Wednesday, April 9, 2008

Drive Systems (Outboards)

There are four things that make your powerboat move:

1. A power source (your engine).

2. A propeller or pump to push.

3. A connecting device to connect the engine to the propeller / pump.

4. Devices to control the amount and direction of the thrust.

Outboard motors range all the way from 2 horsepower HP portable models, to 350 HP bolted directly to the transom stern of the boat or to a bracket that is then bolted to the stern.

The outboard is basically a self-contained unit, consisting of a engine, the drive shaft and the lower unit (gear, housing and propeller). The throttle, gearshift and steering are attached to the power head. To change the direction of a boat using an outboard motor, the entire unit - power head, intermediate housing and lower unit - swivels, changing the direction of the propeller thrust.

Some advantages of the outboard motor are that they're lightweight for the HP that they produce, and because they are located "outboard", they take up little or none of the boat's interior.

A disadvantage is that there is generally a cut-out in the transom for the outboard, leaving the vessel more vulnerable to water breaking over the stern and coming into the boat. Also, the majority of the engine's weight rides outside of the boat itself. This tends to adversely affect the trim of the boat, causing it to be down by the stern.