inboards

Inboards are marine propulsion systems in which the engine is installed inside the hull of a vessel rather than mounted on its exterior transom. Power from the engine is transmitted to a propeller through a shaft connected to a transmission, and often a reduction gear, which allows the engine to run at higher speeds while the propeller operates efficiently at lower speeds. The propulsion arrangement is typically paired with a rudder and provides a clean deck layout with less exposure to the elements compared with outboard motors.

Common configurations include straight shaft systems, where a single shaft runs from the transmission to the propeller near the stern; and drive arrangements such as V-drive or other stern-drive concepts, which route power through gears to place the propeller in line with the vessel’s stern. Inboards can be powered by gasoline or diesel engines, with four-stroke and two-stroke designs represented in different sizes and power ranges. Cooling can be raw water, closed-loop with heat exchangers, or a combination, and exhaust systems are designed to minimize backflow into the hull.

Advantages of inboards include better protection for the propulsion system, quieter operation, reduced deck clutter, and more balanced weight distribution. They are common on many sailboats with auxiliary engines and on powerboats designed for higher-speed or heavier vessels. Disadvantages include higher initial cost, more complex installation, and maintenance access challenges, particularly in smaller boats, as well as potential space and weight considerations within the hull.

Maintenance focuses on the cooling system, fuel system, lubrication, belts and hoses, exhaust, and regular engine inspections. Safety considerations emphasize proper ventilation, fuel handling, and carbon monoxide precautions in enclosed engine spaces.