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26-01-2025, 08:41
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#1
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Registered User
Join Date: Jul 2014
Location: Southeast US
Posts: 466
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Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
On a single spreader mast with inline spreaders, should the cap shrouds be clamped tightly to the spreader ends to prevent movement (no movement = no chafe) or allowed to move? Currently, the wire cap shrouds are clamped to the spreader end and I don't know what I should do when I replace with dyneema shrouds (immobilize or allow to move and protect from chafe).
If allowed to move, I can polish the spreader end notch smooth and lash it in place to prevent it from hopping out. For chafe protection, is dyneema cover adequate, 1 layer or multiple layers?
Currently, the spreader tip has a solid aluminum end welded on (red line is weld joint), then a reciprocal "clamping" end bolted to immobilize the wire shroud.
Thanks
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26-01-2025, 09:23
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#2
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Registered User
Join Date: Aug 2020
Posts: 1,039
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
The more immobile, the better. I once sailed from Maine to Florida without my dyneema shrouds being held to the spreaders in any way (I was in a rush to leave), and it was fine, but the rig was nice and tight. Later I covered the shrouds locally with https://www.spiroll.com/ and lashed them to the (thoroughly deburred aluminum) spreader tips using a method/pattern I think I found in Brion Toss's book. I don't recall if the method was meant for safety wire on stainless shrouds, or maybe rope on traditional rope shrouds, but I used small "Robline". They haven't budged in a few years since. I don't think you need a huge clamping force, just enough to stop the clamping point from adjusting itself slowly over time when there's enough slack in the shroud to allow vibration to potentially move things. I keep an eye on the angle when I'm arriving back to the boat, good habit.
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27-01-2025, 06:41
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#3
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Marine Service Provider
Join Date: Dec 2010
Location: Little Compton, RI
Boat: Cape George 31
Posts: 3,231
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
Definitely immobilize: I can't see any reason to want them to move, since you want the spreader at a certain angle.
Spiroll is good for chafe; leather also, Dyneema sleeve less so. Make sure the hole is well-rounded.
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Ben
zartmancruising.com
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27-01-2025, 07:30
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#4
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Registered User
Join Date: Jul 2014
Location: Southeast US
Posts: 466
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
Thanks. If not immobilized, I didn't know how I was going to keep the spreaders at a the correct angle. I appreciate the help.
Have a good week.
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28-01-2025, 03:20
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#5
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Marine Service Provider
Join Date: Dec 2010
Location: Little Compton, RI
Boat: Cape George 31
Posts: 3,231
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
If it's hard to immobilize, like if enough clamping pressure to do so would maybe damage the line, then you can make "spreader guys" with 1/8" Dyneema, just to ensure the spreaders don't sag. Either from mast to halfway along spreader, or from cap to spreader end, right alongside the shroud (mine twine around the shroud so they're not vibrating against each other).
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Ben
zartmancruising.com
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28-01-2025, 07:53
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#6
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Registered User
Join Date: Aug 2020
Posts: 1,039
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
I actually have the opposite of spreader guys- stack pack lines pulling down instead of up. No issues observed. But I do like the idea, would have done that if I thought of it at the time. Going to directly to the mast sounds safer to me, as it's hard to imagine what happens to the tension in a 1/8" dyneema line that's wrapped around a shroud, as the shroud becomes loaded and unloaded.
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28-01-2025, 10:02
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#7
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Registered User
Join Date: Oct 2012
Location: Guilford, CT
Boat: Bristol 35.5 1978
Posts: 784
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
Cant speak to dyneema for rigging but all new wire standing rigging w/ Hayn gear and since the mast was down asked my rigger (times many yrs) whether I should wire the spreaders to hold in place. He said no need to unless it makes me feel better. He has been rigging x decades and noted no need for wiring spreaders as the downward force from properly tuned rig will keep in place, slightly above horizontal. So no wire on single spreaders and rigging performed well offshore to bermuda. Did get caught in 45-55k winds (est as instruments were dead) over nite with only 1 reef in main and partially furled genoa. Spreaders moved down below horizontal and needed adjustment, but no wire on trip home. thnks
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28-01-2025, 10:20
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#8
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Registered User
Join Date: Aug 2021
Location: PNW
Boat: 35 Ft. cutter, custom
Posts: 2,922
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
As the most common cause of rig failure is spreader failure, anything, (IMHO,) that will keep the spreaders in more-or-less pure compression is worthwhile.
