Does the Power Plant Number need to be an integer?
HG80, page 34 (about small craft design):
Drives: Small craft do not have jump drives. Maneuver drives and power plants are selected from the drive tables and installed. No maneuver drive or power plant may be less than one ton; when a computation produces a drive of less than one ton, use a value of one ton (fractional drive values above one ton, such as 1.7 tons, may be retained instead of rounding). The power plant number must be at least equal to the maneuver drive number, but may be more.
So, I guess they don't need to be an integer, though, AFAIK, there's not so clear notation about spaceshios/starships...