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Old 28-07-2012, 15:22   #46
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Re: Dismasting - Why does it happen, how to prevent it

Having a properly tuned mast with the correct size cotter pins is another suggestion.

I had our mast stepped and tuned at the boatyard before starting our trip to Panama. Even after that, I was not happy with the amount of mast pumping and the stays going slack on the leeward side in strong winds, so once we got to Key West, I decided to tighten them up a bit further.

There I discovered that the rigger had used cotter pins that were one size too small. The turnbuckles had just twisted them out of the way as they unwound. On our next leg to Cartagena, we went through 4 straight days of 30-35 knot winds and 20-25 ft seas. Had I not double checked and re-tuned the mast myself, I'm almost certain that the mast would have come down once one of the turnbuckles unscrewed completely.

Originally, I was not comfortable tuning the mast myself, as it has double swept-back spreaders and a fractional rig, and I just didn't know anything about the proper way to tune it. Paying some professional to do it gave me a better feeling of security. After that, though, I boned up on how to tune a fractional rig, and I'll never let anyone else do it.
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Old 28-07-2012, 15:30   #47
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Re: Dismasting - Why does it happen, how to prevent it

Quote:
Originally Posted by oldjags View Post
and the stays going slack on the leeward side in strong winds,
This is to be expected, and is proper. There is absolutely nothing wrong with loose shrouds on the leeward side. In fact if they don't get slack, it often means the rig is too tight. From a structual point of view, leeward shrouds do nothing to keep a mast upright, and if tight actually pull the rig to leeward causing excessive bending.

I don't know where this theory comes from, and it seems to be exclusively seen in cruising circles, but it is pernicious, wrong, and prone to leading to excessive loading on a rig.
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Old 28-07-2012, 16:37   #48
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Re: Dismasting - Why does it happen, how to prevent it

The mast tuning instructions I got from the mast manufacturer and from general research on the internet said that swept spreader rigs need to have the upper stay tight enough that it does not go slack.

The upper stay is what puts most of the pre-bend in the mast. so if it goes slack, the mast can twist. Also, without enough pre-bend forcing the middle of the mast toward the bow, the mast can invert and buckle since there are no forward lower stays to keep the middle of mast from flexing toward the stern.

The way I've got it now seems about right. The lower and intermediate shrouds will occasionally go a little slack in 15 knot winds, but the uppers stay tight.

I definitely did not like the amount of mast pumping and movement I was seeing before I tightened them up. My mast has only a small to moderate amount of pre-bend it, and I have seen other boats like mine with far more curve in the mast.

Your comments are definitely true if you're talking about masthead rigs with conventional spreaders. Here are some links on tuning the fractional rig and how it differs from a conventional measthead rig with straight spreaders:

Tuning the Fractional Rig* Bruce Kelley says attention to shroud tension is crucial
http://www.kempsails.com/index2.php?...d=18&Itemid=12
http://www.riggingandsails.com/pdf/selden-tuning.pdf

To quote from Selden's tuning guide:
To ensure good fore-and-aft stability for this type of rig,
it is very important that the leeward cap shroud is tight.
This high level of pre-tension will generate plastic deformation
on all grp hulls. As far as strength is concerned,
the hull should be able to support these loads, but the
deformation will make it necessary to check the tuning
while sailing. This is particularly important when the
yacht is new and at the start of every season.
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Old 28-07-2012, 16:55   #49
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Quote:
Originally Posted by Bash

Interesting. Most rig failures I've witnessed have been due to poor judgement. Like when Boat A t-boned Boat B, or when Boat C snagged a jibe mark with its spinnaker.

One of my dock neighbors sailed his 75' mast under a 70' railroad bridge without asking the bridge operator for a lift. That was ugly.
Maintenance has been what I've seen too. Either that or racing boats doing stupid things with too little rigging and too much force. But it's the chainplates with crevice corrosion, right at the deck, where it seems to be the worse. Doesn't matter how strong everything else is and whether or not someone has "rerigged" if every attachment point is held on with a square centimeter of stainless.

I'd mark this as a distinction about "blue water" boats as well. Way overbuilt rigs, including massive chain plates and stem/stern fittings that even if eaten through halfway by corrosion still have sufficient strength. Chain plate maintenance is a pain in the ass but it's really not *that* bad. Pop them out one at a time when you're on a hook or tied to a mooring. Pull down a halyard to use as a temporary support.
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Old 28-07-2012, 23:22   #50
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Re: Dismasting - why does it happen, how to prevent it

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Originally Posted by Rakuflames View Post
Cruisers should be just as diligent about keeping their boat in good repair as racers, and then sail their boat as best they can. I just can't think of a good reason for a cruiser to deliberately sail 1 - 2 knots slower than they can.

