Are your spreaders in compression?

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Are your spreaders in compression?

Postby BananaCollision » Sat May 04, 2019 10:14 pm

When I raise my mast, the spreaders run from the mast to the shrouds, but they are loose. They would only do anything if the mast flexed at least an inch to press the leeward spreader into the leeward shroud. Are they supposed to be loose like that?

I ask because I just removed a funky diamond stay arrangement, which the prior owner had mounted 6” above the shrouds to hold the mast straight and prevent flexing. (It was bent-mast repair. I bent the mast back to straight-ish myself instead as the diamond stay was catching and tearing the jib.) But I noticed that the shroud mounts look newer than the rest of the mast hardware and I’m wondering if the prior owner did something weird with them.
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Re: Are your spreaders in compression?

Postby GreenLake » Sun May 05, 2019 3:56 am

@Banana:
Your spreaders need to be in compression. They also need to be at right angles to the mast (but not at 180 to each other, because they are "swept back"). The spreaders are fixed to the stays, usually with stainless steel wire that is wrapped tight for a few turns around the stay right above and below the spreader and also lead through a hole at the spreader end, so that they do not droop. (Then a spreader boot, or liberal application of self-amalgamating "rigging" tape, would protect the sails

Removing the diamond stays should have no effect on the main stays spreaders. And, assuming that your mast is now straight (as you sight along it) the mast bend repair should not have an effect either.

If the stays form a straight line (instead of bending in at the spreader) then your spreaders have no effect. Now, someone might have installed spreaders that are too short. You might measure how long they are, that might give us an idea. But do check the geometry that I tried to describe above.
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Re: Are your spreaders in compression?

Postby BananaCollision » Mon May 06, 2019 2:46 am

My spreaders should be the correct length -- one of them was purchased last year from DR Marine and the two match exactly. If the spreaders want to be in compression without mast flex, then they will need to be moved higher up the mast.

The mount for the removed diamond stay looks old and solid, and is a little higher on the mast. Perhaps this was originally the spreader mount, but it isn't long enough to reach the mount hole on the spreader, as the spreader mount hole is a few inches out from the spreader's mast end. Was there some older spreader design that used a pin closer to the mast end of the spreader?

My mast also has a hinge/knee added above the mast partners that makes it easier to raise -- could be the mast was shortened when that was done. I'll check my length measurements against the spec tomorrow.

[img]Oddball.jpg[/img]
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Re: Are your spreaders in compression?

Postby GreenLake » Mon May 06, 2019 5:28 pm

The shrouds on a DS (and the forestay) all attach partway up the mast. That location should be close to the location where the "jumper struts" (mini-spreaders) for the diamond stays were located.

The spreaders mount quite a few feet below that.

2671

In the above picture from your gallery, it looks like the original mounts for the spreaders are visible to the right of the wooden supports. If those are in the direction of higher up on the mast, then it looks like your spreaders are currently mounted too low.

I would jury-rig something at the current spreader length and at the original location, the one you show in this picture:

2670

(a piece of wood dowel with a notch at each end would do for this test: you can use a nail as makeshift pin and the tail of a zip tie taped to the dowel to hold it to the nail; also tape it to the shroud). Then you set up your mast and see whether you get the expected compression at that location.

If not, I would make sure the shrouds really connect to the mast where they are supposed to. (If they are overlong and attach higher, the spreader would need to be longer, but you really don't want to attach shrouds higher on the mast than the forestay).

If your test determines that the spreader base location is at issue, just move the new supports up to the location of the old-style ones. You may have to drill out some rivets and put new ones in.

(Note: to include images from your gallery, click on the "Gallery" button right above the text area where you compose your reply. A window will pop up, and you can select the image that you'd like to insert into your post.)
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Re: Are your spreaders in compression?

Postby BananaCollision » Mon May 06, 2019 9:50 pm

Well, mystery solved. The specs say the shrouds should be 7'8" above the mast datum (cuddy top). Mine were exactly one foot too low. Those old mounts were about 2" too low per the spec. So I'll move the new mounts up to the right location I guess. I'm really confused what that old mount is that's in almost the right place -- it has to be the spreader mount, but I don't find any mention of an alternate spreader style, and that mount lets the spreaders swing freely fore and aft -- I think compression on it would encourage the mast to twist.

GreenLake wrote:The shrouds on a DS (and the forestay) all attach partway up the mast. That location should be close to the location where the "jumper struts" (mini-spreaders) for the diamond stays were located.

The spreaders mount quite a few feet below that.


Actually my "diamond stay" is not the factory jumper stays at the top of the mast, raked back about 45 degrees and mounted above the forestay. (I removed those following some advise from this forum.) My boat's previous owner had installed a big diamond stay down lower, centered on the (apparently correct) spreader location and smack in the way of the jib leech when tacking, with struts made out of broad-headed, threaded, hardware-store carriage bolts that caught on everything.

The shrouds look correct; attached up by the forestay on reassuringly ancient hardware.

When I picked up the boat, the mastjack was painted over/sealed to the deck (prior owner never knew it could move), and the centerboard was installed upside-down so it would only deploy about 15 degrees. He said he only ever sailed it once; I guess it didn't perform too well for him.

Edit: Actually the spec mentions "7.10. The shrouds shall pass over spreaders, which may be of fixed, full swing, or limited swing type."
So I guess "full swing" spreaders are a thing. I am debating whether to drill new holes in the spreaders, so I can use them in the old apparently "full swing" lugs, or to drill new holes in the mast to re-mount the newer (apparently) "limited swing" brackets. The newer brackets definitely seem more secure and match the modern boats, but I hate the idea of drilling more holes in the mast. Gotta think on this one for a while.
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