Dismasting - Why Does it Happen - How to Prevent it

[micah719]

Fatigue limit - Wikipedia, the free encyclopedia

The concept of endurance limit was introduced in 1870 by August Wöhler.[9] However, recent research suggests that endurance limits do not actually exist, that if enough stress cycles are performed, even the smallest stress will eventually produce fatigue failure.

[Lagoon4us]

Originally Posted by 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!

How do you intend connecting the mast to the extension?

I have worked on boats with tapered unstayed masts that were a copy of Gary Hoytt's Freedom 40 designs, it never worked.

Steel masts won't work as weight and corrosion will flog you.

Cheers

[Lagoon4us]

Had a mate build a watertight box into his steel boat, inside he placed injector pump spares, injectors starter etc, He placed a burning candle inside and hurriedly sealed the box by way of a bolted coverplate.
When he returned from 6 years away he unbolted the plate to check out his trove, to everybody's amusement it was a mess of rust, the candle was half burnt however the box wasn't quite watertight......
Your comment bought back a smile remembering the look on his face...Priceless.

[mbianka]

Originally Posted by ewsponberg

As for the popularity, such as it is for free-standing rigs, I would say it is DEFINITELY influenced by the status quo of the market. Very few people are building them any more--the modern heyday was the late 1970s to the mid 1980s. Many of those boats are still sailing, and owners who take good care of them hold onto them for a long time because they like them so much. When they come up for sale, good ones go quickly.

I have also seen on this forum and on BoatDesign.net a growing appreciation and new examples of boats with free-standing rigs. I think interest is growing. So it only takes an intrepid boatbuilder to start some more modern designs. But the obstacles can be daunting--not only the design and tooling, but the up-hill marketing that would have to be done. But, I firmly believe that with the right design and the right builder, and the right approach to build the market interest slowly, such an effort would be quite profitable.

Many years ago when I planned to upgrade from my Bristol 24 I was looking at something like a Tarten 30. Then my girlfriend and I did a crewed charter in the BVI with a Captain who was also a navel architect. I discussed my plans with him. He suggested I take a look at the Nonsuch 30 with it's free standing mast. He had done a number of deliveries on them and liked it's sturdiness and simplicity of design especially no stays to deal with. So I did and finally bought a 1986 Nonsuch 30 Ultra in 1995 and have not looked at another boat since. After reading some of the stainless steel failure modes here I feel even better.

[capn_billl]

I looked at a cat-ketch that has unstayed masts. On a larger sailboat the point would be irrelevant, but on a smaller boat I can lift the 30 ft stayed mast on the boat I bought, on the unstayed 30 ft mast,...not so much. 80lbs vs 130lbs.

Stepping a 30 ft 80 lb pole with two stays for stability = doable. Lifting a freestanding 130lb pole into a receptacle with 4 ft extension = not possible.


If a freestanding mast was same weight as stayed mast, and if it had stays to support while stepping that could be removed, or left for added strength, I would go with one.

Remember if knocked down the mast has to hold entire weight of ballast from point of step, with lever arm of mast length. Much easier with shrounds to distribute force.

[Lagoon4us]

Originally Posted by capn_billl

I looked at a cat-ketch that has unstayed masts. On a larger sailboat the point would be irrelevant, but on a smaller boat I can lift the 30 ft stayed mast on the boat I bought, on the unstayed 30 ft mast,...not so much. 80lbs vs 130lbs.

Stepping a 30 ft 80 lb pole with two stays for stability = doable. Lifting a freestanding 130lb pole into a receptacle with 4 ft extension = not possible.


If a freestanding mast was same weight as stayed mast, and if it had stays to support while stepping that could be removed, or left for added strength, I would go with one.

Remember if knocked down the mast has to hold entire weight of ballast from point of step, with lever arm of mast length. Much easier with shrounds to distribute force.

Why would you not use a crane?

If you left stays it would not be freestanding??

That's why calculations are done, engineering is done so the mast does have the strength.....

[PooBeetle]

Dismasting - why does it happen, how to prevent it
Part 10 – Rig Design and Safety Factors

Lets assume that for some strange reason that you want MODERN ENGINEERING instead of your friends and family being killed by falling masts and rigging.

(as happens so regularly that the Coast Guard finally decided that they had to get up off their arse and take (impotent, useless, effeminate) action)

Lets assume that after reading all these previous points, you have decided that you no longer trust yacht rigging companies, or boat salesmen, and that you wish to CHECK all of their assumptions and work.

That means we have to do some simple math to see what sort of Safety Factors they built in.

Wire Rope Manufacturers Published Breaking Strengths Versus the rest of the worlds' using normal alloy data Suitable for Design.
there is a difference which has appeared to cause confusion.

Manufacturers test their ropes on a different time scale to the rest of the engineering world. (ie instantly breaking to destruction Versus the accepted scientific practice of pulling at standard rates and time scales (due to many obscure metallurgical factors))

They also use the Breaking Load because it's so simple for them to test their ropes and find this number, whereas riggers and engineers should use the alloy design yield strength ( published alloy data handbook).

and this difference in perspective causes an over estimation of 316 wire rope strength by a factor of 6, as non-engineers look at the Breaking Load of the wire rope and think WOW! What strong stuff. And they are right, these BL figures are correct. But only for one single load, applied for only one second.

BL figures are far from the truth if a load is applied twice. Or slowly over one minute, or over one week.

i suspect some yacht mast riggers around the world are using manufacturers published breaking loads, and then calculating or using their own safety factors, rules of thumb that work, when they should be using either the manufacturers Safe Working Load as an absolute maximum which includes ALL Safety Factors, rig tension and sail loading and wave loading. ( or even more correctly, an alloy design manual with alloy design criteria. ie somewhere a little less than half the yield strength of 316.)

See?
Rules of thumb safety factors Versus true engineering.

A guessed at factor Versus actual land based engineering because the law requires it and you would be sent to jail if you knowingly cut corners and injured somebody.

