1X19 stretch

[Gunni]

Capta, I think you are alright but it would be good to share some pics and notes with a rigger. Year before last I had my standing rigging replaced by a well respected local rigger. One of the things I noticed afterward on a tack was that my leeward shrouds were clearly unloaded and moving about. Same as you I was concerned and checked mast column and all was good. Had the rigger back and we looked at the situation. His suggestion was 1) the situation was fine and it was good to keep some looseness in the lee shroud. 2) I could take up small amounts by tacking and taking up turnbuckles on each side. He emphasised working in small increments with the goal of not having my lee shroud taut.

I’m not a rigger and have no significant skills in this regard. So I asked him if I should consider buying a Loos gauge. He laughed said he had a box full of them at the shop but rarely used them. My sense is that with a heavy duty large keelboat standing rig you get everything centered, lined up and evenly tensioned and sail it to check.

 

[smokey73]

Gunni, I agree with you. I'm not a rigger either but it seems apparent that the Loos gauge and guide are simply to get things initially set up in the ball park and to not over tension the rig in the initial set up. A good rigger can probably do that by feel just as well. My yard and rigger said pretty much the same thing. That is why I used the word "slack' but not flopping around and to take it up small amounts when tacking back and forth. Seems like Capta is past the initial setup point already and would be in the fine tuning stage. The only "fine point" might be whether the upper and lower shrouds are at the same tension or the lowers are under a little less tension. Hopefully Hood will clarify that point. My lowers (fractional rig with swept back spreaders and a back stay) are at a lower tension, but mostly that is because they are one wire size smaller than the uppers as I recall (could be wrong on that though).

 

[David in Sandusky]

What is “slack”? My understanding is that we don’t want the leeward shrouds to be loose enough that the mast shifts/moves quickly in an accidental gybe or other sudden shift. This dynamic loading from the momentum of the mast will result in shock loading of the rig at much higher tension than the normal static loads of sailing. The masthead should be under some tension from all shrouds at all times to prevent this shock on the rig with its increased probability of damage or failure.

 

[Jackdaw]

All 1x19 SS wire stretches 1mm per every 2 meters for every 5% (of its max breaking strength) load.

65 feet = 20 meters. So every 5% loading = 1cm stretch.

It’s very possible you’re set at 10%. Wind pressure to 30% would result in 4cm (1.57 in) of slack... a very noticeable amount on the leeward side.

 

[DrJudyB]

[Disclaimer: I'm not a rigger, and I'm entirely self taught. Here are my ideas, along with references to the technical sources so you can read what the genuine experts say on this topic. ]

Bottom line for me:

• I would tighten the cap shrouds to eliminate slack when heeled.
  • Noticeable slack in the leeward cap shroud when you are sailing upwind suggests to me that the windward cap shroud is stretching too much under load. That creates shock loads on the rig when you tack. Sounds to me like your cap shrouds may be stretching "too much" when the boat is heeling and generating forces approaching the maximum righting moment.
• I would measure the tension on the 1/2 inch: diameter capshrouds to confirm that they are at about 15-20% of breaking strength. You don't need a Loos gauge, just a ruler, caliper, and some tape. See below
• • Cap shrouds are the longest on the rig, and they are usually set to 15-20% of breaking strength to so they don't stretch too much.
  • SS wire deforms permanently starting at 55-65% of breaking strength. A safety factor of 2.5-3 is desirable, which is why you'll read advice saying don't ever exceed 25% of breaking strength for cap shrouds (Tension for forestays and backstays maybe be as high as 30-40% when adjustable backstays are at their tightest setting on some rigs)
  • If you can't eliminate the obvious slack in the cap shrouds when they're tensioned to 20%, my opinion is that there's a problem serious enough to warrant consulting a naval architect or master rigger or naval engineer. I would worry that we don't have the right size shrouds and stays on your rig in relation to the max righting moment of the boat.

Use the "Rolding Rule Method" to measure the tension on wire rope without a gauge
See p 32 of Selden Mast's booklet "Hints and Advice" at the following link:
http://www.seldenmast.com/files/1416926327/595-540-E.pdf

SS wire stretches relatively constantly under load up to about 55-65% of breaking, after which it deforms permanently. You can use this property to measure the tension on the wire, no matter the diameter of the wire.

Use the "folding rule" method.
You'll need a caliper, blue tape, and a folding ruler (metric or decimal feet)

• First, get the mast in column, with correct rake etc, with side shrouds set to hand tight.
• Open the ruler to be 2 meters long
• Tape the top end of the ruler to the shroud a little more than 2 meters above any swages or studs.
• Put some tape on the wire, in line with the bottom of the ruler.
• Tighten the shroud until it stretches a alittle .Use the caliper to measure between the bottom of the ruler and the tape marking. The wire will stretch 1 mm for each 5% of breaking strength (within the elastic range). Stretch and breaking strength are proportional to cross sectional area, so this method provides accurate results for all diameters of SS wire.
  • 1 mm of stretch per 2 meters of wire => 5 % of breaking strength
  • 2 mm of stretch per 2 meters of wire => 10 % of breaking strength
  • 3 mm of stretch per 2 meters of wire => 15% of breaking strength
  • 4 mm of stretch per 2 meters of wire => 20% of breaking strength

Tuning the rig
See Selden's manual on pages 45-55 for very detailed step-by-step directions for tuning various masthead rigs. They cover static tuning at the dock as well as dynamic tuning when sailing.

