Should Spreaders Clamp In Upper Shrouds Tightly?

[Jackdaw]

I seem to have an unlimited amount of time to contemplate this issue ... see my post in AAS.

;^) Me too it seems!

Scott,

Big Easy has a Double Spreader Rig. TOTALLY different beast in terms of setup. Also in that rig if your rigging is continuous or discontinuous factors as well. On double (or more) spreader rigs, the sequence is much more complex; on our 36.7 it takes half a day. And you do leave them loose as you dial them in. Then you tighten.

As for the EXACT point, its not super important. Within a inch and you'll be fine. Pulling the shroud down to that point as I described DOES however give the exact spot mathematically for the spreader tip (I'll leave the proof to you but it's easy). Keeping them tight is the important part.

I'll concede that some very small boats the designer probably figured that the loads were not enough to worry about. But it doesn't invalidate that they would be better clamped.

 

[Chief RA]

Well, since it has come up: I am a degreed Industrial Engineer and one of my minors is metal. I have great respect for many of you who have commented on this but must say again, my shrouds are NOT firmly secured to the spreader nor are they supposed to be. Even further, I think the wire wrap is the original factory install and there is movement up and down but not sloppy. There are various approaches utilized by factories for these spreaders and shroud lines! There is no doubt about this and it does not take an Engineer to realize this. Chief, IE

 

[stvnm]

An interesting point, but I'd hardly call it 'blindly'. The engineering behind my statement that they should all be tight is widely understood and supported. I'd be interested in ANY engineering-based opinion on why you should leave them loose. If that is what you are implying, I'd be interested in yours.

As a matter of fact I am the one who is following the professional advise of not tightening.While I do respect the professionalism and experience of those people I'd like to find out the why behind their advise or a solid reason to discard it that applies to my case. I am positive that the the source you mention are positioned to give a final say on their spars and rigging. I just can't be sure if and why it would apply to others and in particular to mine.

 

[Jackdaw]

Hey Chief,

If you boat has its original (20 years??) seizing wire on the tips its probably worn, tired, and slipping. It should not slip, but does after time. It's part of the reason nobody makes spreader ends like that anymore. You don't have to take my word for it. Go ask a professional rigger.

CB

 

[Jackdaw]

As a matter of fact I am the one who is following the professional advise of not tightening.While I do respect the professionalism and experience of those people I'd like to find out the why behind their advise or a solid reason to discard it that applies to my case. I am positive that the the source you mention are positioned to give a final say on their spars and rigging. I just can't be sure if and why it would apply to others and in particular to mine.

OK Thats interesting. Did he say why? I'd like to know.

If you ever think about it, have him drop me an email. I'm always up for learning new things.

As for WHY it should be fixed:

The spreader is a deceptively complex part of your rigging. It effectively widens the angle of the shroud base, which drastically lowers the (tension) force on the deck, rigging, and spar. As such it is under huge compression load, and that load absolutely must be applied straight on the spreader so it does not bend or flex. The ONLY way to guarantee that is for the angles of the shroud coming onto the tip be equal. That means it must be fixed in that position. If the shroud can slip through it, it means that the tip has moved up or down, and changed that angle. That applies asymmetric pressure to the spreader and could cause it to fail.

Remember, when it is loose it is NOT the shroud moving up or down, its the spreader tip!

 

[mauruuru]

The purpose of the spreader is to get an increased angle from deck to mast attachment point. That increases amount of lateral resistance. Clamping the stay at that point would put up or down forces on the spreDer to madt connection which does nothing of value and might break spreader attachment. No do not clamp it tightly. I had a guy in a yard clamp the wire so tightly he bent the strands luckily I cauhht it before mast was stepped and loossened them -though the crease is still there

 

[Joe]

I seem to have an unlimited amount of time to contemplate this issue ... see my post in AAS.

You're definitely on a roll. heh, heh.

 

[Chief RA]

All due respect Jackdaw but I think I will rely on that engineer you aluded to earlier, and with over 40 years sailing experience: that is me. I have no more to say as I have already said it! Chief

 

[Jackdaw]

All due respect Jackdaw but I think I will rely on that engineer you aluded to earlier, and with over 40 years sailing experience: that is me. I have no more to say as I have already said it! Chief

With respect chief, I'd be very interested to understand why you think that, from an engineering perspective, of course.

 

[Brian M H23]

I'm a mechanical engineer, though not a mast-maker

This is a rather simple question. Let me ask it another way - what's maintaining your spreader angle?

If you clamp, then it's the length of the mast above the spreader, the length of the spreader, and the length of the shroud. A triangle. simple, structural, and easy to understand

If you don't clamp, well....

If we have enough friction that it can't move, then we might as well be clamping it, so that's a dumb argument.
If we leave it free to slide, then when that spreader is to leeward and slack, it would be sliding up and down the shroud. and then when we tack, it'll get tight and likely stick in whatever position. A different position every tack, with shroud tension jumping all over the place.

Why would you ever want the spreader to slide on the shroud?

