schematic perspective view of the bow thruster of FIG. 1.FIG. 3 is a further enlarged sectional side view of the bow thruster of FIG. 1.FIG. 3A illustrates a side view of an alternative embodiment of the bow thruster of FIG. 1 having telescoping means on the air discharge duct and showing the motor blower reversed.FIG. 3B illustrates a front view of an alternative embodiment similar to FIG 3A hav