A marine transmission includes a synchronizer on a counter rotating shaft to shift into a high speed gear. The synchronizer includes friction surfaces on both sides of the gear body for the high speed gear. The high speed gear mesh is helical and generates axial force that enhances the torque carrying capacity of synchronizing friction surfaces, thereby enabling the shifting into the high speed gear without torque interrupt.

A method for shifting a marine propulsion device transmission between first and second gears transmitting torque from a powerhead with a redline RPM. The transmission has a transition time for completing a shift. The method includes measuring an RPM of the powerhead, comparing the RPM to a first threshold, and starting a timer when the RPM exceeds the first threshold. The method includes measuring the RPM of the powerhead after the first threshold is exceeded, comparing the RPM to a second threshold, stopping the timer when the RPM exceeds the second threshold, determining an elapsed time between starting and stopping the timer, and determining a shift RPM based on the determined elapsed time, the redline RPM, and the transition time of the transmission. The method includes controlling the transmission to shift when the RPM measured for the powerhead reaches the shift RPM such that shifting completes before the redline RPM.