Collectors of Lego City sets might like to consider including a harbour for their city/town (knew most of the city lego fans collected all the modular sets).
Here is a clip of a lego motor boat. If you played with radio controlled motor boats, adding the motor to create the lego boat shouldn't be too difficult.
A motor build of lego will required some knowledge and practice.
Viewed a couple of lego boats/ships clips tonight, I used to have a moc classic lego boat when I'm in primary three and it was my favourite toy. There was a photograph of me holding the MOC ship proudly. I took part in lego building competition during the 80s in Singapore, although I didn't win anything it was a nice childhood memory.