Dismasting - Why Does it Happen - How to Prevent it

[micah719]

Thanks Cap'n Sandcrab. I've come across Mr Sponberg's work before, it's interesting stuff. Unfortunately, he's more into composite, alloy or wood masts, and the link about the mast failures makes me more wary than ever of composite. Some very interesting stuff in there that would be good in the lightning thread. It's not absolutely certain yet that I'll make my masts of steel...alloy is the main alternative. But, I have somewhere in my archive an article (wish I could find it, need to do some cleanup in there) about the relative merits of the various materials. From memory, designing to the kind of loads of the size boat & sails I intend to build, I have the option of wood (solid or hollow), alloy, or steel. The timber loses out because it would have to be solid to get anywhere near the strength, and would be awfully heavy and very thick indeed....windage. The alloy would come out at walls 8mm thick, and the same weight of steel, 2.6mm thick. Corrosion makes me leery of such thin steel, but I've tried compensating for that with fully sealed and well coated masts; halyards running in recessed tracks, with a sealed internal tube from below deck to masthead for electrics such as lights and antenna.

Thanks Cap'n Zeehag....I had intended keel stepped masts, just raising the deck penetration four feet higher than the deck and keeping the mast winch & blocks attached to the extension. In my mind that keeps the stress points off the mast, and reduces the lever length between the wedges and the step, and thus lessening the stress on the mast yet again as well as reducing the amount of water the deck penetration will have to try and keep out. A recent thread supplied me with the idea of a solid cast-in-place epoxy collar rather than wedges. If the horrifying thing happens and I lose a mast, the extension is an ideal stump for a jury rig. The downside is, I can't lower the masts easily to go under bridges, but I wasn't keen on that anyway.

I'm getting closer to the stage where the number crunching really begins, and I'll be building a 1:16 model of her as well for fiddling everything into its shape and place. Weight aloft does concern me, and I don't want a dog in light airs either, though I understand I won't be able to have a stunningly fast boat without compromising non-negotiables. It is working out to be a boat that will really begin to shine when the winds are getting up, when the light fast folks hitch up the skirts and go home. This fits in with the inevitability of getting caught out in gales...and as a shorthanded/singlehanded cruiser I want a boat that is friendly when the sea isn't. With the Junk rig the stress on the rigging is less and there are so many more options, and it's cheap and easy to maintain. A big plus. There will likely be a fair bit of ballast and with the large amount of sail I anticipate an initially tender boat that firms up. Ok, we'll be heeling, but that's life. Otherwise I'd have gone for a multi and be done with it.

It is great to have a lot of salt-stained veterans to bounce ideas off...I'm trying to listen to the experience and advice without being bullheaded about my unusual ideas, or caving too easily and going along with the crowd for the wrong reasons. It seems to me that a lot of modern boating methods are driven more by convention and convenience, and the profit motive, rather than what really works and is necessary. I'm open to criticism and the wisdom of folks who've been there & done it all...but to be able do the unusual means I'll need thorough convincing. A good way to learn, though it has driven many folks to exasperation ever since I pestered mum & Dad with my questions. Fair sailing!

[Stumble]

Originally Posted by capn_billl

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.

Bill,

Unless titanium is brought to over 600F where oxygen embrittlement begins it is actually one of the more flexible metals (thing titanium glasses that can be tied into knots). There is a proportionally small delta between yield and tensile strength, but numerically about the same as 6061 aluminium (or 10,000psi). The difference is that the titanium yield strength is just so much higher.

Most of our replacements have been is Grade 5, which is rediculously strong. With most engineers designing to match the tensile strength of the stainless with the yield of titanium. Since the yield and tensile of the titanium are so close together this seems to be a safer design then matching yield. But even so it results in a part that can be roughly 1/3 the size of the stainless it replaces.

If we do a size for size replacement, typical prices vary between 20% more and about double, depending on the complexity of the plates. With more complicated ones (double and tripple bends, weird tang angles, ect) being more expensive.

A strength for strength replacement is typically between 5% less and 50% more than 316. Yup, we can actually beat the price of stainless sometimes. This is because the amount of metal we need to use (roughly half by volume) means we can use small stock, which is easier to work, and more common.

The trade off for the marginally more expensive plates though is that they just don't corrode. Ever. The only realistic corrosion titanium faces is when in contact with carbon fiber. This can create a galvanic cell... But even then, according to the ABYC they are technically galvanicaly compatible, just at the far range of it. However, compare the galvanic problems with CF and 316, and titanium is a no brainier.

