I use various size bases for a given ship class. However, I use W@S miniatures, so I'm sure my ship bases are larger than most people are accustomed to.
I only base MTBs mutiple units to a base. Corvettes, Frigates, Minesweepers, Sub Chasers get a small base for each ship.
I use .030 or .040 Styrene plastic sheet, with a paper strip with the ship name, type and nationality (Arial, 8 point) glued to the right rear of the stand. Each ship gets it's own name (for campaign purposes).
Example: USS Arizona BB-39 or Roma BB (IT)