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  #21  
Old 09-24-2007
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Practical Sailor looked at this about 15 years ago. They were trying to understand why there had been an inordinate number of mast failures connected with boats sailing under jib/genoa alone. I don't believe there was any distinction made as to fractional/masthead rigged. As I recall, the only pattern they found was that the vast majority of boats that experienced mast failure while flying headsail alone had one common aspect to their rig geometry: Single, rather than double, lower shrouds.
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  #22  
Old 09-24-2007
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It's interesting to me because:

1. I would have thought that having the forstay and shrounds connected to the same point and the rig tightened up to suit the weather, with a hinged mast step you couldn't get any significant mast movement, certainly not flex - unless I've missed something.. which is possible, SD..

2. I've been told that the majority of mast failures with my rig set-up occur at the spreader/mast connection - not at the shroud/mast connection. This could(?) only come with side-ways flex which I would not have thought you'd get under jib alone.

--Cameron
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  #23  
Old 09-24-2007
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thanks all, didn't know I'd spark such a discussion. I'll give it a try in a light breeze on my cal, which does have running backstays, though I don't play around with them much.
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  #24  
Old 09-24-2007
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Quote:
Originally Posted by Hartley18 View Post
It's interesting to me because:

1. I would have thought that having the forstay and shrounds connected to the same point and the rig tightened up to suit the weather, with a hinged mast step you couldn't get any significant mast movement, certainly not flex - unless I've missed something.. which is possible, SD..
Last I checked, any time you put a mast under a heavy load, the shrouds will stretch a bit..and the mast will flex. On a small boat, the loads and the resulting flexing isn't going to be enough to fatigue the mast... but where the line between fatiguing the mast and not fatiguing the mast exactly is, is going to be pure guesswork. Also, how well engineered the chainplates and how well maintained they are will also effect the movement of the mast.

Quote:
2. I've been told that the majority of mast failures with my rig set-up occur at the spreader/mast connection - not at the shroud/mast connection. This could(?) only come with side-ways flex which I would not have thought you'd get under jib alone.

--Cameron
Again... if the mast flexes enough, the spreaders may move enough to fatigue the base connection point. If that happens, the spreaders will detach from the mast and then fail completely.
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  #25  
Old 09-25-2007
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Originally Posted by sailingdog View Post
Again... if the mast flexes enough, the spreaders may move enough to fatigue the base connection point. If that happens, the spreaders will detach from the mast and then fail completely.
... a good reason for nice, tight diamonds. Thanks, SD

-- Cameron
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Old 09-25-2007
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Quote:
Originally Posted by JohnRPollard View Post
Practical Sailor looked at this about 15 years ago. They were trying to understand why there had been an inordinate number of mast failures connected with boats sailing under jib/genoa alone. I don't believe there was any distinction made as to fractional/masthead rigged. As I recall, the only pattern they found was that the vast majority of boats that experienced mast failure while flying headsail alone had one common aspect to their rig geometry: Single, rather than double, lower shrouds.
That’s interesting. Do you remember a year or anything else I can use to track that article down? A mast with a single lower is weaker then the same mast with a double. So if everything else was the same I would expect to see a greater number of mast failures in the single lower rig no mater what the working sails were. I wonder if the article has numbers for the number of failures when both sails were up compared to when the boat was just under a headsail. Do more spars fail under headsail alone then under main alone? Also do more people sail under just the headsail because roller furling is so easy? If a backstay breaks the rig would fail no mater what your choice of sail was so looking at the cause of failure might be worthwhile. Did they do that in the article?
All the best,
Robert Gainer
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  #27  
Old 09-25-2007
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Robert,

The article probably came out in the early-mid-90's, which is when I subscribed to PS for a number of years. I'm sorry I can't be more specific than that -- having it in hand would be far more useful to this conversation than my vague memory.

But you're right, by that time roller furlers had become almost ubiquitous, so more folks were often opting to sail under jib alone for simplicity -- and apparently an inordinate number of mast failures had been observed with this sail configuration.

We're taxing my memory here, but as I recall, they looked at a lot of different aspects of rig geometry and sail combination when they were trying to find a common denominator, which as I previously noted turned out to be rigs that had only single lower shrouds. I also recall that the failures experienced were in the mast section, rather than in any of the shrouds or stays. That is to say, the mast snapped without any precipitating failure of the shrouds and stays. But these mast failures were occurring under jib alone -- there was no similar pattern under other sail combinations. I don't think they did any comprehensive analysis or comparison of other types of rig failures under other circumstances in that particular article.

One circumstance you mentioned was backstay failures, and I would just add it is my experience that backstay failures are not always as catastrophic as upper shroud or head/forestay failures, provided the mainsail is up. If the main is up some of the load borne by the backstay can be carried through the leech of the sail and then to the deck via the boom and mainsheet system. As you well know, many racing rigs sail with their backstays completely or very nearly slack in light air. Some of that load is absorbed by rig geometry (swept back spreaders and shrouds), but the sail and sheet are a factor as well. [I'm not saying backstay failures are inconsequential, only that they can sometimes be managed with quick action (turning upwind, getting the jib down, and leaving the main up sheated tight until halyards are led aft).]

In the PS article, they concluded that this load-bearing aspect of the mainsail and sheet somehow offset the rig stresses that occurred under jib alone on boats with single lower shrouds. Unfortunately, I do not remember why, and I am not qualified to speculate.
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Old 09-25-2007
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Thanks John,
My choice of backstay was just random and not meant to infer that a failure there was any better or worse then any where else. We have back issues in our library and I am going to see if I can find the article. It sounds like it would be interesting.
All the best,
Robert Gainer
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  #29  
Old 09-25-2007
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Robert,

Great! I hope you can locate the article and clarify anything I may have misrepresented here. I would target the time period from 1992-1998 or so, but no later than Y2K. Sorry that's such a wide swath, but if it's any help I think this was the "cover story."
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Old 09-25-2007
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I'd think it would depend primarily on the rig. I'm rigged with forestay's, babystays, side shrouds, check stays and a adjustable backstay on a double spreader rig, with 320 sq ft of high roach main, and 340sq ft of roller jib and a 400+ ft screacher. I'd guess a 7/8 fractional rig.

The designer of my boat (Gemini 105mc) specifically states that if sailing with just one sail, use the main. Having said that, I roll out the screacher when I'm single handing because I'm lazy - but only if the wind is below 10knts.
I've noticed that Jib only in a puff generates a touch lee helm, not a good thing but manageable so far.
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