask for the same deal. The stretch characteristics of 1x19 SS and 7x7 galv are different, when putting the rig under tension, things probably won't add up and I might run out of turnbuckle room... All rig tensioning guides are also written around 1x19 SS rigging, so putting the rig under tension will be a different story alltogether...

How do you size galv rigging? "a little longer"? How little?

I'm going with 7 or 8mm 7x7 galv wire on a 12m mast.

Oh, and a little off-topic for this topic, but would you use it in a roller furler? I'm a tad hesitant because I won't be able to inspect it so easily, but I really kind of don't want to go out and buy a more expensive SS stay just for the forestay...

[Snowpetrel]

I went stainless under my furler. Stretch was eyeballed, I had my bottlescrews at about 3/4 to 2/3 extension with an untensioned stay, and then they took up to about 1/2 to 1/3 extension when tensioned. Loos have some formulas, as does ronstan and a few others for stretch. The amount of stretch for galv should be slightly less than the equivalent stainless, but if you use the figures for stainless you should be ballpark. Use about 15%-20% of breaking strain for the pretension on a simple masthead rig.

[charliehows]

I used 6-8inch lengths of gal chain at the base of mine - means you can be fairly cavalier in your measurements (as long as they're shorter than the existing wires) and cut the chain to fit at setup. If it stretches, you just cut out a link. Havent noticed much stretch in my rig 2 years on. It looks good on an older, less sporty boat, might not be appropriate for yours... For foresails and furler I kept ss - gal is too abrasive and the outer layer of gal gets worn off too easily.

[Jim Cate]

Ben, why would 7x7 galvo stretch less than 1x19 s/s? Seems to me that it would be the other way around due to the 7x7 construction which is inherently stretchier than 1x19>

Jim

[Snowpetrel]

Hi Jim, you are right with your example, 1*19 ss will stretch much less than 7*7 galv. I was referring to the specs for the same construction. Ie 7*7stainless vs 7*7 galv. The galv wire has a slightly higher modulas of elasticity. But its only about 5% or so from memory, so in practice it is negligable.