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  #1  
Old 09-28-2011
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Angle of Spreaders

I have read several rigging articles/books that state mast spreaders should bisect the shrouds at an equal angle. This would normally mean the spreaders would be angled up at the tips. Mine are horozontal and do not bisect the shroud at an equal angel. My understanding the thought is that you want only compressive forces on the spreader, which makes sense, as any other force could break the spreader.

My spreaders have been used for probably 50,000 miles and still look good. Most boats I see do not have spreaders bisecting the shroud at equal angles (most spreaders I see are horozontal, not angled up).

What is the story?

Regards
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Old 09-28-2011
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It's true that ideally the spreader bisect the angle as you describe. The reality is that many rigs rely on friction alone to maintain that angle. Others have various forms of spreader tip clamps, shroud clamps, wire seizing, etc .

The spreader root fitting should be able to absorb or create the proper angle.. some do not.

The worst case scenario is when the spreader has drooped so low that the rig tension will tend to push the spreader further down... this unbalances the rig tuning as the affected shroud essentially slackens. In extreme cases where the spreader and shroud are not secured properly, a slack leeward shroud might separate from the spreader... and nothing good is going to happen on the next tack.

I reckon a general survey around a marina will find plenty of 'droopy' spreaders.. some alarmingly so.
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Quote:
Originally Posted by Faster View Post
It's true that ideally the spreader bisect the angle as you describe. The reality is that many rigs rely on friction alone to maintain that angle. Others have various forms of spreader tip clamps, shroud clamps, wire seizing, etc .

The spreader root fitting should be able to absorb or create the proper angle.. some do not.

The worst case scenario is when the spreader has drooped so low that the rig tension will tend to push the spreader further down... this unbalances the rig tuning as the affected shroud essentially slackens. In extreme cases where the spreader and shroud are not secured properly, a slack leeward shroud might separate from the spreader... and nothing good is going to happen on the next tack.

I reckon a general survey around a marina will find plenty of 'droopy' spreaders.. some alarmingly so.
My spreaders are connected to the mast via a stainless steel fitting that wraps around the mast and has a socket in both sides that each spreader fits into. This fitting will always maintain a 90 degree angle between the mast and the spreader. The shroud is then wire tied to the tip of the spreader (there is a small groove that the shoud sits in at the tip of the spreader). The spreader connection fitting at the mast is very storng, the thing that would break I would think is the spreader base (at mast). So with this set up it seems there would be some downward force existing at the tip of the spreader (based on vector diagram of the forces).

Does this sound ok?
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Are the spreaders tubular? or foil sectioned? Generally the fit of the spreader into the receptacle for it is not a close tolerance fit and may permit the small angle required to get the correct shroud/spreader angles.

The problem is that without a positive clamp to fix the outboard tip at the shroud, the spreader will/may tend to slide a bit unless a) the vectors are balanced or b) the spreader root fitting stabilizes the spreader where it is.

With your shrouds 'wired' into a spreader tip slot they are protected from 'falling out' if the leeward goes slack.. but there's not necessarily the ability to resist the vector forces.. could be you're at the bottom of allowable movement in your spreader cups and they are limiting further droop.

In any case, as you've indicated a lot of miles without any serious issues, you're probably OK. And you're certainly not alone in having so called 'imperfect' spreader angles. As long as all the parts are sound I'm sure you'll be fine.

If you ever get the rig off, see how much play there is in the spreader root fitting, maybe you can correct the angles via the slack available there.. if you split the shroud angles there should be no forces trying to undo that.

Beyond that, I wouldn't worry! (disclosure... I'm not a rigger...We need Knothead to chime in here.)
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Old 09-28-2011
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Quote:
Originally Posted by Faster View Post
Are the spreaders tubular? or foil sectioned? Generally the fit of the spreader into the receptacle for it is not a close tolerance fit and may permit the small angle required to get the correct shroud/spreader angles.

The problem is that without a positive clamp to fix the outboard tip at the shroud, the spreader will/may tend to slide a bit unless a) the vectors are balanced or b) the spreader root fitting stabilizes the spreader where it is.

With your shrouds 'wired' into a spreader tip slot they are protected from 'falling out' if the leeward goes slack.. but there's not necessarily the ability to resist the vector forces.. could be you're at the bottom of allowable movement in your spreader cups and they are limiting further droop.

In any case, as you've indicated a lot of miles without any serious issues, you're probably OK. And you're certainly not alone in having so called 'imperfect' spreader angles. As long as all the parts are sound I'm sure you'll be fine.

If you ever get the rig off, see how much play there is in the spreader root fitting, maybe you can correct the angles via the slack available there.. if you split the shroud angles there should be no forces trying to undo that.

Beyond that, I wouldn't worry! (disclosure... I'm not a rigger...We need Knothead to chime in here.)
Spreader is a foil section. The root fitting socket is about 4 inches long and is a fairly close tolerance fit, it does not seem to allow much if any movement. Here is a pic of a similar boat and rig, although the spreaders on this rig seem to have a slight up angle (but even this up angle does not look to actually bisect the shroud angel as angle between shroud and spreader is not the same at top of spreder and bottom of spreader). The root fitting and spreaders look identical to mine.
Regards
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Angle of Spreaders-sirius%252002.jpg  

Last edited by casey1999; 09-28-2011 at 03:29 PM.
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