The rule of thumb gets it right 90% of the time. Actually engineering the structure results in 100.00% of the time, and then with plenty of reserve safety above the 100.00%.

That is what most people consider a safety factor to be. Exactly as the term sounds.

if we derive the strength of a 316 wire rope from first principles, we see that what most people assume a safety factor is, may not exist at all. (ie is there any safety factor if you go above the SWL of 316?) So is there a mismatch somewhere? Between the term as used by everyday people, the term as used by wire rope manufacturers, the term as used by mast riggers, and the term as used by engineers.

Exactly the same term, spelt exactly the same. But they are all totally different in meaning. And have Totally different physical realities.

I say there is no safety factor at all, and that some riggers using a safety factor of 6 have already deformed the rigging past its yield strength, even before leaving shore.

0.2% Yield Strength is the loading that should be used for 316.

If the load stays below 240 MPa, then the metal part has not been deformed, it will return to its original shape. Little brittleness or work hardening has crept into the wire rope.

If the load rises above this figure, then the wire strand has been permanently deformed. It has stretched, is still continuously stretching, and so is become thinner and thinner. It is well above it's intended use.

"Rigging Screws manufactured in accordance with Australian Standards have a safety factor of 6:1. This safety factor helps to counter possible problems from shock, vibration, fatigue, wear, damage and corrosion"

Please note the cheap dribble implying Australian Standards have been met. A safety factor of 6 times. And then note how yacht rigs are tensioned.

Example
316 Stainless 240 MPa 0.2% yield strength
which equals 24 Kilograms per mm2 before 316 starts to permanently deform.
(ball park figures - 1kg/mm2 = 10 mpa)

Random wire rope makers data;
10mm 1x19 BL 7870Kg SWL 1300Kg Mass 49.5Kg/100m
so 10 mm 316 Wire Rope has 7870 Kg Breaking load as tested by the manufacturer.

Yet the stated mass is 49.5 Kg/100m (with 316 density = 8.027 g/cm³)
pi x r squared => 5mm x 5mm x 3.1415 = .7854 cm2 for the area of a circle

so for a solid wire;
.7854 cm2 x the density in grams per cubic centimeter x 100 cm to get one meter
= .7854 x 8.027 x 100 = 630 grams, or .63 Kg of metal per meter.

this excludes the 1x19 wire compaction factor (ie we multiply the cross sectional area by a reducing factor as 1x19 wire has less cross sectional area than the solid wire)

so the difference between a solid wire and the 1x19 compaction factor must be
.495 Kg/m / 0.63 Kg /m = 0.7857

So;
the 1x19 compaction factor is 78.57%
so for the 10mm rope 0.7857 x 0.7854 cm2 = .617 cm2
so the 316 1x19 10mm wire rope is equivalent to a 0.617 cm2 316 diameter rod
61.7 mm2 x 240MPa = 1480Kg at the yield strength of 316
(above this, there is permanent deformation)

How do they get a breaking load of 7870 Kg? They break it in a few seconds. Vastly different to the real intended usage. even if we use the full 500 MPa UTS and full circle i get only
pi x r squared x mpa/10 ; 5mm x 5mm x 3.14 x 500 MPa =
78.5 mm2 x 70 = 4000 Kg breaking load using engineering data
but the manufacturer gets 7870 Kg when they do a simple pull to destruction test.

See?
they are out by more than a factor of two. the manufacturers have over stated the breaking load by over 100% and this is because of their real world testing method. They pull the cable fast and hard to destruction, and in the engineers data they do it slow in a standardised fashion.

Engineers use metallurgical design data. ie data suitable for designing structures.

Can you see that something is wrong here?

So Do Safety Factors Actually Exist?
First you have to define exactly what you mean. Using land based building codes, the answer is a resounding no, there are no safety factors once the stress goes over the yield. The part has deformed, has been work hardened (made brittle, and far more susceptible to metal fatigue and SCC), and should be thrown out.

Normal people understand a safety factor to be exactly what it implies. Perfectly true and sound, and then, after complete 100% safety, then on top, above and beyond, there exists EXTRA of the same quality again.

And yet we have just seen how the demands of the real world can dilute, twist, and create inconsistencies between pools of discourse.

According to the manufacturer above, 90% of the yield strength of 316 is the safe working load.
Please Note that the 1300 Kg SWL figure seems far too smooth. Too rounded.
So if we investigate by dividing 7870 / 1300 = 6
So it appears we arrive at safety either by using a safety factor of 6, or 90% of the yield.
In other words, rules of thumb.

Sure i hear you say, but it's sensible, real, and it's so close, so who really gives a toss?
Well if you have a think about it, you will see that in reality all true safety factors have mysteriously vanished.

Engineers do things for a reason. There is no safety once the metal part has deformed.

Do Safety Factors Actually Exist?
It all depends then on how you personally define exactly what a safety factor is. I say normal land based engineering practices. What a normal everyday person understands the phrase to mean.

But rigging companies use the wire rope manufacturers breaking loads for their safety factors.
( and this is excluding the extra reality that it is 316 we are talking about, and thin strands, and swaged (turned brittle by fabrication mistakes that show no understanding of the alloy), and in salt water ( ! ), and under big dynamic loads ).

madness This is zero safety factors in the normal everyday accepted use of the term.

The factor of 6 evolved as a rule of thumb because real world experience suggested something that got CLOSE to the normal engineering practice of using alloy data suitable for engineering structures. I've seen wire rope manufacturers data, that although perfectly TRUE, say 1700 MPa breaking load for 316, that's used more than once, and in salt water. crazy stuff.

out and out insane.

If you need more incentive to actually spend ten minutes doing the math, then just compare the righting moment of your yacht, and your rig tension to the true yield strength of your 316 rigging.

So;
what exactly do mast riggers mean when they say they have safety factors. 6 of the instant, once off over one second Breaking Load? Or are all safety factors inside the yield strength?

