Rigging Tension ???

[Dangen]

Hi,
I have a Islander 30, with 7/32 standing rigging. untill now I have always adjusted the rigging tension by feel, only this year I decided use a loos tension gauge. As per their recomended tension I adjusted the shroud at 700 pounds, backstay and forestay at 1000 pounds. I find the shrouds way too loose. When the boat heels, the lee side takes way too much slack to my taste, so I set everything at 1000 pounds, it's all nice and sturdy, but the mast vibrates alot when its really windy and the sails or down. I'm not sure if it vibrates because it's too tight or not enough? I would appreciate to have any pointers. At what tension is it starting to be too tight for 7/32? Thanks, Daniel

[Stumble]

Daniel,

there is absolutely nothing wrong with your leeward shrouds being slack. In fact it is so typical on race boats, I don't even know where the roumor is that its a problem came from.

I would double check your rigging numbers, because 1,000lbs of tension would be a lot for your shrouds. Assuming they are 1x19 316 stainless wire rigging, they have a MBL new of 5,600lbs. 1,000lbs is within the typical working load, but definatly at the high end.

[Sandero]

Too slack cause them to bounce around and that leads to cracked swages... I had the lee shroud break some wires after a 600 mile run on on tack. I don't know that the shroud was too slack.. but it was slack and it did develop some broken strands and was replaced.

[speedoo]

Originally Posted by Dangen

Hi,
I have a Islander 30, with 7/32 standing rigging. untill now I have always adjusted the rigging tension by feel, only this year I decided use a loos tension gauge. As per their recomended tension I adjusted the shroud at 700 pounds, backstay and forestay at 1000 pounds. I find the shrouds way too loose. When the boat heels, the lee side takes way too much slack to my taste, so I set everything at 1000 pounds, it's all nice and sturdy, but the mast vibrates alot when its really windy and the sails or down. I'm not sure if it vibrates because it's too tight or not enough? I would appreciate to have any pointers. At what tension is it starting to be too tight for 7/32? Thanks, Daniel

1. Whose recommended tension?
2. Can you go back to your "by feel" setting and measure the tension with the loos?
3. It's much preferable to have leeward shrouds loose than to have your mast vibrating.

[foolishsailor]

Rigging tension is not just about holding the mast upright. It is also integral to sail shape and upwind performance. Your shrouds induce prebend in the mast and also allow the top of the mast to fall off to lee to help spill wind in heavier air.

If you want optimal tuning for your rigging find a rigger to tune it once and then measure lengths and apply the loos guage for tension. Now you have your base settings and can adjust in the future to that. Local sailmakers also will offer to help tune the rig, usually involves buying a sail though...

There is more to it than just too loose or too tight and it is valuable knowledge to have as a sailor....

[Stumble]

Originally Posted by defjef

Too slack cause them to bounce around and that leads to cracked swages... I had the lee shroud break some wires after a 600 mile run on on tack. I don't know that the shroud was too slack.. but it was slack and it did develop some broken strands and was replaced.

This would normally be blamed on cycle loading, but in order for cycle loading to have any effect on stainless there have to be loads in excess of 30% of the tensile strength of the part. Much more likely there was a crack in the swage before you set out, and the trip caused the wires to part. Or the swag was placed improperly. It would be hard to determine without knowing the whole story.

But the one thing it really can't be is from loose shrouds. As the load on stainless goes down relative to the parts MBL the number of cycles it can absorb without failure goes up. As stainless steel approaches 30% of MBL the number of cycles it can absorb goes up so fast, that beyond a certain point it is assumed to be infinite. A working load of 20% as in this case is still well below the critical load to cause cycle loading failure, but it is getting close.

[cal40john]

Originally Posted by foolishsailor

Rigging tension is not just about holding the mast upright. It is also integral to sail shape and upwind performance. Your shrouds induce prebend in the mast and also allow the top of the mast to fall off to lee to help spill wind in heavier air.

If you want optimal tuning for your rigging find a rigger to tune it once and then measure lengths and apply the loos guage for tension. Now you have your base settings and can adjust in the future to that. Local sailmakers also will offer to help tune the rig, usually involves buying a sail though...

There is more to it than just too loose or too tight and it is valuable knowledge to have as a sailor....

