thats a harsh one, depending on you length of stay in the states, you will a) not be able to refill you Euopean bottles
b) have a hard time finding an 'adapter'
Your best option would be to look for the first threaded fitting from the existing tank and work back to the tank from there... with the goal being to make it fit the US style tank, then get the cheapest US tanks
you can find that fit your application, as when you leave again, the US tanks
will be obsolete for you....
Some other concerns would be what you plan on doing with the boat, if you are staying in the states, same fix, but get better tanks. If you are going south into the caribbean
, keep both... south america
and beyond, to the pacific, forget the US tanks and fittings, keep the EU tanks/fittings....
On the brightside, the brass fittings are available at most hardware
stores to make this happen.... you could even fit it out to use the little disposable US tanks if you are just passing through....