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Originally Posted by Sailor Steve
I'm wondering whether cruising on diesels at two knots wouldn't increase the range in the game just as well.
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No it wouldn't.
I understand what you are saying, but its not a case of the slower you go; the further you go.
Think of riding a bike. You could take all day to go one mile, you could go one mile in a few minutes or you could find a comfortable steady pace.
Even if you have all day, you will chose the steady speed. This is because at the slow speed you use more energy. The extra energy is lost because most motors (and bodies) have numerically constant economy penalties at any speed.
With the bike analogy, one such constant is the energy required to power your brain or keep your body temperature at a minimum. These are unavoidable inefficiencies that will be there at 1mph or at 100mph. A diesel motor has these inefficiencies also and so does a water screw.
The slower you go; the more time constant inefficiencies waste energy; the less efficient you are.
Going fast is also going to use more energy. This is because
some inefficiencies are greater the higher the speed is. A dubbeling of the speed will require something like a squaring of the energy expended. This is mainly because the forces of friction are greater at high speed.
In-between extreme slow speed and extreme fast speed there is a speed that is most economical.
There are a few other factors that involve gearing and external forces on the vehicle that feed back into the motor, but we don't need to go into that. (thank god)
The most economical speed for your car is about 55mph. Your car will go further at 55mph than it will at 10mph.
For a VIIC U-boat the most economical speed is somewhere around 7knts.
It is easy to prove that UBI soft have modeled this. Just run your VIIC at 1knt and ask your navigator for your maximum range (do it twice and take a average)
Now repeat this at 16knts and at 7 knts. The range he reports at 7knts will be the highest.