Example
"standing rigging is all 10mm 19×1 which has a breaking strain when new of 7250kg but most riggers I have consulted tell me that this is over specified for the size and weight of the boat."

"the rig is normally tensioned at up to 20% of the breaking strain, loads will fluctuate depending on sail plan, wind and sea conditions"

So;
if this is true,
then this guys rigging is permanently stressed above 240 MPa, and in a chlorine environment. (as we have just worked out in the example above, the yield strength of his 316 rigging is 17% of 7250 Kg)

get it? if not, then do the math yourself.

See?
He is already above the safe working load of 316, and he hasn't even left the marina.

The SWL of that wire is 1300 Kg, and now he is about to put out to sea and get massive shock loads from big waves and wind.

See?
he should have tensioned to an absolute maximum of the Safe Working Load including what ever dynamic loads he expected from the sails and waves combined.

This is to a maximum of 1300Kg.

if he is correct, and his rig is tensioned to 20% of breaking load, then his rigging is rotten all through, but shiny! and looks great on the outside.

Invisible microscopic cracks propagating all through it, but still looks fantastic!

The real wonder of the situation would then be not if or when his rigging will fail, but why it is still standing. His rigging may last forever in a cold climate, or it may fail tomorrow.

Safety Factors
Zero safety factors due to manufacturers stating 1700 MPa breaking load for 316 wire rope, (which is perfectly true if the load is applied once, and once only, and for one second), but riggers then use this to guestimate a safety factor of 6, when they should be using the Safe Working Load to calculate their safety factors inside of.

Safety Factors
what a load of s***. if anybody gave a damn they'd use a safety factor on the alloy used as well. ie a PREN above 40.

See how cheap words are? The term “Safety factor” by crapitalists. Let me translate that for you. $9.95

PREN Versus cheap dribble when they allude Australian Standards for rigging.
The Pitting Resistance Equivalence Number Safety Factor.
Does your alloy have a safety factor? No? so it's all dribble then stacked on top of other dribble. All ********.

All rigging Companies say 316 is ACE! But a government comes along and says to be called Salt Water corrosion resistant, your alloy MUST have a PREN above 40.

you are NOT allowed to use any steel that has a PREN below 40 because people have died from doing so.

So are any safety standards relevant? Are there any safety factors at all in reality if you are using 316?

Before you even start the bulls*** calculations. ie saying you have a SF of 6 but knowing full well this safety factor is calculated on the Breaking Load, a ONE use for ONE second number; and knowing you are well above the alloy yield strength.

Safety Factors Versus Affordable Toys
Safety Factors, what a load of capitalist dribble. People want TOYS. Shiny TOYS, and they want them now. They don't want to be forced to comply with REAL and expensive engineering laws as for land based buildings, where things have to be done properly.

So they mouth off instead. It's just so much easier to ********.

Safety Factors = cheap dribble spouted by capitalists.

Missing Safety Factors
as you recall from the wire rope analysis, the simple maths we performed led us to the astonishing conclusion that riggers were using manufacturers Breaking Load data to base their rigging Safety Factors on, when they should have been using alloy data suitable for designing structures.

And this led to the complete absence of safety factors.

We saw a NEW yacht rigged by professional riggers that was over the maximum stress allowable on 316 before it had even left the harbour.

If australian law says a TRUE safety factor of 6 inside the yield, but the 316 wire rope they used was already at ZERO true safety factors merely from having the rig tuned up, then what can a normal sensible person to do?

Realistic safety factors.
Never listen when somebody says Safety Factor. Do the math yourself. Ask for the maths or you know you will be getting the weird confluence of realities that leads to misunderstanding the true reality.

Calculate your safety factor inside the Safe Working Load of the 316 wire rope, so that at least you aren't deceiving yourself. 240MPa

If you are claiming safety factors and using 1700MPa breaking load for 316, then you are a normal yacht mast rigger. But if your bum depends on your rig way out in the middle of the ocean, then you should do the math yourself. So you understand that the TRUE reality is nothing like the safety factor that you've been told. The true reality is that it is right on the edge of breaking. It is above its yield strength already.

Calculate your toggles cross sectional area yourself using the 316 yield strength. It is not difficult.
This way you will know exactly how many percent of true safety you have in reserve. (and it won't be 600%)

Lightly built versus heavy built.
how much extra punishment can the heavy boat take? Before starting to put tons of stress into the rigging. Basically, exponentially more punishment before it starts to load into the rigging.

Perhaps the racers and astoundingly light foam and balsa guys should ponder if thin, cheap, very light hulls do have perhaps the tinniest bit more movement than steel hulls. And so then maybe use uhmwpe shrouds instead of 316. (stretchy). Google images “dismasted”. Endless thousands of people loose their masts, but the biggest portion of them are go fast guys. Light hulls flexing and 316 rigging taking big load cycles and stressed hard. Anybody can predict the outcome.

The Real World - Alloy Data Suitable For Design
Alloy data suitable for design takes a statistical approach to failure. A bell shape curve etc. The probability of a structure or metal part failing when used in a specific application.

"Typically, one-half the yield strength is used for safety" in statics. One sixth for dynamics.
"This approach is appropriately conservative” and "suitable for designing structures" etc
so what data is considered "suitable for design" for 316 parts in salt water under stress cycles?

none. don't be so silly. 316 is so totally unsuitable that any maths based on it would be culpable (you go to jail for) stupidity. any maths based on dribble results in dribble. 316 fails in hours in lab tests for cyclic loads in salt water. Modern alloys last forever unaffected.

lets assume you STILL wish to proceed and build your rigging parts out of 316, and do the dodgy, illegal in some countries, culpable, criminally negligent, BOGUS maths and bodgy up some data suitable for design.

the question then is what data suitable for design would you choose for 316 rigging parts, if on land it's 50% of the yield strength for structures, and 17% of the yield strength for normal rigging?

Laws Concerning Rigging on Land
are extremely strict.

