anchor connectors

Thanks, I'll consider that but will try to get Kong's chapter and verse on it.

As for 'stray volts' this is usually caused by stray earth leakage in harbours where boats are plugged into shore power. I can't think of a case where this would happen in an anchorage though it would be a potential hazard mooring stern-to in Mediterranean style with an anchor rather than a lazy-line. You seldom see that these days, though. I think that there is a small issue when mixing stainless connectors (or, worse still, anchors) onto galvanised chain. I'd give my eye teeth for stainless chain and anchor...they say that ss chain pours into anchor lockers like a fluid. No heaps, no tangles. Anyway, the problem would be worse the closer to the stainless fitting, and earlier in this thread another poster mentioned that he had had a problem himself. I commented that the problem was supposed to be small (I don't know that anyone has quantified the magnitude of the problem). Probably it becomes an issue when the galvanising is on its last legs - OTOH, you don't want the dissimilar metal to result in that!!

I shall get magnesium and put beads round my swivel. I will try to remember to report back but if anyone is interested and cares to ask later this year, say August onwards, I should have something to report and will post photos etc.
 
I don't have the exact figures for sea water to hand but the electrode potential between zinc and passive stainless steel is more than 1.5 volt. This would seem to be ample to corrode the zinc in a relatively short time without the influence of an impressed current. I don't really see how something on the sea bed could be affected by any current, which would presumably go to earth potential as soon as it entered the water. Could be affected in the locker, I suppose, but I would go for the galvanic corrosion.
 
I thought that this was interesting.....From http://www.assda.asn.au/asp/index.asp?pgid=18533 [ QUOTE ]

When two metals are connected and in contact with a conducting liquid, the more active metal will corrode and protect the noble metal. Zinc is more negative than steel and so the zinc coating of galvanised steel will corrode to protect the steel at scratches or cut edges. The stainless steels, including 304 and 316, are more positive than zinc and steel, so when stainless steel is in contact with galvanised steel and is wet, the zinc will corrode first, followed by the steel, while the stainless steel will be protected by this galvanic activity and will not corrode. The rate of galvanic attack is governed by the size of the potential difference.

As a rule of thumb, if the potential difference is less than 0.1 volt, then it is unlikely that galvanic corrosion will be significant.

If all three conditions are met then galvanic corrosion is probable and the rate of corrosion will be influenced by the relative area and the current density delivered by the noble metal.

Relative wetted surface area

If a noble metal like stainless steel has a large surface area in contact with the electrolyte while the sacrificial metal (such as galvanised steel) has a very small surface area in contact with the electrolyte, then the stainless steel will generate a large corrosion current which will be concentrated on a small area of sacrificial metal. The galvanised steel will corrode quickly ? first the zinc then the underlying steel ? and so galvanised fasteners in stainless steel are not acceptable.

However, a stainless screw in galvanised steel is frequently used although a mound of zinc corrosion product will accumulate around the fastener. This is because the ratio of wetted noble fastener in an active metal might change from a 1:50 ratio to 1:1 during drying after a rainstorm. If contaminants are significant this means that avoiding dissimilar metal pairs may be a preferred option to prevent galvanic attack.

As a rule of thumb, if the wetted area of the corroding metal is 10 times the wetted area of the noble metal, then galvanic effects are not serious although the larger the ratio the less the effect.

[/ QUOTE ]

In the case of a galvanised anchor and chain with a stainless swivel, we meet the 10:1 rule of thumb. Seems OK to me though it will be interesting to see how my beads survive and the result of GMac's tank tests.
 
All good stuff.
I thought any stray current would be shot out in contact with the water.

We have seen quite a bit of stray current off a couple of boats late last year which were on pile moorings, completely un-connected to any other boat or the shore. All 3 had solar panels on deck and a local expert said at the time these panels are causing more and more issues like this. One of the boats, an old wooden one had a pile of current running from it's bollard down the mooring lines and out through the feet of the pile floater (a round plastic thing with a SS inside frame work and 'legs' which go down into the water approx 100mm. A NZ thing we have in our marinas and you don't from what I've seen). This current was just hammering the SS legs of the floater. We were trying to find out what was causing the floater damage and after rowing around for a while with a metre thing we picked up on this. The amount of current surprised everyone a lot. This is where I got my stray volt comment from.

I've also seen a pile of 10mm SS chain waste away down to 3-4mm well inside a year. On investigation it was found that the anchor and rode (everything was SS) lived in an anchor locker directly on bare carbon fibre. The chain was replaced and the locker lined, 4 years on the whole rode still looks like brand new.