If the rigging is in good condition, sailing fast won't bring it down. Cruisers are destination sailors. Why take 4 hours longer than you should because you don't trust your rigging? Check it out and then go have fun!
I don't think they should be irrational about it, but it's been often said by cruisers on these boards that they are not in a hurry, that their boats are not made for speed, and that they don't feel the need to rush, thus the lack of interest in performance discussion w/respect to catamaran cruising boats.

So to me it makes sense that a cruiser would also not want to stress their boats unnecessarily, whether well inspected or not.

Perhaps I'm making a wrong assumption that fast sailing (or attempting to sail fast) creates more stress on rigs? Or that it will wear out a set of sails more quickly? I would like to get somewhere 4 hours sooner, myself, but if taking a 10% speed hit will signficantly increase the life of my sails and perhaps avert a collapsed rig at sea, I'll take the speed hit. A 20 or 30% speed hit is something else, though, I agree that is a lot.

As I said, that may be all wrong assumptions

-- Edit -- reading back now, I see these same points have already been mentioned
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Old 29-07-2012, 00:27   #51
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Re: Dismasting - why does it happen, how to prevent it

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Originally Posted by ArtM View Post
I don't think they should be irrational about it, but it's been often said by cruisers on these boards that they are not in a hurry, that their boats are not made for speed, and that they don't feel the need to rush, thus the lack of interest in performance discussion w/respect to catamaran cruising boats.

So to me it makes sense that a cruiser would also not want to stress their boats unnecessarily, whether well inspected or not.

Perhaps I'm making a wrong assumption that fast sailing (or attempting to sail fast) creates more stress on rigs? Or that it will wear out a set of sails more quickly? I would like to get somewhere 4 hours sooner, myself, but if taking a 10% speed hit will signficantly increase the life of my sails and perhaps avert a collapsed rig at sea, I'll take the speed hit. A 20 or 30% speed hit is something else, though, I agree that is a lot.

As I said, that may be all wrong assumptions

-- Edit -- reading back now, I see these same points have already been mentioned
They've been made separately, and you put them together. Useful post IMO. But then I'm one of those cruisers who, as soon as I'm clear of the shallow water and the putt-putters, wants to sse what the boat can do.

I don't race her -- if you lived in an RV, would you road race her? But I have my belongings secured, and I like to see how fast she can go. So far the record is 7.3 k with both sails, and 6.5 k just on the headsail.

I look at all the maneuverings that go on at starting lines, and the need to never back off to win a race. I see the damage done to boats in races -- blown out sails, even sinkings. I have a friend with a 19 ft boat that was t-boned by a 37 ft one at a starting line. That had to be pretty terrifying to see that big boat coming down on her! No thankee...

But I deliberately bought a fast boat. To me that's part of the fun, to squeeze every ounce of PRODUCTIVE speed I can out of her. That means doing sensible things like reefing when appropriate. I like a good, hard sail that works my body, my boat and my brain, and time to enjoy the end of the day. My sails are in good shape and I keep an eye on them -- my headsail is being restitched right now while the boat is laid up.

I'm not doing it foolishly. I don't' have the experience to handle a spinnaker, and I like my comforts (translation -- shade in the cockpit). I don't take the bimini down; a hardcore racer would.
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Old 29-07-2012, 00:59   #52
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When it starts blowing like hell you're going to move at hull speed anyway, or at least close to it. It's hard to go "slow" in 40+ knots of wind. The boat's going to want to go somewhere even deep reefed, and chances are you're on a beam reach or wider. So yeah, you're hauling ass.
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Old 29-07-2012, 06:52   #53
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Re: Dismasting - Why does it happen, how to prevent it

The mention of the "upper stay" needing to be tight enough so that it never goes loose is I feel a little mis-leading. I think that comment is referring to the upper diamond, not the upper stay. The diamonds, upper and lower, should certainly stay tight enough to keep the pre-bend ( we have 140mm ) but the upper and lower leeward stays will definitely get loose going to windward.
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Old 29-07-2012, 07:24   #54
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Re: Dismasting - Why does it happen, how to prevent it

I would go with titanium, except most alloys, are hard and can be brittle. My experience is in the avionics industry, so milage may vary. They were also subjected to extreme heat and vibration. But titanium is a very strong metal, a titanium plate with the same strenght as 1/4 inch steel can be almost paper thin by comparison.

Fiber glass is a good material, and can be incredibly strong for it's weight, but there is a reason it wasn't used for chainplates to begin with. Carbon fiber also a good material, but both are subject to failure from shock loads, where most metals would only elongate.

