Yes, the Marinco pigtail adapter Sailmonkey referred to is the right thing.
HOWEVER, be very careful not to overload the circuit. Your
boat is wired to handle loads up to about 30A. The shore source you're plugging into can only handle a maximum
current of 15A or 20A (depending on the circuit). So, you need to be careful what devices/equipment you turn on aboard.
Make a list of the principal
equipment aboard using 120VAC
current, and find out how much amperage each one draws. Any thing with a
heating coil will likely draw a lot of current.
Electric heaters, for example, typically draw about 12-13A so just one of these will get you up to near the maximum you can expect to draw from a 15A shore
plug. This leaves very little room for other items.
Coffee pots, microwave ovens, air conditioners, etc. are also high-current items. You need to investigate and find out for sure rather than play
electrical roulette and burn something up.
Bill