Just working on that 'lots of tiny bits makes 1 bigger problem' theory.

I'll let you know how our test bits go, could be quite interesting.
 
Electric currents don't work quite like that. It's simpler than you think...go back to a basic battery, light and two pieces of wire to connect it. The battery is the solar panel, and the bulb represents everything the output of the panel goes into. Remember that electricity has to flow in a circuit, it cannot flow in one direction by itself, it has to come back. That's true of mains electricity, too, but with mains the network is so big and powerful that there are stray earth currents that cause problems locally.

How did you measure these 'stray currents' around the floaters? Were they ac or dc? Were there any other metallic object in the immediate vicinity especially near to the floaters (or part of the floaters)? When you use meters to measure things, especially in the wild, you need to be careful that you know what you are measuring and that the instrument is not, itself, creating the measured current (e.g. if you use a meter, especially a high impedance digital one, having probes with dissimilar metals and put the probes into the sea you will get a high reading. No stray currents, just a reading due to the electrochemical difference between the metals of the probes and caused by the measuring system itself not the thing you were trying to measure. Just a thought, but if your expert says what you said he said (about current coming down the bollard from the solar panels, etc.) , then he's wrong /forums/images/graemlins/smile.gif

As for SS and carbon fibre, I don't have any experience of CF as an engineering material. Could it be that this was embedded in an acidic substrate and that water was picking up the acid and that corroded the SS? Once you seal the corrosive substrate, the problem goes. Anyway, that story does not sound like 'stray volts' or simple electrolysis as no other metals appear to have been involved. One other possibility; suppose there was a dc leak (+12V) from the windlass. Suppose someone had wired the windlass so that it was switched in the negative leaving the chassis up at +12V. Suppose that the battery negative was earthed via ship's earth to the sea. Then there is a potential of 12V between the anchor chain and the sea. Suppose the CF locker was reasonably conductive, and you now have an explanation. Nothing stray about it, if that was the case.
 
We had a different failure of the sex nut on our swivel connector.

We were taking shelter off the East coast of Sardinia in May 2005. After about 10-12 hours a considerable increase in wind and shift in direction put us close to a lee shore. When we hoisted the anchor to change position we found that the sex nut at the chain end had unscrewed as one piece, drawing the smaller locking interscrew completely through its countersunk hole.

I put the actual event down to the action of the chain applying torque to the body of the screw and thus unscrewing it, however the fact that it could happen suggests a problem with the design/manufacture, and in particular the relationship between the diameter of the screw head and that of the outer screw thread. As I sit and look at it now its easy to see that the screw head would just follow through the 'loose' female thread.

The only reason we did not loose the anchor and possibly the boat was that after the screw had fully unscrewed itself from one side it become wedged at an angle in the other cheek thus preventing the chain from slipping out. Just how many more tugs on the chain that would have withstood I dread to think. We set off to Lipari with a F6 up the chuff and a very sick feeling in our stomachs.

For the record, checking that the sex nuts were tight was part of regular (weekly) routine, as well as a visual check every time the anchor was dunked. There is no make stamped on the swivel and I have forgotten where we bought it from, though at a push I would say Compass. The two ends swivel on an allen bolt that has the head free in one end and the thread welded into the other. Unusually, the sex nuts are cross head csk.

We now use a shackle with the biggest pin that will fit through our chain, and get peace of mind from the visual check of the cable tie used to stop the pin turning, both on deck before dunking and during snorkel sessions if anchored for any length of time.


Steve
 
From your description it sounds very much as though your swivel is the same as mine. I used to check the sex nut tightness on a fairly regular basis but I never thought to inspect the jaws for signs of cracking. In view of its brittle appearance there may have been none, as by implication the fracture occurred instantaneously.

I am reasonably confident of the Kong swivel that replaced mine. In the YM tests it outperformed some shackles a size larger, and I'm happy that the design is good - always assuming that the screw stays attached! I would prefer to see a Nyloc nut on the other side of the swivel, although this would probably compromise the strength of the overall item.
 
I was aware of the relative areas issue in galvanic corrosion but I had not seen the figures for stainless v zinc before. The areas seem pretty clear-cut where there is a good connection to a large galvanised anchor but it must change with stainless links in a chain, especially in a wet chain locker. Electrical connection is presumably fairly hit or miss and there is plenty of water around. Does explain the loss of galvanising adjacent to links on my recently scrapped chain.
 
