I might be able to give you advice, but you need to provide more information.

Where is your patrol area?

How fast are you going?

What class of boat do you have?

Did you follow instructions in ISP regarding the special ability crew?


The Porpoise-class will have about 6,000 nm range, and later classes about 11,000 nm range (@ 10 kn.). The S-class will have less. You should be able to obtain these figures, and if you don't do much battery charging, or see a lot of bad weather, something better than that.

Really, at the start of your patrol, you should 'test' your engines, and have your navigator give you the maximum ranges at the different speeds, so you know. After that, it is a simple matter to calculate what you will use as you transit from one area to another.

For instance, I got the following info for my S-18 class:

at A 1/3 (5.75 kn.) _______9850 nm
at A 2/3 (8.5 kn.) ________4884 nm
at A Standard (10.25 kn.)___3472 nm

These figures were for wind conditions of 5 m/s, so the speeds are slightly lower, but that is ok.

This was at the start, so I know at 1/3, I get 98 nm per point of fuel, and at 2/3, only 48 nm per point, etc., etc.

Knowing how far you have to go to get where you are going (and to get back), you know how much you need. You should always have some extra for contingencies. As a general rule, you don't want to be running submerged, or using high speeds, unless you have a good reason. BTW, running submerged because you are in enemy waters, and you don't want to be bombed and strafed, is a good reason, doing so near Hawaii, just because you feel like it, is not.

When you get to your patrol area, you should operate within a reasonable fuel budget; i.e. not waste fuel. It you are operating within tight limits, there are ways to stretch your fuel.

Ah, that explains it.

Cruising at ~ 9.0 kn. is the most fuel efficient. fireftr18 is right that battery charging will use up more fuel, but I wouldn't freak out about it.

With ISP, you will be able to get better battery performance than you would otherwise. I was able to patrol all day at 3 kn. submerged, surface, charge batteries, and move 30 nm overnight using about 1% fuel per day. That in a S-boat. I don't remember exactly how much fuel is used by charging, but it is approximately proportional to the amount of depletion. So, it you run submerged at a low speed, say 3 kn., you should not use more than about 30 % of your battery. This can be recharged without an enormous quantity of fuel.

That looks about right.

Later on, when you have forward bases, you'll appreciate the advantage.