We need to know the following before we could specifically answer the question:
1. The overall size;
2. Is it a performance boat, cruising boat, or scale ship?
3. What kind of propeller and speed are desired?
For a performance boat we look for high kv motors that can run on 2-3 cell batteries and a high pitch cavitation propeller.
For a cruising boat the best option is something with a little bit lower kv with the option to run 2-3 cell as well with a slightly larger more scale like propeller.
Finally for a scale ship the best option is a low KV motor, like 800-900, specially if there will be 2-3 motors spinning a large 3-4 blade propeller.