Stainless swivel on mooring?

[boggybrn]

I am just about to lay a mooring, and have bought a (large) stainless steel swivel for it. The chain and shackles are plain mild steel.

I wnet for stainless because I read somehwere that they last much longer. However from recent posts I am worried that the differeny materials may cause accelerated corrosion.

Will it be OK, or should I get a galvanised one?

 

[philip_stevens]

No, no, no stainless steel with galvanised under water.

Get a galvanised swivel, or you may lose your boat. It won't take long for the mild steel chain to be eaten through by galvanic action.

 

[cardinal_mark]

I've been intrigued by this as I'm about to replace my anchor swivel; I see lots of boats with galvanised anchor chain and stainless swivels - is this also dodgy practice?

Mark

 

[Robin]

The anchor swivel is a different case because mostly it is out of the water whereas a mooring swivel is always submerged. I would never use a S/S swivel on a mooring, but as big a swivel as would fit. Big is good as the swivel is the weakest point of most moorings at least up to the strop(s), it will last longer too if bigger.

BTW be aware that some S/S anchor swivels have been found to fail (usually the jaws fracture on a side loading) and there are those wise ones who would never use them. We DO use one but did actually change to a beefier version (more metal in the jaw area) having seen pics of some of those that broke. I have to say we never had a problem with the original one and we do anchor often, but the pics I saw came I think from long term liveaboards at anchor for longer periods in worse conditions.

 

[cardinal_mark]

Thnaks for that. I was looking at the Kong ones which came out top in the YM test (last month?) but seem to be at least 3 X the price of anything else on the market!

Cheers

Mark

 

[Bodach na mara]

Round here we are not big on swivels in moorings at all. They are a point of weakness.

 

[Guest]

Oh Dear .... it will start another debate ... BUT >

Keep all metals the same throughout ....

Galvanized

or black metal

or mild

But personally - I wouldn't touch Stainless steel - as it gives no indication of failing ... all the others above will waste and corrode visually giving you good warning of time to replace.

It's the reason for galvanized cable on keel lifts etc. as well.

 

[Guest]

Most moorings I have seen .... including the recc'd ones by such as Langstone Hbr. authorities etc. have the swivel at join of ground chain to riser chain. Therefore it rarely ever gets above water - except on a drying one maybe. Of course there are those that like a swivel at top of riser where buoy attaches ... but that's an additional.

I have the Langstone Hbr board spocs in my archive somewhere if wanted ....

Don't mix metals - simple fact. QED

 

[Robin]

We only used to use one swivel at the top of the riser from the ground chains (Poole), the strops were attached to this with or without a big buoy (no real depth) and the swivel could be inspected easily if needs be. However with no swivel and strong tide flow the chain could twist and shorten in rapid order, pulling the boat bow down with it, it has been known! Otherwise I would agree.

BTW what I really don't trust are swivels in buoys where the bar passes through to another (swivel) eye on top. Much better is to attach a plain buoy to the normal (and big) swivel and take the on board strop(s) from this point as well, with a pick-up buoy attached. This way all the big buoy does is support the weight of the riser chain, all mooring loads are continuous down the strop/swivel/rise/groundchain route. With the strops section now the likely weakest link I favoured chain at least to over the bow roller to avoid chafe.

 

[boggybrn]

Thanks for the advice. I'll be shopping for a galvanised swivel this weekend...

One further question: I was going to put the swivel where the riser joins the ground chain. Would it work equally well between the riser and strop / buoy?

 

[Robin]

[ QUOTE ]
Most moorings I have seen .... including the recc'd ones by such as Langstone Hbr. authorities etc. have the swivel at join of ground chain to riser chain. Therefore it rarely ever gets above water - except on a drying one maybe. Of course there are those that like a swivel at top of riser where buoy attaches ... but that's an additional.


[/ QUOTE ]

I was a mooring party team leader for years at my then club in Poole and we laid all our own moorings, both singles and in trots of up to 6. All were lifted and inspected annually by club members who were required to give a weekend in winter to help. We used very heavy ground chains, about 1" thick links (ex Sandbanks chain ferry or ex mine lift chains) between huge Danforth style anchors (about 150lb). The riser chains were I think 5/8" or 3/4" and shackled with two big shackles directly onto the ground chains, with a doubler of old chain across 'just in case'. The swivels were only ever used at the top of the riser chain, just below the surface and therefore easily inspected from on board or from the mooring launch. Our moorings were on the east side of Poole Harbour and exposed directly to the full fetch across the harbour in a SW wind. Owners were responsible for their own chain or rope strops above the swivels and we never lost a boat due to the club part of the system breaking, even in the famed Michael Fish Hurricane October 1987! The same could not be said of other moorings professional or otherwise in the harbour. Being inspected and serviced by club members meant that 'if in doubt, throw it out' applied very much, these were OUR moorings we were dealing with!

 

[Robin]

[ QUOTE ]
One further question: I was going to put the swivel where the riser joins the ground chain. Would it work equally well between the riser and strop / buoy?

