Dismasting - Why Does it Happen - How to Prevent it

[noelex 77]

Originally Posted by Lagoon4us

Basically every propellor shaft that isn't either, Monel, Bronze or Steel in the free and communist world except the Sahara and similar places of course.

A propellor shaft IS effectively no different to a bolt it has a nut, castellated at times, split or drive pin and washer. It is tapered and a Bronze hub slides on effectively creating a naughty environment for the longevity of the SS...

Most shafts i've seen are 316# every one beautiful after many many years subsurface..

Let alone drive shafts on outboards where replacement nuts are commonly 316# and washers varying from 316# to 304#. Don't see them crumbling worldwide.

Propellor shafts are quite different from bolts. Crevice corrosion occurs where there is an absence of oxygen in the presence of water. For a SS bolt these conditions exist over the entire shaft of the bolt.
This is not the case with propshafts, which are exposed to oxygenated sea water. In addition propshafts can be protected with zincs, which is not practical for most SS bolts.

Drive shafts in outboards are protected by the aluminium casing which in turn is protected by a sacrificial zinc.

[Lagoon4us]

My point was the hub of bronze or even SS that is blued to fit the shaft for the tapers entirety and of course nut area inside the thread?

I'll go along with the theory on a wooden boat where there is nutrients to eat away at a bolt that has no oxide but not generally.

The entirety of a boat is protected by Zincs i have had clamp bolts on the bottom of our rudder (steel hollow wing style) that never showed any corrosion at all #16# with 304# nuts....

[noelex 77]

Originally Posted by Lagoon4us

My point was the hub of bronze or even SS that is blued to fit the shaft for the tapers entirety and of course nut area inside the thread?
.

It's protected by zinc.
Nevertheless it is an area that sometimes subject to corrosion if moisture penetrates. At least minor pitting is quite common in 316 shafts. It's not unusual for better SS to used for this reason. These better SS look identical to 316.

Originally Posted by Lagoon4us

The entirety of a boat is protected by Zincs i have had clamp bolts on the bottom of our rudder (steel hollow wing style) that never showed any corrosion at all #16# with 304# nuts....

The corosion will be inside not on the head of the bolt. So the bolt can look perfect untill it's removed.
Crevice corrosion is not inevitable. It requires moisture and low oxygen (so "stagnant" moisture). If you can seal a 316 bolt underwater and prevent any moisture entering between the joint you will not get crevice corrosion. The bolt will be perfect even when removed and examined.

The risk with a SS bolt underwater is that you can never be sure that the sealant is intact, preventing moisture entering. Indead if the joint is under stress (which is the main reason for using a bolt) it is unlikely to remain watertight long term.

The crevice corrosion cannot be seen from the outside looking at the head of the bolt. (the head is not subject to crevice corrosion because of the oxygenated seawater). So there is no way to examine the bolt without removing it. Once removed the sealant is broken, without any guarantee the new sealant will remain intact.

The above situation is not satisfactory for critical applications.

This is the most common reason why bronze ( which is very resistant to crevice corrosion) is used for critical underwater applications on yachts.

[Lagoon4us]

I think you miss my point regarding bronze, it is the contact with the SS that i'm pointing out, the SS is depleted in that area of it's oxygen to no detrimental effect.

The warnings re: the use of 316# in this thread need to be contained to, you risk failure IF........

Theory is one thing however in the real world SS is here to stay (no pun intended) simply because of availability, its shiny and it's in easy. I have sailed, built boats, fished on the Great Barrier Reef for some 40 years and the only time (and very few at that) that i've witnessed failure was when very poor maintenance was in place after a hell of a long time.

SS will not fail in an oxygen depleted situation PROVIDED there are no chemical or organic agents around. He who slips annually and checks all underwater fittings reduces risk to zero.

I did my trade initially as an Aluminium fabricator with KAISER in the late 60's i gotta tell you there is far more risk in the Aluminium spars we use if they have not been assembled correctly with regard to dissimilar metals.

