Re-securing a Mooring

[PaulGS]

Maybe it's best to keep this hypothetical: you've decided to keep your boat on a swing mooring year round. It's regularly serviced with a half-ton Admiralty sinker holding it down. Despite this (fairly) unusually high winds cause it all to drag. Apart from the obvious need to lift and move back - what's the best (and/or cheapest) option for adding more weight (it's already carrying a good deal of chain so I'm thinking ground weight)? Rest assured I'm already consulting a local professional about this, but you lot are worth asking too.

 

[Stemar]

I've seen a heavy anchor that looks like a fisherman's anchor with one tine cut off. A couple of those with some heavy chain would help keep the sinker in place. Another possibility on a drying mooring would be to dig the sinker into the mud. My mooring has a railway wheel buried 4' into the Portsmouth mud, and it hasn't moved in 20 years. I'm not worried about corrosion because the mud is anaerobic.

 

[PaulGS]

I've seen a heavy anchor that looks like a fisherman's anchor with one tine cut off. A couple of those with some heavy chain would help keep the sinker in place. Another possibility on a drying mooring would be to dig the sinker into the mud. My mooring has a railway wheel buried 4' into the Portsmouth mud, and it hasn't moved in 20 years. I'm not worried about corrosion because the mud is anaerobic.

Yes, plenty of old anchors for sale. Secured to the sinker on a few metres of chain they could be a good way to go.

 

[C08]

It really depends on whether the mooring dries in which case ground anchors like oversized heavy plate danforth shape fabrications would do the trick in beefing up the system by digging them into position. If it does not dry then adding weight by sliding chain looped weights down the riser is another method ( I used old engine blocks cleaned up when I did this to my mooring). At half a ton that is not so heavy unless dug in and well buried so does need work. Good luck with whatever you do.

 

[Daydream believer]

What is an "Admiralty" sinker?

If the sinker is "regularly serviced" one assumes the Op has access to a craft capable of carrying anothet half ton sinker.
In the past we have taken one out with a loop of chain attached. Then having hoisted as much of the mooring chain up on to the launch as possible, at the top of high tide on slack water ,We hooked a temporary buoy to it to hold it straight with a line & slip knot to hold it straight while we did the next operation. The OP could use his boat & pull up a lot of mooring chain at mid tide so it pulls up the chain as the tide rises to get it nice & tight. We passed the loop round the mooring chain & dropped the sinker down the mooring chain as near to the other sinker as possible. Then undid the temporary buoy by releasing the slip knot.

This meant that the mooring chain went from the first sinker, through the loop of the second one & up. It was important to get the loop as near as possible to the first sinker to avoid making the mooring chain too short.
It was not considered a good option, but worked for a season in a couple of gales & was lifted with a tug at the end of the year. Then a larger concrete sinker provided the following year.

 

[Sandy]

Maybe it's best to keep this hypothetical: you've decided to keep your boat on a swing mooring year round. It's regularly serviced with a half-ton Admiralty sinker holding it down. Despite this (fairly) unusually high winds cause it all to drag. Apart from the obvious need to lift and move back - what's the best (and/or cheapest) option for adding more weight (it's already carrying a good deal of chain so I'm thinking ground weight)? Rest assured I'm already consulting a local professional about this, but you lot are worth asking too.

To misquote the film "Jaws", We need a bigger sinker.

 

[NormanS]

What size of boat are we talking about? How sheltered is the mooring? Is the "sinker" iron or concrete?
It's many years ago now, but I laid a mooring for a small sailing dinghy, using a 5cwt iron weight, which had been designed and used for mooring barrage balloons.
Obviously, anchors are much more efficient than sinkers. The mooring for my previous boat was three 150kg anchors laid out at 120° to each other, and connected to a central ring, to which the riser was connected. That was for a big boat. Much more trouble to rig, but definitely not going anywhere.

 

[Daydream believer]

Obviously, anchors are much more efficient than sinkers.

How do you work that out?
How do you get 3 anchors to set at 120 deg in deep water?

 

[neil_s]

I don't know what an Admiralty sinker looks like, but if your mooring drags, you need a better sinker - always supposing you have enough chain for the depth of water. I layed a drying mooring in 2006. On advice from the boatyard responsible for many moorings in the same creek, the sinker should be of a shallow truncated pyramid shape (see attached photo). Mine weighs 400 Kg, chain is 3 times the maximum depth and holds a 28 foot boat - although I don't overwinter on it. It has never dragged.

 

[Daydream believer]

I don't know what an Admiralty sinker looks like, but if your mooring drags, you need a better sinker - always supposing you have enough chain for the depth of water. I layed a drying mooring in 2006. On advice from the boatyard responsible for many moorings in the same creek, the sinker should be of a shallow truncated pyramid shape (see attached photo). Mine weighs 400 Kg, chain is 3 times the maximum depth and holds a 28 foot boat - although I don't overwinter on it. It has never dragged.

