Questions that puzzle me.

[Telemon]

Greetings,
The question is this;
I left harbour, Kiel, with full bunkers and warload in my IIV Uboat.

Transiting the Kiel canal I checked my speed/distances with my navigator and got these results. Distances rounded down to nearest one hundred miles. Sea state calm

5kts 22,300miles ahead slow on telegraph
6kts 27,300miles “ “ “ “
7kts 31,800miles ahead slow or ahead one third on telegraph.
8kts 30,600miles ahead one third on telegraph
9kts 25,400miles “ “ “ “ “
10kts 22,500miles “ “ “ “ “
Optimum speed is therefore 7 knots.

I was able to select 7kts with the telegraph on two settings. I remained at 7kts until I got well into the North Sea and changed speed to intercept a visual contact. From that point on I have not been able to set and achieve 7kts again, even though in this instance in the same sea conditions after brfeaking off the intercept.

If I set the telegraph to ‘ahead slow’ and asked for 7kts all I could get was 6kts. If I went to ‘ahead one third’ my speed rose to 10kts and if I then set 7kts my speed would fall to 6kts and the telegraph returned to ‘ahead slow’. This has been true in all my careers with SH3.

I am at a loss to explain this. Yes, I do occasionally get 7kts in a flat calm and do not expect to reach it in severe weather but surely I should be able to get 7kts all the time in moderate conditions even if I had to go to ’standard’ or ‘full’ on the telegraph?

I repeat this has been the case with all the careers I have started both prior to and after installing GWX3.

Incidentally I noticed the same phenomenon in one career with a MKIX at the 9kts setting.

[frau kaleun]

Ordering a speed of 7 knots doesn't always mean you'll get 7 knots, I've never known the game to behave otherwise in that respect. Weather and sea state will play a factor as will the need to use one of the running diesels to recharge your batteries after spending time submerged.

My guess is that ordering "one third ahead" and then setting the dial at 7 knots is essentially ordering the engines to be revved up (or down) to a state that would, in ideal conditions and with both diesels contributing to propulsion, give you 7 knots of forward speed. On the open sea, conditions are rarely ideal, and if your batteries need recharging some of your diesel power is going to be going towards that instead of propulsion.

Think of when you are driving a car, if you want to go 40 mph you press the gas pedal down until the engine is getting enough fuel to give you that speed given the driving conditions. You can't just push the pedal down to one particular spot every time and expect to go exactly 40 mph whether or not you're going uphill, downhill, getting the same traction, whatever.

[desirableroasted]

What Frau said. When you set for 7 knots, you are "making turns" for 7 knots, but you often won't get them.

Note also that the game calls anything between 6.5 and 7.49 knots "7 knots."

CORRECTION: the game calls anything between 7.0 and 7.9 knots "7 knots."

[frau kaleun]

"making turns" for 7 knots

Thank you, I couldn't think of the phrase I was looking for and that was it. :DL

So basically, if I understand this right, it's the "making turns" for a particular speed that determines fuel economy, because of the amount of fuel you have to pump into the engines in order to make turns for 2 knots vs. 7 knots vs. 14 knots and considering the max distance you can expect to cover at each of those speeds. Set for 2 knots and you will be going way too slow to get the most distance possible for every liter of fuel, even if you use fewer liters per hour. Set for 14 knots and you may cover way more distance in an hour's time, but you use so much more fuel to do so that you still don't get the most distance you can per liter.

Set for 7-8 knots and you've found the happy medium where distance covered per hour, and fuel used per hour, are both optimized as much as possible for maximum range even if the conditions mean your actual speed is sometimes less than 7 knots. If you try to "force" a "perfect" speed of 7-8 knots even in bad conditions by making turns for a higher speed, this would just mean using more fuel per hour and not getting the max possible distance out of that fuel since you had to set for, say, 10 knots just to get an actual speed of 7 knots. So that would be a lose-lose proposition.

[desirableroasted]

if I understand this right, it's the "making turns" for a particular speed that determines fuel economy, because of the amount of fuel you have to pump into the engines

That's how it works for me. You are looking for the most fuel-efficient engine use: the RPMs necessary to move a VIIC (for example) most efficiently in a dead calm sea. That works out (as far as I can see) to a shade under 8 knots, though it's not worth being picky about it.

EDIT: Now that I am in the game, I can see that the most efficient for a VIIB is 200 rpms. After running submerged, your starboard engine will run 500 rpms no matter what speed you set, until the battery is recharged.

[frau kaleun]

You are looking for the most fuel-efficient engine use

Exactly - most efficient "speed" is somewhat misleading, since your actual speed is going to vary depending on the circumstances even if you order "make turns for 8 knots" and never ever change it. But you will still be getting the most efficient use of your engines and available fuel at that setting.