Cheers

Regarding bolting in my 35 years i have unbolted a few SS bolts the only time i have seen any issues BELOW water is in soggy timber hulls, i see no reason for alarm regarding the use of SS when it is used correctly with regard to its environment.

[noelex 77]

Originally Posted by Lagoon4us

SS will not fail in an oxygen depleted situation PROVIDED there are no chemical or organic agents around.

Stainless steel like 304 and 316 does suffer from crevice corrosion. In a low oxygen environment with salt water it will corrode. No other chemical or organic agents are required for this process, believing otherwise will not stop it happening.

[Lagoon4us]

Belief i'm afraid has nothing to do with it, no shaft, no bolt that i've pulled on any yacht, motorboat or marine fixture that has been put in correctly and maintained has shown any crevice corrosion. Yes in a poor spongy timber environment i agree......

Sorry to rain on the parade, every shaft that i've fitted and every bolt i've placed beneath has survived 30 plus years....

[PooBeetle]

thorcat
"enough already." ??

two things;

1/
if you explain too briefly, some peeps don't understand.

ie "3 cents extra moly" should have been enough to explain every single thing i typed, that should have been the whole conversation, the entire thread. but some people needed more. they didn't understand SCC. even rigging companies didn't understand, they also kept asking more and more questions.

ie chlorine is a catalyst - simple chemistry - a catalyst is un-used in a reaction, and so keeps destroying forever. this is different to 316 in fresh water. and some people didn't understand that either.

but then if you explain too much, peoples eyes glaze over.

so i tried to explain in the absolute minimum. the scientific stuff goes on forever, and this was in my estimation - a good enough short summary for most people to have a firm understanding of the true reality.

some people still do not understand, and it shows clearly in their posts.

so;
even rigging companies didn't understand, they kept asking more and more questions, and then? still didn't understand.


2/
the rig is the engine of your boat.

somebody has just shown you how to get many times the performance out of it; in all reality; infinitely better safety, and all for lower cost.

and what was your reaction to this? a $7 32550 never fail chainplate versus a $200 316 guaranteed to fail chainplate.


weird. other people here think this is astounding. revolutionary stuff by a brilliant researcher. the winds of change that you were priviledged enough to see the begining of and to be a part of

( admitedly as part of an angry mob booing and dragging down, but non the less, still a part of )

are you sure you understand what has just happened?

a new never fail engine design for cheaper and safer than your current primitive dangerous rubbish.

or are you disinterested in the thread topic?




Rakuflames

but can you point me to a website where I could actually purchase chain plates, bolts, screws and washers, etc.,

no. there is currently no single one stop shop doing this.

"Could they be combined with the 316 parts on my boat? I cannot afford to strip my boat of all stainless and replace it with something else all at once, so what would the chemical interaction between the two metals be? Safe or not safe?"

yes, minimal galvanic coupling. any electro-corrosion will be powered by acidic 316, not passive 316 (good intact chrome oxide surface) (ie crevice corrosion - ie a split, a big invisible sour crack in a bolt), so if it is any consolation, only the 316 part that was going to fail from crevice corrosion anyway will fail.)

however such 32550/316 effects are very very minor. almost non existant, as they are almost exactly the same metal. so no worse than using titanium. i'd risk it as we're talking very low voltage and decades here. as you already said, it is not 100% perfect to couple dis-similar metals in salt water, but i'd do it, but only for higher alloys or titanium.

replacing a few parts at a time is a very sensible way to do it.


"but are actual parts available of these alloys you speak of? "
no.

a small new zealand rigging fittings manufacturer and a small chinese rigging fittings manufacturer have said they'd make them for me (as well as my local cnc guys). (i'm fairly sure i'm repeating myself here.)

the small chinese rigging fitting company that will undoughtedly end up winning the quoting and making the batch for me could very easily make a bigger run and keep stock on hand if other guys want some. they want new business.

probably cost the same as 316 fittings, but you may save 300% as you'd be buying over the internet and direct from the factory, and not a retail shop.

take a swageless fitting to a local CNC shop and get a quote, just so you know the price difference, and i'll send you chinese guys final quote when they finally finalise. i told them there was no rush.




stillbuilding

"Well done Poo."

thank you.

