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post #21 of 31 Old 07-09-2015
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Re: Question about spreader/rigging geometry

I think the answer to your question is that it is easier and stronger to attach the spreader to the mast at a perpendicular than at a slightly upward angle, and that given that the only part of the spreader that is permanently anchored is that connection, people have chosen to do that. It is not dissimilar to the joinery that takes place in building furniture. Theoretically, if the attachment is overengineered as RichH has suggested, then it is irrelevant the angle they take. Agree that the physics works better when they bisect the angle of the shroud, but that force may be negligible, and when the shrouds "relax" on an opposite tack, if the spreaders were upswept properly, but not significantly anchored to the mast strongly enough and more permanently, they could slide down as it seems yours may have. Anyone stand on them and compromise that joint?
Historically, lashing on a spreader at a right angle to the mast was essentially the only way to do it, so some of it may also be design aesthetic harkening back to that.
Oh yeah- and if you don't like wire clamps, you could do a lashing at the spreader tips, which should allow better access to oxygen to keep those stainless shrouds from pitting/rusting.

Ocean- that which covers 3/4 of a world made for man, who has no gills.

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post #22 of 31 Old 07-09-2015 Thread Starter
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Re: Question about spreader/rigging geometry

Attaching the spreader to the mast in a fitting that holds it at the reqired angle would be much stronger/safer than attaching/pinching the spreader to the shroud at an angle.
To make a connection at the shroud which would match the strength of the spreader socket casting on the mast would compromise the integrity of the wire.

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post #23 of 31 Old 07-09-2015
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Re: Question about spreader/rigging geometry

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Originally Posted by __floater__ View Post
Attaching the spreader to the mast in a fitting that holds it at the reqired angle would be much stronger/safer than attaching/pinching the spreader to the shroud at an angle.
To make a connection at the shroud which would match the strength of the spreader socket casting on the mast would compromise the integrity of the wire.
Agreed, but not as EASY or CHEAP. Remember, these guys are in the business of making MONEY by making boats. Boats are still just widgets. They happen to be beautiful widgets, but if they can cut a corner that isn't going to be a problem while the product is under warranty, well, guess what they are going to do?

Ocean- that which covers 3/4 of a world made for man, who has no gills.
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post #24 of 31 Old 07-09-2015
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Re: Question about spreader/rigging geometry

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This is how you'd think spreaders would be set up and that was the topic of the thread.

Makes sense.

Problem is, I have NEVER seen a boat with the spreaders angled up so that they bisect the upper shroud. Every boat in the marina and in any photographs I have referenced show spreaders at right angles to the mast (not the shroud), which will not result in bisection of the angle at the shroud.

...

I don't buy the claim that spreaders bisect the angle at the shroud, bit I agree that they should.
Well, here's one... Mine have been that way for 45 years...

Of course, that guy Britton Chance was known to have some pretty wacky ideas...

;-)


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post #25 of 31 Old 07-09-2015
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Re: Question about spreader/rigging geometry

As others have said, the spreaders on a fractional rig usually bisects the angle of the upper and lower shrouds (as you may be able to see in this picture of my boat.)


The connections vary widely with the way the rig is designed. My boat has swept back spreaders so there is a weldment on the mast that creates a moment connection between the mast and the spreaders in all directions, and locks in a spreader angle in all directions, but in particular an upward angle which approximately bisects the upper and lower shroud. There is clamp built into the outboard spreader tip that holds onto the shrouds.

Working from drawings, the designer should be able to figure out what the upward angle needs to be to bisect the shrouds and then give that information on their drawings.

On other frac's that I have owned, there have been various types of connections, but the spreaders always canted upward, and all had a way to hold onto the shrouds either with a built in clamp or with a small hole or eye which allowed the end of the spreader to be seized in place so the tip cannot slide up and down the shroud.

There have been boats designed with level spreaders which I see as questionable practice, but I have never seen them intentionally pointed downward. Spreader inboard ends are usually mitered and coped to sit against the mast or spreader base, and when used the through bars are normally made with the angle as well. If your spreaders are flush against the mast and pointing down, or your through bars do not allow the spreaders to point upward, I would suspect that the spreaders and/or the bars were installed upside down at some point.

Jeff


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post #26 of 31 Old 07-09-2015
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Re: Question about spreader/rigging geometry

My topmast not only carried the big jenny it held about 300 sq ft of topsail. Running backs were a bother so big spreaders (7') with SS weldment at the butt had a pin thru it to a socket on each side of the hounds. Pin angled so dihedral was accomplished.It also swivelled so the main gaff could push it out of the way when running . Had mini topping lifts? from the main truck to support the pirates that frequently partied there. Absolutely trouble free for decades once I learned to set up the deadeyes but, not much good on a production unit, I bet.

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post #27 of 31 Old 07-10-2015
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Re: Question about spreader/rigging geometry

I just came to me.

The spreaders are perpendicular to the mast so the the spreader lights shine on the side decks and not the water.

We've all been overthinking it.
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Thumbs up Re: Question about spreader/rigging geometry

Quote:
Originally Posted by carbonsink62 View Post
i just came to me.

The spreaders are perpendicular to the mast so the the spreader lights shine on the side decks and not the water.

We've all been overthinking it.
Boom!

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Re: Question about spreader/rigging geometry

Spreader lights generally are made so that they can be adjusted for the angle of the spreaders. When spreader lights are used which are not adjustable, then there is a mounting wedge that aims them down. When I replaced my spreader lights with non-adjustable lights, I had to make make my own bases for them that both fit the contour of the spreader and rotated them the direction that I wanted them to point.

Spreaders serve a critical structural purpose, and the structural geometry of the spreader angle is far more critical than the small accommodation needed to make 'convenience lights' shine in the right spot.

Jeff


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post #30 of 31 Old 05-22-2018
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Re: Question about spreader/rigging geometry

Floater, Have you considered that improperly installed spreader lights can be an effective bonus when squid jigging from deck. It may be that what appears to be an ignorant design feature actually has value .
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