Metallurgy Question: protecting chain in anchor locker

[lpdsn]

My anchor locker is more or less a three sided inverted pyramid with the lowest point and the drains just an inch or two above the waterline. In any seas (and around here when there's a forecast without a six in it you assume the Met office have made a mistake) my anchor chain gets a good salt water rinse even in the locker.

The bit of the old chain that was at the bottom of the locker had corroded so badly that it took a fair bit of ingenuity and brute force with a block and tackle and a line led back to the winch to get it out and it was just a mass of rust.

I don't want the same to happen to the new chain and have been thinking how to avoid this. By far the easiest of the ideas to implement is to throw a couple of half-spent anodes into the anchor locker then put the anchor chain in on top. I should have enough spare to replace them after each time I lift out.

Any thoughts on why this might not work?

 

[pvb]

Would anodes prevent rust?

 

[vyv_cox]

No, I'm afraid it won't work. Firstly, the chain and anodes would need to be totally immersed to invoke cathodic protection. Secondly, there would need to be good electrical connection between everything, whereas in reality good connection between individual links is a lottery, never mind between anodes and chain.

The only real answer is to keep the water out. I and many others winter our chain on a pallet alongside the boat, or hanging from a rope between the cradle legs. This is in order to keep it as dry as possible, as even fresh water will cause zinc hydroxide to form, depleting the zinc metal. One possible for you is to raise the chain on a shallow platform in the locker so that it is not lying in a pool of water.

 

[sarabande]

Is there any way you can re-route the drain through an inverted U bend or , say, to the bilge in the cabin, so that the salt water cannot ingress ? I think it means creating a lid to the locker as well, which is really watertight.

 

[PaulRainbow]

<snip> One possible for you is to raise the chain on a shallow platform in the locker so that it is not lying in a pool of water.

This would be my preference. Stick some rails along the inside of the locker, a little way up from the bottom, but not right into the corners. Drop a piece of sheathed ply (or whatever you fancy) into the bottom of the locker, again not tightly fitting in the corners. The gaps in the corners will allow the chain to drain, whilst minimising the amount of sea water that can reach the chain.

 

[lpdsn]

No, I'm afraid it won't work. Firstly, the chain and anodes would need to be totally immersed to invoke cathodic protection. Secondly, there would need to be good electrical connection between everything, whereas in reality good connection between individual links is a lottery, never mind between anodes and chain.

The only real answer is to keep the water out. I and many others winter our chain on a pallet alongside the boat, or hanging from a rope between the cradle legs. This is in order to keep it as dry as possible, as even fresh water will cause zinc hydroxide to form, depleting the zinc metal. One possible for you is to raise the chain on a shallow platform in the locker so that it is not lying in a pool of water.

A platform is one idea I considered. But it would have to bear a lot of weight and fitting it would be a nightmare even for an experienced professional contortionist never mind an amateur boat-owning one.

I'm thinking the anodes will fill the bottom of the locker. An inch from the bottom it is little bigger than the palm of my hand (if that). So the idea is that the anodes would be in the water and the chain heaped above it. I'd expect it to be all electrically connected when heaped up like that. I'm not worried about being at anchor as I expect the galvanisation to work in the normal way then.

I sail in the winter so it wouldn't be practical to take the chain off and take it home to store. And anyway I'd never get it up on the luggage rack on the train.

 

[lpdsn]

Is there any way you can re-route the drain through an inverted U bend or , say, to the bilge in the cabin, so that the salt water cannot ingress ? I think it means creating a lid to the locker as well, which is really watertight.

The short answer is no.

The longer answer is. The locker is at the bow, for'd of a semi-bulkhead. Aft of that is a sail/fender locker. Aft of that is a watertight collison bulkhead. There's no way I'd want water coming through those and into the bilges everytime the bows go under in heavy weather.

 

[TC Tuckton]

Quite apart from Vyv Cox's comments; if the anodes you use are the same zinc as the galvanizing on the chain will there be any anodic protection?
Actually, even if there is no protection, the old anodes may help keep the chain out of the water.