"To implement his findings will take some effort by the reader and discussion with smaller engineering workshops but very achievable"

true; but perhaps not even that much extra effort, as the two small rigging fitting manufacturing companies that have said they'll do it for me could easily continue their production. be actually cheaper for them to make more fittings.

so all you really have to do is put your hand up.





I think a brief recap of the good stuff is in order;

Different solutions posted so far:

Unstayed masts - surely the best solution, as it bypasses the entire problem completely, and forever.

Galv and tar - great solution - as steel is very tough. last for a very long time if you can keep the tar on the ropes and fittings.

Better Alloys - you have to visit a small engineering firm and order them yourself though.

UHMWPE ropes and composite chainplates - a fairly common method. cheap, easy as. Dynex dux et al.

Replacing 316 bits as they fail - most do exactly this.

Buy a dye penetration kit - real cheap! and do it often, every 5 months max?

Design redundancy into the rig - solent stays etc

Titanium - great stuff. (except for ropes - fatigue strength gets real low)


Overwhelmingly? the vast majority of posters seem content to stick to 316.

[PooBeetle]

Jim Cate,
and to 316 cheerleaders in general;

"There are NOT "endless thousands" of folks getting dismasted for any reason whatsoever"

You are right, as Google says it could only find 34500 images tagged with the word dismasted. so you are perfectly right. it's not truly endless is it?

but on the other hand, i imagine some guys also don't take photos of their broken 316 fittings though, or name them correctly. i just assumed from decades of experience that what you can find instantly in one second is usually just the tip of the iceberg, and that if you actually sit down and put in years of effort searching, then you generally end up finding many many times more than you did than when you searched for one second.


316 "mostly it works" is not engineering.

i think i made clear that an engineered structure is exactly what i was doing, rather than a non-engineered, unsafe, and illegal in some countries on land structure that most people have.

the two cases are vastly different.


in my defense, i always try and answer in the same tone as the person, and you did call all other alloys "magic". but they are not truly magic are they? just engineered.


i think some of the 316 supporters are getting a bit silly.

everybody here currently has 316, ok? and so actually having 316 is the problem.

almost everybody here, and in the entire world currently has, and uses 316. exactly the same as you.

so then, do you really think the rest of us don't already know 316 at least as well as you? basically then, you are telling experienced sailing guys the astoundingly obvious.


how many posts are there here saying 316 is BRILLIANT! when the thread topic is basically all about 316 failing?

so i think the 316 cheerleaders are all a little silly,

as you are telling experienced sailing guys the obvious, and are actually contributing your efforts in the exact opposite direction of the thread topic.

Do you See? if every one here already HAS 316, and the topic is HOW TO STOP being dismasted, then it sort of follows that what everybody else is talking about is 316 failing and what can you do to stop it.

See?


one picture of capitalists inability to make a simple inert blob that doesn't fail convinced me that they were all appallingly stupid, and so not allowed anywhere near my boat.

linus pauling once said the current paradigm is never defeated, the supporters just die. (can't teach an old dog new tricks poshed up in science lingo)


So to all the 316 cheerleaders;

everybody here is EXACTLY the same as you, and currently has 316, ok? and so this is the exact problem that we are actually talking about. actually having 316.

get it?




Lagoon4us
Regarding my apology; i truly don't understand you at all. i have no idea what you said, or why you posted it.


