Does this allow you to switch between the two? Our next boat will more than likely have 220V but we don't want to change it as it won't be sailed in just the U.S.
Looking for an answer to the original question as well.
See my previous post for information about conversion. In general it is far easier and cheaper to convert a boat from 110vac to 220vac. You know the wiring is big enough and that is the big hassle.
For world cruising you want the ability to use either
voltage/frequency - 220/50 and 110/60. Setting that up is not as hard as it seems with some reservations.
A note about step down or step up transformers...
This is an elegant solution if your battery charger and equipment can take the voltage and frequency variations. Marina shore power is not the best in the world - the voltage can vary quite a bit. You might find that the step-up or step-down puts the voltage out of specification for certain things on your boat. My old inverter-charger refused to run as the step-down from 220vac to 110vac was 1 volt too low so it alarmed on a "low voltage" alarm and refused to run. I could not charge the batteries. The nice part of this solution is that everything on the boat works - as long as it can tolerate the potential voltage and frequency variation. The transformers are bulky and heavy - most are placed on the dock between the pedestal and the shore power inlet with appropriate cords so they need to be waterproof too. Also some equipment might not take kindly to the conversion from 50Htz to 60Htz or 60Htz to 50Htz.
Presuming you want to go the more bulletproof route...
1. Decide on your internal AC usage configuration. You don't want to have to purchase two TV,s two microwaves, etc. So decide if your appliances are going to be 110vac or 220vac. Get a boat that is wired for that voltage. The only downside to this solution is if you have guests that use the other voltage. Lend them the necessary appliances.
2. Have or purchase an inverter that outputs the appropriate voltage for internal use. You have now disconnected the reliance on input voltage from the internal use voltage. For example:
If you have a 220vac system purchase an inverter that outputs 220vac
If you have a 110vac system purchase an inverter that outputs 110vac.
You will run all of the internal appliances from the inverter circuit.
Purchase a second battery charger (I presume you already have one) for the other
If you have a 220vac system you would purchase a battery charger that inputs 110vac
If you have a 110vac system you would purchase a battery charger that inputs 220vac.
As I pointed out in my previous post you may already own a "world charger" that accepts both 110vac/60htz and 220vac/50Htz. If so you are semi-home free. Since the specification calls for the boat inlets to be male plugs (with the pins sticking out) it would be unsafe to wire a 110vac inlet and a 220vac inlet in parallel since plugging in the one would make the other "hot." Also you need a 110vac breaker at the inlet and a 220vac breaker at the inlet with different amperage ratings (remember the 110vac is going to be 30 amp and the 220vac is going to be 16 amp. Also if you have pure AC appliances (such as air conditioning) you run the risk of sending the wrong voltage to the appliances. The better solution is the next paragraph.
Even if you have a "world charger" get a second battery charger of the right input voltage. Wire each charger (with the appropriate circuit protection) to the appropriate shore power inlet. This configuration will not let you use your air conditioning when in the wrong power zone but it is pretty fail safe.
This is basically how my boat is set up as I have cruised in both voltage regions.
Fair winds and following seas