any advantage to smaller ships?

THE WIKI AS SOME GOOD INFO on combat and ship roles.  Generally speaking you want the largest hull possible with the most hitpoints.  small ships are cheap and can be turned out quickly evev from yards with low manufacturing.  This lets you field a large ship count fleet quickly.  he way combat works is basically by rounds and weapon fire rate.  A large cruiser with many guns will only fire on one target / round  resulting in massive overkill one ONE ship at a time. The fleet of smaller ships can pick apart the cruiser.

Combat ship sped (thrusts) let you close the distance to the enemy quicker.  A basic missile ship can get 2-3 rounds off before a kinetic gets into range.  It used to give you a slight defensive boost but i think that has been taken out.

I can't find any really detailed info on the subject, but it looks like small ships are relatively efficient in terms of capacity per point of logistics, only being beaten out by huge ships. Hyperion Logistics or some other logistics bonus could allow you to field massive fleets of small/tiny ships, where medium+ ships wouldn't be affected as dramatically. And of course, there's always those situations where you just have 2-3 points of space left in your fleet.

I also suspect there might be some use in creating large fleets of small ships because any given enemy ship can only shoot one at a time. Theoretically, say you're trying to take down a capital ship with 200 beam attack (you actually see this kind of thing from Godlike AIs, thanks to all their bonuses). If I understand the combat mechanics, 25-hp tiny ships with minimal beam defense will each take 2 hits to kill, with a tiny chance of lasting for 3. A large ship with a ton of beam defense would go down in 3-4 hits, depending on how lucky they got on the defense rolls.

For me, the biggest problem with small ships is that you can't produce more than one per shipyard per turn. I suppose you could set up a multi-shipyard system, where you rotate your major manufacturing world through several shipyards (each with a token sponsor), relying on large amounts of overflow to keep up the stream of ships, but I'm not likely to care enough to go through that much micromanagement.

Good input on their possible advantages, thanks.

Yeah but for that you would just really build a carrier

I sometimes like to build swarms of tiny ships loaded with weapons. I find they are effective against planet defenders and when I want to keep my larger ships intact for possible returning defending fleets.

I'm playing with a mod I created which makes them more useful. Essentially it turns interceptors and guardian classes into specialist units that skirmish around support vessels whilst assaults, escorts and capitals focus on destroying each other first. It can make for some interesting battles where you lose one or two interceptors in the initial volley, but a handful work their way through to transport ships which (if left undefended by guardians) will get destroyed. 

In terms of vanilla though, the most obvious advantage is dividing concentrated fire. This is useful for the initial stages in the game when the AI is only using one or two medium hulls, but quickly diminishes in usefulness once the AI scales up its logistics. 

I've been trying to figure out the usefulness of a guardian type ship.  For example, if I built a ship that was purely focused on defense and set it as a guardian will the AI actually target it since it has zero weapons and threat, just because it is a guardian?

Yes the Ai will shoot guardians and escorts even if they don't have a single weapon.
The most exploitive setup is: escorts completly filled with defenses and no weapons and capitals filled with weapons and no defenses and supports with buff/carrier modules.
I can list you all the target priorities: (def  something = things shooting your something)
Interceptor: Guardian -> Escort -> Support -> Interceptor -> Assault -> Capital
Assault: Escort -> Capital -> Assault -> Interceptor -> Guardian -> Support
Escort: def Capitals -> def Supports -> Assault -> Escort -> Capital -> Interceptor -> Guardian -> Support
Capital: Escort -> Capital -> Assault -> Interceptor -> Guardian -> Support
Guardian: def Support -> def Capital -> def Escort -> Interceptor -> Assault -> Escort -> Capital -> Guardian -> Support
Support: def Capital -> def Escort -> Interceptor -> Assault -> Escort -> Capital -> Guardian -> Support

Again, my mod (I should really upload this) gets around this by making sure capital ships are prioritised by both escorts and assault ships. If no capital exists then assaults will target escorts and escorts will target assaults, leaving support, interceptor and guardians as the last ships they target. In this way ship combat isn't as exploitative unless you alter your ship class in the editor (which I personally feel is an exploitative mechanic).

Yes, I have to agree with you the current system is silly. I don't get why they would allow manual designation when their target priorisation system can't handle it.

What do you mean when you say their target prioritization system can't handle it?

Sorry that was bad wording on my part, but if I can make  the ai shoot away at a ship that is nothing but defenses while geting destroyed by 10hp cargo ships filled with weapons and no defenses whatsoever, the system is no good. One shot to each of the cargo ships and my fleet wouldn't be able to do anything.
The first problem is everything has to shoot escorts.
Second the set in stone target priorities vs manual designation of roles.
I should never be able to get the ai to shoot something that doesn't shoot back while there are still things alive that shoots them.
It's okay that we can tell our ships what to do but that shouldn't mean that we should be able to tell what the ai should do.

The ai should ignore the roles you give the ships and decide on the stats which roles they have for it's target priorities.

