I am going to have to say that a Dreadnaught isn't necessarily going to be big, heavy, heavily armored, and slow. And I'm talking about airships; unless there is some gas that can be found underground, easily made, or otherwise accessible in some way to allow mass-use, then a Dreadnaught would just be a larger, more heavily armed ship, not necassarily slower or more armored. Or we have perfected the technique of compressing hydrogen.

What I'm getting at is that don't define them quite so much. Say a Dreadnaught is a much larger type of military airship, but don't completely define them. For example, I'm focusing on very lightly armored ships, with less weapons overall, but because they are heavier guns with longer ranges. Less armor; more engines and boilers. They'll be able to move faster and fire longer, but if someone else's traditional Dreadnaught comes into range, then this Dreadnaught is a dead Dreadnaught. Same with frigates; less armor and guns, more speed and range. 

Is that acceptable? Or must we all play it like a game, with only a pre-defined ship type that's pretty much all-around?

EDIT: And I see why you may want just a single list of ship types, I do. Much easier to predict the outcome of a battle if everyone has the same pieces. But let people individualize it a bit; set it up like a game. A frigate is this big, can carry this much weight, and can carry this much coal[boilers] and ammunition. A dreadnaught is this big to this big, can carry this much more weight, etc etc

Then every nation adds it to their Nation Application, and to the bottom of their post if in a player-vs-player battle. Let people have so many 'points' to spend on a ship, with more points for the larger ships. A ship may be dedicated entirely to speed, with practically no armor or heavy weapons, and may just have a couple ballista on the top with explosive bolts. Or it could be heavily armored, with only a couple artillery pieces and a mainly a full storage bay of bombs to drop on a city, helpless to stop the armored behemoth. Of course, taking one Frigate and ramming it into a Dreadnaught would result in both going down, regardless of armor: the weight of armor in a Frigate will surely mean getting through a Dreadnaught's armor, getting stuck or just hitting something crucial. The Frigate may drag the Dreadnaught down with it, or just fall right off, leaving the Dreadnaught to die slower. But airships are terribly expensive; you'd have to put someone in quite the spot to have them ram your ships.