Shackle for Fortress Anchor

Snoopy463

Snoopy463

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Apologies if this has been done to death since antiquity, but this concerns fixing an aluminium anchor to galvanised chain. Just had a flyer from Jimmy Green warning of the use of stainless steel shackles between galvanised anchors and galvanised chain. My current set up has a stainless shackle connecting my aluminium anchor to galvanised chain. Should I be using a galvanised shackle?
 
I'd use a galvanised shackle because it will be stronger than a stainless shackle - unless the stainless shackle costs an inordinate amount of money. If your anchor is a actual Fortress, rather than a Guardian, then you can use a bow shackle with the bow through the shank slot. The Guardian has a circular hole for the shackle and you have to attach using the pin through the hole. You can use the bow through the hole but the shackle is then so small it will be too small, and insufficiently strong. Try to ensure the shackle fits both anchor and chain otherwise you will need 2 shackles and have 2 clevis pins to seize.

If you worry about corrosion then consider how the anchor is assembled - aluminium anchor, stainless nuts and bolts. I'd take your anchor apart and liberally coat the nuts and bolts with Duralac as otherwise you will develop corrosion and it will be impossible to disassemble (I speak from experience :( ).

We store our Fortress assembled with the galvanised shackles attached (the spare rode is kept in a milk crate, 15m gal chain 40m rope) - I have seen no sign of corrosion of shackle nor at the shackle hole, after a number of years)

Jonathan
 
I had a problem with a stainless shackle attached to galvanised chain. The boat was at anchor for a month. The seabed in that particular location was mud, which I suspect from the prevalence of peat all around, was very acidic.
The galvanising on the four or five links around the shackle was destroyed.
 
Loss of galvanising from a few links is the worst galvanic effect I have seen after ten years with a stainless shackle between galvanised anchor and chain. My Fortress has a stainless shackle with galvanised chain with no effects at all, although as a kedge it does not spend a lot of time immersed.
 
There is unlikely to be much interaction between a stainless steel shackle and a galvanised anchor, but a stainless shackle on an aluminium anchor is a potential concern, especially a Fortress anchor that is expensive, as a secondary anchor may also be left unused sitting in a wet locker for long periods.

A galvanised shackle reverses the corrosion potential. The shackle will corrode (more correctly the zinc coating on the shackle) before the aluminium anchor. Thus the shackle actually provides some corrosion protection for the anchor rather than the other way around so is a better choice than a stainless steel shackle.

Keep in mind any dissimilar metal corrosion potential depends on the presence of an electrolyte (sea water). If you keep your Fortress in a locker for occasional use, as many users do, the limited sea water exposure is unlikely to cause any problems but a galvanised shackle is safer and provides some peace of mind if the storage location becomes damp.

Fortress offer a lifetime, no questions asked, replacement warranty (for a small delivery cost). The guarantee is more of an insurance policy that will replace any damaged component at no charge even if the fault is user error, but I still think a galvanised shackle is a better match for the aluminium construction.
 
I fear this is one of those cases in which a bit of theoretical knowledge is outweighed by practical experience. I think I bought my Fortress in 1999, since when it has always had a stainless steel shackle (a Wichard 17/4PH countersunk screw type) bought at the same time, attaching it to galvanised steel chain. The anchor has been used extensively and stored in our stern locker when not in the water. There is not the slightest evidence of corrosion at the hole in which the shackle sits, nor anwhere else.

noelex said:
There is unlikely to be much interaction between a stainless steel shackle and a galvanised anchor, but a stainless shackle on an aluminium anchor is a potential concern, especially a Fortress anchor that is expensive, as a secondary anchor may also be left unused sitting in a wet locker for long periods.

A galvanised shackle reverses the corrosion potential. The shackle will corrode (more correctly the zinc coating on the shackle) before the aluminium anchor. Thus the shackle actually provides some corrosion protection for the anchor rather than the other way around so is a better choice than a stainless steel shackle.

Keep in mind any dissimilar metal corrosion potential depends on the presence of an electrolyte (sea water). If you keep your Fortress in a locker for occasional use, as many users do, the limited sea water exposure is unlikely to cause any problems but a galvanised shackle is safer and provides some peace of mind if the storage location becomes damp.

