7x19 Wire Shrouds

[AsterixDeGaul]

Originally Posted by DCockey

Our trailerable sailboat has 7x7 rigging which is much more flexible and less prone to kinking than 1x19 but has less stretch than 7x19. It's not as widely available in stainless as 1x19 or 7x19.

hehehe... Last time I saw 7 x 7, it was used as clothes line

7 x 19 will stretch far too much for any standing rigging but i suppose if you never go out in over 12 knts, you will never notice

[DCockey]

For the same diameter:
7x7 stretches 76% more than 1x19
7x19 stretches 138% more than 1x19

Sounds like a big difference, but how big is it in absolute terms?

Whether that is "too much" depends on the rig and how critical a small performance increment is.

With our boat it's not a noticeable difference, but then we don't race and a performance oriented sailor wouldn't sail our boat.

http://www.loosco.com/index.php?page=wire-rope-stretch

[DCockey]

Originally Posted by philSweet

One "note" regards synthetic rigging. I've heard a couple reports of boats being refitted with synthetics that hummed outrageously. Owners couldn't stand being on the boat. The only thing I can think of is that the spirals on wire rigging trip the vortexes in a random manner and that limits sympathetic vibrations.

Probably a combination of larger diameter and lower mass of the synthetic rigging compared to wire rope or rod. Frequency of shed vortices is inversely proportional to the diameter. Modal frequencies are inversely proportional to the square root of the mass. So if the tension is the same, a larger diameter, lower mass synthetic stay will shed voritices at a lower frequency and have higher modal frequencies. More likely that the frequencies will match and the stay will hum.

[Stumble]

DCockey,

One of the problems with 'stretch' in wire rigging is that often what you see is elongation of the wire as the wire starts to unwrap. This constructional stretch (CS) is fine, but one of the problems with using wire with more CS is that it takes significantly more pre-tension on the rigging to get the same mast bend. This extra load must be carried all the time, and of course adds to the total loads the rig experiences when shock loading. This can lead to faster failing of hardware, oil canning, detaching the deck ect..

Of course this isn't always so extreme, but in one case we measured a reduction of the static load on the top stays of 40% when switching from wire to dynes duc. I highly highly doubt this is typical, but reductions of 10-15% seem normal. The worst case was a very tall mast with lots of rake, and very small wire. This lead to really cranking on the tension to get the right shape in the mast.

[SuperPiper]

Originally Posted by DCockey

For the same diameter:
7x7 stretches 76% more than 1x19
7x19 stretches 138% more than 1x19

I really appreciate a sailor who can quote the numbers. You are good.

Unfortunately, your numbers are not in my favour. You make my 7x19 substitution look questionable.

I did increase from 1/8" 1x19 to 5/32" 7x19 so I may not be too disadvantaged. Also, I'm not sure that a little bit of stretch in the shrouds will be discernible with a mast just the diameter of your wrist. The rig would probably be soft even with SS rod rigging.

Good info. Thanks DCockey.