REAL and TRUE Safety Factors must exist in the alloy, and must be proven to exist. When proven, the rigging part is then registered, stamped, and approved for another time period. The part must be thrown out anyway after its short legal use life span, even if it passes proof testing and is perfectly good.

On land, any 316 part used for Rigging in salt would violate every single Occupational Health and Safety law there is. I've said it before, i don't know how yacht rigging escapes normal laws, Rigging law, Australian Standards, Workplace law, and Occupational Health and Safety laws.

Any load bearing 316 fitting used in salt water fails all Australian Standards, Safety Legislation, and OHS Acts and regulations.

316 fails specific regulations dealing with Rigging Equipment; fails to comply with discard factors in accordance with Australian Standards; fails the use of grade markings for use in salt water; fails passing legally required cyclic load testing in salt water, and other legal requirements.

Workplace Health and Safety Regulations are very strict.

And 316 fails by such a huge margin it's bizarre.

On land based rigging, safety is taken very seriously. You really would go to jail if you tried to get away with the deceptive marine rigging non-existent Safety Factor business. All normal land based rigging Safety Factors are all well and truly inside the yield, any metal alloy HAS to be tested and approved (a real person/engineers arse is on the line – actually liable for the quality of his work) , stamped, certified as approved. Bizarre the difference.

Any talk of having a Safety Factor on 316 is monumentally stupid, and shows no understanding of the basic alloy properties. It was built to make knives and forks stay shiny in salt water, but nothing else. It was built for making cheap static objects that stayed shiny for as cheap as possible, and it does this job well. It was not built to take dynamic loads, and will fail with monotonous regularity if it is used for such. Any talk of having a Safety Factor on 316 is monumentally stupid.

This is a 316 chainplate. Looks perfect.



if you did this on a land based rigging structure, the engineer and vendor would absolutely go to court, and if injuries or deaths were involved, then jail.

[Rakuflames]

Originally Posted by PooBeetle

Dismasting - why does it happen, how to prevent it

Part 9 – Intergranular Corrosion

Corrosion and Stress Fracturing along crystal boundaries.

Attachment 45821

this is not 316, but shows the exact same effect beautifully, of SCC happening along the crystal boundaries.

this is why 316 is only useful for non-stressed parts.

This is why 316 parts will look perfect and then fail suddenly and without warning

It is impossible to manufacture any 316 item without these faults occurring.
Chromium stabilises ferrite, which has marginal mechanical properties, so nickel is added to make FCC austenite the preferred phase.

But cooling after pouring, annealing or investment molding permits chromium carbide (Cr4C) to precipitate along austenite grain boundaries, where the diffusion of carbon is very fast.

The austenite next to these grain boundaries is depleted of the chromium that went into the Cr4C, and so the metal next to those grain boundaries is no longer stainless.

The formation of Cr4C depletes austenite grain boundaries of chromium, and so a non-adhering scale (surface oxide) of FeO forms, and this oxidation then destroys the crystal attachments by rapid diffusion of carbon along the grain boundaries. (and Carbon promotes rust a thousand fold)

There are many photos on the web showing these crystals detaching from any slight stress.

Salt water then enters the cracks around the crystals, and the chlorine then catalyses the destruction of the already weak boundaries, turning the very thin crystal external material into rust. This is called Intergranular Corrosion.

If you supply energy to these defects, stress, or vibrations, then the microscopic cracks pump the salt water and chlorine in and out the Intergranular Corrosion crevices where stress cracks are concentrated and growing anyway, and then we finally arrive at Stress Corrosion Cracking.

The Stress Corrosion Cracks propagate astoundingly quickly.
A big, good looking, solid metal part can fail in hours under cyclic stress in salt water. Mainly because 316 is not really a metal, just a loose collection of crystals, semi held together, much like when the sugar in a glass jar sits for too long, and forms big lumps.

To use the word steel is very very misleading.
people see 316 doing well on static non loaded parts in salt water, they hear the word steel ( erroneously used), and so they think it is ok then to use it for cyclic loads in heavy chlorine.

utterly incorrect, and 100% wrong to use the word steel; it is very very misleading. 316 is not steel. 316 uses iron for cheapness. Which is very different from using it for strength and toughness.

Steel is carbon and iron. Very tough stuff. The term stainless steel is very very misleading.

As different as Chalk and Cheese.

Cycles under stress in salt
how well will a lump of compacted sugar crystals do under cyclic loads in salt water?

A useful test method is to get a round bar, spin it at some RPM while deforming the middle of the bar with a wheel under some pressure at some % of the yield strength, while spraying it with either salt water or analogues (to simulate years).

firstly, normal steel.
lasts a very long time, but doesn't look sexy and shiny. Looks rusty.

316 fails in hours.

The Stress Corrosion cracks propagate astoundingly quickly. Hours in the lab for a solid metal round bar to break clean in half.

Mainly because 316 is not really a metal, just a loose collection of crystals, semi held together, much like when the sugar in a glass jar sits for too long, and forms big lumps.

Modern alloys designed with mathematical models, computers, actual modern scientists, understanding, theory, and endless thousands of tests last forever.

Susceptibility to Intergranular Corrosion "effectively eliminates any safe stress level for infinite life".
Please take note of that statement, as it is important latter on when we consider land based Rigging Law and Occupational Health and Safety Laws Versus alleged and alluded yacht rigging Safety Factors.

There is NO safe stress level for any alloy that suffers Intergranular Corrosion, if you do stress the alloy, then Stochastics say we can't predict when it will fail, but it will fail semi-randomly and unpredictably.

Now compare all this to modern alloys that are immune from crevice corrosion. These alloys have an infinite life. They last forever under stress. You can actually and sensibly claim and calculate Safety Factors.

(ps
Beware of vendors saying all these problems can be fixed by annealing or other highly technical treatments. It's all Bull. The problem is inherent in the stupidity of the metal chemistry. If the vendors claims were correct then no 316 rigging parts would ever fail.
)

This is why 316 parts will look perfect, and then fail without warning.

