Chain Rust Prevention (but then easily removed)

[Neeves]

If those who replaced their chain with G70 and also down sized the chain then their use of the smaller chain would not be that different to people who used smaller chain anyway. Thus if the thesis holds 6mm chain would wear more quickly than 8mm and 6mm would have a transitory life compared to 12mm.

The US Navy/Army have been replacing their conventional chains with smaller high tensile Armorgalv coated chain for both lashing military vehicles into landing craft and as anchor chain for their small craft and they have got it all wrong the increased life they have achieved is illusory the the millions of dollars they budget to save is a gross mistake.

Dashew the proponent of G70 as a means to save weight (because he is suggesting down sizing chain) has made no mention that chain life will reduce. None of the people who have followed his advice have ever mentioned, over the decades, a reduction in life for say 5/16th chain vs 3/8th". None of Dashew's customers for his expedition motor yachts have ever mentioned that chain life 'seems' low.

It may be this is a phenomena that no-one has noticed and that pigs do really fly - but I doubt it.

Jonathan

 

[vyv_cox]

As Jonathan suggests, it seems that the loss of zinc from the last couple of links of chain is due to galvanic effects, most markedly where a stainless steel shackle or swivel have been used but possibly even against carbon steel. My most 'extreme' example is the three links of 10 mm chain I have between my Kong swivel and Wichard shackle. The zinc on these three links was lost in five seasons and I replaced them. The last two or three links of the main 8 mm chain have also lost most of their zinc but I have not seen the need to cut them off as they have yet to stain the decks with red rust.

 

[noelex]

the loss of zinc from the last couple of links of chain is due to galvanic effects, most markedly where a stainless steel shackle or swivel have been used but possibly even against carbon steel.

I agree this is mostly a galvanic effect, but as you note it is easy to fix by chopping off a few links of chain, so it is not a great concern.

The corrosion elsewhere is more of a nuisance and this tends to occur in the area of greatest chain movement and therefore abrasion. Annoyingly, it is often near the middle of total chain length carried.

You can see in the photo below the marks in the sand where the chain has been dragged across the seabed by boat movement. The thinner and therefore the lighter the chain in relation to the boat size, the more movement that is seen.

It would be nice to see some research to quantify the effect on the life of the chain caused by changing to thinner chain (without changing boat size). Unfortunately, the only studies have subjected thin, light chain to the same movement and abrasion as thicker and heavier chain. This is ignoring the major effect (on chain life) of switching to thinner chain.

 

[vyv_cox]

I agree this is mostly a galvanic effect, but as you note it is easy to fix by chopping off a few links of chain, so it is not a great concern.

The corrosion elsewhere is more of a nuisance and this tends to occur in the area of greatest chain movement and therefore abrasion. Annoyingly, it is often near the middle of total chain length carried.

You can see in the photo below the marks in the sand where the chain has been dragged across the seabed by boat movement. The thinner and therefore the lighter the chain in relation to the boat size, the more movement that is seen.

It would be nice to see some research to quantify the effect on the life of the chain caused by changing to thinner chain (without changing boat size). Unfortunately, the only studies have subjected thin, light chain to the same movement and abrasion as thicker and heavier chain. This is ignoring the major effect (on chain life) of switching to thinner chain.

That's a very strange pic. Why is the chain close to the anchor (presumably) off the bottom? Or are we looking from the boat end with the anchor lost to vision ahead? Most I see are more like this

 

[noelex]

The anchor is towards the top of the picture, but out of sight in my photo. This is typical of light conditions, but as the marks in the sand show, the chain is still occasionally dragged along the bottom even with not much wind.

Your photo is more typical of moderate to strong wind. The triangular marks in the sand are caused by the chain swinging back and forth and pushing the sand along the bottom. This occurs with boat movement.

Unfortunately, this wears away the galvanising and this movement along the seabed is one factor in reducing the life of the chain.

 

[Neeves]

Noelex said

'It would be nice to see some research to quantify the effect on the life of the chain caused by changing to thinner chain (without changing boat size). Unfortunately, the only studies have subjected thin, light chain to the same movement and abrasion as thicker and heavier chain. This is ignoring the major effect (on chain life) of switching to thinner chain'.

end quote

I'm glad you posted that as it appears to admit - you have no idea whether small chain is preferentially worn compared with larger chain. Why you have posted ideas you cannot substantiate is questionable.


As I mentioned Americans, who are the first and primary users of G70 chain, have never mentioned, to my knowledge, that when they changed from 'larger' G30 chain to 'smaller' G70 chain (for the same yacht) that the G70 chain abraded more quickly. Dashew has been advocating use of G70 chain, for decades and he has made no mention of reduced gal life. Members of forum are quick to point out problems (less quick to praise anything positive) - if downsizing to G70 has issues - we would know about it.

Some members here have the same yachts as each other but different chain sizes - I often marvel at the yacht owners with 35' yachts using 10mm chain where others use 8mm chain. I don't recall the owners with the 8mm chain suggesting that they have a poor gal life.


If you have ideas on how to test, to answer the question you pose - please feel free to post the details. Even better - do it.

However based on the results of my testing and use of lighter chain - I think you will find that the fact light chain moves more at lower wind speeds (than heavier chain) will be balanced by the lighter chain lifting off the seabed earlier than heavier chain and the 2 facets of abrasion will cancel each other.

To further complicate the issue - you would not be comparing like with like.

