1. Engine Operation: Figures 1 and 2 borrowed in large part from the Yanmar engine manual show the general configuration. The engine input shaft takes power directly from the engine. Two small gears attached to the input shaft drive large reduction gears concentric with the output shaft and with bearings allowing them to turn independently of the output shaft. One of the small gears meshes directly with a large gear (forward) and one meshes with the other large gear via an intermediate reversing gear on a separate shaft (reverse). A drive cone is attached to the output shaft with spiral splines, allowing the drive cone to shift laterally when pushed by a shifter which rides in a central groove of the drive cone. The drive cone has matching truncated cone surfaces on both ends which mate in a clutching action either with the forward large gear or the reverse large gear, depending on which way the shifter moves the drive cone. Once moved into conjunction with one of the large gears, the shifting spring pressure serves to maintain a force between the drive cone and the respective large gear mating surface and under engine operating conditions, the spiral splines in conjunction with the spring pressure serve to generate a multiplying or servo force, assuring that slippage between drive cone and large gear does not occur, either in forward or reverse. 2. ENGINE OFF SAILING UNDERWAY A. Engine in forward. Figure 1 indicates that the propeller shaft tends to turn clockwise, (viewed from the rear) . With the transmission in forward, the shifter spring tends to push the mating surfaces of forward large gear and drive cone together preventing movement of the propeller shaft but the tendency of output shaft to rotate tends to separate the mating surfaces because of the spiral splines, leading to the potential for slippage. Whether it slips or not depends on the through the water speed, the condition of the shifter springs and shifter adjustment, and the characteristics of the propeller. Since the action of the splines and the shifter springs are in opposite directions, if movement does occur, it will be with the shifter cone continually engaged, leading to unnecessary wear of the shifter cone and forward large gear mating surface. [137] B. ENGINE IN REVERSE. Figure 2 shows that with the transmission in reverse, the drive cone is similarly pushed into the mating clutch surfaces of the large reverse gear but now any incipient slippage between the gear and drive cone leads the servo tendencies of the spiral splines to tighten the contact between the drive cone and large reverse gear, preventing movement. In this case, the higher the speed, the tighter the clutch connection so that differential movement between the drive cone and mating surface of reverse large gear is positively prevented. C. ENGINE IN NEUTRAL Figures 1 and 2 show that lubrication of the bearing and gears is largely carried out through the action of the large gears turning in the small amount of crankcase oil in the bottom of the transmission case, lifting and circulating it to the remainder of the bearing and gear surfaces of the transmission. With the transmission in neutral and the large gears not turning, there is the possibility that oil will not reach the bearings of the two large gears which are in motion. Operation in neutral while sailing also imposes wear on the cutlass bearing and stuffing box. 3. CONCLUSION. ALWAYS SAIL BOATS WITH 1GM,2GM AND 3GM TRANSMISSIONS WITH SHIFTER IN REVERSE.