Swinging Mooring

I have just recently replaced the swivel and shackles on my mooring chain. I was actually very lucky: when I took my boat out of the water, I thought to recover the rope which I tied to the chain to go to the bow. I always used a second rope from the boat to the bouy anyway. I couldn't undo the knot so I cut the rope, holding the chain in my left hand. I was just about to drop the chain back in the water when I realised that the end of the chain was not connected to the bouy rope! The swivel had parted. The only thing that kept the bouy in place was the bouy rope being wound round the boat rope. And if I had tied the rope to the swivel, and not the chain, the boat would have drifted off to who knows where....

In the process of replacing the swivel and shackles, I examined the chain. The links are thinning noticably at their ends. How long does a chain last in the water? For all I know, the chain has been there 10 years already, and might last another ten. Or rust through next season. How would I replace the chain - how to get the mooring weight up? or should I start form scratch and make a new one? If I do, how much weight (concrete?), how long of how heavy a chain?

The million dollar question is: How big is your boat?

Other crucial bits are how deep the water, how exposed the mooring? In general, you need 3 times the depth of water as the length of your mooring overall - from anchor to mooring buoy. At least the last 1/3 of this should be chain.

The rate of wear depends on a host of factors - how tough the chain is, the salinity of the water, how much movement your boat imparts to the chain to wear it etc.

I used to retrieve the entire mooring every year and replace the chain/shackles/swivels/rope/etc if need be - a good visual inspection and some experience built up over the years about what your boat does to the mooring anually helps.

There's lots of advice I could give about putting spot welds or copper wire on shackles to stop them working loose etc.

You might be best asking another local or 3 how they do their moorings. Hard to beat on the spot advice from someone experienced. A boat is a lot to leave to chance....

Last edited by x on Thu Nov 03, 2005 1:16 pm, edited 1 time in total.

Doh!

18 ft, 896 kg.

How exposed is your mooring? This will dictate the amount of deadweight your 'anchor' should have if you intend to use a concrete block or an old truck engine etc.

You might mention tidal range and whether your mooring is sea or estuarine. Also where in the country you moor your boat. There'd be a lot of difference between a mooring on the W coast and one in a sheltered creek on the E coast, for example. These factors will also dictate the strength of chain required. And don't just get any old swivel or shackles either. Try for stainless/galvanised with a marked rated working load. A good chandler will put you right there.

I kept a boat on a swinging mooring for 4 years - new boat in a marina. Its amazing how much better you feel when its windy! Worth the expense every time there is a windy night!

The boat is in the Liffey; limited movement, only a couple of feet of water under the boat at spring low. The new swivel and shackles are 1/2 inch galvanised.

Right. I'll post the answer (or my version of it - based on the following assumptions - any variation in these factors will render the result incorrect. Either way, I hereby absolve myself of any responsibility for anything. This is a guide only.)

So you have a fairly wind-sheltered mooring, wind should not exceed 80kts.

You are in a current that should not exceed 6 knots.

The water is reasonably dilute saline.

Tidal range for Liffey is (at a max) 5m, say allow 2m to accommodate flood/storm surge conditions, so 7m.

You said there was only a couple of feet under the boat at spring low.
I'd advise a slightly less shallow spot to allow for big springs and so forth.
But I'll assume 2 meters under the keel at LWS.

If any of the above is incorrect, please say.

So, from the bottom up to worst case HWS, say 9m.

Allow yourself 9m of chain shackled to the anchor - that's 1/3 of your overall mooring length. I'd use a fairly heavy chain for this - no relationship to the weight of the boat etc, it's just that if you use a real anchor, you don't want the boat to be able to tip it. It also wears slower. The last chain I used had about a 3/4 wall if memory serves.

Onto your chain attach the swivel and then splice (or tie & whip - or get an aluminium crimp and eye fitted if using a braided rope) on at least 18m of mooring rope - I'd allow another 3m just to make tying off handy. The rope should ideally be a non-buoant type if possible (I don't enjoy running over mooring lines in the dark). You could use the lighter chain in place of the rope if you wish, but it might be overkill on an 18ft boat. Your call.