That was fascinating (and eye-opening.)

So what should critical parts, such as chain plates and stays/shrouds, be made of?

[stillbuilding]

+1
Thanks Poobeetle.
Been a long time since i have critical maths but your analysis has the ring truth in it. Enough to convert me to Dux and the like!

Suspect that many distance cruisers understand your points and compensate accordingly

[bruce smith]

This is how I handle it on my cruising boat. norsestay on some shrouds (7x7 galv, plastic covered ) and 7x7 ss on others. Oak" chainplates".

[ShaunJ]

Poobeetle
In 17 posts you have typed more word than most have in a thousand. Go for it man. I would like to know what drives you

[Stumble]

Originally Posted by Rakuflames

That was fascinating (and eye-opening.)

So what should critical parts, such as chain plates and stays/shrouds, be made of?

Raku,

My contention is that titanium (with the exception of wire, which should be Dynex dux) is the best option for rigging. It is absolutely non-corrosive, stronger than steel, and has a better fatigue limit, at a price that is pretty competitive with current 316 components.

There are also some super steel alloys, that are much more corrosion resistant than steel, but are more expensive (more than titanium actually), and at the best only slow down corrosion as opposed to stopping it.


While Poo and I are on the same side in this one, I think he overstates the risk of 316. It has been a great material for years, but there are better options now, at not much more cost.

[SimonV]

Poobeetle.
As you seem to have an extreme dislike for 316, what do you use on your boat and at what cost? There must be countless numbers of boats out on the water full of family and friends each weekend and more, I don't see them all heading off to a funeral on Monday following all those predicted dismastings. Seriously is the sky falling.

[PooBeetle]

Dismasting - Why does it happen, how to prevent it

Part 11 - Conclusions – The Answer to Post Number One

After all that background, now comes the answer to the original questions. Remember, i still haven’t finished answering the very first post yet.

ArtM
"I understand basically that dismasting is - under rough, windy conditions the mast either breaks or falls over due to some kind of stress failure in the rigging."

yes. you are right. Invariably from 316 Stress Corrosion Cracking.

316 is the CHEAPEST crappiest metal you could possibly put on your rigging. as it will look GREAT, (which is why it is used) but it will be riddled with an invisible cancer all the way through.

Rather than stretching, it will brittle snap clean in half just when it is needed most. ie under a sudden sharp stress.

There is no other alloy more primitive, more stupid, and more treacherous. ie it looks perfectly good, solid, sound, SHINY and sexy, but will fail suddenly from an invisible crack, and only then when it has broken clean in half can you see the rust and rot that was present.

Embedded 316 Bolts and chainplates need oxygen. If the 0.0000013mm protective chrome oxide (a ceramic) coating gets the tiniest scratch, or a microscopic speck of normal steel from using normal tools damages this surface coating, then the entire part can rot away to nothing.

This is a 316 chainplate deprived of oxygen.



Bolts do exactly the same thing. Sheer madness to use a 316 bolt. They simply disappear, evaporate.



If your bolt has butyl to keep out the water, then you have also kept out the oxygen.

Even if the outside air, oxygen can't get into microscopic cracks, then the 316 bolts will just snap clean in half.




"What I don't fully get is why this happens on modern, production-type boats - particularly a fiberglass catamaran with a good quality mast and rigging."

Answered by the Crapitalism Paradigm. (Part 5). They all of them call their products the highest quality, when they should all of them actually be in jail for killing, injuring, and maiming unsuspecting people by using the cheapest, lowest quality, and most treacherous alloy they can. 316 was not designed to take stress in salt, it was designed to look nice. Quality and safety never exist until a government steps in and puts a floor of minimum safety standards to limit capitalist stupidity.

ASME II says 172 MPa for statics (17.2 Kg/mm), VIII says 108 N/mm2 (10.8 Kg/mm2) for pressure. 316 rated, stamped and legal rigging fittings in australia out of salt water on dry land are rated at one quarter of the proof, and proofed at 90% of the design yield of 316, so 5 Kg per mm2 is legal, but any talk of any safety factors even at this incredibly low level of stress in salt water is just silly, due to the stochastic failure mode of 316 in salt water at 35000 ppm chlorine.

There is NO design data for 316 for dynamic loads in any level of chlorine because that is just so stupid. Yet rigging companies use 170 Kg/mm2 or similar. Astounding stupidity. A prime example of an unregulated industry begging for a government to introduce legislation to put a floor in to limit stupidity.

MacDonalds will sell you a burger with 100% beef in it, but that is lips, eyeballs, and testicles. and this is exactly the same as Yacht building capitalists. They simply must compete with other companies doing this or they go out of business.

thus;
the stainless they use LOOKS FANTASTIC! and shiny, but is invisibly ROTTEN to the core. Do you see how it perfectly mirrors the capitalist paradigm that spawned it?

It is called steel, but it is absolutely not (Steel is tough, steel is iron plus 2% carbon, very tough stuff). It is an IRON alloy that has no carbon in it and so it is very soft, but the chemistry is so primitive and stupid that then it gets very hard and fragile if you give it just one bend, and then it is so brittle that a whole solid metal chainplate just suddenly snaps completely in half. Astoundingly primitive and stupid chemistry.

with simple maths we examined a professional riggers attempt at rigging a new boat that failed twice in 6 months. (he was in the tropics though, and this speeds up SCC vastly)

the poor rigger was probably in good faith using non-engineering data that resulted in the mast stays (probably – as we don't know exactly what riggers know about the 316 alloy and so how much tension they would put on 316) being over the yield strength of the 316 in the rigging, even before leaving port.



"Is it sailor error?"
no.