Fortress offer a lifetime, no questions asked, replacement warranty (for a small delivery cost). The guarantee is more of an insurance policy that will replace any damaged component at no charge even if the fault is user error, but I still think a galvanised shackle is a better match for the aluminium construction.
Click to expand...
 
vyv_cox said:
I fear this is one of those cases in which a bit of theoretical knowledge is outweighed by practical experience.
Click to expand...

I have owned and cruised full time on aluminium boats for for well over a decade and owned an aluminium Fortress and Guardian for longer than this, so I would argue that this is practical rather than theoretical knowledge.

Aluminium is a fantastic marine construction material, but it needs to be managed correctly. Treat it right and it has many positive properties, but connecting aluminium and stainless steel needs care.

This issue is simply avoided by using a galvanised rather than a stainless steel shackle with an aluminium anchor. Easy, cheap and safer.

Note I did say :
noelex said:
Keep in mind any dissimilar metal corrosion potential depends on the presence of an electrolyte (sea water). If you keep your Fortress in a locker for occasional use, as many users do, the limited sea water exposure is unlikely to cause any problems but a galvanised shackle is safer and provides some peace of mind if the storage location becomes damp
Click to expand...
 
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Thank you all for the above. It is a genuine Fortress and its use is mainly for anchoring off in the Bristol Channel while waiting for the tide to rise. I rarely use it for overnight anchoring. I have had the anchor for three seasons and one link of the chain is mildly rusted with no discernible corrosion to the anchor shank. I shall probably keep the existing arrangement with the stainless shackle but will splash the Duralac about the anchor as Neeves suggests.
 
Don't get excited about there being corrosion at the first link, or first few links of your chain. This happens if you use a steel, galvanised anchor, a galvanised shackle and galvanised chain. I don't pretend to know enough about corrosion to pass a comment, I rely on Vyv, on why (but I'll have a go). The components are all based on steels of different chemistries and the chain is the weak link (in the corrosion story) so the first few links corrode.

Now that was easy!

At some point when the rust is starting to annoy you cut the few links off. Cutting a few links off is hardly going to impact the length of chain you carry.

We normally do this every 3 or 4 years - but since we have started to use high tensile chain with an Armorgalv coating the issue has, temporarily, disappeared maybe because the chain and shank are similar chemistries, both are a G80 (though unlikely to be the exact same chemistry). If you have a G209a Crosby shackle it coincidentally is classed a G80 shackle.

I prefer all our shackles to be G80 shackles - then you can mix and match. We don't have any 3/8th" 1t WLL only 3/8th" 2t WLL.

When you cut off the links make sure your anchor is still aligned with the links at the gypsy - or your anchor will always arrive sideways or upside down.

Jonathan
 
For those that do not know

You can source Crosby G209a shackles from Tecni, a UK company. I have bought mine from them (note my location) - Tecni seem to find the cheapest way of getting them to you. There must be other UK sources, but no-one (that I recall) has ever volunteered their name.

Make sure you buy the correct shackles - if the 3/8th"shackle does not have a WLL of 2t - you have the wrong quality. I've tested lots of shackles - Crosby's have been consistently the best, from CMP Titan's Black pin, Peerless Blue Pin and nefarious samples from local hardware stores. Campbell Orange pin shackles are also very good - but AFAIK unavailable in the UK. Van Beest do not make this quality in small sizes.

I'm to test some from Taiwan, Yoke (that look interesting) and a couple of Chinese suppliers.

Jonathan
 
It needs to be remembered that the galvanic series in seawater mostly refers to pure metals, and especially so for aluminium. The galvanic voltage of aluminium can be modified considerably by alloying, e.g. the voltage of aluminium anodes is more anodic than zinc and the corrosion resistant 5xxx series is very much more noble than the pure 1xxx version.

I assume that Fortress use a 5xxx or something similar, meaning that the galvanic voltage between their shanks and stainless steel shackles is probably not that great. Conversely, the difference between the shank and zinc galvanizing will be greater than might be expected.
 
At the back of my mind I think they use a 6xxx alloy as it is easier to extrude, (6063?). But it is a long time ago when I was told.

But I certainly stand to be corrected

Jonathan
 
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