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Old 21-06-2011, 16:26   #31
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Re: Reefed main = greater mast breakage risk???

So EVERY sailboat designer is wrong eh?
Just goes to prove the old saying,

"those that can, DO, those that can't, TEACH"

This idiot probably read some insurance statistic that stated the majority of mast failures happend when reefed and never took into account that they were reefed because they were in adverse weather. A mast isn't likely to fail in calm air with the main fully up after all.
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Old 21-06-2011, 16:52   #32
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Re: Reefed main = greater mast breakage risk???

it is certainly possible that the force on a reefed main can be equivalent, or even exceed that of the force on an unreefed sail.

why?

because a boat with a properly reefed sail with sail more upright than a boat that is unreefed. the unreefed boat will heel and thus spill lots of wind.

so, technically, he could be right.

however, it seems a silly thing to do as he suggests for two big reasons:

1. a sailboat goes fastest when the mast is perpendicular to the water. so reducing sail area by reefing makes the boat goe faster
2. it is more comfortable and easier to sail a reefed boat than one that is on its side

so, while i understand his theory, i don't recommend his strategy, unless you like to sail uncomfortably slowly.
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Old 21-06-2011, 18:17   #33
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Re: Reefed main = greater mast breakage risk???

Quote:
Originally Posted by hoppy View Post
He was not saying to not use common sense, just that you should reduce sail area as if your main has no reef points.
If your conventional mainsail has NO reef points it would be highly advised to immediately take if off the boat. Then take it to a sailmaker and get reef points installed. Only dinghy sailors or wind surfers do not reef.
- - The only other situations are if the boat is equipped with boom reefing where the boom rotates and rolls up the mainsail to "reef" it. Likewise, in the mast mainsail roller furling also has no reef points as your simply roll the mainsail into the mast to reef the sail.
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Old 21-06-2011, 19:06   #34
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Re: Reefed main = greater mast breakage risk???

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I believe you are incorrect in your understanding of the failure mode, the location of the headboard is important because it carries leech loads which are in 2 directions, down which is resisted by the halyard, and perpendicular to the mast which is resisted by shrouds and stays if the headboard is near them or by bending of the mast if not. This combined with mast pumping caused by pounding into heavy seas combined with decreased damping due to less luff length attached to the mast can push the mast out of column leading to a buckling failure. Alternatively if a shroud or diagonal fail then the mast fails in bending. It is unlikely that there would be a crushing/compression failure of the mast unless it had a reduced section.

That said the risks of other problems associated with heavy weather increase faster for most boats than problems tied to reefing the main, so I agree that reefing the main is the answer unless you have a really skinny mast then you should have had a discussion with a navel architect about what to do long before you went out in such weather.
Hmm,bear with me but that seems odd.Leech and luff and foot loads are all Firstly inward to the centre of the sail's force...it wants to be a bag.The resistance to these is indeed the tension along the edges(to control belly and reduce curve) but I am having trouble imagining the mast between curve AFT per a point load at headboard because of them.The vectors being 3...at luff,this tension is in line with the mast ,at foot,in line with the boom at and finally, the angled leech delivers a split load in line with the mast and ,true enough,a force aft you could consider as being perpendicular to the column...
I eally think the above is a red herring too...it's easier to imagine if you pretend the mast and sail is horizontal and full of water and what it would look like then.I do not see the mast bowing aft particularly at the reefed headboard....I see the mast bending between the shroud points (and the boom depending on its sheet blocks)...per the centre of effort.

I probably shouldn't have mentioned it,but "where the mast crushes to powder as a mode of failure",I meant the Perfect Case -the "one hoss shay" where everything fails at once in the perfectly designed machine....
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Old 21-06-2011, 20:16   #35
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Re: Reefed main = greater mast breakage risk???

"Don't reef the Main: It's a Charter boat!!"




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Old 21-06-2011, 20:57   #36
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Re: Reefed main = greater mast breakage risk???

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Well he's quite right that a reefed main puts different stresses on the mast column that require design treatment. Fortunately, well designed rigs take this into account.
+1

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Old 21-06-2011, 21:04   #37
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Re: Reefed main = greater mast breakage risk???