Selden's manual recommends tuning cap shrouds initially at 15% at the dock, but increasing to 20% for certain rig configurations.

A bit of rig design theory
What follows is roughly paraphrased from Brion Toss' book The Complete Rigger's Apprentice, 2nd ed., Chapter 5 "Understanding Rigging Design and Materials, pp 123-174, and pp 285-287

The elastic limit of most SS alloys used for wires is 55-65% of breaking strength. Once the wire is loaded past that point, it deforms permanently. If we use a safety factor of 2.5 or 3, that means we can tighten the shrouds as high 25% of breaking strength, and almost never more than 25%. (Toss, p 145)

In practice, cap shrouds are usually tuned to 15-20% of breaking strength and forestays and backstays may be loaded up to 25% (Selden pp 45-55)

The longest shrouds are generally tuned the tightest because otherwise they would stretch too much. Brion Toss recommends tuning cap shrouds to 15-20% of breaking strength. (Toss, p286-7)

 

[capta]

What is “slack”? My understanding is that we don’t want the leeward shrouds to be loose enough that the mast shifts/moves quickly in an accidental gybe or other sudden shift. This dynamic loading from the momentum of the mast will result in shock loading of the rig at much higher tension than the normal static loads of sailing. The masthead should be under some tension from all shrouds at all times to prevent this shock on the rig with its increased probability of damage or failure.

The shrouds only slack to windward so I've little worry about gybing. Even tacking, there is no movement at all on the rig, and as soon as the pressure comes off the sails, the rig is tight again. It doesn't pump, even in slamming a good sea.
Just for info purposes, the spreaders are straight and the mast has no pre-bend or rake.

 

[David in Sandusky]

If the shrouds are slack (exerting no tension on the masthead) you are risking shock loading of the mast. Those shrouds need more tension.

 

[Will Gilmore]

shrouds only slack to windward

Up to 20 knots to weather the leeward shrouds stay at least straight (firm), but above that they get a little to quite a bit slack

From all that I have read, the slackening of your shrouds in 20 knots or higher is ok. Tuning instruction for racing seem to include sailing on a reach in 15 knots of wind to take any slack out. If your shrouds are dancing, that may be an issue but if they are just a little loose in 20+ knots, that sounds about right.
You have an in-mast furling system that makes your mast heavier than most. Thus, your stays are heavier too. The main goal is to hold your mast straight when it should be straight and prevent movement that could cause damage from the momentum of sudden shifts, rolling, pitching, jibing. Taller masts WILL stretch their stays more (as Jackdaw pointed out, more inches of length equals more inches of stretch) and the movement will be more exaggerated, causing a slackening of the leeward shrouds that a shorter rig might not see. This extra stretch also means there is a natural dampening of the forces in taller rigs. Jarring forces are decreased.

I don't really know what I'm talking about, but it seems like the tension ratings are to determine a balanced rig for designers. If you use heavier stays, your tension needs shouldn't go up. The mast needs a set amount of force to hold it in place, increasing the breaking strength of your stays shouldn't change that. What I mean by that is that if you use a tensioner to set your stays, you are relying on the stays being balance to the rig already. I think it is safe to assume that if everything is to factory specs and new, then your rig is balanced and a tensioner would be ok to use. However, if you upgraded to a high tensile strength stay, then using the tension percentage guidelines will stress your chainplates, your mast, your masthead, your mast step, and your spreaders.

Just some conjunctive thoughts, by no means a serious guide to rig tuning.

-Will (Dragonfly)

 

[Jackdaw]

With all due respect, can people refrain to comment on things that they actually have actually real world experience on? Everyone can Google search stuff and type in what they read. Its not necessary to respond to every topic.

 

[Will Gilmore]

I appreciate your point, Jackdaw. I do not come from a position of complete ignorance, however. While I don't have experience with a rig like Capta's, I have tuned my boats and helped with my father's. That means, I have some idea of what to look for but no real foundation to base my limited experience in. That is why I have read up on it. Applying my experiences, what I've been told and what I've read to, what I like to think is good critical thinking, I felt like it was worth my participation in this discussion. If I have misstated facts, I'm sorry for that. I don't mean to miss lead or muddy the waters.
Following the guidelines laid out buy SBO when I joined this community, I have tried my best to research and support my statements and provide links to articles and sources where appropriate.

