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Old 11-12-2008, 03:43   #1
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Sagging spreader, is that a symptom of something sinister

When we last loosened the rig off to ride the travellifter (about a year ago) upon retightening the rig we noticed that the starboard lower spreader had dropped down about 6" at the tip,. the others remained in their opriginal positions. I loosened the rig again and using a conduit I managed to puh the end up while tightening the rig again and then it remained in position.

Is the drooping in the frist place a symptom of something failing in the spreaders attachment to the mast, or are they all loose to some degree (vertically) until the rig is tightened up ? Dual spreader, cutter rig.
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Old 11-12-2008, 04:07   #2
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Droopy (Sagging) Tips BAD - Elevated Tips GOOD !!!

Spreaders should exactly bisect the angle formed by the shrouds where they run over their tips. In other words, the outside ends of the spreaders (tip) should be slightly higher than the roots at the mast. This ensures that the spreader is only under a compression load. A horizontal, or drooping spreader experiences bending (flexing) loads.

The spreaders are designed to take tension from the shrouds, convert it to compression, and transfer it to the mast.

The force on the fittings, that attach the stays to the mast, is a function of the reciprocal of the sine of the angle, that the stays make as they meet the mast. As this angle narrows, the sine of this angle goes to zero and the function, (and force), goes to infinity. A minimum of about 12 degrees is the current limit for readily available hardware. On a boat with a typical 5 foot distance from chain plate to mast base, the upper shroud attachment point can be no higher than about 24 feet without violating this “12 degree rule”. Spreaders are used to accommodate a taller mast and narrow beam, to artificially increase the natural angle.

Apart from terminal failures, (drooping) spreader flexure may be the commonest cause of sudden rig failure.

Most spreader root brackets (mast attachment) have some play in them, although some high production “class” boats may have custom brackets c/w a permanently built in dihedral*.

* Dihedral is the upward angle from horizontal of the spreaders, often about 5 degrees.
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Old 11-12-2008, 07:42   #3
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The short answer is, "Something is wrong. Get it looked at." - LOL

Great post by Gord as usual but, yes, if 3 spreaders don't sag and one does, it needs a looking at.

It can depend greatly on the design of the spreader and mast bracket. Some spreaders "slide" over a blade at the bracket. Over time, wth flexure, the blade and spreader wear and the angles all start changing.

Bottom line is that I would have a pro look at this as soon as convenient.
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Old 11-12-2008, 10:26   #4
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The problem may be as simple as the spreader tip not being well-secured to the shroud. On VALIS the lower spreaders carry the upper and lower shrouds, so it is literally impossible for the spreader to bisect the angle, since there are two different angles (see attached photo). Since the angle is not bisected, there will be vertical force on the spreader tip.

In this shot (on a Lahaina Yacht Club mooring, Maui, 2003), you can see that the lower spreaders are drooping. The lower spreader tips were not secured tightly enough to the shrouds, and the force due to the angle of the lower shrouds had driven the spreader tips down. We re-adusted the spreaders and lashed them tightly with stainless wire before sailing back home.

I'm no rigging expert though, and if you have any doubts you should have a rigger look at it.
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Old 11-12-2008, 11:02   #5
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Our spreaders hinge at the attachment point to the mast. So when we stepped our mast last time, it looked like the picture below. It was no big deal, we just tied a messenger line to a spinnaker halyard and clipped the shackle to the upper shroud and hauled away until we got the angle bisection Gord was talking about. It happened to us because our spreader boot was attached too tightly to the shroud and not positioned correctly when the crane picked it up.

The short version of the story: if you have hinged spreader attachments, it's no big deal. Just needs a little attention.

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Old 11-12-2008, 11:45   #6
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Just to be sure everybody is clear, your spreader tips MUST be secured to the shourds at the proper angle. This is usually as simple as lashing with monel or stainless wire. Just "pushing" them to the right place is not good enough!

With a properly tensioned rig, in stong winds the leeward shourds will JUST come loose. They won't be floopy loose, but they will no longer be bar tight either. If you are counting just on friction to hold your spreader tips in place on the shroud, they are very vulnerable to slipping at this point, especially with storng winds and a vibrating rig.

If your spreaders "droop" not only MUST you realign them, you MUST fix the reason they drooped!

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Old 11-12-2008, 11:53   #7
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Excellent technical info - Gord ! That will be be especially handy when we re-rig in the near future.

Paul & Janders, thanks for the photos, that is a relief to know that it may be just a tune up thing.

Hopefully the photos attached sucessfully.
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Old 11-12-2008, 11:58   #8
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Bill - there is some fine SS wire wrapped around the tips with some tape over it, I only noticed it this week when I had my first trip up the mast. I figure that it needs to be tightened up on that side so it will only slide for adjustments rather than when it likes to.
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Old 11-12-2008, 14:17   #9
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That s.s. wire is what a rigger will use to secure each shroud into the groove in the spreader end. We stripped and repainted our mast during the winter and replaced all the shrouds and the wire that secures them. Any rigger will sell (or probably give) you a metre or two.

Lisa also made new leather "boots" for the spreader ends: These boots are a good idea for minimising wear on the sails. We used quite a thick leather (about 4mm thick)cut to approx the right shape (but a little oversized) We soaked the leather and moulded it onto the spreader ends (because we had the spreaders off the mast this was easy) and used bandages to strap the leather firmly in place while it dried. Once dry, we trimmed it to get a good firm fit. We then sewed the boots on nice and tight with a heavy whipping twine. Top Tip - use an electric drill with a fine bit (1.5mm or 1/16" or thereabouts) to make pilot holes for sewing, otherwise you will break a lot of needles and fray a lot of tempers Even pre drilling you will need a sailmaker's palm and probably a pair of pliers.

