I usually assign my fighters names alphabetically. F-1 Arbalest, F-2 Ballista, etc.

I actually trend towards a system similar to NATO's codenames for Soviet aircraft,  ie Fighters get names beginning with F (Fulcrum, Foxbat, Fencer, Figjam(honestly!)) bombers with B (Badger, Blackjack) recon fighters with R (Rascal, Renegade)

Matt

To reply on the original question on this thread I think the main reason why so many people end up using ships at around the same sizes and think that a 20k ship is a very large ship is how things scale up in cost, both resource and time wise with size.

Bigger engines and jump drives can be really expensive in research so make it prohibitive to build large ships using such components. Large naval yards is expensive and time consuming to build and large ships can be cumbersome to upgrade if you also have few large yards and several types of large ships. Then there is the thing about maintenance facilities that you need to construct wherever you want to place your ships.

In general you are better of slowly increase the size of your yards with time and technology increase. This way you can also take more advantage of technology such as cheaper expansion of yards etc...

It all depend on the setting you play in. If you play in a setting with multiple factions and there is full competition to maximise your profits then there is not time to invest in monster ships at lower technology levels. If you play a single Earth empire against the AI you can more easily go after more wasteful strategies, or optimise your resource gathering without fear of having them occupied or destroyed.

In my current game, the Terran Union Navy uses the following classifications:

CO - South Carolina class - 6,200 tons
SS - Cleveland class - 6,000 tons
DD - Portland class - 9,000 tons
DE - Brooklyn class - 10,000 tons
FF - Iowa class - 10,000 tons
CA - Fletcher class - 15,000 tons
BC - Arleigh Burke class - 21,000 tons
AT - Ticonderoga class - 23,000 tons
BB - North Carolina class - 28,000 tons
CV - Lexington class - 30,000 tons
CVA - Tarawa class - 30,000 tons

Then my fighters:
F-101 Lightning fighter - 235 tons
F-102 Thunderbolt fighter-bomber - 350 tons
F-103 Lancer heavy fighter - 500 tons

So it's a mix of size and function. DD and DE are for AMM and PD, respectively, FF is for ASM, CA is dual-purpose beam warship, BC and BB are full beam warships but BC is faster so it can hunt down lonely enemy ships, AT is for hostile landings, CVA is for jump point assaults and CV is for general fleet duty. SS is a stealth scout. CO is an experimental meson-armed PD platform.

So, just to complicate matters further, I do both size/function designation. The modern US Navy does it the same way. In actuality, ship naming conventions were not very static in historical navies.

Great example of this would be the age of sail. While ship types were defined by role, they we often designated by sailing rig. So, that would be like designating Aurora ships by engine type. Examples would be Barque, Brig, or Schooners.

Then you have the "class" system that arises in the 18th century. Ships of the line, as the Royal Navy rated them, were rated by decks, and number of guns. 1st Rate ships, were big ships, with mulitiple decks, and a large number of guns. As the times changed, 1st Rate ships, that were still in service, were down rated. The system got confusing, as ships less than 6th rate (still often called frigates), were "unrated" and generically called "sloops".

So in this case, my ships are broken out something like this;
Military
Fighter (pretty self explanatory), can be Light, Medium, or Heavy based on size and loadout.
FAC- short ranged, high speed, low endurance system based attack craft. Could be missile or gun armed
Gunboat- long ranged, longer duration small combatants (usually in the 1000 ton range, but have multi-month endurance)
CT- Corvette- Light patrol craft, system based, or lightweight long endurance warp point guards. Usually 5000 tons or less.
FF- Frigate- Patrol craft, generally smaller than destroyers, usually around 6,000 tons or so. Multi-role, designed for solo or small squadron ops, and cheap. Could be missile armed, but usually gun armed.
DD- Destroyer, fleet combatant, around 8,000 tons or so, gun armed. Single role ships.
DDG- Missile destroyer
ES- Escort- smaller destroyer sized or less anti-missile ships
CE- Escort cruiser, fleet escort, usually light cruiser sized or a bit larger
CL- Light cruiser, usually 9,000 tons or more, smallest capital ship for a fleet leader role
CA- Cruiser, gun armed, 12,000 tons or more
CG- Cruiser, missile armed, 12,000 tons or more
BC- Battlecruiser, could be either gun or missile armed, 15,000 to 18,000 tons. BC's are optimized for speed. I usually use these as the center of a gun fleet.
BB- Battleship, gun armed, 18,000 tons or so,
BBG- Battleship, missile armed, 18,000 tons and up

