Turbine/jet propelled boats?

[Sunner]

Not entirely sure this is where it belongs, but hell, it's hardly general hardware

Me and a couple of friends had a discussion regarding coastal corvettes, more specifically the ones that are propelled by gas turbines, for example the Visby Corvette.

The discussion was pretty much about how exactly these ships are actually propelled.
One thing that kept coming up was the difference between the propulsion of these ships and that of a jet fighter.

Anyways, what Im really looking for a crash course on how the actual propulsion of these things work, I've found lots of sites with info on corvettes and such, but none go into detail about how the propulsion actually works.
Bear in mind, Im a *NIX sysadmin, and my friends are one electrican and one law student, so this is a layman's discussion at it's worst

Anyone?

 

[skull]

http://travel.howstuffworks.com/turbine.htm

 

[Sunner]

Originally posted by: skull
http://travel.howstuffworks.com/turbine.htm

Doh! How could I forget howstuffworks....

Thanks

 

[TRUMPHENT]

Go back and lookat the Visby page. It is propelled by turbine engines for high speed and diesels for low speed. The power is transmitted thru gearboxs to waterjet propulsors. Waterjets must be quieter than regular propellers.

 

[SCSIRAID]

One of the big advantages of a waterjet is their thrust can be directed by rotating the nozzle. No rudders required. Not so easy with a prop.

Edit.... Here is a Link

 

[NickE]

Take a look at this company We're starting some work with them at the moment, not on the propulsion side but on the applications in mixing, emulsification etc. Seen the demo unit in operation and it's very impressive, a boat engine/mixer that can handle gravel, rope etc.

 

[Horus]

Not to mention the tactical advantages of waterjet ships...some torpedo guidance systems rely on the sound of props to home in on it's target. So no cavitation (Bubbles made from propellers), nothing to guide on.

 

[dkozloski]

Here in interior Alaska a large share of the boats used on the rivers are driven by gasoline engines turning turbines. Some are inboards and some are attachments for outboards. Hamilton, Berkely, and Outboard Jet are a few. They are inferior to conventional propellers in every way except that they will operate in very shallow water. The efficiency is much lower than a regular screw and they put a large rooster tail in the air. The water is disturbed into a froth long after they have passed by. They also destroy the nests of spawning fish and are banned from some areas for this reason. The over riding advantage of shallow water operation still makes them popular because their only rival, air boats, are overwhelmingly noisy and even more annoying. I operated an Outboard Jet on a Mercury engine for years alternating between a conventional lower unit and the jet. When the jet was swapped for the prop in order to continue a journey up a shallowing river I estimated I lost about about 25% of my speed which would translate to a loss of about 50% in efficiency. The jet was also extremely sensitive to wear and required constant adjustment to internal clearances when operated in muddy water to preserve what little efficiency it had.