Tie on a mark at the 18m mark - you should when mooring ideally have this point on the boat's anchor roller - you'll then know you have enough mooring in/out.

Tie your buoy on securely. At least if it comes off, with a non-buoant rope the line will sink and not present a hazard to other boaters.

When placing the anchor, you should know what the bottom composition is. There's a world of difference between rock/sand/mud/loose stones/etc.
I prefer sand where my anchor will gradually bed in. Also, take a GPS mark and a few sight lines, just in case the buoy and rope part company etc. Taking a few marks makes creeping for it a lot easier later on if the need arises.

As for the anchor itself: depends on the bottom - and to some extent then on what you want to use. If the bottom is hard and smooth, offering little in the way of a hook hold, then a large mass is perhaps preferable to any conventional anchor configuration.

If you are going for the hefty mass option, here's the question you have to ask. If the wind/current were acting in the same direction at the same time at their theoretical maxima, would the boat pull the anchor? Imagine you're heading into the stongest tide at the place you anchor, and the wind is right in you teeth. How hard would you be driving the boat just to stay still? If you then in calm conditions drove the boat that hard, if the anchor held, it would be at least sufficient. You might want to add a bit, just for the sake of a good night's sleep.

Theoretical masses/forces are all well and good, but the 2 ways I know for sure to make sure your mooring holds are 1. Did the last anchor hold -if, so, duplicate as closely as possible. 2. Make an educated guess - say 250kg - about 1/4 the weight of the boat, give or take - then keep an eye on if through a couple of bad days - then get over your anchor and check if it moved.

Like I said, local advice might help. And about the 1/2 inch galvanised shackles/swivels you mentioned. Bear in mind that the larger the wall size of the links, rings etc, the slower they will wear. I wouldn't use shackles or swivels without a rated load of at least the weight of the boat.

All moorings should be inspected with a fine tooth comb at least once a year. And remember to wire/weld those shackles......

Oh, and make sure at LWS that your boat cannot sit or drift into another boat, shipping channel, rock or other obstruction.

Wave action is always more pronounced in shallow water (ever wondered why waves break in shallow water???) which is one of the reasons I mentioned getting a deeper spot to moor - the boat takes a lot less of a beating on a bad day if your in fdeeper water.

Any more gems of wisdom I think of, I'll add to this post.

Excellent information! Now, how do you get 250kg to the mooring point....

Well, a workboat with a hi-ab arm and a winch and pulley would be good but most of us mere mortals don't have access to that sort of kit.

Dump the weight on the slip/beach at low tide. Put a double rope through the link on the weight to a pulley chained to a few barrels or something else that'll float it out when the tide come. Tow to desired spot and lower way, remove rope....

If it's that shalow where youwere moored, can you not attach to the original mooring?

ABSOLUTELY EXCELLENT ADVICE!!! only one thing to add copper wire to mouse the shackles is not a great idea the galvanic effect will rot the shackle in double quick time stainless is better. new thinking is not to use shackles at all (they are always the weak spot)mine is tied! don't ask how i don't know but it was proffessionally done this year.

While lying awake last night worrying about mooring your boat, it occurred to me that a big block of concrete or an old truck engine would be a fair bulk on the bottom and you said that at low water there was only a few feet of water. Make sure that whatever you use for an anchor, your boat cannot 'sit' on top of it at low water.

Good tip from raymondo about the stainless steel wire on the shackles - prompted me to mention that a spot weld should ideally be stainless as well - conventional welds rust at an awful rate. A dab or two of paint over the weld might help as well.

What I have seen done in the past is to take a ball pein hammer to the threads on the shackle pin where they project out of the shackle body and pein over the end of the pin so that it widens and so cannot work loose.

my mooring is a train wheel big and flat(6inches or so thick) so it really sucks to the bottom and incredably heavy at about 500lbs.

Please don't loose any sleep over my mooring! Clearly the way to go is stainless steel all the way, with a flat weight made out of lead. Maintenance free. Silver solder to lock the shackles.......

my mooring is a train wheel big and flat(6inches or so thick) so it really sucks to the bottom and incredably heavy at about 500lbs.

How did you shift that?

two skate boards and a plank.

ONLY JOKING!
no it was professionally laid by a barge with a crane arm on it.