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Author Topic: Innovations in Propulsion  (Read 1652 times)

Colin Bishop

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Innovations in Propulsion
« on: April 10, 2010, 01:51:05 PM »

The latest issue of Ships Monthly, May 2010, has a very interesting article on how efforts are being made to make ships more economical and environmentally friendly. On idea I had never heard of is to shape the bottom of the ship into an inverted shallow tray and pump air into it. Because the friction between air and water is much less than between steel and water quite substantial fuel savings are possible. Flettner rotors get another mention too - I wonder if they would work in model form?

Colin
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Subculture

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Re: Innovations in Propulsion
« Reply #1 on: April 10, 2010, 07:45:10 PM »

How do they pump air into the shallow- that's going to take power.

Colin Bishop

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Re: Innovations in Propulsion
« Reply #2 on: April 10, 2010, 07:48:47 PM »

Compressors apparently.
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Navy2000

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Re: Innovations in Propulsion
« Reply #3 on: April 10, 2010, 08:17:53 PM »

Here is a link to a brief description of how air is pumped out onto the hull of a ship. It is mainly used of Naval ships.

http://www.fas.org/man/dod-101/sys/ship/weaps/prairie.htm

Duane
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gondolier88

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Re: Innovations in Propulsion
« Reply #4 on: April 10, 2010, 09:13:32 PM »

Hi Navy2000,

That's absolutley fascinating, i've never heard of that before!

However I don't think Colin and yourself are describing quite the same technology- or the same technology but used in a different way.

Your interesting article describes fine bubbles being used as a mask to stop sound detection, a military defence.

However, from what Colin says, I think he is describing a system of pockets below the waterline that would be pressurised with air- these would reduce wetted surface and cause less drag making the hulll more efficient. The golf ball 'dimple' effect as it were. Quite what it would do to the underwater hydrodynamics is quite another thing, perhaps it would actually make hulls less efficient in rough waters where the pockets couldn't be preserved and the flow of water around the hull becomes very turbulent.

Greg
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tobyker

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Re: Innovations in Propulsion
« Reply #5 on: April 11, 2010, 01:37:02 AM »

Quote from "Steam,Steel and torpedoes", pub HMSO 1980, "The Lightning of 1876 was the RN's first torpedo-boat: 80 feet long with a speed of some 18 knots. It is interesting to note that she was originally intended by her builder, Thornycroft, to have an early variant of the hovercraft principle, air lubrication of the hull. The technical limitations of the day were enough to prevent such a futuristic step."
So, some progress after 134 years, eh?
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Colin Bishop

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Re: Innovations in Propulsion
« Reply #6 on: April 11, 2010, 09:14:23 AM »

Yet another example of the idea being there but the technology not ready!

Colin
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tonyH

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Re: Innovations in Propulsion
« Reply #7 on: April 11, 2010, 10:43:43 PM »

I'm probably wrong but I think I remember that some of the Scott Paine designs for MTBs before WW2 had experimental air pumps feeding into the step in the hull to break the suction.

Tony
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tobyker

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Re: Innovations in Propulsion
« Reply #8 on: April 12, 2010, 10:13:38 PM »

Indeed - but would yuu need to pump air in, or just arrange a vent to the centre of the step to break any vacuum/low presure?
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tonyH

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Re: Innovations in Propulsion
« Reply #9 on: April 12, 2010, 11:01:27 PM »

Dunno, but probably just a vent to break the suction.

I can't remember the full details.

Going back to the original post, apparently a reduction of 25% in drag costs just 3% of the vessels overall power output for the pressure system.
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