There would in theory be more restrictions and thresholds.

Size of ships being based on 4 or more technologies rather than just 2 (not counting components taking up less 'mass' in more advanced research versions).

Upkeep per unit mass is an easy way to stop size abuse.

That isn't what I meant in the slightest. And in point of fact the current situation (as of GalCivII) supports this idea anyway. I.E. Tiny hull with a end game beam/missile/driver weapons.

I agree and power generation should/would be one of the limiting factors to how much 'mass' and other assorted tech you can put into a ship

You don't agree primarily because of a reason that makes no sense. And as I said in my OP I think that there should be a variety of factors affecting what sizes you can make you ships.

I just feel that arbitrary sizes are perhaps not the only, or even best, way ship size management could be achieved.

Hull sizes or mass is a good first guide to ship classification. I remember playing a naval war game that used displacement as a measure of ship class.

I also agree that with research, the lines between ship classes can be blurred, creating some special classes. However these special classes should be limited and expensive to build to help balance the game.

Other ways to classify the ships would be its function, say destroyer, frigate etc.

Citing an example from David Webber's Honorverse series, as the technology for weapons and ships became better, the Destroyer classes for the Manticoran Navy became as big as some Light Cruisers of other navies. Thus, the designation of the ships depended on its role rather than the size of the hull (to an extent)

Whatever the choice, game balance is important especially in multiplayer (though I don't know if I have time to play this as my schedule does not really permit multiplayer  . 

Just my thought on this..

Agreed, perhaps then the idea of bracketing ship mass into something could provide a rule of thumb whilst still allowing the choice to make something stupidly oversized should tech and resources permit.

I felt that the point of the shipyard was to remove things like ship 'classes' as enforced by the game developer and make things more free form (something I am trying to suggest ways to augment by the removal of size limits)

For me personally, the name of a design was all the identification I needed when creating a Frigate or Destroyer type ship.

I see your point, but would also mention that size should not equal power. The SG-1 episode  'It's Good To Be King' where O'Neill destroys a Goauld Ha'tak with a Puddle Jumper with one shot due to much more advanced tech is an example of what I mean.

Love that SG-1 episode, though in this case, it would have to be a really special ship and not many are available to help balance again. SG-1, Galactica, Star Wars and Star Trek battles have always been visually awesome. For books I love Webber's Honorverse series as it has massive space battles.

We should get a first look at the ship building side once it goes to alpha. 

Another interesting thought is for other species, how would the ships be categorised? Taking a leaf from Warhammer (or Starcraft) for the alien Tyrannids (or Zerg), their ships are bio-ships. Would we encounter a race with bio-ships? Can we design one like Talon from Farscape?

I understand that you want more and more option.  I hope you understand that to me you are just asking for more and more complexity.  The three sizes work well for me.  The variation of what I can do within those three sizes seems more than sufficient to me.  Big ships with lots of hit points and little guns.   Little ships that are nothing but a gun and a hull.  All have been done and all have been both useful and entertaining.  Please do not break that part for others.

I see it as flexibility, if you want to make a big ship go for it, if you want to make a stupidly large ship then again, just go for it.

Quite a few different ways to implement it, having preset values like there are now as well as the ability to go way beyond them (or just in between them). Personally I would prefer to be able to design a ship and then tell the ship yard how long my design actually is and then have the game work out the width, height and 'mass'.

Modern games AI can be very complex, I don't see this as a step too far, in fact I would prefer the AI to be able to choose exaclty the best size for it's in game situation (position, resource levels, tech...) if there are just presets then so be it but the more choice the AI has the better.

I'm not breaking anything, just suggesting more choice. The concept itself just allows for more choice, the exact implementation would determine what, if any, extra complexity would be added.

The current system of classification is about as logical as any your going to come across. Starships should be designated by tonnage and size-not arbitrary and meaningless titles, like 'destroyer' or cruiser, which are meaningless terms when applied to spacecraft.  If your current empire is only capable of constructing hull sizes up to a certain size-then that is the system you should use. 

Galciv calls them Tiny, small medium etc-all perfectly logical as they equate to a specific range of tonnage and volume. The best that your industry can produce at a given time.

They could just as easily be called class I II III IV etc. Same idea. Tonnage and mission profile matters-not wet navy titles like frigate etc. Also, the idea of standardized hulls and sizes is likely something a space-faring empire go for in a big way. Making custom hulls for every purpose would in 'real life-be prohibitively  expensive and time-consuming. Cookie cutter hulls that can preform a wide variety of functions and be easy to roll out would be much preferred by industry.

The galciv2 system works rather well and makes perfect sense. No real need to alter it.