"I've read most of your post's but i still do not understand your logic on bolts?"

i spoke to a modern alloy bolt supplier to marine/oil rigs/chemical plants. he supplies literally thousands of different alloy bolts for weird chemical plants etc (ie you can use 686 for phosphoric acid plants, but not for paper pulp bleach etc etc) so he supplies thousands of different alloys for different chemical plants and industries.

according to his engineering tables, he would not give 2205 bolts for use under sea water, as they will fail if used efficiently. (if you use a specific alloy, then you get as much value as you can out of it; ie the bolt MUST hold exactly the maximum weight it is specified to hold IF you expect your commercial plant to give an efficient return on investment)

2205 has a PREN of 34
304 has a PREN of 17
316 has a PREN of 23

so 2205 kicks the sh!t out of 316, and is still not good enough for real and true engineered structures. only for dodgy untrained back yard boat builders that don't know any better saying "she'll be right mate, as my aunty betty had a 14 foot boat that had a 316 bolt underwater, and she was just FINE". but if you were an engineer and did this, then you'd be sacked for being a complete moron. Engineers even electro-copper coat 2507 bolts for under water use. (and they have a virgin PREN of 43)

so do you intend being a dodgy back yard builder? or a true, engineered, safe structure builder.

intergranular corrosion between the crystals is catalysed by chlorine. so you need very very little chlorine, and any tension on the bolt spreads apart tiny stress cracks, chlorine enters the intergranular cracks, the bolt stress supplies constant energy, and so Stress Corrosion Cracking is the inevitable result.

to bypass all this dribble, the alloy that you use must be immune from corrosion in the first place. a PREN above 40 for salt water.

in Appendix 1 have a look at that 316 turnbuckle bolt that split exactly between the first few threads. and this bolt even HAD access to oxygen. according to the Outukompu metallurgist and a few other yacht surveyors web sites you can easily find, they all of them say exactly the same thing. this is exactly where your bolt will fail.


have a look again at the pictures of 316 bolts that simply disappeared. this is different to SCC. this is lack of oxygen. if oxygen, then the bolt head will appear very shiny and look perfect, but the bit that is starved of oxygen simply evaporates. disappears.

so if they get air they look good and live, if they suffocate, they die.


i'm sorry to be blunt, but that's the straight truth. why gamble? when ALL normal engineers are exactly like the bolt supplier guy, and do the job to the correct, agreed on, international standard? PREN above 40.

"my aunt mary once used a 316 bolt and it was a GREAT! bolt" stories cut no mustard. can't you see that other people have had very bad experiences?

the tinniest invisible scratch on the 316 bolts 0.0000001 mm thick ceramic coating, a single invisible speck of iron on the surface, a single drop of water in an anaerobic environment, and your 316 bolt dies, quite quickly.





"socialist worker cooperatives won't have Stainless Steel but good old soviet non rusting material. The rest of us filthy capitalist supporting boat owners will be out there suffering with our old SS fittings that haven't failed despite the pronouncements of the the collectivist leader Poo Beetle."

you can suffer as much as you like.

all i can say is your 316 chainplate costs $200 from a shop, and mine cost $7.

yours is absolute rubbish that has killed people, dismasted thousands, and mine is 4000% stronger than yours under load cycles in salt water.

so all up?

$200/7 x 40 times better strength x 100 for percent

so that's 114000% better value than yours.


you bought yours from MacDonalds, i had to actually get up off my arse and drill a hole. we each got exactly what we wanted.



"SS is not a forever material". perfectly true for you, as your SS is the cheapest rubbish you can possibly buy.

a thousand other SS's are forever materials. MacDonalds is not the only restaurant.


"316 is all that is available to us "poor normal people, however."

if you can't be arsed to make a phone call to a small local engineering firm or to write an email, then that is perfectly true.





my last post here.

i'm so bored.


i may reply, but only to guys actually, and genuinely interested in the thread topic. how to stop yourself from being dismasted.

all 316 cheerleaders, have a nice day.

bi all :o)

[cruiz9]

made me so paraniod i'll never go sailing again

[Lagoon4us]

This sums it up,

[Mr B]

Originally Posted by Lagoon4us

This sums it up,

That says it all,

[Lagoon4us]

The amount of 316# SS Prop shafts with nuts and drive pins that suffer a lack of oxygen on the taper and is exposed to the salt through the keyway, has a demarcation line where the bronze hub stops where attack can occur YET the hundreds we have removed showed no attack, pitting nothing at all.

