Mushroom Anchor

[Johnjo]

Noticed there is one in the forsale column,
Showing my ignorance now but i have never heard of it before!
Obviously some kind of a static anchor, but how do they work ? the name mushroom possibly
suggests the shape and with that suction,
Can anyone enlighten me? No sorry I don't want to buy it!..

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[ccscott49]

It does look just like a mushroom, with the chain connected to the "stalk" You bury it I think, or the action of the tide buries it for you, they work anyway!!

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[Johnjo]

Oh a shaped sinker !
thought it was somekind of anchor that was pulled in !.....
thanks Colin all clear now.


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[Moose]

Looks like this:

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Moose

 

[ccscott49]

I always thought that was an ashtray! Now I know why it was so bloody heavy to empty!

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[Gunfleet]

Also known as a 'plug' they are used on the Norfolk broads. I expect you could use them anywhere similar. They also use an anchor called a 'rond' on the banks of the Broads. I've never seen one anywhere else, though YMMV

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[Jacket]

They're used (or at least were used- don't know if they still are) a lot for large ship moorings. I believe that they were originally developed for the RN.

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[Gunfleet]

RN and the mushroom anchor

Very interesting. I think we would be describing different sized anchors, though. The Broads one is max 20 lbs. Knowing the RN they will go for something bigger than would fit in the 'For sale under £200' column here! ;-)

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[Sybarite]

They are used I believe for mooring oil rigs.

John

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[ccscott49]

Sorry, no they aren't. We use mainly for jack ups and semi's admiralty halls pattern or sometimes bruce, although they always say "the bruce was developed for anchoring north sea oilrigs", I've never personally seen one out here and I've been around a while, H00 would know.

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[Gunfleet]

Colin what on earth are 'jack ups' and 'semis'?

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[ccscott49]

Jack up rigs, are those which float with very long "legs" which jack down to the seabed and jack the rig up in the air, becoming a temporary fixed platform. When the well(s) are finished, the rig simply jacks down, until it floats again and then jacks the legs right up and moves to a new location. Semi's are floating rigs, with large ballast tanks, when they reach a location to drill, they set out an anchor pattern, often eight or more anchors, then they flood the ballast, until the rig partially sinks, becoming "Semi submersible" and more stable than say a ship, there is another type of semi, called a dynamic positioned semi, which partially sinks itself, but doesn't have anchors, it has giant thrusters, (props in shrouds) which swivel, which keep the rig in a predetermined spot, by GPS and wellhead transponders linked to a computer, then the thrusters. These are normally used in very deep water and for wildcatting.

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[Gunfleet]

Thanks

You learn something every day
John

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[Twister_Ken]

dynamic positioned semi

Wow.

How far off-centre can they get? Or put another way, how bendy is drilling pipe?

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[ccscott49]

Re: dynamic positioned semi

It's not the drill pipoe you need to worry about, thats really bendy, or I couldn't do what I do, it's the riser! Which is large diameter pipe, from the blowout preventers and wellhead template on the sea bed, to the rig, it's not very bendy, but does have giant sliding ball joints. The rig normally doesn't move more than 10-20 feet sideways, in normal weather and in a blow can "heave" about 30-40 feet, when they weather gets too bad, we simply hang off the drill string at the seabed and disconnect the riser at the seabed and move the rig until the weather calms down.

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[Twister_Ken]

Re: dynamic positioned semi

Cor! 'Sgood innit?

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[Johnjo]

Re: dynamic positioned semi

Wonder how long before a mini version of this becomes available for yachts !
Just imagine no more anchoring or worrying about dragging!.....

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[ccscott49]

Re: dynamic positioned semi

Bloody noisy though with an engine thundering it's guts out all night! We also have dynamic positioned ships and diving tenders. All good fun!

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[fluffc]

I had a lecturer in Scotland who claimed to work with Bruce, who developed the bruce anchor. He had come up with a mad cap scheme to make an area of calm water around oil rigs, so that work could be safely carried out. This scheme required a large inflatable donut shape to surround the rig. On thinking through and developing the idea, the problem of anchoring was encountered.

Various anchors were tried out - particularly for use in the shallow and soft-bedded north sea. As a result the Bruce anchor was developed. The donut widget disappeared as interest rapidly grew in the design of the Bruce - viz. no moving parts etc.

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[TheBoatman]

I seem to remember them trying one of those floating donut thingies out around the Tory Canyon, but it blew away with the first wave (and it wasn't that rough) can't see it working out in the N.Sea in a bit of a blow?

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