I know I am wordy and often insert myself where I may not strictly be welcome, I aften speak with authority about subjects I know little about, but I never intend to give bad information or mislead someone into poor choices. I don't really see me changing my ways so you are going to have to practice a little patience and know that I am just full of sh!t.

-Will (Dragonfly)

 

[Will Gilmore]

P.S.
Jackdaw, I have developed great respect for your knowledge and approach to sailing on this forum. Don't think I am being contemptuous. I have no desire to show you anything but the same respect everyone else on this forum obviously has for you.

-Will (Dragonfly)

 

[Jackdaw]

Will, yes sorry, that was about 100 more direct than necessary or intended.

 

[David in Sandusky]

Capta, are the half inch shrouds original equipment on your boat?

Selden’s tuning guidance says there should be no slack at 20 degrees or less heel. They mention mast stability as an issue for less tension on the cap stays.

 

[capta]

Capta, are the half inch shrouds original equipment on your boat?

Selden’s tuning guidance says there should be no slack at 20 degrees or less heel. They mention mast stability as an issue for less tension on the cap stays.

Yes, I believe so. I've been on several other 530's and they have the same shrouds, even if they don't have the same mast.

 

[DrJudyB]

The shrouds only slack to windward so I've little worry about gybing. Even tacking, there is no movement at all on the rig, and as soon as the pressure comes off the sails, the rig is tight again. It doesn't pump, even in slamming a good sea.
Just for info purposes, the spreaders are straight and the mast has no pre-bend or rake.

Capta,

If it were my boat, I'd retune the rig. I've never tuned a rig as big as yours, so take my advice with a grain of salt.

If the shrouds go slack from one tack to the other, that is proof that there is significant movement between the rig and the hull. That conclusion is self-evident by mathematical deduction, even if you can't observe the mast moving using the naked eye.

I'd be very curious to know what the tension is on your cap shrouds is. You can loosen both side to just hand tight, counting turns carefully, then measure the stretch on one side (in mm) as you retighten both of them them to the prior condition. Do both sides to get accurate readings, since the tension on one affects the reading on the other.

I don't see any downside to re-tuning the rig, with particular emphasis on tightening up the shrouds so the leewards don't go visibly slack when heeling, as long as you don't exceed Selden's and Brion Toss' advice about exceeding approx 20% of breaking strength. (Assuming the rig and hull were well engineered and are properly maintained.)

Respectfully,
JudyB

 

[SG]

It’s not a Sheldon Mast?

From Capta’s original post (which I started readingtoo late. ;^))). ) This is a massive, double section Hood Stoway mast, capable of freestanding for a bit, if ashroud broke, according to onerigger I talked to back when Ibought the boat.

The tensioning of the shrouds at rest is really prestressing. You do not need that tension to simply keep the mast vertical n those conditions. The pre-tension you are applying is “anticapory” of balancing for the loads that will be imposed while sailing from wind, pitching, and otherwise moving. The prestressing needs to be balanced. When you are sailing, without getting into the structural analysis, you are adding load on the windward side — however, if it is balance, you are “rereleasing ” the leeward stays’ pretension. If the stays are set right. The leeward stays don’t get over releaved, they just get reduced while not “flopping” around. It the mast stays “in column”, (as we understand it was at rest and under sail, then the simple answer is to tighten the leeward stays just enough to take out the slack. That’s the answer assuming that nothing is torn, loose, or broken.

As everyone knows, with in-the-mast furling one doesn’t want the mast to be arced or bent (it might be canted) because furling is pretty dependent on straightness.

The elastic elongation (rebouding deformation) of the stays probably are less useful unless something has come loose or is broken.

The symptoms that Capta cited are not indicative of way too much tension unless something let go or is failing. I kind of doubt that is the case; and I think Capta needs to “tuck his shirt in” a little and see if it works.

It’s posible that a fitting or shroud is screwed up. In that case the adjustments on the loose side will not result in the “fix” holding. Procedure: thighten, tack, observe, tack back, observe that the slack was taken out. It should stay that way in the same conditions — or something is wrong. I’d not over work the loose side tightening too much.

 

[smokey73]

I've started another thread on a related note about shroud tension - particularly the effect of cold weather. Please visit and give me your experiences, especially those of you in colder climates. My shrouds seem to have "un-tensioned" in the cold weather.

 

[uncledom]

My boat has been to Bermuda and wintered in Hilton Head which is right down the way from Beaufort. It is now wintering in Connecticut and I have not noticed any difference in shroud tension through all my travels on the boat.

 

[Ron20324]

The big suspension cables on bridges are actually made up off many smaller cables. Each smaller cable has to be tensioned on it's own, then secured. To make sure each cable is done equally, they only tighten them at night to delete the effect of sun and/or shade during the day..

 

[justsomeguy]

...they only tighten them at night...

Now there's an interesting factoid.