Zincs were not mounted on the shafts in all cases and if they were they were well back from the hub.

Has nothing to do with the bronze and some of these boats sat more than they were used.

I turn 60 next week, lived by the sea and built many boats as previously mentioned sailed out of the local club, cruised the Qld coast many times.
In this meagre lifestyle i know of one dismasting due to impact, one due to being an unstayed tapered 'HOYT' Freedom 40 style mast sections that were ally glassed over and there was 'Satin Sheets' a one tonner in the 80's that broke 2 bell ends on rod rigging.....
Club Marine directed most rigging jobs to me over a 12yr period and the above were it...
Sail confidently guys lightening is as bigger concern......

[sparau]

If i am understanding things correctly

1: In the end if you can make a rig that isn't susceptible to crevice corrosion for similar cost that is a good idea?

2: If you can make a rig that doesn't need replacing every 10 years then that is good. (would that be the case with poobeetle's rig as claimed?)

3: as best as i understand from this thread the images of chainplates in two were as stated from boats with issues (alignment, causing stress bending) or not maintained, the failure should have been discovered far earlier. in fact the images were used to educate people how not to rig a boat. the experienced folk state that 316 failings are few and far between.

Question: would the more modern metals fare any different for instance in a boat where the alignment of the shroud / tangs is out?

If the answer is no or possibly worse, then it appears the actual failure rates of 316 might be fairly similar to the new metals at least for the 10 year life expectancy given humans are fitting them.

[Dockhead]

I'm a latecomer to this thread and am quite amazed at all the sound and fury on what would seem to be a dry, technical subject.

Certainly crevice corrosion of chainplates is a real problem. I myself broke a cap shroud chainplate this year on my father's boat while hard on the wind in a stiff breeze, heeled over with a lot of stress on the rig.

But broken chainplates surely don't result in dismasting all that often -- how many boats have no redundant shrouds? My father's boat has a pretty simple rig with a single pair of spreaders, but the lowers kept the mast up. It was not that big a deal.

On my boat, I have three sets of spreaders with lowers and two sets of intermediates besides the cap shrouds, plus an inner forestay. The spreaders are swept back so even a broken backstay is not likely to result in a dismasting. Will I dye test my chain plates every 5 months? Hell, no. They are 30mm thick anyway and built up in a truss; I think it would take a few centuries for crevice corrosion to seriously weaken them.

It's always good to understand these theoretical weaknesses, but I think it's also important not to get hysterical about them. If I were building a boat from scratch, I would surely use titanium for the chainplates. For a few hundred bucks worth of material, you simply scratch this potential problem off the list. I think Grade 2 Ti is only like twice the cost of 316 stainless (for the same size plate, not the same mass).

Otherwise, however, occasional inspection and redundant staying is surely enough. If you want to be really safe, then just pull the chainplates out every 10 years and have them dye tested -- anyway, most boats will need them resealed at that interval.

Surely we have bigger things to worry about.

[John_ZA]

You are right, as Google says it could only find 34500 images tagged with the word dismasted. so you are perfectly right. it's not truly endless is it?

Poo, your succinct summary on 316 loses credibility when you post crap like this. You chastise members for not reading or understanding your posts and yet you have no understanding on the very basics of search engines and use them to erroneously further your argument. The majority of the images you quote are of the same vessels (one vessel is shown 12 x), their owners being interviewed, instruments on deck etc, and then thousands of images having absolutely no relationship to anything nautical e.g. the England cricket team, wire stripping and crimping tools, the list goes on.


Keep it real please.