Anchor chain life

[Rum_Pirate]

Appreciated that you dowse the anchor to wash off the sand, mud before bringing it aboard.

However when hauling the anchor and chain aboard do you hose off the salt water with fresh water?

How much would the anchor chain like be extended if the salt water on the anchor and chain is hosed/rinsed off with fresh water?

 

[dankilb]

Not every time (a waste of fresh water if you’re using the hook, by definition) - but definitely when back to base (or the next place with a hose). Or you can leave the anchor locker open if it’s raining!

Presumably most people wash hook/chain/locker at the same time as the rest of the boat - and therefore relatively regularly (if not after each use/trip).

Couldn’t comment on the longevity impact.

 

[Minchsailor]

I anchor a lot, and wash it with fresh water at the end of the season, and also turn it end for end

 

[Neeves]

I know I will be accused of being wordy and too focussed but..........

The chain will only corrode if it is wet and will corrode more quickly in the presence of salt (in the water). If you leave the chain in a damp salt water environment, like a locker, it will corrode more quickly than a chain left in a dry locker. Salt in the locker will absorb water and will thus always be damp.

If you take new chain and soak it with salt water it will corrode, not the underlying steel but the galvanising - google 'white rust'. Even new chain needs care.

White rust and normal brown rust will hold water and always be damp in a locker (unless you live in a low humidity environment - which is a contradiction in a chain locker ).

So whenever you have access to fresh water, when you wash the deck, then rinse down the chain and locker. Make sure the drain holes at the base of the locker are not blocked. Allow the locker to dry out, leave it slightly ajar. If you don't have access to fresh water from a hose - when you are on board and its raining open the hatch.

All of this will prolong the life of your chain - unless you are a livaboard. For liveaboards the same regime does still apply as the part of the chain in the locker will corrode as quickly as a non-kiveaboard and this portion will need replacing simply because it sits at the bottom of the locker slowly festering.

I cannot think of any way to prolong the length of cain that is sitting on the seabed as it is subject to corrosion, being fully immersed in salt water and subject to constant abrasion (or the bit actually on the seabed is constantly abraded).

The idea that small chain suffers more abrasion because it sweeps the seabed more quickly is a phurphy. Think about it for a few minutes - abrasion is about mass divided by area??? Some people claim the advantage of heavy chain is because it is on the seabed longer than light chain - there are contradiction in this paragraph (which they don't seem to think about). - but the gurus sound soooo convincing - because they repeat the phurphy, again and again.

But to me the idea of being critical of a 4 year galvanising life is a joke and harsh on chain makers. The coating is typically 70 microns thick. This means you are losing 17 microns a year. What on earth would you expect. Seabeds are abrasive, some muds are anaerobic and result in an acidic environment (that rotten egg smell), people do not wash their chain nor locker. Lockers are badly designed, the drain holes are too small for one, people also store rope in the chain locker which acts as a 'reservoir' for salt water (the rope is saturated with salt water). Its amazing that chains last 4 years and the life underlines the miracle of galvanising.

Being critical of a 4 year life without knowing the background, to me, is simply trolling.

If you are leaving your yacht on the hard for a prolonged period (your winter) take the chain out of the locker, wash it (with fresh water) and store it neatly on a pallet under the yacht. Vyv hung his chain on the cradle that holds his yacht, sort of, like laundry. If you do take all the chain out - look at the locker - having a fetish I'm constantly looking into lockers and I'd say at least 20% always have a puddle of water at the bottom (bad design). Adding a false perforated base to the locker will keep the chain above the puddle - but see if you can enlarge the drain holes.

Every year we used to cut off 3-4 links of chain at the shackle end. They appear to preferentially rust. This seems a common issue and 3 or 4 links in 100m of chain is.......nothing. The corrosion appears to occur because you are at the junction of different steel compositions, shank, shackle and chain. Since we moved to G80 chain (which has a similar chemistry to the shackle) we have not cut any links off. But check the bitter end, commonly a stainless 'U' bolt in the locker, a HT shackle and then a mild steel chain. Better the bitter end is secured with rope, that you can easily cut - but have the bitter end at the top of the locker (where it is accessible and not in the puddle).

If you have a mixed rode then the chain at the splice corrodes preferentially - underling the effect of rope in contact with chain - cut the splice off and make a new splice.


How much you might prolong life by being careful - don't know. But it cannot do any harm and it takes very little time.

At the end of the day liveaboards are the only ones with a, possible, continuous use of their rode (and some, many of them will be in a marina, or boatyard, for some of their time. Those who only use their yachts for weekends and the occasional long break are unlikely to document their time at anchor nor summarise it over a period and 4 years of anchoring is going to be longer than the period for which they own the boat. Having said that if you leave your yacht on a mooring or in a marina - the gal will be deteriorating - because it is not washed, it is not in a dry locker - so like a live aboard it will degrade, but in the absence of abrasion.

