Marine Transmissions

1) Explain the different types  of gear selection systems found 

a)In outboard gearcases and stern drives.
b) Inboard marine gearboxs.
2) what types of gears are used in out boards and stern legs.
a) give an explaination of why manufacturers choose this type of gear box.
3) explain what A duo propellor system is and how it works/operates
4)why would a V drive be used  instead of a standard shaft drive system
5) compare a jet unit with a surface drive unit and give reasons why you would choose one system over the other.
1).Inboard Marine Gear Cases:
engine is spinning the drive shaft but the direction of prop shaft is different.The direction of the prop is changed by the pinion at the end of the shaft.
All the three gears turn at same time.
pinion gear is smaller with smaller tooth and it turns two and half times for every rotation to the forward and reverse gears.
Inside the reverse and forward gears is the prop shaft  has four large “dogs”. When the shift lever is moved the dogs connect with either the reverse or forward gears. Only one  can engage the drive shaft at a time. The dogs are strong. If the reverse and forward gears were always engaging and disengaging with the pinion gear.  These are also known as constant mesh gears.
Stern Drive:It is a basic transmision. A locking mechanism (clutch dog) is moved by a cable and a lever to change from forward gear to reverse, with a neutral in between. It can't jam it in reverse  as it is linked to the throttle cable to prevent the engine when at full rpms.