One of the fundamental rules of electricity is that when you double the voltage from 120 to 240 you cut in in half the amps required to do the same work required. The amps are the big thing and these are the actual workforce. By using less amps he can now use a smaller wire size which means his runs were easier and actually weighed less. In theory the motors should run cooler too because a byproduct of more amps is more wasted heat. This does have other complications because he will still need 120V to run all the standard daily plug
in stuff and will need 12V to run other boaty stuff too. This is when other electronics
are needed to step down the voltage. Kaching!
FWIW boat aircons are available in 12V DC, 24V DC, 120V 60 Hz AC, and 240 AC (50 or 60 Hz) plus other voltages for the really big boats. Only really small units can run on 12V DC because the amp load is so high and 24V units are rare. DC is direct current
like your car battery
and has a positive and a negative side, AC is alternating current and alternates the positive and negative 60 times a second here in the US and 50 times in Europe
and elsewhere and that is expressed in Hz for hertz. We use 120V 60 Hz for our basic stuff but use 240V 60 Hz for larger items like electric
stoves and the central air in your house. The Euro voltage is 240V 50 Hz for everything but the 50 Hz part might cause some problems with some appliances
here (like boat aircons) so buying
a boat wired that way has this and other potential issues. In fact the wire may be too small (but not always) to convert the boat to 120V US specs. Kaching!
ABYC (American Boat and Yacht Council) certifies marine
electricians and I suspect that the hourly rate might be close to a regular electrician. You do need a marine
electrician though. The systems are different. I think that it is a rule
but not a law that one has to be certified to do marine electrical
work in the US and many yards may have really good uncertified help. In OZ it is a law I think.
And I left out the best part. A boatbuck is a $1000 and you will be spending these regularly. Kaching!