We make ours round so that the chain will not snag on the corners. If the tide scours a corner the chain can hook under the corner & it can flip..
For a mooring in 4-M, CD with 5 m of tide & 1 M of storm surge we allow 14.5M of mooring riser. 18 M for larger craft. There is no tide at the top . Only the effect of wind & waves & we make the sinkers much heavier. Our biggest is 2.5 T & is a scary operation with a 20 ft launch. But we prefer to keep to 1.5T which is easy enough.
Once the tide drops a bit the current builds but is not an issue for mooring rode length. I some areas the mud is thick & the sinker digs in after 3-4 weeks before we place a boat on it. Sometimes in other areas the bottom scours & a sinker sits on top though & that can cause issues on a small area of sea bed. That is why we do not like square sinkers

 

[zoidberg]

My mooring contractor friends at 'Diving Belle', by Saltash, would make up concrete sinkers, with embedded steel for extra weight, and would deploy them from their lifting barge. They actually dived on every mooring they looked after, producing an annual Condition Report and Recommendations - a service second to none, which was scuppered by new diving safety rules and regs.

In conversation, they reckoned the very best configuration for a mooring sinker was a large flat steel plate, well sunk into the mud, with very hefty chain from remaindered Saltash Ferry chains, then a riser chain to a mooring buoy. Regrettably, suitable flat steel plate was rarely available, so the next best thing was a steel wheel from a railway wagon.

 

[NormanS]

How do you work that out?
How do you get 3 anchors to set at 120 deg in deep water?

1. Doh.
2. We managed quite well in 14m.

 

[neil_s]

We make ours round so that the chain will not snag on the corners. If the tide scours a corner the chain can hook under the corner & it can flip..
For a mooring in 4-M, CD with 5 m of tide & 1 M of storm surge we allow 14.5M of mooring riser. 18 M for larger craft. There is no tide at the top . Only the effect of wind & waves & we make the sinkers much heavier. Our biggest is 2.5 T & is a scary operation with a 20 ft launch. But we prefer to keep to 1.5T which is easy enough.
Once the tide drops a bit the current builds but is not an issue for mooring rode length. I some areas the mud is thick & the sinker digs in after 3-4 weeks before we place a boat on it. Sometimes in other areas the bottom scours & a sinker sits on top though & that can cause issues on a small area of sea bed. That is why we do not like square sinkers

Thank you for that - interesting! I guess there is a mass - chain length trade off. Harbour authorities obviously prefer short chains so that they can fit more moorings in, but I find that the boat snatches badly when I have used them. I can walk to my mooring at low water springs so I check for scour although the sinker is now buried to the top surface. The shuttering I used was flat sheets of ply - quite an achievement to get a round truncated cone!

 

[Daydream believer]

1. Doh.
2. We managed quite well in 14m.

So how do you lay 3 anchors at once whilst connected & maintain symetry & what lengths are the connecting pieces/bridles between the anchors?

 

[NormanS]

So how do you lay 3 anchors at once whilst connected & maintain symetry & what lengths are the connecting pieces/bridles between the anchors?

By using doubled tripping lines on each anchor, so that the anchors can be pulled out towards their desired positions which are marked by small temporary buoys. From memory, I think each of the 35mm stud link ground chains were 15m. This was a mooring for a 60ft converted MFV, so we had two masts with substantial booms, and a powerful hydraulic winch/windlass.

 

[Daydream believer]

By using doubled tripping lines on each anchor, so that the anchors can be pulled out towards their desired positions which are marked by small temporary buoys. From memory, I think each of the 35mm stud link ground chains were 15m. This was a mooring for a 60ft converted MFV, so we had two masts with substantial booms, and a powerful hydraulic winch/windlass.

So basically it is just a one off & not a regular yacht mooring for the average yachtie, or MOBO owner

 

[andsarkit]

As with all anchors the aim is to dig into the substrate and not just weight. When I laid my own mooring I used a substantial stud link ground chain with a single fluke anchor at either end. The centre point is free to lift off the seabed in rough weather which avoids shock loads to the boat. I don't think the anchors saw any load once the ground chain buried into the mud.
I have also made a mooring of 2 RSJs welded into a cross which never dragged but the shock load bent the steel bollards on the boat in bad weather.
Any weight that is wide and low profile is going to bury faster and have a suction into the mud to resist dragging. A thin perimeter will tend to dig in as soon as it starts to move. Railway wheels could almost have been designed just for this purpose.

 

[afterpegassus]

So basically it is just a one off & not a regular yacht mooring for the average yachtie, or MOBO owner

On the contrary, it's a far from uncommon mooring in my part of the world, though for most up here moorings are an assembly of what is required and what is available.

 

[NormanS]

So basically it is just a one off & not a regular yacht mooring for the average yachtie, or MOBO owner

So?

 

[Halo]

Nobody has mentioned the advantages of a good sized flat bottom on the sinker. If the bottom is muddy or soft then the holding power of the stick y ness of s awesome.