Inboard, outboard, and I/O (Inboard/Outboard) are different types of boat propulsion systems. Each has different uses and strengths that are laid out below, along with a basic overview of the engineering.
Inboard boats have their engines mounted inside the hull of the boat, typically toward the center or stern. The engine's power is transferred through a shaft that runs from the engine to the propeller, which is located at the exterior of the boat. Inboard boats are known for their smooth and efficient performance, and they are often found in larger vessels like yachts and some sports boats.
Outboard boats have their engines mounted externally at the stern of the boat. The engine combines the powerhead (engine), the gearbox, and the propeller into a single unit. Outboard motors are versatile and commonly used in a wide range of boats, from small fishing boats to recreational vessels. They are easy to install, maintain, and offer good maneuverability.
I/O boats are a combination of inboard and outboard systems. They have an inboard engine mounted inside the hull like in inboard boats, but instead of a direct shaft to the propeller, they use a sterndrive unit. The sterndrive unit is mounted outside the back of the boat, combining elements of both inboard and outboard systems. The power from the inboard engine is transferred to the sterndrive, which has the propeller attached to it, providing propulsion. I/O boats are popular for their performance and space-saving design, as the engine is inside the boat, and the sterndrive unit doesn't take up as much space on the transom as an outboard motor.
The choice between inboard, outboard, or I/O boats depends on factors like boat size, performance requirements, budget, and personal preference. Each type has its advantages and disadvantages, so it's essential to consider your specific needs and usage before making a decision.