seems to be up to the discretion of the dockmaster/.marina. i had a 15' beam, was placed in 14'wide slip.....go figger.....was many yrs ago. most seem to place the boats appropriately-give the marina the dimensions of boat and they are w=able to find a slip, if there is one.
btw--my , at the time, power boat
, actually did fit the slip--the overhang was the decking overhanging the fingrs--the hull
fit fine between the fingers of the slip..all the slips there were 2 finger .....