"Poor maintenance? "
to do it properly you'd have to dis-assemble the entire mast rigging and do X rays or a dye penetration test every 3 months. 6 months is TOO LONG.
On land out of salt any rated 316 fitting has to be proof tested, all components stamped with the working load limit, and issued with ‘Proof Certificates’. If you tried proof testing your 316 fittings that had lived in salt water in the tropics, depending on the stress they had seen, the temperatures, and the chlorine, I suggest they would fail proof testing within 6 months. If you live in a cold climate with heaps of rain washing the fittings all the time, then they may last forever. 316 stochastic failure mode says you can never be sure when it's going to fail on you. You should read up on the chlorine ppm, temperature, and stress, and how if they all combine they can kill 316 very quickly.

so the answer is NO. it is not due to poor maintenance or negligence. SCC is invisible.



"Construction flaws? "
if balsa then bell shaped curve individual fiberglass strand stress fractures equals gradually loosing stiffness; or, if a foam core and Polyester then it may be possible as they can delaminate on their first hard sail, and if delamination does occur, then the hulls become sloppier and sloppier, and loose their stiffness over time, so the stress on the rigging, the chain plate loading and mast base movement gets worse and worse, until something pops. And more stress gives a much shorter life. 316 in chlorine stochastic failure mode suggests double the stress gives incredibly shorter life.

you can't expect a little crap 316 rig fitting to take the weight of an entire boat hull for one million cycles. there should be no load input from the hulls flexing, hogging, or sagging when sailing in heavy waves. the hull should be stiffer than delaminated foam and polyester sandwich which was designed for cubed stiffness suddenly becoming a linear stiffness relationship allows.

so it is possible for light sandwiches to put more hull loads into the rigging than stiff, heavy hulls.



"Or an unpreventable eventuality that is going to hit sooner or later to anyone sailing blue waters?"
no. it won't hit everybody. some people are TOTALLY and utterly immune from this 316 SCC disease.

ie. me.
Custom made Super Duplex fittings and rope. There is NO 316 anywhere on my rig. Zero. And also the go fast guys who use uhmwpe ropes and composite chain plates. Real cheap, but you have to replace the ropes every so often due to sunlight degradation.

Some guys are starting to use 6% moly alloy chain plates, also in the NEVER FAIL category, others are starting to use 2205 (cheap crap - designed from the outset to be CHEAPER than 304), and other guys are just now starting to use Super Duplex stainless for chainplates.



"IOW, is this a totally preventable mishap, or an endemic risk of sailing open seas? "
yes it is TOTALLY preventable, but you will never do it unless you;

1 - AVOID any professional rigging person; as they will ONLY sell you what they have on hand to sell you, the awful, twisted, sick and perverted fruit of capitalism.

ie it LOOKS BRILLIANT!!! sexy and shiny, and you will fall in love because it looks so beautiful,
but in reality it will actually kill you and your family.

i refer you again to American Coast Guard Alert 07 09, mandatory rigging inspections due to deaths in 29 dismastings over the last 6 years due to 316 Stress Corrosion Cracking

i refer you again to $9.95. They actually, and in reality, will burn you and your family alive for $9.95.

The fruit of capitalism? you are going to SEA, with your family and you wanted 100% beefy fittings, and so that's exactly what they'll give you.

A 100% all beef patty (eyeballs, testicles, and lips. rubbish in other words, but it'll look fantastic) that everybody else is eating without complaining. Yumbo!


2 - AVOID talking to the soul-less vampire muppets that seem to infest this forum. The idiots who drag the tone of the discussion down. The guys who don't contribute or refute with data and instead insult others. The guys who can't use Google themselves and expect you to google it for them.
The guys that say that there is NO PROBLEM. it was YOUR fault for speaking up.
The vendors who say they KNOW EVERYTHING and there really is NO PROBLEM.
Don't listen to them. if you do, you will just accept your plate full of testicles, lips and eyeballs and start to call it a 100% all beef patty.

The real story is that they have ZERO passion, and so are never willing to do any reading or work.

Other guys raise the tone of any thread, increase the meat in the sandwich, deliver chunky goodness. I skip over the evil muppets of the dark side of the force, and only read the guys who help others.


3 - AVOID reading ANY rigging companies web site. The reason is they do not love you, they want to stay off un-employment, and as a result, they will slowly twist, pervert, and dilute the truth until you start to believe them. This is called marketing.

the ONLY thing on their web site is marketing. and YOU WILL be infected, and once their information is in your head, it will take 1000 hours of hard work to get it out, and arrive at a sensible opinion.


4 - RESEARCH yourself. it is the ONLY way. Do not let yourself be pushed around by know nothing muppets because they will push you around if they can. On this forum right here.

ie We are PROFESSIONALS, therefore we KNOW ABSOLUTELY what the truth is. absolute dribble. they are capitalists. They know how to quash rebellion, how to keep you in line, how to move their lips so as to get more money from you. They are NOT interested, and so they have no understanding of the whys and wherefores of why such a perverted reality exists, because they are NOT interested.

IF they were interested then they would have ALREADY done the reading needed to arrive at these conclusions. They would be the guys that knew all this stuff and they would be the ones telling all this to you.

yes, I admit they do know other stuff, and it is great if they actually contribute rather than trying to stifle other people. i ignore people i don't think are straight, as if they were truly interested, then they would have already Googled and be contributing instead of hassling or insulting others; and for those people that are actually interested in the topic and who contribute their time and experience and what they've got, then i do the same.


5
- do the maths for your rigging yourself. That way you will know exactly where you stand.

- redundant rig design; add a solent stay, add baby stays, nested diamonds instead of a single or twin diamonds. see how easy it is? Cheap too.

- redundant rig design - you can design a rig so that if a single toggle fails, you loose the entire mast, or you can design the rig to be redundant. ie if a single stay fails, then the remaining super duplex stay has more than enough tensile strength to hold the mast up, and with no problems. Use one Super Duplex chainplate per stay; don't do what the cheap arse capitalists do and have two stays on a single 316 chainplate. Absolute insanity. Astounding Stupidity. Asking for trouble. Just begging for trouble. ie 316 Stochastic failure mode vast increase.