P.S. Nice looking boat, btw
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Old 11-12-2008, 14:23   #10
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Quote:
Originally Posted by Paul Elliott View Post
The problem may be as simple as the spreader tip not being well-secured to the shroud. On VALIS the lower spreaders carry the upper and lower shrouds, so it is literally impossible for the spreader to bisect the angle, since there are two different angles...
...I'm no rigging expert though, and if you have any doubts you should have a rigger look at it.
Neither am I an expert rigger - but I believe that the Upper (outer) shroud should be of the most concern, in achieving a bisected angle.
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Old 11-12-2008, 15:37   #11
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Neither am I an expert rigger - but I believe that the Upper (outer) shroud should be of the most concern, in achieving a bisected angle.
That is my assumption as well, and my rigger does like to set it up that way. I guess my point was that when both the uppers and the lowers go over the same spreader tip the forces will be different than if there was only one shroud, with the spreader bisecting that angle.
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Old 11-12-2008, 19:36   #12
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While it is commonly claimed on forums that the spreaders should bisect the angle at the shroud I would have thought much more commonly the spreaders are not required to do so. Did a quick double check on this looking through photos and found that seems to be so - cruising boats, race boats (including IACC boats) and super yachts seem to often go with horizontal spreaders (including the top spreaders where the angle is greatest).

My own, for example, are not intended to bisect the angle as they are mounted on solid through bars.

I also would have thought it has been a long time since spreader tips needed wiring to the shrouds - it is not needed for rigid spreaders for preventing vertical movement and as far as I know most manufacturers provide capturing guides at the tips to stop the shrouds flopping out (should ones rig turn out to be that floppy ).

Of course, if ones spreaders are just riveted to the mast or otherwise not strong enough to be regarded as rigid then ones mileage will differ to the above.
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Old 11-12-2008, 21:38   #13
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While it is commonly claimed on forums that the spreaders should bisect the angle at the shroud I would have thought much more commonly the spreaders are not required to do so. Did a quick double check on this looking through photos and found that seems to be so - cruising boats, race boats (including IACC boats) and super yachts seem to often go with horizontal spreaders (including the top spreaders where the angle is greatest).

My own, for example, are not intended to bisect the angle as they are mounted on solid through bars.

I also would have thought it has been a long time since spreader tips needed wiring to the shrouds - it is not needed for rigid spreaders for preventing vertical movement and as far as I know most manufacturers provide capturing guides at the tips to stop the shrouds flopping out (should ones rig turn out to be that floppy ).

Of course, if ones spreaders are just riveted to the mast or otherwise not strong enough to be regarded as rigid then ones mileage will differ to the above.
REMEMBER ALL: Internet based advice is worth exactly what you pay for it! Ignore the rules of physics at your cost!

I'll give the poster the benefit of the doubt, and assume that they are thinking of lower spreaders on multispreader rigs. The angles these spreaders make is more complex and they are frequently horizontal, or close to it. Of course if he had actually read the comments, nobody talked about spreaders "flopping out" of their attachment to the shrouds, what was discussed was spreaders shifteing vertical alignment. Remember, just because that's the way YOUR boat was built, does NOT mean it is the right way!

Spreaders are COMPRESSSION members. If you don't understand what that means, then you aren't qualified to comment. You ARE 100% qualified to ask questions, however. Understand that on a forum like this you are going to get multiple answers, including answers from people who don't understand rigging. So you still have to sort out the right answers. So you might not actually be better off than you started.

I suggest, if you don't know the answer, and don't know how to pick the right answer from the multiple answers you will get here, you go out and buy a good book on rigging and use that as reference source.

It will cost more than asking questions here, but you'll get a good consistant story about what to do and why.
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Old 11-12-2008, 21:48   #14
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You ARE 100% qualified to ask questions, however.

<snip>

It will cost more than asking questions here, but you'll get a good consistant story about what to do and why.
It took me years before I was qualified to ask questions. I still ask a few dumb ones

There are a lot of smart guys here and over time you figure out who they are.

One difficulty is that there are many many boat types and build methods and rig types. Often the advice given is valid but it applies to another boat.

I consider myself a decent engineer and understand physics pretty well. Regardless of that if my spreaders were sagging I would get an expert to look at it.

Last time my rig fell down it cost $15,000 to stand it back up - plus sails.
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Old 12-12-2008, 01:05   #15
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I like the diversity of information on these forums, it stimulates thinking on the subject. If we are going to cruise and do not have a background in sailing then here is where the lessons begin.

Our only encounter with a professional rigger was not at all a plesant one with our first vessel a few years ago. Very poor work, the bill was double the quote, in the end he had to pull the mast down again and fix it all up. After the drama then some colourful stories surfaced about his work, but nobody would tell us before contracted him, and we did ask around. It just reinforced our already staunch DYO nature and if it falls down then there is only me to blame.

In the end the key to finding a solution is to listen to many opinions (books, forums, etc) with an objective mind and formulate your own solution.

I am more than happy with the postings so far on the Cruisers forum on this subject, and other questions posted previously. The Cruisers forum is the most friendly, diverse and informative forum we have been viewing. Keep up the good work !
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