Dropping mooring

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smithy

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Just how much difference does it make to to the life of mooring chains if you don't drop them? At the moment we get about four years. The contractor usually does this but we are looking at ways of cutting costs.
The trot moorings are a few metres of riser chain then mutiplat with a soft eye, the supporting buoy is just tied on. If we sink these ourselves do they need a weight on them to stop the multiplat being dragged about the bottom? Intend marking with the pick up buoy and some polyprop.
 
The bit of chain that is subject to most wear, when there's no boat on the mooring, is the bit that just touches the bottom. With the tide going up and down, and waves if any, the length equivalent to the tidal range is constantly moving in the mud or sand of the bottom. It acts like grinding paste. So yes, there is a lot to be gained by dropping the chain to the bottom.

With mine, I heave it up, and remove the multiplait, then attach a messenger line with a buoy, to the chain, and lower it to the bottom. It means that the chain is not moving at all, and indeed tends to get covered by the mud, which helps to protect it.

In your case it depends on whether the riser is long enough to come to the surface. If you leave the multiplait on, and just drop the lot, with a pick-up buoy on it, I suppose there might be some wear on the multiplait, but it would still be better for the chain.
 
Mooring wear is primarily in the chain links where each link grinds on the next link. So inside the oval shape at each end of the oval. This is caused by load on the chain and movement which grinds away the protective galvanising then rust layer. Grinding load will be much less with no boat attached however there will still be movement on the faying surfaces so best to drop the chain down on a rope so there is minimum chain movement.
Can't suggest however just how much difference it will make btween dropping it and not dropping it. Of thousands of swing moorings on Swan River I have never heard of anyone dropping the mooring to the bottom as is apparently done in UK.
What is really important is to inspect the chain and shackles for wear each season. If there is any stainless steel compnent contacting iron this will be a really critical wear point. good luck olewill
 
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I have worked on a lot of half tide moorings, the topchain undoubtedly corrodes much faster than the much heavier bottom chain, I change my topchain every 3 years or so.

Pay particular attention to swivels, almost always the ' weakest link ' which fails.

After 37 years on the same mooring ( which I laid and 20 years ago re-laid a new sinker on ) I wouldn't dream of having rope anywhere in the equation, chafe is a big problem - when I had a deep water mooring for another boat I mistakenly used two rope strops in plastic tubing - I found these looped around the permanently afloat buoy and were cut to pieces by the razor sharp barnacles under the buoy.

A friend had his boat destroyed when the rope strop chafed through; it had been a series of gales and he wasn't able to get out there in a dinghy to check her.

All chain every time !
 
I can't tie the messenger rope to the chain as its too far down, it would have to be tied to the multiplat. What I'm trying to determine is whether I need to weight this to stop the pick up dragging the multiplat around the bottom. The set up of the trot will remain the same as it is "professionally laid and maintaied". We are just trying looking at ways of reducing costs.
 
I must admit I've never thought about doing this although it makes sense. I have a drying mooring with chain riser and strop. It's now empty for the winter but is still lifting and dropping every tide. What do others do in winter?
 
ghostlymoron said:
I must admit I've never thought about doing this although it makes sense. I have a drying mooring with chain riser and strop. It's now empty for the winter but is still lifting and dropping every tide. What do others do in winter?
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My insurers want my mooring professionally maintained, so I don't fiddle with it myself. I've just paid £200 for a new riser, after five years. I can live with that.
 
At my club with half tide drying moorings some people take off the topchain and just put a bit of line and a grotty buoy or plastic can on for the winter ( must have the number marked on it though or the world will stop turning according to the harbour conservancy ) - most people inc me don't bother as a new topchain is around £30.00 and lasts 3+ years, is moused on with monel wire and it's a pain going out on the slightly dangerous mud in winter cold and rain.
 
I think it's something like the top 6 or so meters of water that contains more oxygen so will help rust develop but again the most ware is in movement of the links, my mooring is full chain so I tie a small bhoy to the end of the chain then a riser rope with a marker bhoy, all goes well over winter and we pull it up at low tide with the small riser rope and attach the main bhoy and worse case of the marker bhoy coming away there is the small bhoy floating just off the sea bed for a diver to find easily, wrap some chain around the multiplat aye which should hold it down
 
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What do semi-submersible oil exploration platforms do with their huge anchor chains when they are not required?
Answer, they drop them to the sea bed.
 
My understanding is that moor chains with no boat on them wear more quickly. So dropping them reduces the free movement and extends the life of the chain.

Dropping seems to make sense, especially if a club has many moorings. It can produce a significant saving. How much will it save for just one owners mooring. Probably not that much.

However, this does not answer the op's question about his rope strop. Chaff would be the enemy and dropping it may or may not reduce this. I'd question how you'd check the chaff if it was too deep to see even at low water?

Have you tried pulling it up at low water springs to have a look?

If you can't do that and it did chaff how would you replace it? If it is looped through the top chain link you'd have some options, but more problematic if tied or spliced.

Rough shelled critters might well be a problem in this regard.

Economising on mooring equipment may be penny wise and pound foolish
 
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As already stated, the greatest erosion occurs on the upper section of the chain in the warmer and more oxygenated water. One life-extending option is to turn the chain after a while to even this out. Personal experience of a drying mooring confirms this. The most stable location for the chain is in the mud where only anaerobic activity can occur which has minimal impact.
 
Keith-i said:
As already stated, the greatest erosion occurs on the upper section of the chain in the warmer and more oxygenated water. One life-extending option is to turn the chain after a while to even this out. Personal experience of a drying mooring confirms this. The most stable location for the chain is in the mud where only anaerobic activity can occur which has minimal impact.
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I don't think I would agree with that . My mooring chain definitely wears most in the part that joggles about on the bottom, over a length that corresponds with the tidal range. If you are on a drying mooring that will be the top few metres, but not otherwise.
 
The contractor billed us for £60 to drop each mooring and more to lift them. I thought there must be more to it than untying the supporting buoy and tying on a messenger line. Unless he raises them on the hoist to get at the top of the chain and ties the messenger here. There is no way we can do this without lifting gear.
When they are checking them most of the mooring is pulled onto the boat and jet hosed, a diver is sent along the trot chain to check it.
 
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