The 125/250V
shore power is much more available...
What is your
boat 50 straight or the 4 pole 125/250V?
If your boat is straight 50A then a 50 to 30 to
plug in is all that is necessary.
If your boat is 125/250V, then the much more expensive 2-30 to 125/250 50A smart adapter would be required.
You can get a 125/250 50A adapter that plugs into a
single 30A
dock receptacle...but it really limits your boat power.