[mbianka]

Almost Demasted!! Full Report On Near Demasting While Crossing The Atlantic 2009 - YouTube

[ArtM]

Originally Posted by Rakuflames

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've lived and traveled in a number of different RV's of many styles, sizes, and configurations.

In RV's, performance characteristics include the ability to climb hills at a reasonable speed, stopping power, and sufficient suspension to carry the weight of the vehicle safely and comfortably, even under hard braking conditions.

Generally, you don't want to race RV's because air resistance increases exponentially with speed, and therefore fuel economy drops substantially. As a result, RVer's typically are happy to "cruise along" at 55mph, even though their rigs are perfectly capable of doing 75 or 80.

I see some parallels to the desire for "performance" in a cruising catamaran. "Uphill climbing" (sailing to the wind) is going to be a strong consideration, though not an overriding one. Just like I don't want my brakes failing in a downhill run on my RV, I don't want my rigging to fail on my catamaran when I'm pressing to the wind. Not being in a hurry will save wear and fuel in an RV - the question is "will it save sail wear and rigging damage in a Catamaran"?

So I think that performance really is important to RV'ers and cruisers, although it is not defined in the same way as it is for j-boats and race cars.

[ArtM]

Originally Posted by Rakuflames

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.

I'm with you on all these points, for sure. I want to be a destination sailor, but I also realize that a cruiser has to be prudent. Burning money is just not an option for most of us. Yet, I would rather arrive in 3 days instead of 5 days if I can.

Once there, though, I might stay for 2 or 3 weeks on the hook - maybe months, so I definitely won't sacrifice livability for that performance. A slow day at sea i s better than a fast day in the office!

That means that I'm in the Lagoon/FP/Leopard camp, but I have found that few owners of those boats want to talk about performance, except to say that their boats are "fast enough" and that they are not in a hurry, and that is not what cruising is about.

[impi]

Sometimes simple things can make a mast come down ... I had a buddy sailing up through the Caribbean a while back ... he said he looked to his port side (leeward side) whilst under full sail and saw his main shroud dangling around totally detached from his boat. Quickly he called for his son to fetch a wrench and they literally re threaded the turn buckle whilst sailing. The lock nut had come loose and the turn buckle slowly loosened until the shroud came free ... his description of the events had us in hysterics ... you can only imagine the feeling when seeing that in strong winds

[Stumble]

Mbianca,

That bolt didn't sheer, it corroded away. That is a perfect example of crevice corrosion taken to the extreme. Had you looked at it five minutes before failure, there was probably just a thin line wrapping around the bolt. Just look at the end of the bolt where it has already oxidized, had it been a sheer, the end would have been bright and clean where fresh metal was exposed.

[capn_billl]

I'll take a set. I see the price of stainless going up, it is good news that titanium has crossed the price point.

If you have a list of chainplates for varius popular models of sailboats, and prices, (I see you are in the business). Post it, (if the mods allow), or PM the list of people interested, (if they don't). I would like the list, chainplates don't last forever, and having the price of new chainplates, may influence my decision on the next boat, Thanks.

[mbianka]

Originally Posted by Stumble

Mbianca,

That bolt didn't sheer, it corroded away. That is a perfect example of crevice corrosion taken to the extreme. Had you looked at it five minutes before failure, there was probably just a thin line wrapping around the bolt. Just look at the end of the bolt where it has already oxidized, had it been a sheer, the end would have been bright and clean where fresh metal was exposed.

Greg:
For the record that was not my boat but, I came across the video on You Tube and thought it would be of interest to this discussion. My boat actually has an unstayed mast and I'm quite happy about that and so is my wallet. Though there is always something to worry about breaking on board besides the mast.

[Stumble]

Mike,

Sorry for that, I thought it was your boat.



Cptn Bill - check your private messages.

[PooBeetle]

Factor
"Rig Failure is not a given."

i've spent minimum 100 hours reading on 316 Stress Corrosion Cracking. I say it's GUARANTEED to fail, and EVERYBODY knows this. it's just CHEAP is all, (and looks SHINY!)

The real miracle is why 316 actually stays up for ANY longer than 6 months (residual stresses caused by manufacturing etc ie. microscopic corrosion pathways, cracks, fractures that the chlorine preferentially dissolves incredibly quickly. etc)

so do ONE hour of reading and get back to me.

i'd be interested to hear your opinion AFTER you've done one single hour of reading about 316 Stress Corrosion Cracking.

one single hour of reading.






