I often start with very low tech as you have done and I do much the same. Cruisers is a late edition to my fleets and generally very large to incorporate everything they need to be effective. The way the game
mechanics work it is not possible to build truly independent ship until you researched many levels of jump-drive technology. I never allow more than 30% total space for engines (normal+jump). So true cruisers will come late, later than battleships. I don't require jump-drives on battleships (I usually end up building carriers rather than battleships or batte-carriers), they are not suppose to cruise and mine need jump-gates to move from system to system in most cases.

My frigates are generally smaller then my destroyers but they don't have to be. The destroyer as the role I use them as seem to be similar to yours. They carry both offensive and defensive capabilities and are the biggest ship I can generally quickly deploy to forward bases with maintenance facilities. This means that destroyers general grow from around 6000t to about 12-15000t with mid tech levels. It's not unusual that I keep both a larger and a smaller type of destroyer as game progress. I also don't usually deploy frigates with destroyer TG unless really necessary. Destroyers also usually are faster than my frigates.

When I build cruisers I generally also design a larger escort frigate to accompany them. Not as large as the cruiser but a ship that has more defensive capabilities. You might say they are light cruisers, but that would imply they actually were truly independent ships, they also lack the offensive force to be a true cruiser.
This small but powerful group can act completely independent for at least 18-24 months from any bases and 36-48 months away from any maintenance facilities. The cruiser and frigates have enough hangar space to even accommodate a full squadron of attack crafts or geo/grav-survey shuttles. The cruiser can then act as the mothership for a survey mission.

I'm still very new to Aurora. However, I want to chime in on this subject.

I do see how it could be more useful to have ship classifications based on role or purpose rather than by size. And using 2, 3, or 4 letter abbreviations seems especially useful.

That said, it is very tempting to classify one's ships based on size, purely for the sake of simplicity - especially for other games. From my limited observation, there does seem to be a tendency for ships of certain roles to more or less fit within certain size parameters. Though, it's not as accurate or useful.

But if one does tend to use size to classify one's ships, wouldn't it make some sense to reserve some of the largest class names for mid to late game? I'm rather fond of the idea of reserving class names like "Dreadnaught" or "Leviathan" for one's largest ships. Though, I'm now leaning towards classifications based on role. Perhaps a Dreadnaught is best used for a large multipurpose military vessel with, say, lots of missiles and fighters? Or perhaps it would be used for a flag ship or "capital ships" (a navy's most important warships; possessing the heaviest firepower and armor)?

Alternatively, perhaps it would be useful to use both a shorthand abbreviation for class based on ship role, combined with a size category represented by a simple scale of 0 to 9? So, for example, one might have a BB4 early in a game, but have BB6 or BB8 in mid to late game? Or maybe one might see GCT (cargo ships) ranging from 1 to 9?

BTW: Several years ago I had some ambition to design and program a space exploration or 4x game of my own. (Though, while I did some background research and preliminary designing, nothing became of that.) Towards this, I looked up stats on a number of real-world naval and commercial ships and compiled some averages:

***** MILITARY *****

Large Aircraft Carrier - 1,100 ft (335 m) approximately 6,000 crew
Aircraft Carrier ---- 1,000 ft (300 m)
WWII Battleship ----- about 900 ft (274 m)
Amphibious Warfare Ship - 800 ft (244 m)
Cruiser ------------- 600 ft (180 m)
Modern Landing Ship - 500 ft (150 m)
Destroyers ---------- 371 to 563 feet (113 to 172 m) [420 ft or 128 m avg.]
Submarines ---------- 142.7 to 561 ft (43.5 to 171 m) [350 ft or 107 m avg.]
Dreadnought --------- 500 ft (150 m)
Ballistic Missile Submarine -- 380 to 550 ft (115 to 168 m), 500 ft (150 m) avg?
Frigate ------------- 445 ft (136 m)
WWI Destroyer ------- 300 ft (91 m)
Corvette ------------ 150 ft? (46 m?)
Minesweeper --------- 150 ft (46 m) (classified as "small combatant")
Missile Boat --------- 130 ft (40 m) (classified as "small combatant")
Patrol Boat --------- ? (classified as "small combatant")

***** COMMERCIAL *****

Super Tankers ------- 1,500 ft (457) <500,000 Short Tons or 450,000 Metric Tons>
Ore / Bulk / Oil Carriers - <250,000 S.T. or 227,000 M.T.>
Multipurpose Carriers - <150,000 S.T. or 136,000 M.T.>
Ore / Oil Carriers ---- <100,000 S.T. or 91,000 M.T.>
Ocean Liners -------- 1,000 ft (305 m) <2,700 passengers + 750 crew>
Roll-On / Roll-Off Ships - 958 ft (292 m)
LASH ---------------- 875 ft (267 m) <370 Short Tons or 336 Metric Tons)
Dry Bulk Carriers --- 700 ft (213 m) <25,000 S.T. or 22,700 M.T.>
Container Ships ----- 700 ft (213 m) <12,000 S.T. or 10,900 Metric Tons>
Tankers ------------- 300 ft (91 m) <2,300 S.T. or 2,090 M.T.>
Car Ferries --------- <800 passengers & 360 cars>

