Here is a link to step up-step down transformers.
Step Up Voltage Transformer Converter - Step Up/Down Voltage Transformer, Step Down Transformer, Step up Transformer, Step up Voltage Transformer, Step UP/Down voltage converter/Regulator, step up and down voltage converters
USA 240v 4 wire power has two hot wires with 240volts between them, a neutral, and a ground. Using the two hot wires you get 240 volts, using either of the hots and the neutral gets 120volts. The ground is a safety ground.
You can try google search on the terms 'step up transformer 120volt to 240 volt'
Another google search would be 'convert usa marine electricity to european marine electricity'
Hope this gets you started in the right direction.