Marine Transmissions General Features

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 Classification

The marine transmission is classified according to their location in the boat as In-board transmissions and Out-board transmissions or lower units.
Additionally, the inboard transmissions possess different gear ratios and output torques depending on whether they are designed for diesel or gasoline engines.

In-Board Transmissions

The inboard transmissions are classified according to the configuration between the motor and the propeller shaft into a)  In-line shaft, and b) V-drive shaft.

 

 

Gear Box or Transmission?

In technical terms, the gearbox is part of the transmission. A gearbox is basically a synchronized group of toothed wheels that are used to transfer motion from one shaft to another. And a Transmission is a gear box controlled, manually, hydraulically, or servo-assisted.
The marine transmission is a perfect combination of the three systems with a constant gear ratio on forward and reverse.


 

In-line Transmission (Parallel Axis)

In this configuration, the input and output shafts are parallels, with a short separation due to the gears thickness and bearings thickness.

 

In-line Transmission (Straight Axis)

In this configuration, the input and output shafts are on the same axis due to the use of hollow shafts with plain bearings. 

V-Drive Configuration

The V-drive transmission systems of yesteryear possessed a bad reputation for their racket and gear noise. However, today’s V-drive transmissions from companies such as Twin Disc, Velvet Drive, and ZF offer smoother and quieter operations. Gearing can be specified to suit the boat, engine, and style of boating.

 

 
Get here the Marine Transmissions Book where you can find all the information on this and many other topics.
 


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V-Drive Vs. Stern-Drive

Why?. because an inboard running gear generates a lot of drag, reducing speed and miles per gallon versus a stern-drive. Also, a stern-drive’s angle of thrust is virtually horizontal, further increasing efficiency over the 7- to 12-degree down angle of an inboard’s prop shaft.

 
 

 
 
 
 
 
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