GCT   General Cargo Transport
   ...[snip]...
MTV   Main Transit Vehicle (Civilian Jumpship)
   ...[snip]...
CTV   Combat Transit Vehicle (Military Jumpship)

I like your designations. However, personally, I would switch MTV and CTV around: MTV = Military Transit Vehicle; CTV = Civilian Transit Vehicle. Or maybe use MJV and CJV, instead? Much less confusing that way!

As a Navy officer I want to point out in the USN and most other Navies weight has little to do with classification on the military side, it's all about role. Cruisers in the USN means AAW warfare which is why the Ticonderoga-class CG is classified a cruiser when it is literally built on a destroyer hull (Spruance-class DDG). Similarly the Zumwalt class is described as a DD even though it is thousands of tons heavier than an Arliegh Burke-class DDG.

To complicate matters many times ships are described not based on anything related to size or role, but rather what will make them easier to sell to the public or legislature you are trying to squeeze money out of which can lead you to making something seem grandios or small regardless of the actual ship. This is why a lot of European navies call their ships frigates or destroyers when the resemble neither in size of role. Or better yer, take a look at the Japanese Hyuga Helicopter Destroyer, so named to avoid breaking their constitution and to sound less awesome to lawmakers and voters.

Finally there are just some historic naming conventions that just don't translate we'll into modern navies such as frigate or destroyer. Frigates were originally self contained light units that could operate independently for extended periods to either scout for large fleets or project power into places that did not justify a larger ship. Destroyers were meant to screen larger ships against quick torpedoe boats (and their later outgrowth the submarine) the slow heavy guns of battleships could not track. Today frigates basically do what destroyers did and destroyers are hybrid destroyer/cruisers. But then you end up with things like AAW frigates which would just seem weird being called cruisers because in the popular imagination we still associate cruiser with something not a battleship but still big.

As far as I can tell the tonnage association is basically a consequence of video games that had to provide prearranged sizes and roles for simplicities sake. Since they are generally trying to recreate WWII IN SPACE! We end up with names in a sequence the reflected the role/size ratio of 1945.

I usually play conventional start or with reduced amount of research points in a newtonian start. Early sensor systems are very bad and get expensive fast and your build speed is not that great in the beginning. There is no problem to get missiles with good range, they are just slow... 

Personally I just call most of my long range self sufficient none attack ships a frigate. If it's purpose is recon, patrol or the protection of other ships it is a frigate so I have no designation such as area-defense cruiser or some such.

I also have no designation such as jump-(frigate,destroyer,cruiser) or even leader for that matter. I might however have different destroyer models who carries different types of sensors and weapon system that can be used in various combinations to form more complete destroyer squadrons. Although I try for most of my destroyer models to be as complete as possible so I'm not vulnerable to a single loss. The role of a destroyer is to perform almost any task, from direct attack to reconnaissance in force etc.

I might have different destroyers if I have types that are very different such as mainly missile or beam armed destroyers. But in any case a destroyer will have both offensive and defensive capacity so I don't have a single point of failure and to reduce research/production costs necessary.

My jump ships are almost always some sort of support and/or command ship. They carry better sensors (often good passive sensors) and extra supply and/or magazines as well as a flag bridge for bigger jump ships. They will usually lead the supply or auxiliary part of any battle group and ferry ships across a jump point or form up with a destroyer squadrons to make a JP assault.
They might also be equipped with hangars for different types of utility ships from shuttles (cryobeds, magazines or fuel) to recon and scout ships.

Ship sizes also tend to bloat as an empire grow, that is my experience. So an early destroyer might be 6-7000t with very limited defensive/offensive capability, usually also quite short ranged at about 50-75million km and very little armour. While later a destroyer might grow to 10-15000t and incorporate all kinds of sensors and weapon systems although offensive capacity is still imperative and its range of engagement grow with sensor technology as does the number of different weapon systems. A destroyer must be able to defend against both small and large ships and also able to engage them in battle, therefore they need to be bigger as time goes by.

The role of the ships classes would remain the same, it's just the size and quality/quantity of its equipment that develop. So they still perform the same type of missions in the fleet... they just get better at it with time.

