Endurance voyages - Battery vs Diesel

[Letum]

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.

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.

[Corsair]

OK here we are again...

Without making tests, it's easy to make a fast calculation.

Let's say a VIIb has an autonomy of 8000 miles at 8 knts (it's close and makes it easier).
We run it on the surface at 8 knts, this gives us 1000 hours (which is the unit used on boats for fuel consumption)
Assuming the weather stays nice and beautiful (for making things easier) our sub A will run 8000 miles @ 8 knots in 41.66 days (1000 hrs / 24)

The same sub B runs in the same nice weather conditions, but is submerged 12 hours @ 3 knts, reloads batteries 3 hrs @ 5 knts and runs surfaced 9 hrs @ 8 Knts every day. This gives us 36 + 15 + 72 = 123 miles a day, which is average 5.125 Knts.

Since our sub B uses its diesels only 12 hrs a day, the 1000 hrs of autonomy give us now 83.33 days, for a total distance of 123 * 83.33 = 10 250 miles

So although it will take twice the time, sub B will travel 2.250 miles i.e. roughly 28% further than sub A in the same weather conditions.

Merry Xmas to all of you..

[fredbass]

Ducimus: I think you'd better drop this one. It seems somebody is confused between the game and reality. (I won't name names) He might have some sort of autism. :hmm:

[Letum]

Originally Posted by fredbass

Ducimus: I think you'd better drop this one. It seems somebody is confused between the game and reality. (I won't name names) He might have some sort of autism. :hmm:

I take it you are referring to me? Please let me refer you to the calculations I have made in game. They give good proof that SH3 is faithful to real-life fuel usage.

http://www.subsim.com/radioroom/show...8&postcount=18

Originally Posted by Corsair

OK here we are again...

Without making tests, it's easy to make a fast calculation.

Let's say a VIIb has an autonomy of 8000 miles at 8 knts (it's close and makes it easier).
We run it on the surface at 8 knts, this gives us 1000 hours (which is the unit used on boats for fuel consumption)
Assuming the weather stays nice and beautiful (for making things easier) our sub A will run 8000 miles @ 8 knots in 41.66 days (1000 hrs / 24)

The same sub B runs in the same nice weather conditions, but is submerged 12 hours @ 3 knts, reloads batteries 3 hrs @ 5 knts and runs surfaced 9 hrs @ 8 Knts every day. This gives us 36 + 15 + 72 = 123 miles a day, which is average 5.125 Knts.

Since our sub B uses its diesels only 12 hrs a day, the 1000 hrs of autonomy give us now 83.33 days, for a total distance of 123 * 83.33 = 10 250 miles

So although it will take twice the time, sub B will travel 2.250 miles i.e. roughly 28% further than sub A in the same weather conditions.

On the bit I have underlined:
You are assuming that because the speed setting is the same; you are using the same amount of fuel. Sub B only uses it's diesels 12 hours a day, but one of the diesels is running at 500rpm for 3 hours in order to charge the batteries. Because one of the motors is running faster the 1000hrs of autonomy no longer applies.

[Corsair]

Oh my God ....

No comment. I let you do the math yourself.
Assuming a differential fuel burning per engine is modelled and the reload engine burns 2 x fuel you will find there is still 1000 extra nautical miles...

Now I am out of the thread

[Sailor Steve]

Corsair, I see two problems:

1) Why isn't sub B recharging his batteries for 3 hours and then diving again? This would seem more practical if you are correct.

2) Asking the same question for the third time, if this works in real life then why aren't surface ships equipped with a similar system to increase their range?

The problem is that the energy available is finite, no matter what the source, and evergy is lost during a transfer process such as recharging batteries. If it worked in real life then real life submariners would have talked about it, and I don't recall reading about anybody claiming to extend patrol distance by this method.

It's a game thing, and if it works in the game then I think the game is wrong.

[Letum]

Originally Posted by Sailor Steve

Corsair, I see two problems:

1) Why isn't sub B recharging his batteries for 3 hours and then diving again? This would seem more practical if you are correct.

2) Asking the same question for the third time, if this works in real life then why aren't surface ships equipped with a similar system to increase their range?

The problem is that the energy available is finite, no matter what the source, and evergy is lost during a transfer process such as recharging batteries. If it worked in real life then real life submariners would have talked about it, and I don't recall reading about anybody claiming to extend patrol distance by this method.

It's a game thing, and if it works in the game then I think the game is wrong.

And according to the mesurements I have done in game, it doesn't work in game so the games not wrong.