Stabilisers - at anchor - how do they work?

[Gludy]

I know that normal hydraulic stabilisers work like a pair of plane wings - they rotate on their axis dipping or raising like a dive or a climb in a plane. The faster you go the more effect they have as they rely on the velocity of the water over their surface to generate the lift or dive - underwater wings.

Gyroscopes tell the software what is happening and can actually learn the wave situation and anticipate the motion so that it learns the sea pattern.

These work I know from trying them out - you can go into a sharp turn at 25 knots and will not bank at all. They reuce rolling at sea a great deal.

Ok with that preamble out of the way, there is another use for stabilisers - at anchor. These stabilisers must act in a different axis and in effect flap up or down. I do not know, I am guessing - but this seems to be a very limited option - I mean once you have flapped down you have to get up again and this may not be convenient - you appear to also need a large surface area to have any effect.

I have used witches hats - lots of them to help dampen a boat at anchor and I cannot see even a largish pair of stabilisers being more effective than that. My guess is that they must use the same stabilisers but operate them in another axis. So they are not very large.

I am curious because at present I cannot see them being very effective. If they consisted of a circle of cup like ends on a wheel that could roate either way and hence create a lift or a dive type motion 0 a sort of underater windmill - they may work but as wings, I just cannot see it.

I have tied to find out how these at anchor systems work - google came up with nowt - does anyone out there know?

 

[BrendanS]

Re: Satblisers - at anchor - how do they work?

I suspect the most effective methods of damping roll at anchor are the gyroscope systems, which google will throw up a few examples. Fin stabilisers at anchor are not going to be as effective as when moving for obvious reasons

 

[Gludy]

Re: Satblisers - at anchor - how do they work?

But the gyroscopes control all stabilsers that does not tell us how they apply power to the water to keep the boat still and prevent rolling that can only be done with physical force and its how that is applied that fascinates me.

 

[BrendanS]

Re: Satblisers - at anchor - how do they work?

We seem to be talking at odds here. A gyroscopic system which stabilises a boat needs no outside devices like fins. The gyroscope stabilises the boat. Not the piddly little things which are used for navigation. The mass of the gyroscope needs to be in proportion to the size of the boat

If you don't think a gyroscope cannot stabilise a boat, try the rotating chair test. Run up a decent size gyroscope - need a kilogram or more mass - with a drill. Hold the Gyroscope in your hands, then get someone to try and turn your swivel chair. Simplest demonstration possible

 

[Gludy]

Re: Satblisers - at anchor - how do they work?

Aaaahhhhh.. I understand what you mean now.

But surely that sort of thing, to make a difference when at anchor would have to be enourmous. In effect you are changing the CG of the boat to compensate for movement.

Are you telling me that you think this is how they do it or you know this is how they do it?

So on the new Ferreti, they have a massive gyro?

I really do not know but my feeling for it is that it would have to be too bulky and too much space would be sacrificed.

 

[JKay]

Re: Satblisers - at anchor - how do they work?

O B Can O B Remember your motorcycle thread earlier o'wise one
goodnight Joe /forums/images/graemlins/wink.gif

 

[Gludy]

Re: Satblisers - at anchor - how do they work?

Bredan
This is, I think, what you mean
http://faraday.physics.uiowa.edu/mech/1Q50.72.htm

Still seems it would have to be big to have any effect but fascinating.

 

[Gludy]

Re: Satblisers - at anchor - how do they work?

You were right!

Read this:-
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Mitsubishi Heavy Industries, Ltd. (MHI) has signed an agreement with Italian luxury yacht builder Ferretti Group to supply and install 140 stabilization systems. The contract is worth approximately YEN 500M (US$4.5M) with the systems to be delivered over a 2 year timespan. The Anti-Rolling Gyro (ARG) stabilisation system employs satelite-linked 'control moment gyro' (CMG) technology to minimise excessive rolling movement and thereby increase crew and passenger comfort.

Before signing the agreement, the Ferretti Group Engineering department in cooperation with MHI's team tested the effectiveness of the ARG system in comparison to a conventional fin stabilizer. The results convinced the Ferretti Group of the benefits offered by this innovative system.

In Japan, MHI has already sold 220 ARG systems for public-sector, commercial and private use, including cruise ships, sightseeing boats, fishing boats, pleasure craft and patrol boats.
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searching with the gyro bit in the search did it!

 

[Gludy]

Re: Satblisers - at anchor - how do they work?

more
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ARG (Anti Rolling Gyro System) ensures absolute comfort which is the new frontier of Ferretti Yachts which will be installing the anti-rolling gyro system ARG on its craft. This is exclusive on the European market and represents an important innovation in yacht technology, with over 50% reduction in the rolling caused by waves.

