Ship Tonnage by Class

[Bremen]

Ah, the eternal topic

I like to use max size (2,500 ton) engines for my warships, because they have the best fuel efficiency. Because of that class designs fall nicely into divisions based on number of engines. I sometimes further divide based on design purpose.

Frigate: 1 engine, 6,000-8,000 tons. Designed to provide support to other ships and light beam weapon capability, generally loaded with railgun or gauss PD. Railgun versions tend to be smaller to get better speed off one engine.
Destroyer: 1 engine, ~8,000 tons. Like frigates, except designed for anti-ship roles (either missiles or heavier beam weapons).
Escort Cruiser: 2 engines, ~16,000 tons. Point defense like frigates, but usually using AMMs since I find them hard to fit in to a smaller hull but wasted on a larger, multi-purpose vessel.
Light Cruiser: 2 engines, ~16,000 tons. Generally pure missile based anti-ship platforms.
Cruiser: 3 engines, ~24,000 tons. My smallest multipurpose combatant, usually armed with a combination of ASMs, beam weapons, and beam PD.
Heavy Cruiser: 4 engines, ~32,000 tons. Similar to cruisers, though I sometimes give them a heavy beam weapon focus.
Assault Cruiser: 4 engines, ~32,000 tons. The idea is to have a slow, heavily armored cruiser designed for jump point assaults, but it's mainly theoretical since I've never had an AI guard a jump point.
Battleship: 6 engines, ~48,000 tons. My command ships; about the same weapons as a heavy cruiser, with the extra space filled up with a flag bridge, extra armor/shields and PD, and a jump drive.
Battlecruiser: 6 engines, ~48,000 tons. Same size as a battleship, but gives up on being a command ship with extra defenses in favor of filling all that space with weapons.

I generally don't go bigger than that; the mechanics of shipyards and jump drives in Aurora means it always struck me as more efficient to have a squadron of battleships and battlecruisers instead of one or two dreadnoughts. If I ever get a game that far I might try going bigger, though. I also tend to eventually start phasing destroyers and frigates out, partly because fighters and battle riders start filling their roles and partly because giving orders to 30+ ships gets annoying.

Carriers I generally go with "the biggest I can make them" and then give it an appropriate name, I.E. light carrier, escort carrier, fleet carrier, etc.

[83athom]

But the thing is, larger ships are more efficient with armor costs, build time, and crew requirements.

[Bremen]

But the thing is, larger ships are more efficient with armor costs, build time, and crew requirements.

To a certain degree, sure. But it's a lot more efficient to have 5 40,000 ton ships, one of which spends 5,000 tons on a jump drive, than it is to have 1 200,000 ton ship with a 25,000 ton jump drive. Similarly, it's cheaper to build a 40,000 ton naval shipyard and keep it constantly producing than build a 200,000 ton one and use it a few times. Not to mention the very real risk that your 200,000 ton flagship will be severely outdated by the time you finish building it, or in the middle of a maintenance overhaul when an enemy shows up.

If you economy is big enough to support fleets of super dreadnoughts, then sure, building them is fine. But IMHO building as big as you can and only having a few flagships is pretty inefficient.

[Iranon]

Shields also benefit from a larger ship size, perhaps more so than armour. Concentrated in one ship, it takes considerable firepower to even scratch the paint, and all shield units contribute to the regeneration rate.

However, there is less wastage through overkill against a single big ship.

[83athom]

To a certain degree, sure. But it's a lot more efficient to have 5 40,000 ton ships, one of which spends 5,000 tons on a jump drive, than it is to have 1 200,000 ton ship with a 25,000 ton jump drive. Similarly, it's cheaper to build a 40,000 ton naval shipyard and keep it constantly producing than build a 200,000 ton one and use it a few times. Not to mention the very real risk that your 200,000 ton flagship will be severely outdated by the time you finish building it, or in the middle of a maintenance overhaul when an enemy shows up.

If you haven't tried it yet, I recommend it. Here is where you are mistaken on some things. 1) 5 40,000 ton ships can jump with a single 5,000 ton drive, however the 25,000 jump drive can also jump 5 200,000 ships. 195,000 tons of ship excluding JD on one side, 975,000 tons of ship the other. An exact factor of 5. 2) While yes, it is cheaper to build a single 40,000 shipyard over a single 200,000 ton one, the 200k one will build ships faster as well as it can grow while producing ships. 2.5/3) You are severely mistaken on how long t takes to build these ships. Most of the time, my destroyers and cruisers can build faster than my frigates, but I have more frigate slips to compensate. And it being in overhaul is the same risk any other ship no matter the size has. And like Iranon said, shields in bulk (only able to do well in large ships) can make it so nothing can even touch the ships.

[Bremen]

If you haven't tried it yet, I recommend it. Here is where you are mistaken on some things. 1) 5 40,000 ton ships can jump with a single 5,000 ton drive, however the 25,000 jump drive can also jump 5 200,000 ships. 195,000 tons of ship excluding JD on one side, 975,000 tons of ship the other. An exact factor of 5. 2) While yes, it is cheaper to build a single 40,000 shipyard over a single 200,000 ton one, the 200k one will build ships faster as well as it can grow while producing ships. 2.5/3) You are severely mistaken on how long t takes to build these ships. Most of the time, my destroyers and cruisers can build faster than my frigates, but I have more frigate slips to compensate. And it being in overhaul is the same risk any other ship no matter the size has. And like Iranon said, shields in bulk (only able to do well in large ships) can make it so nothing can even touch the ships.

