people put Isolation transformers on their boats for protection and not to step down down the 220v to 110v.
- if you have a 50a/220v; means that you have two 30a/110v split phased to create 220v on the boat if needed ( most likely everything on your boat is 110V). All your panel breakers (on the boat panel) are divided between the two hot legs accordingly to create a balanced load.
- if you have X2 30a/110v; means that you use two 30a/110v split phased or not.
Unlike boat with 50A/220v shore power, everything will always work on boats with x2 30A/110v regardless if you are two split phase 110v or not. the 50/220v boat need the two split phase 110v to run 220v items.
I hope that i did not confuse you,
Regards,