Quote:
Originally Posted by Vanilla
I believe that both sources are more than credible. A linear speed-RPM dependency is normal for propellers in water (as opposed to air) for an example look at this chart and we here are talkin about very low RPMs at which this linearity would be even more pronounced. Let linearity here not confuse you: water, as opposed to air, is almost incompressible at these speeds that is why propellers are not loosing much of their effectiveness. It would be way more interesting to see speed-P.S. charts where there would be a lot more 'curviness'. As in terms of max-speed: I would go with British repots since German ones most probably give a brand-new boat specs as opposed to the British 'old-boat' ones and while at the moment we don't have a possibility to 'degrade' engines' performance we better set it slightly lower straight from the start. |
Thank you for your clarifications, Vanilla, they make perfect sense
Talking about min/max speeds reported in the second set of data, the one taken from the Germanan manual, after having a closer look into the aforementioned source I have discovered what they are for. Diesel engine speeds are relative to two different (sea ?) conditions, named A and B. As for Electric propulsion speeds, max speeds apply to surface navigation, thus the big difference with min speeds (due to the extra drag caused by boat's superstructure and armament during submerged navigation). Unfortunately, I don't think the game takes the above factors into consideration.
Concluding, given the linear proportionality between r.p.m. and speeds, I think that the best way to set EngineProperties relative to each speed order, is calculating them from rpm's, as rpm'sr are lesser affected by disturbance factors (such as weather conditions, drag, etc.) compared to navigation speeds. In order to do it, we need to know maximum operative rpm's. The "U-boat Information for U-boat Type VII C" reports the following figures for both M.A.N. and G.W. Diesel engines (pp. 118, 124)
Full load: 470 RPM
Overload: 480 RPM
Maximum load: 490 RPM
Coparing the two sources I have recently mentioned, I think the "Maximum load" was the theoretical maximum speed that an engine in operational conditions wouldn't have been pushed to. Therefore I would set max diesel rpm to 485. As for Electric motors, this limit had to be a bit higher than 300 RPM, though I couldn't find any explicit mention to it in the sources I have consulted so far.
Using the above figures (480-485 and 300 rpm's) as reference, we should set EngineProperties as follows:
According to British Admiralty records:
Code:
[Diesel]
AheadSlow=0.33
AheadOneThird=0.54
AheadStandard=0.64
AheadFull=0.97
AheadFlank=1.00
[Electric]
AheadSlow=0.20
AheadOneThird=0.37
AheadStandard=0.53
AheadFull=0.78
AheadFlank=0.93
According to specs reported by the German manual:
Code:
[Diesel]
AheadSlow=0.37
AheadOneThird=0.57
AheadStandard=0.71
AheadFull=0.91
AheadFlank=0.98
[Electric]
AheadSlow=0.18
AheadOneThird=0.37
AheadStandard=0.53
AheadFull=0.83
AheadFlank=0.95
Note that I have not included backward speed orders yet. The German manual lists their respective rpm's, but not their resuting speeds. I ignore if propeller's hydroninamic efficency is the same in both ways, and I am therefore hesitant in homolgating reverse rpm's with backward speeds the same way I did with astern speed orders; nonetheless, assuming that propellers work the same way in both directions, we would have:
Code:
[Diesel]
BackSlow=-0.37
BackStandard=-0.43
BackFull=-0.52
BackEmergency=-0.82
[Electric]
BackSlow=-0.18
BackStandard=-0.37
BackFull=-0.53
BackEmergency=-0.83