"Sensible initial design and sensible maintenance result in no rig failure."

no. perfectly untrue.

again 316 is lucky to last 6 months before Stress Corrosion Cracking (SCC) breaks it.

and in some cases NEW 316 fittings fail (TWICE!) in 6 months
Shroud failure « Camomile


(almost certainly due to SCC on residual stresses caused by cold working during manufacturing (due to chlorine accelerating the corrosion along crystal boundaries while the crystals are under stress))

Stainless Steel - Corrosion Resistance

an easy place to start. and the absolute tip of the ice berg.



i'm sure you'll take the ball and run with it, since you are a responsible person, and will soon know more than me about the subject.

(as being a vendor, and me a customer, perhaps should know more about this than the average person does. so when customers ask you questions, you'll know the answers.)








bruce smith
"The cheapest possible materials are used , not the best."

Factor
"What an extraordinary thing to say. etc"

i apologise, but i'm squarely on Bruces' side.


i say he's BANG! on the money.
316 is so cheap and shitty it's bizarre.


actually bizarre.

in any other land based industry they'd be SUED out of business for using 316 anywhere near salt water. (chlorine)

i repeat SUED out of business and rightly so.

(especially when they KNEW about 316 Stress Corrosion Cracking and how ANY metallurgist would say 316 CAN NOT be used near chlorine (salt) and under stress.)

with a single hour of reading, even a lay person can understand 316 just can't be used near salt water, and if it is, then people are going to die.



Stress Corrosion Cracking.

read up, and tell me your thoughts. i'd be interested to hear your thoughts AFTER you've done some reading.


m

[rebel heart]

How is 316 likely to last six months when I had a stem bracket that was 36 years old? There was corrosion in the lower sections and I had a new one re-fabricated since I had removed it already, but saying that stainless chain plates last six months is nuts.

Spend an hour walking around looking at multi-decade old chainplates and explain how they're still holding load, if they break at six months.

Additionally, every pressure vessel that contains the nuclear core on a Navy submarine is made out of 316.

[foolishsailor]

Proper standing rigging if cared for properly does not need to be handled with kid gloves. I.e. you don't need to not press the boat to get every ounce of speed out of her.

In heavy winds the boat will lay on her side before rigging will pop.
In gusty conditions the sails will blow before rigging will pop.
Poor sail handling can blow masts if you have a spinny up in heavy winds with you main down and insufficient backstay for example but that is user error.

All stainless rigging needs to be replaced every 5 to 10 years depending on usage due to cycling loads. The primary failure point for stainless rigging is at the swage fittings for the upper shrouds. These blow and the mast usually folds at the top spreaders.

Properly sized rigging, properly maintained, excluding user error - should never come down. Since the rigging needs to be replaced periodically as well there is no reason to use a newer boat for crossings, newer riggin yes, newer boat irrelevant.

[carstenb]

PooBeetle,

Gotta diagree with on 316. Virtually every fishing boat in the world uses 316 stainless fittings on their hydraulic systems. Most hydraulic motors that run the winch systems on fishing fleets have 316 stainless shafts.

Most manufactures of hydraulic fittings will give you all the test data you can read regarding salt water corrosion on their 316 fittings.

NOt to mention the 316 stainless vales out on the market for use in nuclear facilities. Oh, don't forget that in the submarine world every fitting is stainless

[zeehag]

poob---my formosa had original chainplates and tangs--they were TAIWANESE ss, 316---2 had cracks--i replaced them with 304---and heavier duty.
a friend has a cheoy lee--boat was 35 yrs old with original chain plates and tangs--he did pop chainplates in pacific , then tangs--all one has to do to make sure stuff doesnt happen is to change em out before ye sail out of port. make sure all is new or at least within 10 yrs, and go. within 10 yrs is good. change the tangs and chainplates every 20 yrs and all is good.
only thing wrong with my formosas chain plates was--the boat , before i got her she was laid over on the breakwall in santa barbara for a week. there were cracks in 2 chainplates--i replaced em for a total of 200 dollars, specially made for me.
even if chainplates and tangs fail, one doesnt necessarily need to lose mast--use halyards and sheets to secure mast to boat and go to port. or replace.repair at sea. is doable. folks have done this without dismasting.