Conclusion: If you can get a pair of titanium chainplates for a reasonable price, pick me up a pair too, thanks.
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Old 29-07-2012, 08:20   #55
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Re: Dismasting - Why does it happen, how to prevent it

I very much doubt I would lose my mast if only one guy wire snapped,

As you can see in the piccy, I have seven separate wires holding up my mast,

If one broke, I could easily replace it, and very quickly, before it became a safety hazzard to my boat,

Dropping the main and Genoa only take a few minutes, So there would be no strain on the mast, I also carry spare rigging wire,

I have all the gear to get up my mast and replace or repair any thing missing or broken up there,

The Gemini has one of the strongest rigs going,

Cheers,
Brian,
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Old 29-07-2012, 08:27   #56
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Re: Dismasting - Why does it happen, how to prevent it

Monel chain plates anyone?
Didn't think so .
SS is the culprit.
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Old 29-07-2012, 08:36   #57
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Re: Dismasting - Why does it happen, how to prevent it

rebel heart--i think you need to practice sailing in BIG winds--they happen a lot off mexico, and much of the time sans warning.
in BIG winds, one does not necessarily sail at hull speed. we didnt until we put up all sails--with main, we were a lil out of control with much weather helm in a sloop in gulf of mexico--10 kts speed at 0300 isnt what is fun. actually is a gas, but is terribly hard on boat and not exactly safe activity.
to slow boat, we shortened sail to using piece of rollerfurled jib and then cruised comfortably at 5-6 kts in 45 kts winds and up.
in my ketch, 60+kts brought us 8.4 kts boat speed and handled quite nicely with only the mizzen and jib, each reefed to first reef point, mizzen, and 3 wraps jib.
you may wish to practice for a while in your cutter to see how it handles in BIG winds before you leave for mexico. aint like driving a tuna trawler.
the sloop i sailed in gom had a prior problem with forestay and rollerfurling-- the stay snapped in 40 kts winds. he repaired that... when we were in dry tortugas, there was a shrud decided to snap -- there was just enough threading to re-install same bit--lasted quite nicely until we got to louisiana, many many miles later.
there are things that happen without forewarning---look a the racing sleds--they dismast despite maintenance and inspections. their masts break--they do sail in huge winds, and sail with much torque on the boat. racing isnt that easy on boat--not like cruising. they fight their boats and force em to do what they do. is a twist o flex action on the hull and rig.
inspect the boats that have raced and next to one , inspect one that has not raced--you will see a difference in the wear patterns.
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Old 29-07-2012, 09:37   #58
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Re: Dismasting - Why does it happen, how to prevent it

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Originally Posted by micah719 View Post
Is there anyone with experience of unstayed masts with something to share with regard to dismasting?

I'm planning on unstayed steel masts, and was considering instead of the deck penetration at deck level, to weld a standpipe to the deck so the top is about 4 feet off the deck. This would keep it out of most of the deck wash, provide a handy and solid attachment point for winches and blocks, and de-stress the mast both from attachments at the area of most stress, and also decrease the leverage between keel-step/collar. Since the unstayed mast experiences only bending moments from sails and wind, and depowers the sail by bending in strong gusts, I expect the only reason my masts will fail is if I get slack on maintenance, a material or construction defect, or a humdinger of a rollover/pitchpole. What say you?
This is the unstayed guy
Sponberg Yacht Design Inc.

and here's his story on four mast failures
Four Mast Failures

His entire site is a good read.

I'd avoid steel masts because it's so frickin heavy and will give you a really crappy motion.
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Old 29-07-2012, 09:48   #59
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Re: Dismasting - Why does it happen, how to prevent it

micah--the way you are speaking of doing your masts creates a stress point where the post and mast attach above deck. could pose a problem. if your mast is a single piece above decks would be more practical for durability--think about it fora bit and consider the physics of the stress on mast....
have you reserched the reasons behind the breaking of the carbon fibre unstayed masts used in some freedom built boats?
if your mast is keel stepped, the potential break area leaves enough of the mast to jury rig something with which to sail home or to a nearby port for repairs.
if mast is deck stepped, the break point is deck and leaves a great hole.
be prepared for anything and you should be ready to jury rig at sea.
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Old 29-07-2012, 09:52   #60
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Re: Dismasting - Why does it happen, how to prevent it

1. So who is the Chinese mast manufacturer and who built the boat that used them?

2. Other than the above, all the cat manufaturers use masts from the established mast manufaturers. It is in both these companies best interests that the sticks stay up. They usually do.

3. Fiberglass may have a working life but all the composite chainplates I've seen use more exotic variations like carbon and always epoxy. I beleive these are typically overengineered so a little fatigue is not going to matter.

4. Here's a pic I posted before.
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