 

[geem]

Our chain locker floor is below the waterline. We have a skin fitting in the bulkhead between the locker and the boat with a pipe that runs through the bilges to the main bilge sump. Any water that comes in with the chain as it is hoisted runs out through the pipe. We clean the chain locker annually to remove any silt. I have also added a strainer about a foot from the bulkhead fitting inside the boat so I can keep silt from going down the pipe. It works well and was an original design feature of the boat. We also rinse the locker with fresh water annually before we put the chain away for a few months so the chain doesnt sit over the Caribbean summer in a salty environment. Hopefully should allow our chain to last longer. It might be a solution for you if you can thread a suitable pipe through your bilges

 

[lpdsn]

Our chain locker floor is below the waterline. ...

Thanks for the suggestion, but there really is no room to put a skin fitting in the bottom of the chain locker, even if I could reach it other than by drilling a hole in the hull. There's already the two small covered holes which come out at the cutwater just above the waterline, which work fine in harbour.

I'm minded at the moment just to put the old anodes in anyway. I reckon they'll fill the bottom few inches and if nothing else won't have an adverse galvanic reaction with the zinc of the galvanised chains.

 

[lpdsn]

A picture might help make the arrangement clearer.

There's a small compartment at the bow that contains the windlass and furling drum (latter not shown). The anchor is partially housed with this and the forestay and foil come up through the top so the sea will always find a way in. Although it is in theory separate from the rest of the boat water can flow past the windlass when it is more than just a bit of spray. There are small drain holes that lead water outside the boat but obviously they could never drain water fast enough in heavy weather.

Anchor locker is below this with drain holes at the bottom.

View attachment Anchor Locker.pdf

 

[Neeves]

Chain lockers are commonly very badly designed and are the ideal place to corrode steel as you have found out.

I have a lovely picture of a new yacht, AWB, with a locker having its drain hole about 200mm above the locker base. The yacht is at a boat show with a parsimonious length of chain - allow full view of the locker half full of what looks like brown windsor soup. If it had a decent length of chain - you would not see the water. I guess the chain will last about 12 months.

The other danger is the the hole blocks with mud and the water breaking over the hatch slowly fills the locker until its about the weight of 1 or 2 crew members. Keep the chain and locker clean.

It is possible to buy fibreglass gratings, used in industry as flooring and you might see them, or something similar in marinas as decking. They are around 30mm-40mm thick and exceptionally strong. You need an offcut to use as a false bottom to your locker. Try Lockers - in the UK (unless they have succumb to a purchase). There are a number of manufacturers worldwide - but I don't know any specifically in the UK. If you cut correctly it will need no support and will simply fit into the bottom of your locker.

You could chop up a milk crate but that would not be quite as strong - but you perhaps could use it as a former (for the grating)

You need to get the water out of the base of the locker.

Consider - depends how deep the water is. Imagine your yacht on the hard, slightly bow down, fill the space occupied by the water with resin up to the the level of the drain. Water would naturally flow out. Ideally you want to lighten the resin, use some form of lightweight filler.

If the water is left in the locker it will continuously wick up through the chain - and you know the result.

You need to look after the chain, in the locker. Wash the locker out with fresh water, get rid of the salt and mud as frequently as possible. Doing it once a year is not sufficiently frequent, you wash the deck, why not wash the locker. Leave the locker hatch open when you are at anchor - you are in the UK - the rain will wash the chain and get rid of salt. Leaving the locker open will also 'air' the chain. By all means try loose anodes, it can do no harm.

Put a clam shell cover over the outside of the drain hole - this will reduce seawater ingress.

As Vyv suggests taking the chain out and leaving it on the hard is good practice, but if you sail 365 as we do - not practical. During AF (and any other maintenance) when we are in a boatyard or marina) we would discharge all the chain, wash with a power wash and wash out the locker. Its a good time to replace your chain markings (and service the windlass). Its not difficult to do this when you refuel or top up the water.