There are certainly exceptions around, but every single mast failure that I've seen or read about happened immediately after something else broke. A stay broke and the mast came down or the boom broke and the mast came down. The only time I've heard of a mast breaking alone is when the boat got knocked down and rolled and then it came up with a half of a mast. Nobody seemed to be paying attention to the stays when that happened because they were otherwise engaged.
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Old 21-06-2011, 21:21   #38
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Re: Reefed main = greater mast breakage risk???

Quote:
Originally Posted by HappySeagull View Post
Hmm,bear with me but that seems odd.Leech and luff and foot loads are all Firstly inward to the centre of the sail's force...it wants to be a bag.The resistance to these is indeed the tension along the edges(to control belly and reduce curve) but I am having trouble imagining the mast between curve AFT per a point load at headboard because of them.The vectors being 3...at luff,this tension is in line with the mast ,at foot,in line with the boom at and finally, the angled leech delivers a split load in line with the mast and ,true enough,a force aft you could consider as being perpendicular to the column...
I eally think the above is a red herring too...it's easier to imagine if you pretend the mast and sail is horizontal and full of water and what it would look like then.I do not see the mast bowing aft particularly at the reefed headboard....I see the mast bending between the shroud points (and the boom depending on its sheet blocks)...per the centre of effort.

I probably shouldn't have mentioned it,but "where the mast crushes to powder as a mode of failure",I meant the Perfect Case -the "one hoss shay" where everything fails at once in the perfectly designed machine....
Looking at the way tri-radial mains are constructed gives you an idea of where the loads are going. In the line drawing attached the panels are parallel to the leach and at an angle to the luff. Others I have seen panels are oriented along the luff as well as the leach. In all cases the panels are aligned along the leach.

The photo of the tape drive main brings home point even more clearly, the darker tinting of the sail along the leech of the sail indicates a lot more tapes are installed along the leech than the luff implying there is a lot more load to resist along the leech than the luff.

The leech load is directly related to the amount of force needed in the vang to counteract twist and mainsheet forces to gain the desired trim.

Tape drives really bring this issue home, the tape alignment indicates the predominant direction of loading in the cloth, and the density of tapes indicates the relative magnitude of loading. Once again there is high loading along the leech and the head has a lot of load coming in at an angle.


Let's assume the boat is making 7kt in 15kt wind.

Let's assume the wind increases to 28kt, a reef is taken, the jib is dropped a size and the boat is still doing 7kt at about the same angle of heel. Given that speed and angle of heel are the same it is reasonable to assume the drive from the sails are about the same. Actually the drive would be somewhat larger to deal with increased wave action.

Given that the total loads coming out of the main are about the same the headboard loads would be about the same except that being concentrated at the top of the mast where shrouds and stays attach, it is now in the middle of the panel between shroud positions, and the distributed load along the luff of the sail is increased proportionally because the same load is distributed across a shorter length of mast. Structurally this is a very different loading situation than with the full raised main.
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Old 21-06-2011, 21:41   #39
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Re: Reefed main = greater mast breakage risk???

Insurance statistics show that most dismastings occur @ 25 knots of wind or under. The only time there would be significant shock loading on the mast would be in a head sea condition at which point your sails would be furled anyway. Having ridden out a 24 hour period of 45 knot winds astern with all sails up fully; the biggest hazard was broaching due to exceeding the hull speed coming off the face of a wave. (We were too stupid at the time to realize how dangerous it was). We also made 200 nm in a 24 hour period with a monohull. (Only time). I would keep the balance by reefing the main sail and reducing the size of the head sail. As long as the integrity of the rigging has not been comprimised due to age or over stressing (Racing), the mast should withstand the stresses of the reefed main. As stated in an earlier post, I have never heard of a mast failing by itself, usually it starts with a parting of the boom or stays, and when one pitch poles, who knows?
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Old 22-06-2011, 01:03   #40
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Re: Reefed main = greater mast breakage risk???

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Originally Posted by Honey Ryder View Post
so, while i understand his theory, i don't recommend his strategy, unless you like to sail uncomfortably slowly.
It's nice to see that some people understand his point.

Quote:
Originally Posted by CarlF View Post
Well he's quite right that a reefed main puts different stresses on the mast column that require design treatment. Fortunately, well designed rigs take this into account.