- use titanium toggles - 316 toggles or 316 chainplates will most likely be the cause of a dismasting

- guys have lost their rigs due to split pins failing (SCC cracking in half and disappearing) so either inspect your pins religiously, or try and learn from seeing all the other people here that have lost their rigging, and so buy a packet of titanium split pins, or higher alloy split pins. Cost you $5 for an entire bag full. So get your act together. Spend an hour on google. Or order them off one of the guys here on this forum.

- avoid 316 SCC by avoiding 316. use titanium toggles, pins where ever you can. You can order better alloy bolts and pins from heaps of places online. Use anything with 6% moly, or the Super Duplex stainlesses.

- AL6XN or 254SMO chainplates - cheap as. NEVER have to inspect them EVER. Many many guys have lost their mast due to 316 chainplates suddenly breaking in half. Broken chainplates and all the real tears stories that go with them are all over the web like a rash. Super Duplex Stainlesses are of course better, and what you should use if you want true, real, and indisputable safety factors that will last forever, and not vanish after 1 year in the tropics as 316 safety factors do, but these will cost you an extra 2 cents. Or maybe SHOCK! HORROR! Having to get up off your fat arse and drill a hole yourself in some flat bar.

- order Super Duplex wire rope - there are many companies out there that build these ropes - Ferralium 255SD50 has a big edge due to being the most modern chemistry available, the copper increasing malleability, self healing microscopic cracks via electrolytic deposition, and side stepping cold work hardening due to thrumming at frequency while under heavy load. Never fail. Absolutely never fail.

- If you listen to capitalist verbiage, you will go as soft in the head as their hulls are after the first hard sail. Their smooth honey marketing will seep into the cracks in your brain, much the same as water flowing into the cracks and crazes of their cheap polyester.

So go and talk to a boat builder instead. Commission a custom build with hulls that will still be stiff after the first hard sail.

- 316 cold working can kill a part in months ( promotes metal fatigue and SCC by a HUGE factor ) but with other modern alloys you can't even make manufacturing fabrication mistakes.

- 316 wire rope - just stunningly ridiculous. the concept of 316 used under STRESS in salt is so stupid it hurts. Metal fatigue wise, stress hardening wise, SCC wise, yield data wise, swaged fittings wise, rig tuning wise. the whole concept is so stupid it hurts. Download a scientific study on 316 SCC and read it. It won't kill you.

- swaged fittings - hide the fractured 316 strands, and promote metal fatigue due to both a change in density when pressure/shock wave frequencies hit the boundary layer of the structures density change, and swaged fittings promote cold work hardening. Swaging WILL promote fractures close to this boundary. (heaps of pictures of this phenomena on the web) so use swageless only.

- pushing too hard – the faster you sail, the stresses rise exponentially, but the life expectancy of the 316 fittings falls even faster. with a true math rig in any MODERN alloy of course this would not matter, but with 316 rigging it matters a great deal.

- temperature plays a huge role. ie a 316 fitting is stressed for 10 years on a yacht in a cold country, so there's nothing but tiny microfractures that never grew, or they are only growing very slowly. But then one day the yacht gets sailed somewhere warm and tropical. The salt water fills all these tiny cracks that have never given any trouble and suddenly Stress Corrosion Cracking explodes, and grows a hundred times faster due to the temperature. 6 months till dismasting would be about right.

- you want a modern cars performance, and would hate to have to accept the performance of a horse and buggy. It would drive you mad. You would hate to be forced to accept the performance of a record player versus an MP3 player. The modern product beats the **** out of the old version. 316 is no different. You have a modern, sexy, no expense spared racing yacht? And you're still using 316 rigging parts? If you use a modern alloy you will get exactly the same performance increase. ie an astounding difference. Super Duplex Stainless Steel. Say it . . .

- Google images “dismasted “– thousands of people dismasted. most are racers. They spend a million on the sexy yacht and nothing on upgrading from crap 316 to Super Duplex wire and fittings. It is so easy to avoid being dismasted. 3 cents molybdenum the difference between being dismasted and loosing a race and winning. If they really were serious they'd spend the tiny bit extra like me.

- some modern cats are being made very very lightly, as less material used equals a cheaper boat, but it also means less inertia (stiffness), so they therefore transmit more of the whole boat flexing loads into the rigging. Have your hulls strong enough to take any wave loads without buckling, hogging, sagging, or flexing, and without transferring ANY hull displacement loads into the mast rigging.

- if you absolutely must be a racer and so foam or balsa are your only options, then DEFINITELY use the SUPER DUPLEX wire ropes, as they can take FAR more punishment than the mere 0.2% yield data indicates. Orders of magnitude more punishment than the simple yield figures indicate over 316. (ie chlorine, temperature, crevice corrosion, stress corrosion cracking, fatigue especially etc etc etc). You will then never loose your rigging.

- if you absolutely MUST use balsa, understand that even if a hard stressed balsa sandwich doesn't bell curve sloppy glass, then the balsa is absolutely going to rot away, again leading to an (alleged) cubed sandwich stiffness dropping to single thin laminates either side of some rotted powdery wood stiffness. Make sure you treat every single piece of it with boron before you fiberglass. (use nothing else, only boron (as chemicals will break down or decompose or degrade over 20 years)). Make sure you read all the thousands of posts on the boat building forums of guys having to strip out rotten balsa. If there is one thing balsa does, it's rot.

- Light cats are MUCH better than heavy is the perfunctory mantra. And it's dribble. They are competing to stay in business and sex appeal equals selling product. Half the weight of materials equals half the cost, therefore a much cheaper boat. That is the product they have to make to stay in business, so their spin doctored verbiage then turns the negative into a positive. Marketing works. Therefore the normal mantra today is that everybody knows cat hulls should be half the weight they should be. Everybody knows this. But Ponder the inertia and life expectancy of light hulls versus wood sandwich, solid glass or steel hulls. You can side step some of the vibrations heading into the rigging by using different, better alloys that can easily take the cycles. Or you can buy a dye penetration kit and check your rigging often and replace all the different bits that keep failing and breaking all the time. Me? I'd be ordering those titanium toggles real quick. And i'd install Super Duplex chainplates straight away.