CVE- Escort carrier, usually a dedicated system defense or interdiction carrier. These are used to get some fighters into a system for long durations. Not for fleet use.
CVL- Light carrier, smaller than the usual fleet carrier, usually 1 to 2 squadrons, meant for smaller fleets or high speed fleets.
CV- Carrier, usually 4 to 5 squadrons, standard fleet carrier
CVH- Heavy carrier, 5 or more squadrons, major fleet combatant, usually command ship for the fleet, space control ship
CVA- Assault carrier, heavily armed and armored carrier meant to go in a warp point assault

In my case, patrol ships, or ships operating alone, tend to be multi-role capable. So, for example, my patrol frigates would be fast, gun armed, but have full sensors. Fleet warships are optimized for specific roles, and don't waste space on unnecessary systems.

As my ships change, the roles and designations may change as well. Especially as ships refit. I also tend to reclass ships as they are rolled out of main line service, and are not slated for refit.

Personally, I build a 50HS Commercial engine, and then a 20HS Military engine with similar power and worse efficiency.

Ever since the engine overhaul, I've pretty much based my classes around the new engines. Fuel efficiency is a big thing now, so I almost always use 50 HS engines, which sets a lower bound on practical full warships at around 6000 tons. This is a bit of emergent gameplay, so might be one reason why there's some standardization between different players.

Beyond that, I divide by a combination of size and purpose. Frigates and Destroyers are both single engine craft, for instance; frigates are designed as support/point defense ships, destroyers are dedicated fast combatants. So a destroyer might well be smaller than a frigate to give it the extra speed on a single engine, and have a spinal laser or large missile tubes; a frigate would be designed to keep pace with larger vessels, so have less speed but some sort of turreted PD or anti-missile tubes. A larger multi-engine version of the destroyer (fast, no frills anti-ship vessel) might be called a battlecruiser, whereas a slower general purpose vessel would be a heavy cruiser.

Perhaps a bit late to the party, but this is a topic that always fascinates me, partially because I tend to build ships on the small size I've found out.  I swear I remember a similar thread to this a year or two ago, maybe even a thread I started, that had some great info.  Maybe I'll see if I can dig it up later.

But anywho, I'd just like to chime in that not only do I designate by function, but a good 75% of the time my "escorts" are larger than my mainline combatants.  

Basic Battle Fleet Layout:

1-2 Command Ship (15k-ish psudo-capital ship, sometimes unarmed, sometimes minimal missile defense.  Basically large sensor and jump tender)
6-10 Missile Cruiser (8-9k-ish capital ship, exclusively ASM launchers.  May or may not have emergency sensors for if the CC is hit)
6-10 (Escort) Destroyer (8-9k-ish screening vessel, beam armed defense, frequently with emergency sensors, used for both missile defense and close ranged engagements (and as such, frequently has a 'main gun' that's a bit larger than the turrets))

Optional Ship Types:

Missile Escort (Destroyers) (12k-ish screening vessel, AMM armed ship, frequently with backup sensors, built in numbers equal to beam escorts)
Monitor/Cruiser/Battlecruiser (8k-ish capital ship, multipurpose beam offense ship, name depends on if it's intended for JP defense/independent operations/fleet support, has sensors for offense but generally lacks missile defense beyond CIWS if that)