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I thought diesels were supposed to be economical ???

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waveydavey:
Believe it or not it's more of a Ferrari (Not a name I like to mentiona t the moment).

32.4 knots average across the pond, basically for anything else to do that it has to be nuclear. I'm now on QM2 and we can do about 29.8

waveydavey:
As another thought I actually worked out the per person fuel consumption on here once:

If a Diesel Disco carries seven people and does 30mpg then you have 210 people miles per gallon. Or 180 if you don't count the driver to get them there.

A bus might do say 10 MPG but carries 52 people so does 520 people miles and as such is much more efficient.

QM2 works out at about 1550 people miles per gallon. I didn't believe that so I worked it out three ways from actual data and kept getting the same number.

thermidorthelobster:

--- Quote from: "Hangover" ---Just out of intrest the QE2 has it's props driven by electric motors,the power is generated by 5 or so large generators similar to a diesel electric train but bigger.
--- End quote ---

This seems a strange design to me.  If you have an engine driving the shaft, then you have to take into account the efficiency of the engine, then the gearbox.

If you have an engine driving a generator, and motors driving the shaft, then you have to ALSO take into account the efficiency of the generator, and the motors.  Surely each of these can't be more than 90% efficient...  in which case you end up with only 81% of the efficiency you'd have if you didn't have them, which is quite a lot given the scale of the application.

Anybody know how efficient they actually are?  I know some generators/motors are about 95% efficient but I thought this was the exception rather than the norm.

Hangover:
What you loose in ineffeciency you gain in other places ie better control and probably less vibration etc which on a liner is more important than on a cargo ship,also the parts on the engines and actually working on them is cheaper and easier,i was told that when the QE2 went to the Falklands it was still steam but was refitted with diesel afterwards,don't forget they run them on bunker fuel which is heated and then fed to the engines.

waveydavey:
You are 100% correct that it is not quite so efficent but it is actualyl close.
There are various advantages:

You only need to run as many engines as you need, very rare to be nine and stopping an entire engine gives the gains back.

You can work on the stopped engine even at near full speed.

Massive redundency; the ship can keep moving on any selection of engines rather than those connected to to a particular prop.

The engines always run at efficent speed. IE they always generate at 60hz, big 'black boxes' change the frequency for low speed and at full power they go synchronous and vary power on the prop pitch.

The big one:
It was steam in the falklands and was converted in 1986. That meant that the new plant had to fit into the old hole. IE Diesels where the Boilers were and Motors where the turbines & Gearboxes were.

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