The ARG stabilisation system was developed for Ferretti Group by Mitsubishi Heavy Industries. It comprises of a complex gyroscope within a chassis supported by shock absorbers, which enables the craft to naturally reduce the rolling effect with a rotation that opposes the movement of the waves.

Powered by electricity, the Ferretti Yachts Anti Rolling Gyro System generates a counter-movement that absorbs the kinetic energy of the craft that is hit by the movement of waves. The same system is used in aerospace to keep satellites in their correct orbit position.

As the rolling itself starts up the ARG, the system does not require controls. It simply has to be switched on or switched off. Spending time on board a Ferretti Yachts motor yacht is now even more comfortable, both when cruising and when at anchor or moored in the port.
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My questions answered.. thank you Brendan

 

[BrendanS]

Re: Satblisers - at anchor - how do they work?

You'll have to remind me. I don't participate in many bike threads

 

[JKay]

Re: Satblisers - at anchor - how do they work?

the medium eg water / land is not relavent the gyroscopic effect still effects wot it's effecting(SO THERE) /forums/images/graemlins/confused.gif

 

[BrendanS]

Re: Satblisers - at anchor - how do they work?

I don't read all the threads here for no purpose, not to mention all the boating forums I frequent. The Gyroscope thread I think was instigated by jfm.

 

[trev]

Re: Satblisers - at anchor - how do they work?

I guess its all down to the forces of precession - very clever stuff.
Its good to find an informative and intelligent boating post

 

[rickp]

I think the likes of Naiad have enhanced their control systems to try and generate lift by turning the fins hard at just the right moment to counter the rise or fall caused by the wave. It seems to be predictive, so better countering swell than wash perhaps. I also think that the faster the boat, the smaller the fins that are used, and the less effective any 'stabilisation at anchor' system is going to be.

There's a bit of blurb about it here and that also goes on to talk about gyro stabilisation.

Rick

 

[jfm]

3 methods of at anchor stabilise

Gludy:
Ignoring Nordhaven style buckets dangled over the side there are 3 systems:

1. Active fins, that flap up and down with hydraulics. The most common system on recent superyachts. The same fins function as stabilisers underway

2. The mitsubishi/ferretti system I mentioned in the SD threads and also mentioned in your posts in this thread. These are unique to ferretti right now and are suited to smaller boats - ferretti will fit them to a 50 footer. They come in different sizes and you can mix and match, eg several small ones = one big one, etc. They have a heavy flywheel spun fast by an electric motor, takes several minutes to wind up to speed (40mins in the biggest one). Also they need to be engineered in from the start, becuase the forces they exert on the hull mean they have to be mounted on chunks of grp/wood similar to engine mounts. But, a fantastic innovation, ferretti deserve much credit for this system. Hence my comment on the other thread that the boat to buy in your size range is actually the ferretti 731, and as an added bonus you get an interior to die for. This system works underway and at anchor

3. The proprietary Feadship flume system. This has a big water tank each size of the boat and as the boat tips the water passes a flume and suddenly gushes across the boat, and by careful design the water slooshes back and forth in antiphase with the waves, so cancelling them (partly). Very efficient power wise, but takes up significant internal volume in the boat. Someone kindly sent me fairly full engineering specs but may be confidential/proprietary so not sure if I can send them to you...will see.

 

[duncan]

Re: 3 methods of at anchor stabilise

there's a 4th that works well in very shallow water for small craft (flounder fishermen use it to keep the boat level when making bacon butties on a little stove) - drive 2 long stout poles into the sea bottom either side of the boat and attach to mid cleats.
Possibly not one for craft greater than 17ft in more than a slight chop but it does work.

 

[jfm]

5th method

Duncan, if the water is shallow enough they could just leave the road trailer attached? Would avoid the need to fiddle around pile-driving the poles into the sea bed.

 

[kimhollamby]

Another system

Sorry, cannot tell you who it is manufactured by but have seen a system on several large Dutch steel boats a few years back that uses a large weight on rails controlled (from memory) by hydraulic rams.

It looked fearsome in operation but apparently was quite effective at anchor.

 

[jfm]

Re: Another system

What type/size of boat Kim? I suspect sub30m. Difficult to see the internal size/noise being acceptable on say a 50m yacht

 

[Gludy]

Re: 3 methods of at anchor stabilise

It was your mention in the other thread that left me with the residual questions.

I agree the Ferriti system is a great innovation and the forces generated must be large so no wonder it has to be built in from scratch!