(This is off topic, but I couldn't help myself. Perspective is everything. “Cats are more weight sensitive than yachts”. You hear that so often, and it is True, but why? Only because your 10 ton cat doesn't have 5 tons of lead in it's bum in the first place (to be on par with a yacht). So any less lead than this, must be a pure bonus. All gravy anyway; “Cats must be light to sail fast”. Again true. But for every 400 Kg extra load, my cat sits 1cm lower in the water. Ridiculous buoyancy. Ridiculously huge extra load carrying capacity. And how much of a difference will 1cm extra displacement make to sailing FAST? So these statements are all perfectly true, and yet utterly silly. Formula One race car owners talking to Caravan owners really. So yes, everything the light hull, go fast boys say is true, but they also have carbon fiber toilets and the handles sawn off their toothbrushes. Not a home, a toy.)

- Sex sells – ie going FAST! sells. And everybody knows that cats must be as LIGHT as possible to go fast. (as forced by the demands of capitalism post ipso facto rationalisation) And so there are astoundingly light balsa and foam things out there that look just fantastic. smooth, sleek, and sexual. Great for racing. But a lightly built racer is vastly different from a heavy cruiser in terms of life expectancy, the beating they can take from waves, and what hull loads will transfer into the rigging. If you already have a Polyester, foam or balsa boat (admittedly GREAT affordable fun toys) you really should give serious thought to replacing whatever you can with higher alloys. Cost you very little if you do the work yourself. Going on a big cruise to the tropics? Replace whatever parts you can with a PREN above 40 alloy. Titanium or Super Duplexes mainly.

- Safety Factors and Capitalism.
Safety factors my arse. A safety factor of 6 is what they are talking about. just remember that. and what does a safety factor of 6 TRULY mean? Zero. Absolute zero safety. Which is exactly why we are having this conversation. If you want to get real, get a safety factor on your alloy first. And then do your maths, keep your safety factors inside the yield, and ignore capitalists utterly (because there is no law forcing them to real safety standards as on land, they mouth off complete dribble instead). This is the only way to get what normal everyday people would call approaching real and true safety factors. Remember though, there really won't be any safety at all, as susceptibility to Intergranular Corrosion "eliminates any safe stress level".

Capitalists will blind you by science, by maths, by claiming their own years of experience, they will sooth your fears, they will pour honey in your ear, they will tell you black is white. They'll do anything, except do it properly, up to beyond reproach quality, as demanded by law on land.

They will sell you nothing but what they have on hand and on the shelf.

They will do anything except spend the $9.95 extra the job actually needs.

- Remember; a safety factor of 6 means that the wire is already deformed, rubbish fit to be thrown out, and would be thrown out by any professional engineering firm on land, as they would go to jail if they tried this sort of deceptive maths on land based rigging.

- If any of your crew is injured by falling rigging, then sue your rigging company. Make them explain how the safe load allowable on land is 5 Kg/mm2, and yet they sold the rig to you while alleging and alluding that they actually had a safety factor of 6, when in reality they were using 170 Kg/mm2 and claiming safety factors on that, and that is still excluding the fact that the actual alloy they used has absolute zero safety when used in warm salt water, as it fails randomly.

If for normal, dry land, rated and stamped 316 lifting and rigging safety factors as required by law are to be inside the proof strength, then by using Breaking Loads, how many percent are yacht rigging firms really out when they say they have a safety factor of 6?

They sure sound like dodgy criminals to me. Any jury of normal people would be convinced they were con artists being deceitful. This is because they are knowingly misleading you as to the true safety that actually exist.


"is this a totally preventable mishap?"
yes.

316 is the CHEAPEST crappiest metal you could possibly put on your rigging. and the reason it is used is because it was great 100 years ago when people had nothing else. So it slowly took off and became a tradition. De Rigueur. The yacht standard. And if you never stress it, it looks good.

it is merely a legacy tradition from the time when they used to cure all disease with leeches.

316 is exactly the same as leeches. and of exactly the same quality, calibre, and stupidity. Surely one single photograph here on this thread is proof enough that something is very very wrong.

In some countries it is illegal to use in building structures exposed to salt. If you used it you could be sent to jail, sued etc

Why mast rigging fitting companies have escaped any law or legislation so far is beyond my understanding, particularly as deaths have been caused by their negligence. Of course they know more about metallurgy than you or me. They know all this stuff. Yet sell it anyway.

the stupidity of using instant fatigue (one bend) 316 under stress in a tropical salt environment cannot be over stated.







(
hmmmmmmmmmmmmmmmmmmmmmmmmmmm . . . . . .

crew stupidity
polyester sheaves
joke
316 is ace
joke
kidding
should be diligent
you know nothing, 316 is the best
joke
you know nothing, and vendors are ACE!
joke
you know nothing, and vendors are ACE!
joke
slow down
speed up
composite chainplates
dye test at 5 years
drive faster
close inspection
316 is good

all these replies were FUN, and i did enjoy reading all of the answers here.

I had a personal interest in this subject because I was recently designing my own rig to never fail, and so passion had motivated me to hit this subject hard many months ago. After reading all the answers, i felt that nobody else was really interested, or had put in 100's of hours of study, and so arrived at my own conclusions. I felt that some people knew less than they should, that some were actually saying that black was white, and some were actually just speaking out of their arse.

So i tried to answer as best as i could,

to the best of my ability,

and to the full extent of my own understanding.


hope you enjoyed it,

m

[bruce smith]

I am about to get a stress crack after trying to read that .
but, how many here replace their ss after 10 years?
crikey ,i get 15 years from the cheapest galv 7x7 or even 7x19 wire rope!