This is very much abbreviated - for more detail I have an article on chain lockers and caring for chain in a forthcoming issue of SAIL, look out for it. I'm not sure of timing.

Jonathan

 

[lpdsn]

Chain lockers are commonly very badly designed and are the ideal place to corrode steel as you have found out. ...

Thanks for your reply. The water that is retained at the bottom is probably 1/2" at the most. I reckon almost all the water that gets in there comes up the drain holes at sea. There is a cover over both holes, but they're never going to stop water coming in when the holes are four or five feet below the crest of a wave. And in a damp climate like this it'll likely take a long while for the chain to dry out once it has got wet.

I have been thinking of a platform for a few months now, but have been put off by the difficulty of fitting it in such a confined space. The other idea was to sacrifice an anchor warp at the bottom of the locker, but of course that'll retain moisture itself.

Rinsing with fresh water is a good idea. At least it'll get rid of the salt.

 

[vyv_cox]

This is the chain locker on my motorsailer. All of this is now above the waterline, although it was not originally. The floor is 20 mm plywood, epoxied to the hull. It seems perfectly strong enough to carry the full weight of chain. Beneath the chain, and just about visible at left of the chain, is a small platform made from perforated stainless steel that was used to provide some drainage previously. There are two of these, made from 4 mm plate bent into a [ shape. I imagine you could fit something like them in your locker.

Not the black perforated stuff which is rubber to protect the hull from the chain.

 

[sarabande]

Suggestion #2.


Can you arrange a one-way valve (perhaps a as used in bilge pumps) in the locker drain to the outside. Or a rubber flap on the outside to prevent the 'oggin coming in ?

 

[PuffTheMagicDragon]

I had a similar problem when I had a Centaur, the bottom of the locker being below the drain hole. My solution was 'Fast in' fast out'.
I wedged a triangular piece of hardboard in place such that it sloped downwards towards the hole and being slightly below it (say 6mm). I then applied resin and CSM until the level was close to the drain hole. Result was that there was never any residual water in the locker.

On my present boat, the previous owner had shackled around 50 metres of 20mm polyester rope. This acted like a wet poultice with the chain sitting on it. I had to cut off the last 5 metres of chain because they had rusted into one solid lump. Needless to say that rope now lives in another locker to be used, maybe, when it is really needed. In the five years that I have had the boat I have never needed it because 40m of 8mm chain are more than enough in my area.

 

[lpdsn]

On my present boat, the previous owner had shackled around 50 metres of 20mm polyester rope. This acted like a wet poultice with the chain sitting on it. I had to cut off the last 5 metres of chain because they had rusted into one solid lump.

That rules that one out then.

 

[lpdsn]

I've just taken some photos but the lead to connect the camera to the laptop is at home. Typical! I'll try posting them when I'm home.

 

[reeac]

Many years ago I made a rudimentary liner for my chain locker to prevent the anchor flukes from damaging the inner surfaces. I bolted together lengths of ex-tender-gunwales hardwood battens to make a triangle for each side of the locker with the two triangles being laced together along one side of each so that the assembly could be collapsed to get it into the locker. The bottom points of the two triangles rested in the bottom of the locker and the whole assembly has been sitting in there for around 12 years now. You could make a squat version of this as a base for a perforated floor. The nice thing about using old gunwale timber is that it is permanently curved and just matches the concave curvature of the sides of the locker.

 

[Ian h]

How about these people

Looks like they do off cuts
https://www.globalwalkway.co.uk/cat...MIgprDz67a1wIVLLHtCh2a4QPQEAAYASAAEgK6ovD_BwE

OR
something like this
https://www.coopersofstortford.co.uk/garden/terracotta-pack-of-5-garden-tiles/

But this looks ideal
https://www.slip-not.co.uk/productd...-with-Drainage-Holes-for-Pool-And-Wet-Areas-A