[Spaceships] Ship sizes and other categories (cruiser, battleship etc.)?

[Whitestreak]

One of the unofficial rules of thumb I've used when designing combat capable star craft is that its armor should be able to handle at least half the damage its own main gun can cause.

Space 3e has a good suggestion chart for vehicle type/sizes.

[Lord Azagthoth]

I also use a rule of domination and pride.

A Imperialistic nation at the huight of its power has larger ships than other nations. Not because their more effective, stronger or faster, but to induce fear and terror onto their opponents.

In peace time (when nations are restricted by peace time rules like the number of ships and/or size) they tend to become smaller but more powerful.

That way, you can really surprise the players too.

[jacobmuller]

Originally Posted by vicky_molokh

Okay, so what system ratios and/or presence/absence of what systems typically qualifies a ship as that or another?

I think the encyclopaedic genius known as Pulver mentioned 70% armour as battleship material. I'm in no wise quoting him (I might even have the wrong genius listed - I believe all experts are awesome: your kung fu is mighty).
But, as a comparison to Whitestreak's excellent guideline, the armoured battlewagon classes I ended up with are practically immune to their own "guns" and can take a few missile hits to destroy (mission kills are easier).

Ratios?
Frigates are multirole, a bit of everything, 15-20% armour, 20-40% motive (drive/ power/ fuel), 5-15% mainly anti-merchant weapons, hangers (ships boats and a few fighters), extra habitat (factory, business, offices, hospital);
cruisers are either mid-weight mid-gunned hunters or missile boats, 20-50% armour, 15-30% motive;
destroyers were fast lightly armoured and armed torpedo boat stoppers but are now what cruisers were. 15-20% armour, 10-20% weapons to suit their role, 20-50% motive.
Carriers 20-50% hangers, 5-10% weapons, 15-50% motive.
Battlewagons 50-70% armour, 5-20% weapons, 10-20% motive.

[Kissamies]

^^That's somewhat similar to how I arranged my ship roles:
Cruisers are supposed to be multirole warships capable of operating independently. They usually have a sort of jack of all trades design and often have some fighter complement.
Frigates are similar to cruisers, but don't have the size to do multiple things well and tend to specialize more.
Destroyers are not "torpedo boat destroyers" in my navy. Instead they are fast, heavily armed and lighty armored weapons platforms.
Corvettes are either miniature destroyers or anti-fighter/missile screening vessels.
Battleships are heavily armed and armored battlewagons dedicated to beating other capital ships. A few are designed as flagships and act more like heavy cruisers, though.

But enough of that, here's another existing setting example:

FreeSpace series:
Fighters = SM+5 to +6
Bombers = SM+6 to +7 (Few cases of SM+8)
Transports and Freighters = SM+7 to +14
Cruisers = SM+9 to +10
Corvettes = SM+15
Destroyers = SM+18
Colossus and Sathanas = SM+21

[vierasmarius]

Originally Posted by Kissamies

FreeSpace series:
Fighters = SM+5 to +6
Bombers = SM+6 to +7 (Few cases of SM+8)
Transports and Freighters = SM+7 to +14
Cruisers = SM+9 to +10
Corvettes = SM+15
Destroyers = SM+18
Colossus and Sathanas = SM+21

Interesting that they set Cruisers as the smallest of the Capital ships. Is the rationale that they are strictly force-projection vessels, operating across vast stretches of space, and therefore smaller and cheaper to cover more territory?

[sir_pudding]

Originally Posted by vierasmarius

Interesting that they set Cruisers as the smallest of the Capital ships. Is the rationale that they are strictly force-projection vessels, operating across vast stretches of space, and therefore smaller and cheaper to cover more territory?

"Destroyers" as the largest class of warships seems common in scifi, for inexplicably reasons. People probably think it sounds cooler than "Battleship".

[Kissamies]

Space opera scifi especially. Maybe not as much in military type. In Freespace cruisers cruise and destroyers destroy. Corvettes were added in FS2 as an intermediate type. In terms more like modern navy, FS cruisers are frigates, corvettes are cruisers and destroyers are battleship/carriers or "battlestars."

[sir_pudding]

What about GSV/GCU/ROU?