If you want to prioritise gal life, comfort at anchor and safety then:

If you use lighter chain you are sacrificing catenary and to compensate you should be using a well designed snubber, which would need to be more carefully chosen than a snubber (bridle) than if you were using heavier chain. A good bridle system will reduce yawing, (not only on a multihull but mono hull also) and thus you would endure less dragging of the lighter chain across the seabed. An even better bridle system will also reduce the effects of chop and stop the chain thrashing on the seabed (as evidenced in Vyv's photo above).

The rode is not simply a length of chain but all the components, bridle/snubber, chain etc..

Jonathan

There is an article in the current issue of Practical Sailor, the May 2020 issue, on a bridle system, primarily focussed at multihulls but adaptable for monohulls and the system improves scope ratio and manages/reduces yawing and horsing.

 

[vyv_cox]

The anchor is towards the top of the picture, but out of sight in my photo. This is typical of light conditions, but as the marks in the sand show, the chain is still occasionally dragged along the bottom even with not much wind.

Your photo is more typical of moderate to strong wind. The triangular marks in the sand are caused by the chain swinging back and forth and pushing the sand along the bottom. This occurs with boat movement.

Unfortunately, this wears away the galvanising and this movement along the seabed is one factor in reducing the life of the chain.

The marks you see are certainly in stronger wind, force 7 or so. However, they are mostly made by the chain lifting off the bottom at the end of each yaw extremity, rather than being dragged across. I watched this happening for about an hour. You can clearly see individual link marks as the chain lifted and dropped, with few lateral drag marks.
Most of the galvanising loss on my chain is in the middle, rather than at the ends.

 

[noelex]

The marks you see are certainly in stronger wind, force 7 or so. However, they are mostly made by the chain lifting off the bottom at the end of each yaw extremity, rather than being dragged across. I watched this happening for about an hour. You can clearly see individual link marks as the chain lifted and dropped, with few lateral drag marks.

The pictured significant disturbance in the sand will cause abrasion to the chain no matter how the chain pushes the sand around.

Most of the galvanising loss on my chain is in the middle, rather than at the ends.

This is where the abrasion is greatest. In the most commonly encountered in light or moderate winds the chain near the anchor is likely to be stationary most of the time and so suffers less abrasion.

 

[Neeves]

That is a great picture Vyv,

To have the chain thrashing the seabed, in this case, has led to the anchor moving, you can see how the shank has pushed the sand to each side. The anchor might also have moved forward - but it is not clear. It is also clear that even though the anchor has moved and the chain is thrashing itself to death - the anchor is still offering good hold - whatever movement is occurring does not appear to impact hold - or not enough impact to cause concern.

I wonder - why did you not deploy more chain - no room?

It seems an ideal case where a longer and more elastic snubber might have been invaluable.

Jonathan

 

[vyv_cox]

That is a great picture Vyv,

To have the chain thrashing the seabed, in this case, has led to the anchor moving, you can see how the shank has pushed the sand to each side. The anchor might also have moved forward - but it is not clear. It is also clear that even though the anchor has moved and the chain is thrashing itself to death - the anchor is still offering good hold - whatever movement is occurring does not appear to impact hold - or not enough impact to cause concern.

I wonder - why did you not deploy more chain - no room?

It seems an ideal case where a longer and more elastic snubber might have been invaluable.

Jonathan

This was towards the end of a very memorable 24 hours! The forecast was for southerly winds of about force 4-5, veering to north-westerly 7-8. We headed for the easterly anchorage of Sandbar Bay on Kythnos, where we were with three other boats at anchor in about 5 metres. All was well in the evening, not perfect shelter but OK. When the wind began to veer towards midnight it blew alternately down two valleys, causing serious yawing. We were not in a position to lay a second anchor, so had to put up with it. The anchorage is fairly small and we were surrounded by the three other boats. From memory we had about 35 metres of chain out (with a snubber) but our movement was so severe that it left the marks shown in the pic, as seen the following morning.

This photo was taken at the same time. A big Manson Supreme with 12 mm chain attached to a 55 ft USA-flagged boat. The witness marks from the initial southerly wind are visible, upon which the anchor rotated without dragging at all, the later north-westerly pattern being pretty similar to ours. He had a shorter scope than we did, about 4:1 he told me.

 

[Mudisox]

And what pretty patterns the chain makes. I wonder with lockdown the seabed has changed, some, but not me, might say recovered.

 

[noelex]

This was towards the end of a very memorable 24 hours! The forecast was for southerly winds of about force 4-5, veering to north-westerly 7-8. We headed for the easterly anchorage of Sandbar Bay on Kythnos, where we were with three other boats at anchor in about 5 metres.

I hope you managed to enjoy the outdoor rock pool hot spring spa when things settled down.

 

[Neeves]

There is a fine line for the timing to end for end. If you leave it till 'too late' the used end, that now becomes the bitter end, sits at the bottom of the chain locker, unloved, uncared for and rusting (because it has lost 'too much' gal). Better to end for end a bit earlier - at the first signs of rust spots and then with care - air the locker, wash with fresh water when it is accessible, make sure the locker drains properly - the whole rode remain usable (Instead of one half being a rusting solid lump). You can end for end again and eke out a few more years.

All best done when you are alongside a pier/pontoon - and the exercise is cheaper than paying for gym membership

Jonathan

 

[vyv_cox]

I hope you managed to enjoy the outdoor rock pool hot spring spa when things settled down.

Indeed we did