Smaller ships can be a little cheaper to build, but the cost of engines, weapons and shields will make a good small ship almost as expensive as a good medium. The real difference is that a small ship can take a smaller number of damage points before dying.

Generally I focus on improving my medium ships and cranking out a decent number of them, then researching logistics techs so I can put a lot of them in one fleet.

After I research carrier techs I move to large hulls. I've never really needed to go on to huge hulls, but if I'm far ahead on research I build some huge carriers.

Could you upload your mod?  It sounds like it could add a critical balance needed to the game.

So when you say alter your ship class in the editor, are you talking about when you design your own ship and designate what its role should be or something else?

again thanks for sharing this

in your opinion what would be the more fair and handicapped way to play if you do not do what you suggest which is pump out escorts full of armor and no weapons with, capitals covered up in weapons and 0 armor

Actualy somebody already took his time to put this on the wiki so it was unnecessary for me to read it out from the xmls but whatever.
Tips hat to whoever updated the wiki since the last time I checked.

Well in terms of fair play, try to stick somewhat close to the default designs or use a mod that changes the stock templates to something less bad. I think the InsaneAbundantBalance Mod does some things in that direction but I don't use it because as the title says it's balanced for insane and abundant map settings and I'm more of an insane occasional/rare player.

I'll probably start moding as the professional improvement of the game by the devs will take a while as it's usual with these kinds of 4x games.

If they allowed more than 1 shipyard per planet small ships would be really good.

But, they dont, so...

Just checked out the mod forum and nexus mods to look for interesting stuff and what did a find a mod that changes the target priorities also the forum thread.
It does the job okay, as long as you don't exploit the priorities but it can still be done better, so I'll probably do my own version that will try to improve the system further.

Larger hulls are sufficiently advantaged in potential strategic mobility relative to smaller hulls that I consider it unlikely that you'd be able to get enough smaller hulls to make up the difference. A ship built on a Huge hull, for example, can be as fast as the fastest possible ship built on a Large hull while still having 50% better attack and defense scores than the most powerful possible ship built on a Large hull which uses similar weapon and defense component ratios. A ship built on a Large hull that spends a Small hull's worth of capacity on hyperdrive components has the same strategic speed as a ship built on a Medium hull which spent the same amount of capacity on hyperdrive components, and the Large-hulled ship is about twice as powerful as the Medium-hulled ship, assuming both are built as warships with similar weapon/defense components and component ratios.

Moreover, especially later in the game, the hull manufacturing and especially maintenance costs become increasingly negligible by comparison to total ship manufacturing and maintenance costs, so the cost of a ship built on one hull class relative to the cost of a similar ship built on a different hull class is similar to the capacity ratio of the two hull classes. This would suggest that a Huge-hulled ship costs roughly as much as ten Tiny-hulled ships. A single Huge-hulled ship can have five times the strategic speed of the fastest possible Tiny-hulled ship while still having about five times the attack and defense scores (~= notional power) of the most powerful possible Tiny-hulled ship designed with similar weapon:defense component ratios. If the Tiny-hulled ships being compared to the Huge-hulled ship have exactly half the speed and power of the fastest possible and most powerful possible Tiny-hulled designs, that single Huge-hulled ship offers the same total number of actions per turn and ten times the notional power available per action as all ten of the Tiny-hulled ships you could get for a similar cost (assuming the Tiny-hulled ships are all operating independently; if you begin collecting the Tiny-hulled ships into fleets, the Huge-hulled ship gains more and more of an advantage in actions per turn and will never have less than parity in notional power per action). The Large-hulled ship described in the first paragraph only costs ~33% more than the Medium-hulled ship while having twice the power per action and the same total number of actions per turn.

Arguably, the smaller ships have an advantage in their higher tactical speed, but due to how battle resolution works higher tactical speeds are as often a disadvantage as an advantage. Arguably, the smaller ships have an advantage in the number of opponents that they can target per round, but larger ships can more or less make up the difference with a carrier module or two and often don't need to sacrifice that much for them.

End result is that there really isn't that much going for the smaller hull sizes under current mechanics unless you're in a situation where you don't have the economy to pump out the bigger ships at a reasonable rate (producing additional scouts for initial exploration can be an example, if you're unwilling to rush Cargo-hulled scouts and don't want to use construction or colony ships as scouts; using turn-0 tech, a Cargo-hulled scout costs about as much as three Tiny-hulled scouts to produce and the Tiny-hulled scouts reveal about as many tiles per turn, and depending on the map layout having more slow ships with short sensor ranges can be better than having fewer faster ships with larger sensor ranges, at least for a while).

Well, I agree for patrol ships and offensive invasion fleets. Small ships could really find a niche in key planet / starbase / shipyard defense though, where their lack of movement but superior fighting capability would make them extremely difficult to dislodge

I did this in one of my games once. Tiny hulls combined with the Hyperion Logistics allowed me to pack 64 well balanced ships around a planet for defense. That fleet destroyed several huge ship fleets with logistics at 60. And, it wasn't hard to replace any of the defending ships, if any were lost.