Catamarans are typically a small-medium ship with 2 hulls connected with beams. This is a beginner guide for novices and people who want to start building catamarans. You may have noticed, they have incredibly high stability, often 300+. It is rare to see a half battleship, half carrier catamaran(on the hulls). Don't try to mix the two, because well-placed volley wil easily knock your ship off balance. Stick with one type.
Building A Catamaran
To conserve space, use large 3x2x1 armor/hull. 2x2x2 is also an option. A catamaran, as mentioned above, is basiclly two small hulls with one connection part. Put the guns onboard to hulls, and the bridge on the middle connection. If building a carrier, put the runways on the hulls instead of guns. Make to speed tweak your catamaran, see the Speed Tweaking page for details. It is possible to get rid of the bridge, and use the connection part as a gun platform. Use the recon plane instead.
Catamarans are effective combat ships, but their main issue is this- The two hulls will limit the total size of the said ships. 46 cm guns aren't very common, because your ship will have to be very wide to accomadate them, and that makes a perfect target for enemy gunners. Use 30.5+ guns, and 40cm triples in lieu of 46's. One way to sink a catamaran is focusing all your firepower on one side. It's harder than it looks, but still a legitimate strategy.
Overall, act like whatever your design was, aircraft carrier or battleship. Catamaran subs are pretty much impossible. Some people have made catamaran subs, so congrats to them.