*Not sure if this was related to my comment about 2 x 30A cords.* In our case and chosen marina (not there yet)*there seems to be an option of taking 50A at 110V split with a 'Y' connector from a 50A shoreside socket.* I belive this comes from a* 415V 3 phase marina supply circuit to the docks, split to give 208V/50A outlets*which can be further split to give 110V (nominal, really 104V max) and 50A via a 'Y' connector and 2 x 30A cords to on board* Like I said your systems have a really confusing array of options!*
Is this marina in the U.S.?* I don't think 415V 3 phase is used here, but perhaps that has changed.* Seems like there would be lots of transformers involved to do what you are suggesting.