Draught is the most common and often most arduous constraint to meet. Draught restrictions arise from areas of operation (i.e., in shallow water, particularly where transiting into brackish or freshwater), depth available for moorage at port, the capability of local drydocks for maintainability, physical restrictions of the constructing shipyard to launch the hull, etc. Where general parameters of a concept design approach a draught restriction, it is typical to design to that constraint. This allows for the largest possible propeller diameter and immersion, generally maximizing propulsive efficiency. For two designs with the same hull depth, increasing draught also increases displacement without increasing steel weight.