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post #1 of 13 Old 04-07-2002 Thread Starter
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Swept back spreaders

What is the purpose of swept back spreaders vs those perpendicular to the mast on a rig that still has a backstay?

Aside from the issue of chainplate attachment, can swept back spreaders be moved forward? The stays on my rig terminate approx 10" behind the base of the mast and it is an obstacle to tabernacleing (sp?) the mast to fit under a bridge.
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post #2 of 13 Old 04-07-2002
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Swept back spreaders

Swept back spreaders help prevent the mast from pumping and help keep the forestay tensioned in a number of ways. Eliminating them is usually a major operation involving relocating the chainplates and beefing up the rig and often means going to running checkstays or running backstays. Since the mast generally hinges aft with a tablernacle the aft set shrouds and swept back spreaders should help rather than hurt dropping the mast.

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post #3 of 13 Old 04-08-2002
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Swept back spreaders

monark192,

The main purpose of swept back spreaders( vs those perpendicular to the mast on a rig) is to allow tighter sheeting angles for the genny? This typically translates to pointing a few extra degree''s higher.

This is how the boat was designed, and as Jeff said I am not so sure I would go to all sorts of changes as it would be a major hassle. But, more importantly, it might drasically change your boats sailing characterisics. Swept back spreaders in and of themselves are not there to prevent the mast from pumping that would be function of the your stays . But if you "did" go to a perpendicular spreader AND you have a backstay (as you described) then you probably won''t need running checkstays or running backstays and you will end up with a very tradional (and sturdy) single spreader rigged boat.

I would pose this question at a very good site on rigging for Boats its http://www.briantoss.com/ and you can post the question in the "SPARTALK" section.
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post #4 of 13 Old 04-08-2002
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Swept back spreaders

As Jeff said "Swept back spreaders help prevent the mast from pumping and help keep the forestay tensioned in a number of ways." As a matter of fact they replace running checkstays.

Ive started seeing swept back spreaders back 20 yrs on cruising fractional rigs, thus obtaining the performance of such rig in cruising conditios.

But agree with my colleagues, eliminating swept back spreaders is a major operation.

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Fernando
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post #5 of 13 Old 04-08-2002
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Swept back spreaders

With all due respect, swept back spreader have nothing to do with sheeting angles for a genoa. The side loads that they impart are determined to a great extent by their distance from the centerline of the boat. Swept back speaders allow the elimination of forward lowers while reducing the mast tendancy to pump by introducing a forward pressure on the mast in much the same way as forward lowers would do. They first show up in the late 1930''s on boats like the Folkboat.

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post #6 of 13 Old 04-08-2002
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Swept back spreaders

I stand corrected....some swept back spreaders do have the added benefit of better sheeting angles, but obviously not the sole purpose of design.....I still beleive its a bad reason to change the intended original design of the rigging on this (apparent) trailer sailor
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post #7 of 13 Old 04-10-2002
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Swept back spreaders

But I would say the main purpose of swept back spreaders is to replace the need for running back stays. When we moved from a traditional wooden mast with plenty of wire to carbon fibre the rig got a whole lot more simple and we did away with the runners. Now the backstay is essentially their for bend ratrher than holding it all up. I did worry that 22.5 degrees of spreadback would to all intents and purposes be the only thing that stops the lot going forwards and that was asking a lot but as far as I understand it, that is the set up you get in the high tech rigs. Anyway it works for us and so my worries have slowly turned to self confidence in our rig (includes rod rigging and some high stress numbers)
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post #8 of 13 Old 04-13-2015
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Re: Swept back spreaders

i was reading on this topic and found another advantage if not the biggest or "only" in my opinion was the building cost because it allowed the builders to under build parts of the hull and just relying on certain parts of the boat to distribute most of the load in rig to the boat as far as pointing a few more degrees by allowing us to sheet in tighter this can be accomplished with other technique such as running the sheets inside the shrouds or using twings it does seem to help with pumping but the trade off of not being able to run downwind for a long time with out serious chafing doesn't seem like a fair trade when most sections of mast come with places for a running back to be installed
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post #9 of 13 Old 04-13-2015
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Re: Swept back spreaders

The modern transition to sweptback spreaders is to eliminate the running backstays, checkstays and babystay while keeping the mast itself somewhat light and flexible.

Another factor was that racing boats were becoming quicker downwind, sailing much higher angles, so their was not so much need to have the main way out. And somebody figured out how to make the standing rig parts all smooth so the main didn't get abraded too badly.

I've never heard of the sheeting angle advantage. It is not obvious why this would be. Generally the spreaders are longer when swept back, and the shroud loads greater, so it is not obvious how a smaller sheeting angle would be one of the benefits. Smaller sheeting angles are achieved by using more...3,4,5... spreaders.

Switching from one design to the other is very complicated (expensive). Just for accommodating mast lowering for bridges would not seem worthwhile. Make some temporary lower shrouds to control the mast while lowering.

"...there are two kinds of opinions, those based upon tradition ... and those having something in their favor." B. Russell
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post #10 of 13 Old 04-13-2015
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Re: Swept back spreaders

I would think that swept spreader rigs, esp with a fair amount of induced bend, would put much greater loads on the hull structure with the increased compression loads.. rather than allowing a 'lighter' build??

Ron

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