Jonathan

 

[vyv_cox]

The galvanising on the last chain I bought lasted only three seasons despite end-for-ending. It may have been Maggi chain, not quite certain (bought in Corsica). At the time Maggi seemed to be suffering poor galvanising life. I had it regalvanised and it is just about ready to be replaced or regalvanised some 10 years later. We anchor for most nights for half the year. The chain is wintered in dry air, hanging beneath the boat ashore.

The message is that life is totally dependent upon galvanising quality. Manufacturers would be wise to emphasise the value of zinc thickness for improved life of their product.

 

[Neeves]

Galvanisers tell me that they have a specification for coating thickness. If this is the case one has to wonder why they don't publish the information. Galvanisers themselves agree that the thickness of the alloyed coating and the strength of the bond between the alloys and the base steel determines the galvanising life and in our case this is a 'few' years (for engineering products it can be decades). If a chain maker specified the alloyed thickness we would prioritise that, or those manufacturers - if that thickness was deemed to be adequate.

Historically Europeans bought locally made chain - now much of it comes from China - whether Chinese manufacturers of anchor chain prioritise coating thickness is unknown and it is equally unknown whether importers worry about it. Measuring gal thickness takes (approximately)a stg50 bit of kit and takes seconds. There have been no complaints about Chinese galvanising quality, or not that I am aware. In the past I have tested CMP Titan chains - they have been fine.

One comment that was consistent was that re-galvanising was better than the original, but having chain re-galvanised is becoming increasingly difficult.

Whether the market place, us, is motivated to a specification becoming declared and how that might be achieved - a bigger problem.

As I mentioned on another thread Vyv has a neat test on his website, cut a link and twist into an 'S'. This determines the strength of the bonded alloy to the underlying steel - but does not measure thickness. It is worth completing as the bond will impact the life of the coating (but is not the whole answer). Measuring the 'gal' thickness, with a coating thickness meter, is again not the whole answer as some of the coating is zinc - not the Fe/Zn alloys (and determining the thickness of the Zinc layer (I think) needs optical microscopy, a bit expensive to prepare as a one off, or something even more sophisticated.

I have tested galvanised coatingss from a range of manufacturers, American, Australian, Maggi and Chinese and the 'worry' is that different samples from the same manufacturer are inconsistent and knowing historical data offers little value - its the batch you want to buy that matters.


Its not much use, or interest, to most but Armorgalv, Thermal Diffusion Galvanising (there are at least a couple of other processors) offer the ability to provide a very precise coating thickness, to say, within 10 microns, the coating is harder than that of the alloys of HDG and is all alloy - no raw zinc. Body Cote (spelling?) in the UK used to offer, may still do, TDG (originally known as Sheradizing).

Jonathan

 

[MM5AHO]

There is a published standard for galvanizing that includes the thickness of the coating. Its international standard ISO1461. Its not published by galvanizers, as they don't own it, its published by standards institutes such as BSI etc. For steel that's 6mm or more, the standard minimum average coating thickness is 80u (the standard defines that term "minimum average coating thickness too)
I've never heard any galvanizer claim that the life expectancy relies on the thickness of the alloyed coating and the bond strength, rather that the life expectancy is directly proportional to total thickness of the coating (alloy and zinc). Increasing thickness is most commonly achieved by shotblasting first, which increases the surface area and so more alloying reaction, and so greater thickness.

What is far less researched is life in the harsh conditions that an anchor and chain endure. Studies in the UK over 10km squares show life expectancies from only 30 up to 170 years in outdoor land based situations. In marine environments, most studies are on fixed installations on, in, or over the sea, such as wharves, marina ladders etc. These typically suggest 10 -20 years, but highly dependent on tidal cover. For example the worst conditions and shortest life is in the tidal rise and fall zone - less that always out or always in(submerged).

Galvanizers typically have little control on coating thickness and cannot achieve what sherardizers do (as mentioned by Neeves above). Its as "coarse" as shotblast or not. And that typically raises 80u to 140u. But immersion time is an influencer, and that is determined by size and shape, and steel chemistry (Si, P being most influential). This is likely the reason that despite whichever supplier, its the batch that counts, as that will be the same chemistry. Even within a steel grade there's variation in galvanizing thickness due to chemistry differences in the steel. Galvanizers typically end up with excess of the standard, to their cost in zinc.

There are a number of sherardizing companies in the UK handling surprizingly large items. (eg 2 x 0.5 x 0.4m)