Maritime Engine types

[Tzoli]

Hi!

Nowadays and in the past few decades the combined engine types of Steam and Gas, Gas and Gas, Gas and Diesel or Diesel and Diesel are quite popular propulsion systems for the various warships classes frigate size and up. These systems are quite versatile and economical to my understanding. I also know the difference between the OR and the AND versions. But there were mixed propulsion systems during the WW2 and pre WW2 eras as well. Like the mixed Steam and Diesel propulsion of most German warships.

My question is how would these mixed systems categorized with modern Combined systems?

Like would the mixed propulsion of the H class battleship designs or the Königsberg, Nürnberg and Leipzig class crusiers categorized as COSAD? (Combined Steam And Diesel) or COSOD? (Combined Steam Or Diesel)
Eg does they need all engines running at full power to achieve the maximum speed or only with turbines they could travel at max and the Diesels were turned off?
Many of the Yamato preliminaries too featured such mixed propulsion and I'm sure 60-70.000tons could not reach it's full speed on two shafts alone out of 4 if we think about two diesel and two steam powered shafts for economical or full speed runs.

 

[Jemiba]

...Like the mixed Steam and Diesel propulsion of most German warships

Not quite sure about this. The H-class was never finished, so the Königsberg and Nürnberg class
were the only fighting ships combining steam and diesel propulsion, AFAIK. According to Gröner, in the Königsberg
class the system clearly was COSOD, because the Diesel engines had to be shut down before using the steam
turbines and vice versa, so actually a kind of a handicap for any situation, when combat maneuvers had to be
expected. With Diesel only, the ship was limited to the speed of about 10 knots. There was a so-called "alarm
ignition" procedure, giving steam pressure "in some minutes" (?), but this probably was pricy and this method
is mentioned as only to be used "by bypassing all safety standards"
In the Nürnberg/Leipzig class it was a kind of COSAD. The ships had 3 shafts with only the inner one driven by Diesel
engines. The outer shafts could be driven electrically to avoid drag losses, when the steam propulsion was shut
down. Full power meant steam + Diesel here.

 

[Tzoli]

So if both engine types used on the same shaft that means a COSOD type as the diesel could not provide the extra shaft horse power next to the turbine?

 

[Jemiba]

Such was the arrangement on the ships of the Königsberg class, yes. There probably were
other types, were both engine types could work simultaneously on one shaft, but I'm not aware
such a type in the German navy. In the Leipzig class, the ship could use Diesel and steam turbines
simultaneously, as the Diesel engines were driving the central shaft only. If you look at the arrangement
drawings explaining all those combined engine arrangements, generally using the same shaft is meant,
I think. So in the Leipzig/Nürnberg it was a kind of a trick and I'm not sure, if it qualifies as a real COSAD
arrangement in the true sense.

 

[Tzoli]

Question would be, what arrangement to be used on the Yamato preliminaries?
Because you sure need 4 shafts to move 60-70.000 standard tons (lightest being A-140 D with 55.000tons and all diesel) and for max speed I'm not sure two shafts will be enough to go at max rotation.
I'm not an expert in water flow but probably having 3 or 4 shafts in which 2-1 or 2-2 moves at a different speeds are not helping to reach the desired speed.

 

[Tzoli]

Another question:
Is there any difference if I use COSAD or CODAS arrangement? Am I suspect that the firs letter designates the main propulsion type?

 

[Tzoli]

I know that steam turbine power output can be increased to a degree if we add more boilers to generate more steam but surely there is a maximum a set sized turbine could achieve.
Eg a setup of 4 Turbines and 8 boilers for 80.000shp but the same turbines could go to 100.000 with 10 boilers and maybe 120 with 12.
Now can the same be applied to Reciprocating engines like Vertical Triple Expansion? So using the same expansion engines but putting more boilers or more powerful boilers to incresse the power output of the engines in the ship?

 

[1635yankee]

I know that steam turbine power output can be increased to a degree if we add more boilers to generate more steam but surely there is a maximum a set sized turbine could achieve.
Eg a setup of 4 Turbines and 8 boilers for 80.000shp but the same turbines could go to 100.000 with 10 boilers and maybe 120 with 12.
Now can the same be applied to Reciprocating engines like Vertical Triple Expansion? So using the same expansion engines but putting more boilers or more powerful boilers to incresse the power output of the engines in the ship?

