Below is a basic explanation of each type of drive.
1. Inboard Drives
The term drive is interchangeable with motor and engine, so an inboard drive is simply a marine engine enclosed inside the boat. With an inboard drive, the shaft, rudder and props are beneath the boat leaving the transom clear. Inboard drives can either be gas or diesel, and single or twin engines are optional. A marine V-drive engine is a modified conventional inboard drive that is placed closer to the stern of the boat than a conventional inboard drive.
2. Outboard Motors
Outboard motors are self-contained units mounted to the transom. Each has an engine, propeller, and steering control through the lower unit that acts as a rudder. Outboard motors are the most common type of boat propulsion.
3. Sterndrives
Otherwise known as the inboard / outboard marine motor, sterndrives are thought by some to be the best of both worlds. The engine is mounted inboard forward of the transom with a shaft that goes through the transom to the drive unit. Similar to the outboard lower unit, this portion of the engine has a propeller and acts as a rudder to steer the boat.
4. Surface-Piercing Drives
Surface drives are specialized drives, mostly used by high performance boats, with a propeller that "pierces" the surface of the water to provide increased thrust. They operate half in and half out of the water in the planing wake of the boat, with a propeller shaft that exits almost horizontally through the transom.
5. Jet Drives
Most often used in personal watercraft or very large boats, jet drives replace propellers to push a boat through the water using high pressure air forced out of the stern of a vessel. The water jet draws water from beneath the hull, and passes it through impellers and out a moveable nozzle that steers the boat. 6. Volvo Penta Inboard Performance System
6. Volvo Penta Inboard System
The Volvo Penta IPS is a newer drive system set up directly beneath the engines. Forward-facing propellers pull on the water beneath the boat, increasing efficiency and speed by up to 20 percent.
