Out of Fuel

[wanderer1825]

I was sent to patrol East China seas. Set out from Pearl Harbour, refueled at Midway but get to East China with very little fuel left to get back. I was travelling at 8 knots and submerging at every opportunity to run on batteries to save fuel.
What am I doing wrong?

Tony

[Raptor1]

You do realize it takes fuel to charge the batteries, right?

[Doolittle81]

Try running surfaced at 10 Knts. Submerge only when threatened by Jap planes (usually no more than ten minutes each time).

Whenever your charging batteries you run at flank fuel.

[OneTinSoldier]

Originally Posted by Lynx2069

Whenever your charging batteries you run at flank fuel.

I'm sorry to say that this doesn't sound correct. Perhaps I'm misunderstanding what your saying but you should try to be a little more detailed in exactly what it is you mean, as in give an actual explanation as to how/why you run 'flank fuel'.

It seems to me that you're saying that if you run at ahead standard that fuel flow is at flank speed fuel flow in order to charge the batteries. I might not know exactly how the battery recharging works exactly, but let me explain why I think flank fuel flow is incorrect.

1) If running at ahead standard it takes longer to recharge the batteries than if running at flank. So, If I'm running at ahead standard then why does it take longer? If I really had flank fuel flow while running at ahead standard then it seems to me that it should take the same amount of time to recharge the batteries that it does if I were running at ahead flank. Or even less time actually! If it's set to flank fuel anytime the batteries are being recharged then that should mean that more energy is going towards recharging the slower I go!

2) What happens if I run at ahead flank? From your statement I would tend to think that all fuel flow is now going towards running at flank speed with no fuel flow(engine energy) left to go towards recharging the batteries. Yet, at flank speed is when the batteries are getting recharged the fastest.

3) I would think that the batteries are recharged by a belt driven alternator, and the alternator saps power from the engine when it's engaged. This is why you have a lower speed when the batteries are being recharged(as opposed to the speed you normally get when the batteries are not being recharged). The faster the engine is cranking the faster the alternator goes, and the faster the batteries get recharged.


Note: I believe WWII Skippers rarely ever ran their diesel engines at ahead flank. Only when they really 'needed' to I believe, because running at flank is hard on the engine. And you know, when your way out there in the middle of the ocean your really counting on those engines, so you take good care of them and don't run them 'hard as hell'. This includes times when the batteries needed recharging.


I could be wrong about all this and if so I hope someone will correct me, with a fairly good explanation of how, why, ect.

Regards

[Sailor Steve]

The generators were geared, two to each propellor shaft. The diesels drive the generators, which supply the electrical motors. Speed is governed by the motors. When submerged the generators are driven by the batteries, and when surfaced they are used to recharge the batteries. If two generators are driving and two are recharging, it is beneficial to have the diesels driving the recharging generators to run as fast as is feasible, even if the others are driving the boat at ahead slow. That's what he meant by "ahead flank" - not the speed of the boat, but the speed of the recharging diesels.

http://www.maritime.org/fleetsub/elect/chap2.htm#2A