No offense to anyone that don't agree with me but I just don't understand why (for logical or logistical reasons) you would designate a name for a weight of a ship rather than the role it serves. Calling any ship between 6-10000t a destroyer does not say a thing about it's purpose and the tonnage is there to show its size anyway. I'm not saying its wrong or anything, I just don't get why it's practical to do so other than confirming a sort of level system.

There is also the tendency that the game favor bigger ships as technology rises as it speed up production, lower production cost/time on refits and so on.

In one game I had a cruiser at 45000t escorted by 15000t frigates while destroyers where 9-12000 tones. The difference in the ship where its intended role, deployment time and armament layout. The frigates where mainly for protecting something else and large enough to accommodate all the weaponry and auxiliary vessels to do their job. The destroyers were built around the concept of squadron warfare and for self sustainability in that role or as a picket or screen for a bigger cruiser task-group or perhaps a reconnaissance in force where stealth is more important than brute force of a cruiser. In this game I also had very small frigates at about 3-5000t that were just beam or missile armed escort ships. Basically just one type of weapon system and not able to operate alone. The reason I call them a frigate and not a patrol ship, corvette or anything like that was because they have a long deployment time and are suppose to operate with a fleet on long missions (usually above three months). Any ship with a deployment of three months or less would be a patrol ship, corvette or something of that sort no matter its size. Obviously there are no real reason to build such ship larger than maybe 2-6000t but there might be.

The reasons why I decided on these designation are because of the historical background of different ships. A frigate was basically the smallest military ship equipped for long voyages and able to (cruise) perform more or less independent action. The ship of the Line was the battleship of its age while the frigate was the cruiser of its age. A ship of the line was a large ship that would perform the majority of military battles together with or without frigates. So the ship of the line became armoured ships became armoured frigates and then battleships. In WWII a battleship is mainly equivalent of a heavily armoured cruiser and actually they were not all that much bigger for the most part to a very big cruiser just heavier and also wider so they would not sink...

Cruiser was in the beginning a smaller warship intended for longer missions while "battleships" was only meant for shorter more decisive action. Cruiser was more a type of ship than a real classification and could be a sloop, corvette or a frigate. Cruiser were later changed into the armoured cruiser and then into the type of ship they were in WWII.

So in my world a battleship is just a cruiser with a smeg load of armour and shields as a significant part of their total size. Cruisers have weaker armour but can certainly be as large of even as heavy, it all depends in technology level in my opinion what is what and on what other ship you have in your fleet.
I could even declassify a ship from battleship to cruiser if I no longer deem a ship to be an actual battleship in comparison with newer ships or changes in the fleet structure. In practical terms there is no difference in the role of a cruiser or battleship. A carrier on the other hand is just a ship that can be of any size that just has the majority of its space dedicated to hangars in some capacity. In Aurora though the difference between a large cruiser and a carrier can become a grey area so I also use the term battle carrier which basically is a mix between a carrier and a cruiser, size still have no real meaning here.

I'm trying to somehow relate to what I think would be a realistic interpretation of how humanity would go about naming ship classes in space in reality. Today for example the term cruiser is almost an extinct type of ship in place of frigates and destroyers. Even the term frigates are starting to shift because today the only difference between a frigate and destroyer are it's size and when that happens the classifications tend to shift and change. Most really modern frigates are becoming more short ranged coastal or amphibious or recon multipurpose ships while destroyers are the escorts for other ships with both defensive and offensive capacity in many varied sizes.

So, basically, my interpretation of the difference between a destroyer and cruiser in space would be that cruisers would carry larger capacity fuel, crew and auxiliary vessels for truly independent long range action while destroyers would always act with other destroyers and intended for shorter missions and closer to their base of operation. That is also why cruisers would naturally be much bigger than a destroyer and why you would ever need to build one over the other because they serve totally different roles.

In my opinion there are no real reason to build large multipurpose ships (other than for fun) if you only control a couple of systems. But by the time you control several real sectors and your empire span over a very large area you can really benefit from being able to deploy larger long range multipurpose ships. These ships can only be build and maintained at very few places in your empire but there is other benefits that outweigh those drawbacks.

There is obviously nothing wrong with classify ships by weight... it's being done today as we speak in our own navies. Even if there is a tendency to shift classification to role rather than size over time.

I think it is safe to say a majority of the original players of Aurora got their start in Starfire and SFB. Starfire classed hulls by tonnage and I think that practice carried over into Aurora.

I generally class vessels by what they do rather than how big they are;  Frigate are generally Anti-Missile ships,  Cruisers independant action* ships, Battleships are the core of my combat fleets.  It's not unusual for late game Frigates to be larger than early game Battleships.

Matt


* By Independant action I mean my cruiser squadrons are fast response before the main battle fleet gets involved formations,  not the Star Trek wandering around alone idea