A motor for driving a propeller is disclosed which has a drive shaft (10) which is coupleable to a propeller shaft (20) by bevel gears (12 and 14) so as to rotate the shaft (20) to in turn rotate propeller blades P of an outboard motor. The drive shaft (20) has an internal concentric shaft (30) which enables the adjustment of the pitch of the propeller blades P by mounting the propeller blades P for rotation about a pitch axis and coupling the mounting (72') via an integral bevel gear (104) to a bevel gear (102) on the shaft (30). A phase adjustment mechanism (40) is provided for rotating the shaft (30) relative to the shaft (20) to in turn rotate the propeller blades P around the pitch axis to change the pitch of the propeller blades P. The phase adjustment mechanism comprises ring gears (48 and 50), together with planet gears (48) in engagement with a gear on the shaft (30) and planet gears (46) in engagement with a gear (26) on the shaft (20). An anti-backlash mechanism for preventing movement with propeller blades P about the pitch axis due to backlash within the gears of the phase adjuster mechanism (40), includes a screw-threaded section (252) coupled with the shaft (30) and the yoke (270) on the section (252) for movement on the section (252) in the longitudinal direction of the shaft (30). Engagement between the screw-threaded section (252) and the yoke (270) forms a rigid coupling of the shaft (30) to the propeller blades P so that any backlash in the phase adjusting mechanism (40) is not transmitted through the coupling to the propeller blades P.