[/ QUOTE ]

See another reply above, but yes that would be my preferred choice, others say at the ground chain to riser join. We used to shackle the riser to the centre of ground chain between 2 big anchors and add a second shackle a foot or so along the ground chain (riser laying along the ground chain), alternatively we would use an old discarded bit of riser chain as an extra link from the ground chain to the riser, doubling up being the idea. We always used galvanised or plain fence wire about 1/8th inch diameter as the mousing wire and always put TWO pieces on, but we were using very large shackles to match the heavy chains we used and there was room for two. We never found un-moused shackles on re-inspection a year on doing this, but when one year monel was used we found several, we think maybe they simply wore through on the seabed.

My personal preference is for a big soft lobster pot type fender buoy as the support buoy, attached to the top of the swivel as is the strop, with a line from the strop to a small pick-up buoy. The big buoy is then non load bearing, it just holds the weight of the length of riser at HW depth. I preferred this as the wind against tide conditions in Poole meant the boat would ride up on the buoy, so soft and gentle was best and I hated buoys with metal top eyes as well as mistrusted them with bits hidden in the buoy. All IMHO of course and different harbours will have different needs and solutions.

 

[tedbarnes]

If you put the swivel at the bottom of the riser and the riser is longer than the water depth, it may jam up.

If you do use a stainless swivel, put it above the water to avoid electrolytic action.

 

[Guest]

Re: Stainless swivel on mooring? ----- Poole bridle type OK

Thats a different ball game and swivel should be higher up the system.

My fault for not clarifying that I refer to the single block type mooring with single ground chain .... not divided of as a bridle style.

The bridle style I have helped lay - had a swivel halfway up the riser ..... but then again as long as it meets or exceeds Harbour req'ts - then there's no problem.
On another note about moorings :

It is surprising that even a club I belonged to had cm'ttee meetings to decide the "upgrade" of moorings to get more in ... When they finally passed it to a Club Meeting for us to comment / vote - they had ignored one vital matter - they had contravened HM specs and were going to a) have scope of ground + riser too short, b) moorings were going to be too close together. The Cmttee members who had pushed for this work - may I suggest that they were also pushing for club boat size limit to be relaxed ... bristled when a copy of HM specs were placed for all to see ...............

The moral of that little story - check with HM about specs for moorings req'd - if you don't and your boat breaks free - I had the unfortunate job of surveying a constructive loss for claim ... and found out during the survey that his mooring was not quite up to spec - he had followed an "experts" advise locally ... I advised him. I did not comment in the report - I am working for him the claimant ... the Ins. co themselves investigated and found out - result he lost his claim for loss as a result of mooring failure.

 

[Robin]

Re: Stainless swivel on mooring? ----- Poole bridle type OK

Single block moorings and sinkers etc are not up to Poole conditions hence we used anchors. In places the bottom is hard sand in others deep mud. Although a 'club' operation the laying of moorings was well thought out if not as well from a HSE point of view (different story!). The club has a proper mooring barge with now a diesel powered winch but when I did it it was hand cranked job but we did have 6 people working, one in the launch and 5 labourers on the barge... We used far heavier tackle than other clubs or mooring contractors locally and had an excellent insurance reputation, the biggest risk was from other boats breaking adrift elsewhere as we were on the lee shore side of the blows. I think the club hold a licence related to mooring 'area' rather than number, or maybe a combination of both, however it is academic now as we belong to a different club these days and have a marina berth.

 

[William_H]

Re: Stainless swivel on mooring? ----- Poole bridle type OK

Our local water authority 5 years back bought in licensing for mooring in Swan/Canning Rivers. To sweeten the new tax they provided and insisted on being used, a large yellow buoy with pin up the middle and integral Stainless Steel swivel. The pendant to the boat was intended to be connected to the top, the chain to the bottom.
The SS certainly accelerated the wear on the iron shackle attached to it but this is manageble being at the top it is easy to inspect.
Some (a handfull) have failed in the SS pin due to inclusions or some form of crevice corrosion but mostly the several thousanf are still in service. However the authority have deleted the ring from the top so that the buoy can not now be part of load path for mooring the boat. Mine has used the SS in the load path for 5 years but I do worry a bit. Only a fraction of the thousands bypass the SS inn the buoy.
The buoys are an eyesore (the usual self supplied tiny white ones were less obvious. they are too heavy to lift onto the deck so get fouled easily and thye bump the hull dammaging the gel coat. My little winge....

My conclusions are that while the SS is not good it is not as bad as might be suggested especially if it is a large SS swivel (grossly over sized) and you inspect the iron shackles attached on a more frequent basis. (But you must inspect them anyway)
Lastly yes swivels are vital although I don't think it matters whether they are fitted at the top or bottom of the riser.

olewill.............. now 22 years on self maintaiined swing mooring.

 

[Trevor_swfyc]

The easy way to avoid loss of metal from the shackle connected to the stainless swivel is to fit a zinc anode. I use my old pear anodes first drill out one end of the anodes iron bar so that the shackle pin will pass through it and the risers first link, bolt the other end to the riser chain. This not only protects the shackle but also the lower links in the riser.

Trevor