With continuous uppers I do like spreader lifts.
I went with dis-continuous uppers, (wire,) Dyneema would present its own set of rules.
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28-01-2025, 10:57
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#9
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Registered User
Join Date: Aug 2020
Posts: 1,039
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
Yea, seems to be a low-effort and harmless way to maybe save the day in some unusual corner case. Not needed most of the time, as that rigger showed.
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28-01-2025, 11:27
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#10
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Registered User
Join Date: Mar 2007
Location: Santa Cruz
Boat: SAnta Cruz 27
Posts: 7,196
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
Quote:
Originally Posted by Benz
Definitely immobilize: I can't see any reason to want them to move, since you want the spreader at a certain angle.
Spiroll is good for chafe; leather also, Dyneema sleeve less so. Make sure the hole is well-rounded.
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I would want them immobilized enough that you could stand on the spreader without breaking it off.
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28-01-2025, 14:41
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#11
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Marine Service Provider
Join Date: Dec 2010
Location: Little Compton, RI
Boat: Cape George 31
Posts: 3,231
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
Quote:
Originally Posted by markxengineerin
I actually have the opposite of spreader guys- stack pack lines pulling down instead of up. No issues observed. But I do like the idea, would have done that if I thought of it at the time. Going to directly to the mast sounds safer to me, as it's hard to imagine what happens to the tension in a 1/8" dyneema line that's wrapped around a shroud, as the shroud becomes loaded and unloaded.
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It's not enough to disturb the relatively low-loaded 1/8" line, who's only function is to keep the spreader from sagging. We spend a good deal of time standing on the spreaders, looking ahead or spotting coral, and even that doesn't put a visible strain on the spreader guy.
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Ben
zartmancruising.com
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28-01-2025, 15:01
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#12
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always in motion is the future

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 20,093
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
So how do you deal with stretch and creep?
The spreaders must split the angle with the capshroud which probably isn’t horizontal.
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28-01-2025, 16:00
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#13
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Registered User
Join Date: Mar 2022
Location: Canada
Boat: Grampian 30
Posts: 341
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
I'm surprised your spreaders clamp the wire shroud such that it is immovable. My boat, and every other mast with continuous cap shrouds I've helped step (my experience is limited in the grand scheme of things, admittedly) the shroud lays in a groove, or is captured by end caps, but is able to move/slide in the spreader end. I always assumed this was because as you tighten the shroud once the mast is up it needs to slide through the spreader. If it didn't, it would pull the spreader in one direction or the other the tighter it gets.
Based on this limited experience, and considering Jedi's point about the expansion/contraction of dyneema due to creep and temperature, I would say let it slide in the spreader end. If you're worried about chafe file or sand the edges of the hole smooth, and ensure no burs on the inside.
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28-01-2025, 16:22
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#14
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Registered User
Join Date: Aug 2020
Posts: 1,039
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
The stiffness of dyneema and wire is such that you can produce huge changes in tension with very little displacement, not enough displacement that it would change the angle of the spreader appreciably. The effects of thermal expansion are also there, but also small. The clamping/lashing should be tightened with the rig tight or close to tight. See page 16 and 17 here for Selden's recommendation:
https://www.riggingandsails.com/pdf/selden-tuning.pdf
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28-01-2025, 16:23
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#15
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always in motion is the future

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 20,093
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Re: Dyneema Cap Shrouds on Spreader Ends: Immobilize or Allow to Move?
Quote:
Originally Posted by Nekton73
I'm surprised your spreaders clamp the wire shroud such that it is immovable. My boat, and every other mast with continuous cap shrouds I've helped step (my experience is limited in the grand scheme of things, admittedly) the shroud lays in a groove, or is captured by end caps, but is able to move/slide in the spreader end. I always assumed this was because as you tighten the shroud once the mast is up it needs to slide through the spreader. If it didn't, it would pull the spreader in one direction or the other the tighter it gets.
Based on this limited experience, and considering Jedi's point about the expansion/contraction of dyneema due to creep and temperature, I would say let it slide in the spreader end. If you're worried about chafe file or sand the edges of the hole smooth, and ensure no burs on the inside.
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Indeed. Mine are captured in slots. They can’t get out the slots but they can slide up/down.
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