From some of the comments here I can only deduce that there are a lot of people who watch Fox News or read The Sun and only see things in black or white
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Old 22-06-2011, 01:54   #41
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Re: Reefed main = greater mast breakage risk???

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Originally Posted by hoppy View Post
It's nice to see that some people understand his point.






From some of the comments here I can only deduce that there are a lot of people who watch Fox News or read The Sun and only see things in black or white
Wow. Did you read any of these replies? Your instructor's point was pretty clear, and it is mostly wrong. Many responders have explained why.

Sure, a mast can forced out of column with improper loading, but a properly-reefed mainsail is not likely to cause this, for several reasons that have been explained.

Your instructor seems to be advocating having the main at full-hoist with a furled or dropped jib as the first stage of reefing, then completely dropping the main as the next stage, and claiming that since the boat speed is the same (?) the loads will be the same. This is also wrong, as has been explained.

And why does your instructor worry about metal fatigue in the mast, but seem to be unconcerned by metal fatigue at the stays and shrouds, and their fittings? These points are much more likely to fail than the mast itself.

Under some conditions you may want to reef the headsails before touching the main, but certainly not for the reasons your instructor is suggesting.

Now please show me where I saw this on Fox News.
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Old 22-06-2011, 02:10   #42
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pirate Re: Reefed main = greater mast breakage risk???

I'm puzzled... but then I often am....
For many years I've heard that the weakness of the Sloop main is the top 20% is more or less useless... other than as something for the rest of the sail to hang off...
Now I'm reading about 'Headboard Loads'....
this is'nt one off those 50yrs from now boats we're talking about is it..??
From my Cromagnon viewpoint the biggest load is exerted from the central belly of the sail and the bulk of rigging below the spreaders seems to support this reasoning... also any taper of the mast.. it get more slender as it rises.
This fact is also what puzzled me during the 'Boom Debate'.... but you guys seemed to be having fun.....
If you kept full sail up it seems to me that the compression loads transmitted by the increased strain on the shrouds in rising winds with full main would encourage/create a crumple effect... and it would not have to be much to alter the dynamics and cause rig failure by creating a reduced shroud tension...
I would not condem the man as a "B S'er"... I'm not clever enough in the fancy techie stuff... but logically... it don't make sense..
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Old 22-06-2011, 03:02   #43
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Re: Reefed main = greater mast breakage risk???

He was not advocating a complete roll in of the headsail or even furling it in to the size of a storm jib before dropping the main. His suggestion was to drop the main fully at the point you may normally reef the main for the first time.

I'm not sure what others do, but back in my youth we would reduce down to a no.3 jib and full main as the wind picked up. Only when that was still to much sail area (or we could see squalls coming) would we reef the main. His suggestion was to drop the main completely at this point rather than reefing. Again, his attitude about this only applied to masthead rigged yachts with no cutter or baby stay and no running backstays.

I'm sure any mast manufacturer will tell you that a reef main does exert different stresses on a mast compared to a full main and I am sure that these forces will put more bending pressure on the upper part of a mast. I don't think it takes an engineering degree to be able to see that. BUT I'm also certain that all mast manufacturers will also tell you that the mast and rigging design takes the different reefing forces into consideration and therefore it is extremely unlikely that it will be the point of failure.

Paul, the metal fatigue is one of the reasons that many people say you should replace your rigging every 10 or so years. The Fox News comment are for those who close their minds and shout "dangerous" without entering into any discussion or even thinking about it one minute. Your posts were not of this kind.

Like I said before, he is not advocating a dangerous practice, he is advocating an overly cautious approach which dictates how he believes a yacht should be rigged. His Najad has a masthead rig with a cutter stay and running backstays. He reefs his main and feels comfortable that the extra stays are helping spread the load.
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Old 22-06-2011, 03:51   #44
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Re: Reefed main = greater mast breakage risk???

I suspect something lost in "Translation".

Either that or the instructor is an idiot

Could maybe direct him to this thread?
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Old 22-06-2011, 05:11   #45
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Re: Reefed main = greater mast breakage risk???

From Selden mast tuning guide
•" Reef the sail and check for lateral straightness. If the
deviation from the straight line is greater than 5 mm, the
lower shrouds must be adjusted".
Suggests load on the rigging is different
Suggests that tuning your rig correctly allows for safe reefing
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