[ QUOTE ]
How did you measure these 'stray currents' around the floaters? Were they ac or dc? Were there any other metallic object in the immediate vicinity especially near to the floaters (or part of the floaters)?

[/ QUOTE ]
We had a metre thing which looked quite like a std multi-metre. He put one wire onto the rope and one into the water then read the number. AC/DC? Sorry don't know. He keep referring to 'volts' mostly 0.X or the worse at 1.2. He may have been using the word volts for the benefit of the dumbarse on board, me /forums/images/graemlins/smile.gif The floater was around a wooden pile (only the SS centre touches the pile) and the closest bit of metal to that would have been something on the boat, the next would have been 12mts away (another floater).

[ QUOTE ]
When you use meters to measure things, especially in the wild, you need to be careful that you know what you are measuring and that the instrument is not, itself, creating the measured current (e.g. if you use a meter, especially a high impedance digital one, having probes with dissimilar metals and put the probes into the sea you will get a high reading. No stray currents, just a reading due to the electrochemical difference between the metals of the probes and caused by the measuring system itself not the thing you were trying to measure. Just a thought, but if your expert says what you said he said (about current coming down the bollard from the solar panels, etc.) , then he's wrong /forums/images/graemlins/smile.gif

[/ QUOTE ]

The worst boat was an older 30ft wooden clunker (that was close to the end of it's time). The mooring line was around a SS bollard over a bow fitting to the floater. No winch on board. When the 3 offending boats were removed from the piles the problem went away.

[ QUOTE ]
As for SS and carbon fibre, I don't have any experience of CF as an engineering material. Could it be that this was embedded in an acidic substrate and that water was picking up the acid and that corroded the SS? Once you seal the corrosive substrate, the problem goes. Anyway, that story does not sound like 'stray volts' or simple electrolysis as no other metals appear to have been involved. One other possibility; suppose there was a dc leak (+12V) from the windlass. Suppose someone had wired the windlass so that it was switched in the negative leaving the chassis up at +12V. Suppose that the battery negative was earthed via ship's earth to the sea. Then there is a potential of 12V between the anchor chain and the sea. Suppose the CF locker was reasonably conductive, and you now have an explanation. Nothing stray about it, if that was the case.

[/ QUOTE ]

Don't know much technical about this one only just the consensus was 'bare Carbon + SS + seawater = battery'. Whatever it was it had many spooked, my insurance company included.

With the amount of electrical stuff aboard these days your bound to get a bit of stray (possible poor use of the word) drifting around somewhere on some.

Interesting subject, I just wish I was more up on the technical side of this including terminology. Learning more each day at the moment, thanks /forums/images/graemlins/smile.gif
 
[ QUOTE ]
I just wish I was more up on the technical side of this including terminology.

[/ QUOTE ]Terminology was the problem with the cases you described. None of those were due to 'stray' anything (in the terminology used over here), they were due to a potential arising between two dissimilar metals placed in an electrolyte (seawater). When you place two dissimilar metals into seawater and connect them with a resistance (wire, chain, wet rope, etc.) then a current flows. If you put a voltmeter across them, you read volts. You have a battery, pure and simple. While the current flows, material from one electrode dissolves and goes into solution, and this is called 'electrochemical (or galvanic) corrosion'. The currents are very tiny but they do a lot of damage because they go on 365/365 withouth even a day off for Christmas. We are usually talking about microamps, or a maximum of a few milliamps ('micro' is one millionth and 'milli' is one thousandth). Sometimes, one of the electrodes is not actually in the water but is mounted on saturated wood, in the sea, and it is just like being in the sea.

This explanation does not answer the PV panel issue you mentioned earlier. There was some other confusion over that, or the PV panel had nothing to do with it, which is more likely.

'Stray' volts or currents are not due to that mechanism but to imbalances and leakages from the 230V mains system. You don't need to be connected to the mains to suffer but you do need to be somwhere in the vicinity. You might suffer from strays in a marina even though you are not connected to shore power (but it is fairly unusual). All mains equipment leaks some electricity to earth because the voltages are high, the insulation is not perfect, some leakage is inevitable by inductive and capacitive coupling, and the supplies are bonded to earth somewhere in the utility's supply.

Detection: Meters come in two basic sorts. Those that measure ac and those that measure dc. ac has an average voltage of zero as the + swings are exactly cancelled by the - swings. Ordinary dc meters read zero even with high ac inputs. So if you are hunting for strays you need to use an ac meter.

