In my opinion this is a problem with the current model of the drive systems in Aurora and one that most players don't realized yet.

It is by far smarter to use commercial engines in Military ships and just strap on twice the amount of them.

Very interesting, but why is this a problem? I mean, commercial vs military is just a label, right? If you renamed 50% engine efficiency as "normal" you could say "In most, but not all, circumstances it is best to have a normal efficiency engine. Overpowered engines are only really useful for smaller military ships, or in cases of serious shipyard/maintenance/jump drive size constraint".

I'd much rather see the whole military/commercial engine labeling removed altogether.

Shipyard capacity isn't a problem. I routinely build my ships bulky with 55+% engines. They're less capable than more compact designs and I may need 50% more ships, but they're correspondingly cheaper and faster to build. Total expenditure and build time for a fleet of a given capability is mostly unchanged (and I get fuel efficiency and redundancy for free).

In my opinion this is a problem with the current model of the drive systems in Aurora and one that most players don't realized yet.

It is by far smarter to use commercial engines in Military ships and just strap on twice the amount of them.

They use much, much less fuel which translate into a much smaller fuel industry needed, much cheaper to research, less crew and maintenance on ships. It is also much cheaper to build commercial jump drives to jump the fleet and require much less research in general.

The only real drawback is a larger heat signature if ships start to bloat in size but since the engines are so much cheaper then adding stealth also is much cheaper too.

In my opinion the game need a redesign in how engine, speed and fuel efficiency work. Military engines must be worthwhile to build on regular ships and not just on really fast ships.

First of all I would like to see a metric that make larger designs cost more the faster they go. Any form of maneuvering on a larger mass will become more stressful on the construction as a whole, there are no real mechanic to represent this.

There also need to be a mechanic that promote military drives and the importance of a larger mission tonnage per ship. Perhaps maintenance facilities could only service a certain size and total tonnage, this would promote more mission tonnage per ship. But it has to be more economical than the fuel you save.

Commercial drives could be more prone to explosions since they are not built for sustaining injury or have the same redundancy in protective systems. This means bigger drives that are easier to hit and will more easily injure a ship further.

I suppose there are other ways you can "fix" these problems. As said... from an economical standpoint military engines are almost pointless on ships from about 10.000 tons and up. Smaller ships still benefit from more powerful engines since there the stealth component is more important and you will need at least a decent mission tonnage part on those ships.

In one of my games I have a fleet that uses size 50 engines with 40% power in their military ships of Size 107 (5350t).   Yes, half of those ships is the giant engine, but they are quite cheap to build and you won't need hundreds of fuel harvesters to feed your fleet.  You won't get FACs equipped with these engines, but I wouldn't build smaller ships if I didn't use commercial engines, so increased sensor footprint isn't an issue for me,  as I can always put the stuff into multiple smaller ships.  Sure, at some point I will probably want to have bigger ships due to efficiency, but that is not much different when using more powerful engines.

Yes... the Jump Drive system ONLY care about what drives is installed.

A military Jump Drive can jump any ship, if memory serves. Commercial Jump Drives can only jump ships equipped with Commercial Engines, it does not matter if the ship itself is flagged as a military ship or not.

That's an easy one to test - create a new game, whip up a commercial jump ship and a military ship with commercial engines, SM that you know where the jump points are and attempt to jump the military ship through.

Yes, but is "commercial" solely defined by the engines, and is it different from "civilian" which is about whether the ship qualifies for cheap maintenance?

Commercial and civilian are two different things. Civilian ships are classed as commercial, but you own your own commercial ships. They are not only defined by engines, but a number of other modules and settings. If the design screen says "Classed as commercial for maintenance..." at the bottom, a commercial jump drive can jump it. If its marked as military, only a military drive can jump it.

I remember doing the math a decade ago for freighters and colony ships, that the optimum engine ratio for maximizing cargo*distance/time per build cost was different.  The more expensive the cargo system, the higher the engine ratio was optimum.  So for really cheap cargo holds, you went cheap on the engines.  For more expensive cryo tanks, the optimum ratio was significantly more engines per cryo tank.

This is actually kind of a problem in that the colonists are likely to arrive before the infrastructure.

Also, the shorter the haul, the more important cargo handling systems were over engines.

Might be fun revisiting the math on survey ship size too.  What is the ideal ratio for a survey ship spent traveling vs time spent surveying?