1) Yeah, but that doesn't work if you can only afford 200,000 tons of naval ships, as in my example. Or even if you can just afford one 200,000 ton ship on each front, since in that case they all need jump drives.
2) Again, my example was if you can only afford a few giant ships. If your economy can support continuous production of 200,000 ton leviathans, than yes, they're more efficient.
3) There's diminishing returns to shipyard build rate; larger ships take considerably longer to build. If your smaller ships take longer than your bigger, then you've got something odd going with their designs. I'm not disputing that there are combat advantages in having larger ships; I'm just saying that there are considerably larger disadvantages in just building one or two huge ships (in which case none of your points apply) instead of a bunch of large ones.

[AL]

3) There's diminishing returns to shipyard build rate; larger ships take considerably longer to build. If your bigger ships take longer than your smaller, then you've got something odd going with their designs.

You post got a little confused here it seems, but I take it you mean that smaller ships should build faster than bigger ships. Let me show a quick example I threw together to illustrate how build times scale with ship size:
I created two designs, one at the 10kt mark and the second at the 100kt mark. They were created by removing all possible components first, and then adding fuel tanks of appropriate sizes to get to their target tonnage.

Off-Topic: Screenshots • show

After doing those two designs, I went ahead and made a third at the 1mt mark, and that had a listed build time of 4 years (not shown, but one can easily recreate this design comparison).

It can be seen that although the second design is a 10x scaled version of the first, the build time listed on the left is not 10x the smaller design (it's actually about 1.3 times). This means that building larger ships will actually allow you to accumulate more ship tonnage faster than if you were to build a greater number of smaller ships, which is what I think 83athom was getting at.

[Sheb]

The BP cost is only 5* the cost of the small ship. I wonder how that scale with real designs.

Also, you've got to keep in mind that while you're building your shipyard to some huge size, you could be adding slipways instead.

[Iranon]

Probably using smaller fuel tanks, larger ones are cheaper.
Things scale almost linearly for decent-sized ships, although there's some overhead that makes larger ships more efficient (1 layer of armour takes less as a percentage of the total size, you only need 1 bridge).

*

Regarding building rate: On the same capacity, (1 shipyard with 1 100.000t slipway vs. a shipyard with 10 slipways of 10.000t), large ships build more slowly.
You can also split the latter into multiple yards for more flexibility, but note that this increases manpower needs (there's a fixed million per shipyard in addition to manpower proportional to the total capacity).

[Bremen]

Regarding building rate: On the same capacity, (1 shipyard with 1 100.000t slipway vs. a shipyard with 10 slipways of 10.000t), large ships build more slowly.
You can also split the latter into multiple yards for more flexibility, but note that this increases manpower needs (there's a fixed million per shipyard in addition to manpower proportional to the total capacity).

Even matching slipways (say 1 100,000 ton yard vs 1 10,000 ton yard) a comparable small ship will build faster. It's not linear; a ship twice as big takes less that twice as long; but it is a direct result of how build rates work.

Edit: I will clarify that the 100,000 ton yard is still pumping out more tonnage per year, it's just taking longer per hull. It does mean that larger ships are more vulnerable to being obsolete before they even finish construction, though.

[Drgong]

Varies by era, in a early game a 5000 ton ship might be a cruiser!

I generally do not build big ships (I am of the large number of  smaller ship navy)


Fighters < 500 tons
FAC < 1000 tons
Corvette 1000-5000 ton - designed to be cheap, many times with limited missile defense.  Used to patrol backwater systems, escorts, and so on
Frigate 1000-5000 ton - generally armed with Anti-missile defenses that can also be used for limited anti-ship use.  Can be detached
Light Cruiser  5000-10000 tons - Generally lightly armored, but fast and well armed.   
Heavy Cruiser 10000-15000 tons - Armored, single use (ASM, or AAM with full sensor suite)
Ship of the line 15000-25000 - Smallest capital ships
25000-35000 - Battleship
35000+ dreadnought

Of course, you have Carriers, tankers, supply ships, gunboats, and so on that are determined by use then size.  I am currently developing my Carrier task force techniques.   

[Borealis4x (OP)]

So I decided that the next class should be at least 3 times as large as the previous one. So now I have:
3,000 ton corvette
10,000 ton frigates (rounding up)
30,000 ton destroyers
100,000 ton cruisers (decided to round up)
300,000 ton dreadnoughts
1,000,000 ton super dreadnoughts (again, rounding up)

Its large, I know, but I usually give my ships a lot of extra utilities like tractor beams and emergency cryo and Gauss point defense. I also have a rule of having an ECCM for every fire control and 1 fire control for every six weapons.

I might also have sub classes in between, like a batlecruisers at 150,000 tons or something. These large jumps give me some flexibility.