I don't know, when we started the project we ran with the "OBD-M" and determined that it _should_ be J1939. From there it was just a decision to cut the cable on the ScanGaugeD to see if we could get anything useful from the data on the bus and we lucked out. I happened to have the ScanGaugeD since I was going to use it my VW TDI, but using it in the boat was much more useful.
I would suggest the first step is figuring out if/where the OBD-M connector is in your boat, and from there try to identify what protocol it uses for communication. The guys at obd2allinone.com are very helpful too, their website (or a phone call) should be able to help you determine what protocol your MEFI controller uses and you can go from there.