It will be tough to do. Just converting from 220V Euro to 220V US will be tough, much less to 110 V.
Euro 220V systems use a hot a neutral return and a safety
ground. If you measure the voltage from the hot to ground you get 220V, not 110 as in a US system. US systems use 2 hots, a neutral and a safety
ground. 110 US wiring
is much like Euro wiring
with a hot a neutral and a safety ground.
The other problem is that 110V appliances
typically draw about twice the current
as 220 V ones. Take a 1000 watt toaster. For a Euro system it will draw about 5 amps. A US 110V toaster will draw about 10 amps. The problem you will face is that the wire size may be too small to handle the increased amperage.
All US home and boat 110V circuits are at least 15 amps, some 20 amps. I suspect that the outlets on a Euro boat are rated smaller than that and the wire is smaller- less than the 14 gauge required for 15 amps.
So to do a full conversion will be very expensive. Most appliances
will have to be replaced and the wiring serving them will probably have to be replaced as well.
So.... My advice is to budget
lots of money
, probably $20,000 if you want to do it right.
There is another way to do it but I doubt that it meets US electrical
code. Install a 220/220 V isolation transformer. One side is wired to the US shorepower system and the other side is wired to the Euro boat system. You can only use 220V shorepower though, never 110V.