If the marina you are planning on visiting can handle the depth and
length of an Amel, they will most probably supply 50 Ampere / 220Volt
power. The supply outlet may in the form of a single twist lock plug.
The plug contains 4 connectors which are both phases of 110 volts, a
common and a ground wire. Many boaters (the majority are power
boaters) in the USA will then use a "splitter" to separate this
supply into two 110 volt cables which are then plugged into their
vessels as two separate cables. For the Amel, we simply plug the
single 220V cable directly into the boat.
Some marinas supply two 110 volt twist lock plugs on a post. These
outlets are of opposite phase so they can be combined to produce a
220 volt supply. This is the inverse of the "splitter" mentioned
above and can be purchased from WestMarine (www.westmarine.com).
WestMarine call this a "Reverse Y Adapter" Model 491985 and it sells
I have only once had to use a transformer to get 220V from 110V and
that was because I did not have a 220V extension cord at the time.
This approach is also very limiting as you probably won't be able to
take enough power off the 110 volt supply to run air-conditioners
without throwing it's breaker.
BTW, anything that has 220V on it tends to cost a fortune in the USA.
For example, a 50 foot 110 volt extension cord may sell for US$40 but
a 50 foot 220 volt extension cord may cost near US$600. If you are not
afraid of using a screwdriver, you can cut the plugs off a 110 volt
extension cord and replace the plugs with 220 volt plugs.