Kedge anchor, chain and shackles.. corrosion?

Sticky Fingers

Sticky Fingers

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I've acquired an aluminium Fortress anchor, to which I intend to attach a rode consisting of a shortish length of galvanised steel chain spliced onto a much longer length of octoplait.

The Q is this. Aluminium anchor. Galvanised steel chain. Some kind of shackle. Infrequent use so long periods hibernating in the dungeon of a lazarette on my boat. I assume there must be some corrosion risk from the use of the different metal materials in contact. How best to attach said chain to the anchor whilst minimising corrosion risk.
 
It's not a plain aluminium (aluminum) anchor but treated and plated with some clever chemical process.


If you leave the anchor and octoplait soaked in salt water, any weak point in the chain galvanising or a deep scratch on the anchor might experience corrosion (most likely the chain).

BTW I'd suggest the minimum length of chain is about 2 and 1/2 fathoms (say 5 metres in Eurospeak)

The answer is to pour some fresh water over the anchor, chain and octoplait after use. Keeps everything clean and corrosion free.

As for the connector, I use stainless shackles.
 
For something like 15 years now I have had an aluminium Spade as my stern anchor. No chain, only rope, but the shackle is galvanised steel. Yes, there are signs of corrosion around the hole in the shank, but only very slight.
In retrospect, I think a stainless shackle would have been better. And maybe a short piece of hose or some heat shrink tubing on the shackle pin and other likely points of contact between the metals?
 
Yes, no significant corrosion will occur on anchoring gear simply because it does not spend sufficient time immersed. My bower anchor is galvanised steel, with a stainless steel shackle to three links of galvanised chain, then a stainless steel Kong swivel connected to galvanised steel chain. We anchor for most nights of six months every season. After five years the zinc was lost from the three links, red rust began to appear and the links were replaced. After about ten years the galvanising on the last four links of the main chain is now black as the surface zinc is corroding away. Ultimately I will cut these links off and start again, or regalvanise the chain.

My kedge is a Fortress, with a stainless steel shackle, short length of galvanised chain, another shackle and a plastic thimble on Anchorplait. This setup is used several times per season and appears as-new.

The one problem area with the OP's suggestion is the Anchorplait spliced to galvanised chain. The rope will remain wet for long periods, especially if it is stowed in the anchor locker forward. Eventually (years) the chain will corrode. My mooring buoy strop is made up in this way and I had to scrap the chain after something like seven years.
 
Overall, a galvanised shackle and chain will be a better choice than stainless steel in reducing the possibility of dissimilar metal corrosion.

Fortress anchors are made from 6061 aluminium and then anodised. 6061 is reasonably seawater resistant, but not quite as good as the 5 series aluminiums, such as 5083. Personally, I think it is a good idea to try and isolate the stainless bolts when assembling the Fortress. Products like Duralac or Tefgel are ideal.

Fortress anchors are covered by a comprehensive lifetime warranty so if you do have any corrosion the parts will be replaced for little cost.
 
I like the idea of a piece of plastic pipe to cover the pin of the shackle to reduce contact points between shackle (galv or SS) and the anchor, but am concerned that it will be crushed under anchoring load.


Thanks to Noelex for the techy info on aluminium :) Much better than my " treated and plated with some clever chemical process." :)
 
vyv_cox said:
....The one problem area with the OP's suggestion is the Anchorplait spliced to galvanised chain. The rope will remain wet for long periods, especially if it is stowed in the anchor locker forward. Eventually (years) the chain will corrode. My mooring buoy strop is made up in this way and I had to scrap the chain after something like seven years.
Click to expand...

Thanks to everyone for their input. With ref to Vyv's remark, would you suggest I go for your setup, ie another shackle to a plastic thimble? It'll be stored in the aft lazarette and rarely used, so may be OK as I originally proposed? But if it's better to go the shackle route I'll do that.
 
Scala said:
Thanks to everyone for their input. With ref to Vyv's remark, would you suggest I go for your setup, ie another shackle to a plastic thimble? It'll be stored in the aft lazarette and rarely used, so may be OK as I originally proposed? But if it's better to go the shackle route I'll do that.
Click to expand...

If, as you say, it will be rarely used, and you are worried about possible dissimilar metal problems, why leave it permanently connected at all?

In the real world, it doesn't take long to attach a shackle. My Fortress second bower/kedge is stowed lashed to the taffrail. The length of chain for it is kept in a compartment in the chain locker (forward), and its nylon (climbing rope) rode is kept in the lazarette (aft). Sounds very inefficient, but has never presented any problem.
 
Scala said:
Thanks to everyone for their input. With ref to Vyv's remark, would you suggest I go for your setup, ie another shackle to a plastic thimble? It'll be stored in the aft lazarette and rarely used, so may be OK as I originally proposed? But if it's better to go the shackle route I'll do that.
Click to expand...

I originally selected a thimble and shackle so that the Anchorplait would be available as a long shore line or possibly tow rope if ever needed. When I use my kedge anchor the chain and rope are invariably stowed wet in their bag in the lazarette, so having the two separated by a shackle is no doubt better from a corrosion point of view.
 
We use all alloy anchors, 3 different styles, and have been using them as 'primary' anchors for 8 years now. One sits on the bow roller come rain or shine the other 2 are in lockers. We use galvanised shackles (I don't think stainless strong enough, unless you go grossly oversize, but many use stainless without issue). The main rode is all gal chain, 75M X 6MM and the spare is chain, 15M X 6MM, and nylon (3 ply) (38' X 7T Cat). We store the spare rode neatly coiled in a milk crate. The spare anchors are not stored attached to the rode - its too cumbersome to retrieve from a locker when joined. All three anchor are demountable and are held together with stainless nuts and bolts (which we grease). We did think of using Duralac but have found it unnecessary. After 8 years of using the anchors and the Spade is constructed from 5083, the Fortress from 6061 and the Excel from 5083 and 7075 we have no signs of alloy corrosion (despite uninformed comments from the armchair gurus). We did get corrosion, as Vyv mentions, on the first few links of the original chain (and they can simply be chopped off) but we got the same corrosion when we used steel anchors. The Fortress if not in use is stored assembled, the Spade and Excel, which ever is in the locker are stored in 2 parts (shank and fluke) as they are quick to assemble (even blindfold) and are easier to store in pieces. The Spade bolt was supplied with a plastic sleeve - I soon lost that.

We have separate lines for shore lines (which could be used for towing).

Don't worry.

Jonathan
 
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