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Originally Posted by PepsiCan
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Originally Posted by Ducimus
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I was under the false impression that the longer I stayed under travelling to assignment the more fue I saved.
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That was true in SH3, because the battery recharge only took around 3 hours. Now they take around 7 hours (give or take an hour). The 6-7 hour recharge being more realistic of course. |
There's also plain physics involved. If you burn diesel to charge your battery for the energy value of 100 kilowatts, then you will not charge your battery for 100 kilowatts. A lot of energy (as much as 50%) will be lost in the form of heat, friction (resistance in the .
So, the cycle looks like this:
- you start with a full battery and you use up 50 Kilowatts to transport yourself 50 miles.
- you then need to burn a 100 kilowatt to recharge your batteries (50% energy loss)
- so, you actually used up twice the amount of diesel to cover those 50 miles then you would have had to use if you'd run on the surface.
Conclusion: running submerged is very inefficient due to the way the recharge process works. |
On the surface, applied physics would seem to indicate that running submerged on batteries would have less overall range than running on diesels alone, but this is not neccesarily the case.
While it's true that the energy in the batteries used for submerged travel is not "free" and has to be gotten from fuel reserves and that the fuel-diesel-battery-motor energy chain is not 100% effecient, it's still possible for battery / electric engine use to increase, not decrease the range of the submarine. I will try to explain using the most extreme case of diesel/electric mixed propulsion.
Version A: A stopped sub with 0% charged batteries will run the diesel engines strictly as a generator to charge the batteries. Once the batteries have a charge, the sub uses its electric motor to move 10nm.
Version B: A sub uses its diesel engines to drive 10nm.
Which version uses more diesel? You may be tempted to say Version A uses more diesel fuel since the recharging, eletric motor process has more steps and thus more chances for energy to be lost due to heat, friction, 2nd law of thermodynamics, etc but it is not neccesarily the case.
It is because the diesel engine does not have the same effeciency at all RPM! It is possible to charge the batteries at the RPM that is the most effecient for the diesel engine while maybe the best RPM for the diesel engine/ boat hull is not so effecient for the diesel engine. The convoluted fuel-engine-battery-motor process, despite having more steps CAN (in theory) be more fuel effecient than the diesel engine alone because of the variable effeciency of the diesel engine under various loads.
Now I am completely uncertain about the following two concepts:
1. Were real life WWII submarines more effecient under mixed diesel-electric propulsion compared to pure diesel? It's theoretically possible but was it actually the case? Unknown. I thought German U-boats benefit from the mixed propulsion.
2. Are WWII submarines as modeled by the game (vanilla, modded?) more or less effecient under either method? Again unknown.
MORE INFO AND CITE:
http://www.ossapowerlite.com/tech_li...efficiency.htm
Not all of the points made in this article apply to WWII submarines as they are designed, but there are plenty of valid points made that do.