"Possible" and "practical" are two different things, so it's likely possible to build something like a 60,000 hp VTE or uniflow engine for marine use, but it's not likely to be practical due to size. Turbines scale up very well -- power generation turbines of over a gigawatt are common (driven by a single boiler) -- but the largest marine units aren't a tenth that size.

 

[Tzoli]

I know that steam turbine power output can be increased to a degree if we add more boilers to generate more steam but surely there is a maximum a set sized turbine could achieve.
Eg a setup of 4 Turbines and 8 boilers for 80.000shp but the same turbines could go to 100.000 with 10 boilers and maybe 120 with 12.
Now can the same be applied to Reciprocating engines like Vertical Triple Expansion? So using the same expansion engines but putting more boilers or more powerful boilers to incresse the power output of the engines in the ship?

"Possible" and "practical" are two different things, so it's likely possible to build something like a 60,000 hp VTE or uniflow engine for marine use, but it's not likely to be practical due to size. Turbines scale up very well -- power generation turbines of over a gigawatt are common (driven by a single boiler) -- but the largest marine units aren't a tenth that size.

This was not my question. I know that very well.
My question is if you use the same VTE engine but use more boilers will it increase it's output or you simply need a larger VTE engine to use the extra steam?

Think of this way: you have a pre-ww1 warship with VTE Engines, you want to modernize it but not replace the main engines just the boilers, either use more powerful boilers or more same output boilers. Will the VTE could cope with the extra power the boilers produce or not?

 

[1635yankee]

I know that steam turbine power output can be increased to a degree if we add more boilers to generate more steam but surely there is a maximum a set sized turbine could achieve.
Eg a setup of 4 Turbines and 8 boilers for 80.000shp but the same turbines could go to 100.000 with 10 boilers and maybe 120 with 12.
Now can the same be applied to Reciprocating engines like Vertical Triple Expansion? So using the same expansion engines but putting more boilers or more powerful boilers to incresse the power output of the engines in the ship?

"Possible" and "practical" are two different things, so it's likely possible to build something like a 60,000 hp VTE or uniflow engine for marine use, but it's not likely to be practical due to size. Turbines scale up very well -- power generation turbines of over a gigawatt are common (driven by a single boiler) -- but the largest marine units aren't a tenth that size.

This was not my question. I know that very well.
My question is if you use the same VTE engine but use more boilers will it increase it's output or you simply need a larger VTE engine to use the extra steam?

Think of this way: you have a pre-ww1 warship with VTE Engines, you want to modernize it but not replace the main engines just the boilers, either use more powerful boilers or more same output boilers. Will the VTE could cope with the extra power the boilers produce or not?

If you have either a turbine or reciprocating engine designed for x amount of steam at a given pressure, putting more steam than the design amount of steam in is unlikely to increase output by much.

 

[Nicknick]

A steam turbines conumes steam like a corresponding Laval jet, so without design modifications, you would need more steam pressure to increase the mass flow and power output. To keep the efficiency on a reasonable level, the speed should bei increased, so that the new peration point will have a similar ratio between blade speed and gas speed. I doubt, that turbines have a lot of reserve to increase the power significantly without mecanical breakdown.

In a steam engine the cylinder filling and speed might be increased which will result in lower efficiency and higher wear.

 

[Tzoli]

Apparently a Reciprocating engine's power output could be incresed marginally by more steam or higher steam pressure say 5-10%? But a turbine can go up as much as maybe 30-40% not sure of even 50% more power because you only need to increase the rotation speed of the shaft and having more steam easily helps with that.

 

[Nicknick]

No, you can change the speed of a turbine, but this will only change the efficiency and not the amount of steam flowing through it, meaning reducing effective power ouput. You have to increase the pressure to increase the steam flow and you should do it in combination with an higher rotational speed to keep the efficiency about even.

 

[1635yankee]

Most turbines using a compressible fluid (this excludes hydraulic turbines) run with the inlet nozzles choked. You can't shove more steam through it without increasing the inlet pressure. That would likely reduce the level of superheat, which would result in either condensation in the last stages of the turbine or significantly greater pressure (and temperature) at turbine outlet.