Kent and all:

By way of explanation:
220 AC (alternating current): Picture a wave on the ocean (actually a sine wave). You measure the height of the wave from the trough to the peak and come up with 220 feet, (it is a really big wave). The boat sees that wave and thinks, "wow, that is a big wave". The boat doesn't KNOW whether the 220 feet from peak to trough is measured relative to mean sea level, mean low tide, or mean high tide. All the boat KNOWS is that it is a 220 ft wave. Now if the wave passes under the boat (hopefully) 60 times a second, that is equivalent to sixty hertz. If it passes under the boat 50 times a second, that is equivalent to 50 hertz (a hertz is a cycle per second when speaking of all things electrical). I think you can see that more energy is expended/used/dissipated by the boat going up and down 60 times a second compared to going up and down over the waves at 50 times per second.

Now to electricity. The load (washer, microwave, heater or whatever is using electricity) doesn't know if it is seeing 220 volts generated in Europe or in the US (actually EMF or electromotive force). All the load sees is the peak to peak change in voltage and that is identical in the US or Europe except for hertz. The difference between 220 volt European power and 220 volt US power is only in Hertz and the color codes of the wires. The load sees no difference in voltage but does run at a different speed due to the difference in Hertz. Granted less work is done per minute by European power (fewer cycles) than by US power. Motors and electronics using timers etc are sensitive to the hertz (frequency) of the power. Grounding and bonding are different between the US and Europe but that is a whole different story. Neutral in the US (white wire in household US wiring) is just that. It is Neutral, that means that it SEEs the sine wave power at 1/2 way between the peak and the trough of the wave 220 volt wave. Since it only SEES 1/2 of the wave height it only SEEs 110 volts. In the ocean wave analogy, Neutral is 1/2 way between the peak and trough of the wave.

On my Amel SM Hull 335, the 220 volt cable is sized for 30 Amps at 50 hertz.. I have the 110 volt cable with the 110 to 220 volt step up transformer (installed as an option by Amel with the change over box in the engine room) like you. You have to be able to draw 60 amps at 110 volts to equal 220 volts at 30 amps. Furthermore, when plugged into 60 hertz power that cable must be able to handle more POWER than when plugged into 50 hertz power. I do not know the amperage ratting of the transformer but 60 amps is a fair amount of power. Consider that the average US house has 200 amp service. I sized a 60 foot extension cord for my Amel that could handle 60 amps at 60 hertz.. My thinking was that, that way I could use it for either 110 or 220 power. This was a mistake on my part since the cable is 1 inch in diameter and weighs about 100 lbs. I paid about $500 for this cord and couldn't return it, so I lug it around being mad every time I use it. Even if you upgrade your Amel 110 volt cable, the wiring downstream in the boat (i.e. from the garage to the step up transformer might need to be upgraded too. I suggest that you just use a little less power, and install a multimeter before the 220 volt panel that will show you Watts, Volts, Hertz, Amps, and that way you can monitor your power usage. See my Photo section under watermaker service (I think that is where I put a picture of my multimeter). I will post subsequently with a link to the vendor.

Don't feel bad about getting different answers about this from most electricians. My experience is that 95 % of US electricians don't have a clue about European power. By the way, as you know, we in the US are a minority in the world for our power. Virtually the rest of the world uses 220 volt /50 hertz power.

Hope this helps.

Gary Silver

Amel SM #335 s/v Liahona