Diesel Electric Propulsion Optimization for Coast Guard Cutter

[SonofDworkin]

Greetings all! I'm designing my first largish ship, a Coast Guard cutter, for use in my current Career Mode save (so biggest things I have are medium engines, medium generators, and large propellers).

My ship has two large propellers, each attached to a medium electric motor. Each motor is supplied power from two medium generators. Each set of medium generators is connected to a 3:1 gearbox (pointed towards the engines) which is connected to a drive shaft connected to 5 medium diesel engines (10 total).

I built a small test rig with throttles, a helm, and dials for speed, the battery, and the generators. No matter what I do I can't seem to get the generator power output above ~275 a piece which is not enough to run my electric motors at full throttle. I tried adding a second gearbox in series - it actually reduced output because the engines couldn't generate the necessary torque. Paradoxically, when I went from a fourth to a fifth engine per drive shaft, output dropped as well, and also dropped a bit when I increased the motors above 15 RPS. I'm also wondering if somehow I don't have enough air intake/exhaust capacity.

I have attached the build to the workshop - would be happy to get any suggestions/fixes from the community. Thanks!

https://steamcommunity.com/sharedfiles/filedetails/?id=2067834645&searchtext=coast+guard+cutter

[SonofDworkin]

After creating my own engine test bed, I determined that I can get 3 diesels at 18 RPS running through a 3:1 Gearbox to produce 600 units of electricity from the generator. Running the engines any higher RPS-wise does not have any effect and adding a gearbox lowers the power output because the engines don't have the torque. Does that seem right to folks?

[Ra-Ra-Rasputin]

That sounds like a decent figure for 3 medium diesels. I believe i have a setup somewhere in my workshop uploads, let me see if i can find it.
https://steamcommunity.com/sharedfiles/filedetails/?id=2036541914

Here you go. The problem with running them at a high-ish RPS is the efficiency of the engine as far as fuel goes. The fuel consumption curve is pretty significant at the higher end. If you drop the gearing on that to 5:9, you'll notice that it'll run slightly more than 200 charge at 16.3 RPS.

The reason for this is that generators resist turning when they go faster and faster, requiring more torque.

As far as your ship goes, it's relatively late for me, but let me see if i notice anything immediately off. I'll definitely give it a more thorough look tomorrow.

[Ra-Ra-Rasputin]

Well, i tinkered with it anyway.

https://steamcommunity.com/sharedfiles/filedetails/?id=2068721665

Generally you don't want to share air and exhaust pipes, especially without heavily pressurizing them, and pressurization of air is sometimes dodgy. I do like your general engine room layout and setup, really neat instead of the usual cacophony. I streamlined it a little bit more, and installed my Super Invisible Exhaust system (pat. pend) to stop the cascading exhaust hurting your FPS :)

It can't run the quad engines at full tilt, but at that point i realized the time and called it a day. This game keeps stealing hours off of me.

[SonofDworkin]

Originally posted by Ra-Ra-Rasputin:

Well, i tinkered with it anyway.

https://steamcommunity.com/sharedfiles/filedetails/?id=2068721665

Generally you don't want to share air and exhaust pipes, especially without heavily pressurizing them, and pressurization of air is sometimes dodgy. I do like your general engine room layout and setup, really neat instead of the usual cacophony. I streamlined it a little bit more, and installed my Super Invisible Exhaust system (pat. pend) to stop the cascading exhaust hurting your FPS :)

It can't run the quad engines at full tilt, but at that point i realized the time and called it a day. This game keeps stealing hours off of me.

Thanks for the help! And I would hope my engine room setup is neat - I'm a Naval Officer - can't be letting the service down by making everything untidy.

[Ra-Ra-Rasputin]

Oh, just to clarify, with the setup you have there, you should be able to run about 1.6~1.7 of those medium electric motors on each side with a neglible hit to fuel consumption. This means you can remove 2 engines on each side if you're content with going slower at an increased fuel efficiency, instead of removing engines, you can nudge the ratios of the gearboxes up by one on each gearbox to get significant fuel saving and less engine noise. It should still be able to run 1 medium motor on each end with ~ 1000 charge.

Otherwise, if you do want to go faster, swap out the medium motor in pink for a cluster of around 6-8 small motors on each side. Remove one small motor on each side until you reach equilibrium in drain rate, or a net positive. The clusters of small motors allow very quick tweaking of the drain rate of the main engines by just nipping them off one by one if the drain ever grows too high.

[SonofDworkin]

Brilliant! I will tweak around with this. Just to clarify - when you say "up one" by the gearboxes, do you mean going to a lower ratio? I.E. - from 2:1 to 9:5 on all of them?

[Ra-Ra-Rasputin]

I mean upping the ratio, since it is a positive ratio gearbox (1:2 vs. 2:1) it's positive because the arrows are toward the engine :)
It will reduce the output of the generators since it makes the engines run slower, at very fuel efficient ratios.