Picture I found for an Islander 30 is a masthead single inline spreader with fore and aft lowers. Doubt he has an adjustable backstay, so prebend will be set by the lowers, if the sail was cut for any on an old rig like this in the first place. I would think mast top bending off to the lee on this rig is going to be pretty subtle as well.

[Sandero]

Stumble,

Thanks for that post... You probably are correct and I can't dispute your explanation. I simply assumed the shaking of the shroud worked the swage and it failed... This was my assumption.

Jef

[foolishsailor]

Originally Posted by cal40john

Picture I found for an Islander 30 is a masthead single inline spreader with fore and aft lowers. Doubt he has an adjustable backstay, so prebend will be set by the lowers, if the sail was cut for any on an old rig like this in the first place. I would think mast top bending off to the lee on this rig is going to be pretty subtle as well.

Lowers always play a role, but the uppers are the ones that induce compression on the mast, the lowers tension level is the one that allows the compression to become prebend.

Not familiar with the boat but The rig you deacribe doesnt soind like it would have much "tunability". The prebend can be even more important for an old sail as you can increase the prebend to additionally flatten an old blown main.

But again we come to the rig, as you said - you can only work with what you have

[Stumble]

Originally Posted by defjef

Stumble,

Thanks for that post... You probably are correct and I can't dispute your explanation. I simply assumed the shaking of the shroud worked the swage and it failed... This was my assumption.

Jef

Jeff,

It is possible for a very loose shroud to cause the turnbuckle to turn, though they should be pinned in place. But a cracked swag is almost definatly crevice corrosion. In fact I have never seen a broken swag that wasn't though it could happen. If it was the wires that parted, there could be a number of problems, but again if they are stainless you most likely had crevice corrosion issues.

Sometimes there can be residue from the polishing process that can cause accellerated corrosion on the wire, but that is pretty rare.

[barnakiel]

Originally Posted by foolishsailor

(...) Your shrouds induce prebend in the mast and also allow the top of the mast to fall off to lee to help spill wind in heavier air. (...)

In Islander 30? I thought they were top rigged.

b.

[cal40john]

Originally Posted by foolishsailor

Lowers always play a role, but the uppers are the ones that induce compression on the mast, the lowers tension level is the one that allows the compression to become prebend.

Not familiar with the boat but The rig you deacribe doesnt soind like it would have much "tunability". The prebend can be even more important for an old sail as you can increase the prebend to additionally flatten an old blown main.

But again we come to the rig, as you said - you can only work with what you have

These lowers are fore and aft. The middle is fixed in place. The only prebend going on here is if the forwards are tighter than the afters.

John

[barnakiel]

Originally Posted by Dangen

(...) At what tension is it starting to be too tight for 7/32? Thanks, Daniel

Daniel,

Much depends on your boat. There is no one bullet rule for all designs. If there are other boats of your design around, ask their owners how much tension they apply. This may be a good first step to finding out the optimum rigging tension for your boat.

Then go to Selden's website and download their rigging manual. Using Loos gauge pre-tune as per Selden's advice (different % forces depending on the piece of rigging you are tuning). Then test sail. If your rigging goes slack, something may be giving - no need to alarm as some boats bend some, others bend more. If the slack is significant then check all fittings/ mast base/ etc..

Avoid rigging too slack, especially if you have deck stepped mast.

If tops are tensioned right, you can often remove wind induced vibrations by changing, if only slightly, the interplay between the fore and aft lower(s).

b.

[Cheechako]

I'd adjust it under way. Adjust the lee ones so they are just barely slack, but no wobble. Tack the boat and do the other side.

[Sandero]

Greg,

Perhaps I was not clear in my writing.... the damage was to one or two (can't recall) of the 1x19 wires in the shroud AT the swage. Swage was fine.

I had filled the swage with beeswax to keep water from living in the spaces between the strands. A old salt told me this would prevent rusting inside the swage.

We didn't have to tack so that shroud didn't really work for the passage... I replaced it and saved the old wire and did a Norsemen end which I can use with an extra toggle to make up the lost distance ...in a pinch.

My turnbuckles are locked shut so they can't unwind... I think this was really a case where the rig tension was a bit slack and never noticed. My bad... It was a fast passage in heavy air... I don't know the actual cause of the failure of the wire... but your explanation makes sense.

Jef