In modern naval terminology:

A corvette is a small and maneuverable light warship commonly used for short-range patrol and escort, or as a defense for ports and naval bases.

A frigate is a light warship commonly used as an escort for larger warships, merchant vessels, and various types of transports. Frigates are typically larger than corvettes and smaller than destroyers.

A destroyer is a fast and maneuverable warship capable of extended deployment commonly used as an escort for larger vessels, as well as for independent patrols or raids. Destroyers are typically larger than frigates and smaller than cruisers.

A cruiser is a mid-size warship capable of extended deployment which is commonly used for commerce raiding, for hunting commerce raiders, as escorts of important convoys and capital ships, as flagships or primary components of squadrons or task forces, as heavy patrol or sentry vessels, or as scouting elements for large formations of ships. Cruisers are typically smaller than capital ships such as battleships and large carriers, but larger than destroyers.

A battleship is a heavy warship intended for use as a direct combatant in major fleet actions, capable of destroying anything below its weight class and matching anything equal in its size class. Battleships are the most powerful individual warships in the fleet. These vessels are the primary units composing the battle line of a fleet, and are theoretically capable of defeating any other warship, if that warship can be brought to battle.

A battlecruiser is a capital ship similar to the battleship but lacking the level of protection given to the battleship (a rule of thumb is that the vessel has the firepower of a battleship and the armor and speed of a cruiser); as a result it is faster, which makes it good for hunting down heavy cruisers employed as commerce raiders. In theory, it is capable of outrunning anything it cannot beat and defeating anything else; in practice, it tended to be used as part of the battle line since capital ships tend to be too valuable to employ for hunting cruisers, which meant that such vessels had to encounter warships with similar firepower but much greater protection, which placed the battlecruisers at a disadvantage.

A carrier is a large vessel which carries small craft, which it relies on, alongside any escorts it has, for its primary offensive and defensive capabilities. The carrier may also have a relatively small collection of light defensive weapons, and generally (though not always) does not carry heavy weapons of its own, although the small craft it carries may carry weapons which are abnormally strong for the size of the craft, as these small vessels need not carry sufficient supplies or ammunition for extended deployments, instead making use of their mother ship to repeatedly repair, resupply, and rearm. There may also be smaller carriers used as escort vessels for important convoys or fleet elements, as support for the large carriers employed in the main fleets, or as support vessels for operations not sufficiently important for the diversion of a larger carrier or which may be better served by several small carriers than one large carrier.

What, exactly, in the above set of definitions is meaningless when applied to spaceborne warships? We get:

1. Corvettes - short-range defensive vessels for protecting space near planets or within a star system
2. Frigates - light escort or patrol vessel
3. Destroyers - utility vessel
4. Cruisers - independent raider, backbone of fast squadrons of light warships, escort and support for heavy warships or important convoys
5. Battleships and Battlecruisers - capital ships with significant direct combat power and (usually) relatively strong defenses
6. Carriers - different style of capital ship, capable of bringing multiple light craft with lower endurance and/or range to the battle, but somewhat lacking in direct combat ability

I don't see how any of those roles are incompatible with warships simply because the warships are spacecraft instead of seagoing vessels.

I agree with Tridus. The more constrained the optimization problem is, the better the optimization code can be made to work. Humans are much better at finding good (or at least decent) solutions for poorly defined, ill-constrained, or loosely-constrained problems than computers are, even if it's only by trial and error. For that matter, what is the 'best' size for a given in-game situation? When is it 'better' to build 100 size-50 frigates than it is to build 10 size-500 battleships, assuming all else is equal? When is it 'better' to build superships that can defeat all comers than it is to build ships which are good enough for general use, or ships that you can make wave after wave of for wearing down enemy defenses? The answers to these questions and others are non-trivial, and by no means are they simple to program into a computer, and the more complicated the underlying mechanics are which affect the optimization, the more difficult it gets.

What computers are good at is doing lots of computations rapidly. If you can set up a simple optimization problem that merely requires you to find the roots of, say, a 7th order polynomial, then the computer is usually more capable of solving that than a human is (for the record, I don't recommend that anyone try solving polynomials of order greater than 3 without the aid of a computer unless that polynomial happens to factor very, very easily or is unusually simple - e.g. X^7 - 1 = 0).

A choice between any of a few dozen pre-designed vessels is something a computer is much more likely to be able to handle relatively well than a complex design problem. It's also much less susceptible to errors in the optimization coding, which can lead to some fairly bizarre solutions to relatively simple problems, and it can be very difficult to fix, or even find, the cause of these unusual solutions.