Guide to fuel conservation

[Von Tonner]

Originally Posted by Go4It

Never new SH4 had sub tenders, if so, were does one find one....

They are those striped anchors you see on the map. You can refuel and rearm at them but not effect any repairs. Just be careful, I have been attacked at one and sunk.

Thanks for that info Ducimus, I was under the false impression that the longer I stayed under travelling to assignment the more fue I saved. Now I see why I could never handle coming out of Pearl and resorted to always playing Asiatic Fleet. Thanks.

[Ducimus]

I was under the false impression that the longer I stayed under travelling to assignment the more fue I saved.

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.

[THE_MASK]

Thanks for this awesome fuel summary .

[PepsiCan]

Originally Posted by Ducimus

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.

[Steeltrap]

Another thing to consider is this: do I have to go anywhere IN my patrol zone? In other words, having reached your patrol zone there is no actual need to go anywhere until you find a target or have one reported you wish to intercept. That's why I lie motionless on the surface in my patrol zone once I'm in a likely encounter position.

O'Kane did that in Tang...he said to lie to like that took some getting used to!

[Snuffy]

Good Tips Ducimus! Thanks!

I for one have always been very conscious of my fuel, realizing that if I wanted to get the boys home to see the girls we needed certain amount of fuel for doing so.

Of course now that I'm in July 44 and tenders are showing up all the time as the allied lines advance over the Pacific, (the Marines just took Siapan yesterday! ) so having more places to refit before heading to home is allowing me to take on more and more assignments from HQ.

The only times I head home now are if I have damage to the point of batteries not reaching full charge or I have wounded that are taking a long time to recover. Also I don't go home unless HQ tells me too. (After sighting and reporting a contact sometimes HQ says RTB at your discretion.)

[pocatellodave]

Good job Ducimus.Thanks a lot.
Pocatellodave

[PepsiCan]

Originally Posted by Steeltrap

Another thing to consider is this: do I have to go anywhere IN my patrol zone? In other words, having reached your patrol zone there is no actual need to go anywhere until you find a target or have one reported you wish to intercept. That's why I lie motionless on the surface in my patrol zone once I'm in a likely encounter position.

O'Kane did that in Tang...he said to lie to like that took some getting used to!

I do that too. Near Kyushu or near Formosa/Taiwan the ships will come to you. So, wait and you'll get a contact :-) Waiting near busy harbours is also beneficial.

[ReallyDedPoet]

Nice Ducimus, just saw this.


RDP

[Tom C]

O'Kane did that in Tang...he said to lie to like that took some getting used to!

Steeltrap, did O'Kane say whether he kept all or some diesels idling (instead of shut off), in case he needed to move in a hurry?

I'm still playing the archetypal over-cautious early-war skipper and I see Japanese periscopes under every whitecap!

[SteamWake]

Good job D. Confirms alot of what I 'believed'.

About 'drifting' at your patrol zone. Its really not a bad idea but dont get caught out there at a dead stop in the day time by aircraft.

Also if the sea state is pretty rough it would be a good way to tear up your boat and make your crew pretty unhappy. But hey its just a game

[Frederf]

Originally Posted by PepsiCan

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.

[Tom C]

Frederf, I don't know about SH4 but in RL I think you're on the right track. Not sure about the S-boats, but AFAIK all the fleet subs had the diesels driving the electric motors, i.e. the diesels never drove the propeller shafts directly. Any difference in efficiency must lie in charging efficiency versus motor efficiency, and I don't know which was the bigger loss-- as you said, if they were different the diesel rpm could be optimized in either direction.

But, the US WWII sub hull and propellers were optimized for surface running, not submerged running. IMHO if you're not losing efficiency in the drive train, you're losing it in hull drag underwater, and you still won't get the same mpg as on the surface.

[Mylander]

Originally Posted by Frederf

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...

Is the above some kind of cruel pun?

All kidding aside, great thread and great info.

Mylander