Pivoting Spreaders

[Scott Carter]

If my spreaders pivot (please don't ask me why I want them to pivot) in the horizontal plane, will this affect their ability to keep the shrouds spread? I think I've determined the answer for myself already, but wondered if any of you have any experience with pivoting spreaders.
It's been cautioned to me that their ability to pivot will prevent them from keeping the shroud directly alongside the mast, which will give the mast leeway to bend, counter to the intended purpose of the shroud to begin with.
The mast has a 5 degree rake, 2 sets of spreaders keeping a single topmast shroud spread. There are also 3 lower shrouds per side terminating just below the lower spreader hounds.
The line which defines the plane of the shroud between the mast head and the chainplate leaves the spreaders raked aft about 4 degrees.
Any thoughts?

[Omeron]

Ok i am not asking you why you need your spreaders to pivot,but i can
tell you a story about why you should not.
Many years ago, i was crewing on a boat, returning to the marina, just before sunset. All of a sudden, a not so loud bang, and the mast is
gone over the side.
The mast had pivoting spreaders,with a pin securing it in the
desired position. We never found the pin, but apparently it sheared
and made the spreader collapsed.
If something is allowed to move in an undesired way, it is almost certain
that one day it will. And it will do so at the most inconvinient place and time.

[Robert Gainer]

Depending on the geometry it works fine. If the wire gets tighter as the spreader pivots then it will work. If not the spreader will want to move and everything just comes down. Even with a fixed base you want to design the system so that the base has no twisting moment in it.
All the best,
Robert Gainer

[yipster]

some books discussing spreaders:
"riggs and rigging" by Richard Henderson
"the complete riggers apprentice" by Brion Toss
on page 124 in "skene's" the forces

[Frosty]

I want to know why you want your spreaders to pivot?

Personally I think it will be unstable in its tension direction, especially if they are wide--as wide as the boat. Just another thing to worry about in a force 9 at 4 am in the morning.

[fastwave]

Pivoting spreaders have been done and are nothing strange. Check out the Open60 Ecover and Maximus just to name a few.

[yipster]

axial with the mast rotating speaders in a pitching boat swing

[garydierking]

All of the cutter rigs on Jim Brown Searunner trimarans have "single pin ended limited swing spreaders". I put my set through 20,000 miles of the Pacific with no problem. The pins must be big and the shape of the spreader end is such that it can only swing maybe ten degrees either way. I see this as a great way to reduce high transient loads at the spreader base.

Gary

[yipster]

pins are great, scanned a few pages from Richard Hendersons good book "understanding rigs and rigging"
if the scans are readable notice the logic and realise that even the weakest link can bring a rig down

ooch, if anybody want a better scan yell ;-/