Anchor swivels ... a safety tip

[TradewindSailor]

I have always been cautious about fitting swivels in the anchor rode. I don't like them and I think that they constitute a weak point. However I have the following tips:

1 If you fit a stainless steel unit ..... the galvanising on the chain and anchor in its vacinity will gavanically errode. So use a quality galvanised unit instead or be prepared to cut links off the chain periodically.

2 I often see the swivel connected directly to the anchor. In some designs of swivel this is madness as the swivel may have to take a high bending moment if the anchor shank is out of allignment with the pull on the chain .... If a 1 foot length of chain is used between the swivel and the anchor, the chances of high out-of-line loads are minimised.

3 Don't forget to seize the shackles properly and check them regularly.

On another note. I recently picked up a mooring in the Pacific. The lanyard was chain and nylon. The chain looked suspicious so I dived on it. The chain was over 50% corroded and there was daylight around the pin it was so corroded...... the pin was only held in with a single turn of seizing wire /forums/images/graemlins/shocked.gif The mooring owners were not concerned.

 

[vyv_cox]

<<< So use a quality galvanised unit instead or be prepared to cut links off the chain periodically. >>>

During testing for my articles in YM, we destructively tested a variety of stainless steel and galvanised connectors. Some of the galvanised items were intended for lifting and hoisting applications and some were apparently directed at the marine industry. In general, the stainless steel items were consistent and the best of them approached or even exceeded the strength of the appropriate chain.

Galvanised shackles intended for hoisting duties all made their very conservative SWL figure but several did not come near the strength of the chain. Shackles and other fittings that were not intended for hoisting were extremely variable, and in some cases highly disappointing. To quote myself - 'With most of the galvanised shackles in the bottom half of the range and all of the stainless ones in the top.'

Swivels are not intended for hoisting duties and can be expected to be variable in performance. Galvanised ones are frequently based upon a threaded joint that connects the two eyes together,

or sometimes upset like

This construction is inherently weak, especially the threaded one, and in no way can compare with the best stainless steel swivel construction, like this

My experience has been that, yes, the galvanising will be corroded galvanically on links adjacent to stainless steel swivels but the steel of the chain lasts very well and corrosion does not seem to be accelerated to any significant extent. A dab of Hammerite once per year is sufficient to keep the rust at bay.

One of the problems of using a large galvanised swivel is finding a shackle that will go through both it and the chain. Often, the only one that will has a large eye that will not pass through the bow roller. My personal solution to this problem is to use a Wichard 17/4 PH stainless shackle with a countersunk socket screw pin. This type performed particularly well in the tensile tests. However, it cannot be moused. Over the past season I tested Loctite on the screwed threads of both the shackles and swivel in my rode. I anchored for more than half the nights of last year. At the end of the season there was no sign that the Loctite had degraded to any extent and all screwed joints were tight.

I entirely agree about the possibility of lateral load on swivels. Here's my arrangement. The links between the anchor and swivel are 10 mm, the rest of the chain is 8 mm. The shackle is 10 mm.

 

[Marmalade]

As I've said before in these forums - we have (Marconi SC) more than 100 moorings laid and electrolytic corrosion - esp around shackle pins is by far the most common cause of failure. We've also found that swivels suffer when grit and sand get in the workings - far more likely when the swivel is on the ground. Not sure how you'd do this for an anchor set up, but for a mooring we put the swivel above the buoy or at worst just below it.

We put anodes in-line as part of our risers (chain through a zinc block c. 5" x 5" x 5")

Simon

 

[damo]

Vyv, why have a swivel at all on an anchor rode? I have never found that my (all chain) rode gets twisted, and prefer one less thing to go wrong in the system.

I can understand the need on a short mooring riser, but otherwise....?

 

[vyv_cox]

I think it depends upon the anchor, and maybe the rate of ascent. My Delta visibly rotates as it is being hauled, I'm estimating about once per 5 metres hauled. I have seen chain twisted in a gypsy and jammed tightly (not mine), and in my own case the chain sometimes twists in the gypsy but has never jammed badly. I have also seen an anchor twist so violently when it broke the surface that it knocked a large chunk of gelcoat from the bow of the boat, also not mine.

 

[Searush]

[ QUOTE ]
Vyv, why have a swivel at all on an anchor rode? I have never found that my (all chain) rode gets twisted, and prefer one less thing to go wrong in the system.

I can understand the need on a short mooring riser, but otherwise....?

[/ QUOTE ]

For most family cruisers that's fine, probably never anchored fro more than a day or two at most. BUT, a liveaboard may be anchored for several weeks waiting for weather/ supplies/ crew or whatever. That's when a swivel may be of benefit.

 

[Rob_Webb]

[ QUOTE ]
On another note. I recently picked up a mooring in the Pacific. The lanyard was chain and nylon. The chain looked suspicious so I dived on it. The chain was over 50% corroded and there was daylight around the pin it was so corroded...... the pin was only held in with a single turn of seizing wire /forums/images/graemlins/shocked.gif The mooring owners were not concerned.

[/ QUOTE ]

Which is a very good reason to not pick up moorings of unknown ownership/care. Out here, once you leave the marina, you live off your anchor. Even if there appears to be a vacant mooring in the vacinity of where you want to stop, nobody does it. If you have the right ground tackle and technique you should be able to rest more safely and comfortably on your own anchor than a random mooring of unknown reliability. Also prevents the risk of an irate owner turning up in the night and turfing you off!

 

[vyv_cox]

Here's a mooring picked up by a boat close to us in Mallorca. It only lasted a couple of hours and failed when the wind picked up slightly.

 

[TradewindSailor]

Thanks Rob .... let me clarify the situation before someone gets the idea that this was an abandoned dayboat mooring ...

This mooring is owned by the marina and is part of their med-moor system. I am paying for this mooring while I am away for a few weeks.

I usually anchor year round on a chain/nylon rode ..... although at the moment my boat is fitted with 200' of 10mm chain and a decent 50 lb claw type anchor .... a little like a Bruce.

As cruisers we tend to anchor a lot more than anyone else. Swivels that have hidden moving parts should have no place in our rodes ..... and I wont have a swivel on my rode at all. I've also never had a problem with twisted rode ..... probably because I allow the chain to untwist as it is coming up.

 

[DaveS]

[ QUOTE ]
I usually anchor year round on a chain/nylon rode ..... although at the moment my boat is fitted with 200' of 10mm chain and a decent 50 lb claw type anchor .... a little like a Bruce.

As cruisers we tend to anchor a lot more than anyone else. Swivels that have hidden moving parts should have no place in our rodes ..... and I wont have a swivel on my rode at all. I've also never had a problem with twisted rode ..... probably because I allow the chain to untwist as it is coming up.

[/ QUOTE ]

Well, there are always those who like to believe that what they currently do is the best of all possible options. You might be right. But, on the other hand, you might not. One of the great virtues of these forums is to expose preconceptions to critique.