MARINE TRANSMISSIONS

Explain the different types of gear selection systems found in an:
Outboard gearcase:
An outboard gearcase uses a dog clutch system, that works by sliding the dog clutch to engage either forward or reverse gear. When the required gear is selected, the dog clutch locks that gear onto the output or propeller shaft. This type of engagement is very rough and is noisy.

Sterndrives:
A sterndrive works by having it's gear selector located vertically in the top housing of the ''leg''.  When forward or reverse is needed, a tapered brass cone moves up or down to lock the required gear onto the shaft. The cone type engagement works alot like a baulk ring in a manual car gearbox. Normally used in boats with smaller inboard  engines, that require smooth gear engagement.

What type of gears are used in outboards and stern legs?
Give an explanation of why manufacturers choose this type of gear.
Outboard and stern leg gear cases normally constant mesh, which mean all gears are moving even when not engaged. Constant mesh gears normally use helical cut gears, as they provide more contact between the driving teeth.

Explain what a duo propeller system is and how it works?
The duo prop system was invented by Volvo Penta and works by having two counter rotating propellers. One prop is mounted on the mainshaft, while the other is mounted on the counter rotating shaft that runs through the main prop shaft. This is used for increased acceleration, straight tracking, faster planning, better handling, lower

 vibrations and noise reduction.

Why would a ''V'' drive be used instead of a standard shaft drive system?
A ''V'' drive system is used to change the direction that the  engine is mounted, and to move the bulk of the engine back towards the stern of the boat, which also creates more space . This provides easy access to the main components driveline components.

Compare a jet unit with a surface drive unit and give reasons why you would choose one system over the other.

A jet unit works by sucking up water and forcing it out at high pressure through a directional nozzle. Jet units are common in shallow waters as they are mounted level with the bottom of the hull. Jet units have some drawbacks, which are that they have no control at low speed and if debris is sucked up, the impeller can get damaged.
Surface drives are normally found on high powered inboard boats (racing), and only have 2 to 3 propeller blades in the water at any one time. Surface drives provide excellent acceleration and quick planing but, expensive to buy.
I would personally choose the jet unit over the surface drive as it is a better all round

 propulsion system.