As for setting up the rig, while "ideal" is probably getting the spreader into perfect bisection and then tightening the clamp with the rig tight, I can't imagine any serious problems being off by an inch or two

 

[Scott T-Bird]

mauruuru makes a good point. You would never clamp the tip down to the point where the wire strands are crimped or severely compressed. I think the slots and captive tips must be (or should be) shaped to prevent actual crimping, which means that the shrouds aren't actually fixed at the spreader tip, merely held with very mild compression ... not too much different than as if held captive by the monel wire.

If the tips could actually compress the shroud, wouldn't there be instructions or a warning to prevent over-tightening to the point of crimping the wire?

 

[Scott T-Bird]

To answer your question, Brian, the angle of the spreader is fixed by the ears. The ears are angled to create the bisected angle such that tension on the shroud will not allow the spreader to move in either direction (equal forces of friction in both directions at the opposing vectors). My painted spreader tips have never shown any sign of worn paint within the slot where the shroud is held. This is evidence of the fact that even though the shroud is not clamped, merely held captive by the wire, the tip does not move and the angle of the spreader is never compromised.

We all agree that slack shrouds and poorly designed spreader attachments to the mast are a recipe for a problem. But the good boats are designed with a robust attachment point and the proper angle. Don't we also agree that slack shrouds are to be corrected? I actually suspect that a frictionless spreader tip would work equally well (at least in theory).

Wouldn't you say that the objective is to provide an equal distribution of stress along the entire length of the wire without interruption or interference? This would best be accomplished without an actual clamp at midpoint to interrupt the stress distribution.

See my comments above about the danger of crimping the wire strands.

 

[Jackdaw]

To answer your question, Brian, the angle of the spreader is fixed by the ears. The ears are angled to create the bisected angle such that tension on the shroud will not allow the spreader to move in either direction (equal forces of friction in both directions at the opposing vectors). My painted spreader tips have never shown any sign of worn paint within the slot where the shroud is held. This is evidence of the fact that even though the shroud is not clamped, merely held captive by the wire, the tip does not move and the angle of the spreader is never compromised.

We all agree that slack shrouds and poorly designed spreader attachments to the mast are a recipe for a problem. But the good boats are designed with a robust attachment point and the proper angle. Don't we also agree that slack shrouds are to be corrected? I actually suspect that a frictionless spreader tip would work equally well (at least in theory).

Wouldn't you say that the objective is to provide an equal distribution of stress along the entire length of the wire without interruption or interference? This would best be accomplished without an actual clamp at midpoint to interrupt the stress distribution.

See my comments above about the danger of crimping the wire strands.

I think, Scotty, that he was asking rhetorically... ;^)

Your point about the final goal being to keep the spreader bisecting the shroud angle is correct.

But its generally now accepted that locking the shroud to the tip close to the angle is the best way to do that. 20-30-40 years ago, not everyone agreed or maybe cared. But it IS the general consensus now. Go find any NEW boat in the range we are talking about and look for loose tipped spreaders.

Now on any given boat that a person currently owns, if you can't lock them, you can't. Just go sail. But if your spreader tip design allows for locking the shroud, do so.

 

[Jackdaw]

I'm a mechanical engineer, though not a mast-maker

This is a rather simple question. Let me ask it another way - what's maintaining your spreader angle?

If you clamp, then it's the length of the mast above the spreader, the length of the spreader, and the length of the shroud. A triangle. simple, structural, and easy to understand

If you don't clamp, well....

If we have enough friction that it can't move, then we might as well be clamping it, so that's a dumb argument.
If we leave it free to slide, then when that spreader is to leeward and slack, it would be sliding up and down the shroud. and then when we tack, it'll get tight and likely stick in whatever position. A different position every tack, with shroud tension jumping all over the place.

Why would you ever want the spreader to slide on the shroud?

As for setting up the rig, while "ideal" is probably getting the spreader into perfect bisection and then tightening the clamp with the rig tight, I can't imagine any serious problems being off by an inch or two

Yup.

 

[BigEasy]

Well, Jack has confirmed that SELDON indicates that the shroud clamps should be tight at the spreader tips and I have confirmed the same from US SPARS. These are the two biggest manufacturers in the country. Obviously they wouldn't design clamps at the spreader tips if there wasn't a sound engineering reason. Again, I would do what the manufacturer specifies with regards to clamping vs not clamping. This doesn't mean torqueing the clamp to point that the shroud is permanently deformed. And no, there was no torque value specified, Just "tightened".

 

[Scott T-Bird]

I cry "Uncle!"

Yikes! I hope we didn't scare Dino from the forum. It was a worthwhile discussion in my view. I learned something! That's always a good thing.

 

[DinoKanuck]

Thanks to all....

Yikes! I hope we didn't scare Dino from the forum. It was a worthwhile discussion in my view. I learned something! That's always a good thing.

Takes more than debate to scare me.... It is all good advice. Now, because the LM 28's end cap capture the wire not all of the advice is applicable.

As the situation sits.... Spreaders are at upper end of travel, shrouds are pulled tight above the spreaders with 15' 10" +\- 1/2" of wire to toggle insert and I've marked the positions with tape and markers. I'm calling a reasonably safe approach " slash " science experiment.

 

[Chris Blubaugh]

Thanks for the discussion - very helpful for me to read as I am about to get new rigging on my boat.