So, coming back to where we started, yes, terminology is the issue here. Your expert seems to have used the right sort of meter for the job and found the problem. It's just that it gets confusing when he says he has found a problem with strays when what he has done is to prevent galvanic corrosion by removing one of the electrodes. But then again, it doesn't matter much to his customer as long as the problem goes away, I suppose. It's a bit like your surgeon getting confused between a tonsilectomy and a castration - no problem as long as he removes the right bit in the theatre /forums/images/graemlins/wink.gif And no problem until you tell your mates about your recent op /forums/images/graemlins/blush.gif
 
[ QUOTE ]
hylas

ps - he's French and I think he spelt it 'toogle' /forums/images/graemlins/smile.gif

[/ QUOTE ]

FixaHylas2.jpg


Soory ( /forums/images/graemlins/smile.gif) for the delay.. I was wandering around Argentinian Patagonia; without Internet connection...
 
Thank you for posting that photo of the rigging toggle used as an anchor connector - it does make sense for sure, and seems to be a lot more logical than the 'conventional' connector (ie without a swivel) - we have one of these on our CQR, and it would appear that something might give if a large sideways force was applied to the connector.

I tried to find a 1/2" double jaw toggle in the chandleries when I was in England last September, but none had any - think I might resort to getting one by mail order from West Marine.....

What does the forum think about toggles used as anchor / chain connectors?

PS - Am tres impressed / horrified by that photo of the rather unhappy shackle! Do you know the circumstances that caused it to fail in such a spectacular fashion?
 
Looks like a shock load causing brittle fracture, to me. The alternative would be crevice corrosion but that is a slower process and does not leave the virgin crystal appearance that we see in this picture. I would bet that the load (a chain or maybe and more likely another shackle pin) was lying in the corner where the fracture took place and that a shock load resulted in fracture.

When a load is applied to normal stainless it extends with the load (Hooke's Law) until the 'elastic limit' is reached, when it fails in a deformed state (i.e. bent or pulled out of shape). However, if the stainless was too brittle (was not properly annealed after casting) then the elastic limit could be much lower and a brittle fracture could occur at a much lower stress level than intended.
 
Looks like an excellent solution to me - compact, strong and perhaps the most secure attachment possible - split pins in clevis pins.

Not knowing anything of the history of the failed shackle it's difficult to give a precise diagnosis. There is visible pitting on other parts, which suggests that it may not be made from AISI 316 (A4). It may therefore be rather more susceptible to seawater corrosion. The fracture faces seem to be discoloured, suggesting a progressive crack mechanism. I can see some indications of chevron marks initiating at the central portion of the threads, suggesting a fairly rapid brittle fracture.

Stress corrosion is the most likely but this happens theoretically only at a temperature above about 65 degrees C. However, in practice it has been observed in stainless steel repair plates in the human body, so much for theory! The location of the crack transverse to the axis of the shackle shows the mechanism to be stress related, assuming a straight-line pull. I would certainly suggest that a stress relief anneal following original manufacture has not been carried out. Otherwise the non-threaded side would probably have failed also.
 
Very interesting photo. I have tried to locate a manufacturer. Have found an identical looking product in a Spanish catalogue but there are no load ratings. Do you have the name of a reputable manufacturer who also states the safe and max. working loads?
 
This swivel has been used by a living aboard friend on his anchor, He gave it to me after it fail..

The swivel seems to be of 316 stainless steel, but there is no indication of the manufacturer. The failure occurs with relatively low winds (about 20 knots) but the swivel should have been in bad conditions before the failure..
 
It's interesting and useful to try to find out why they failed. The most dangerous time is, of course, when bringing the anchor up, as the rode shortens. If he had been bringing the anchor up in 20kts with some chop or sea, then when the rode became short there could have been some bad snatching. That could be reason it failed. If you speak to your friend, could you ask him about the circumstances?
 
It's chinese made and the version of the story of how it failed is now up to about 6.
See my swivel photos earlier. The dodgy looking one is the same as the one in Alain photo.

Why it failed is very simple - too many dashboards and seats left in the steel /forums/images/graemlins/smile.gif The contents of the photo is nothing new or un-common. That's just what those things do sooner or later.
 
We're having a discussion on these items and I wondered if there is any test or information you might offer on the following swivel connectors: Kong, McDuff the NZ brand, Suncor, and Wasi Ball. They seem to be the best and only choices worth considering.

Thanks

Michael
SV Se Langt
Westerly Berwick 31
 
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