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Inboard Engines and Components

An inboard engine is a type of marine propulsion system in which the engine is enclosed in a housing within the hull of the boat. It connects to the propeller with a propulsion screw that is powered by a driveshaft. These engines require maintenance and occasional repairs in order to ensure that your boat can enjoy its expected level of fuel economy, power, and performance.

How do marine diesel engines work?

Marine engines using petroleum-based fuels were invented in 1895 and modeled after the combustion engines of other machinery. The engines were refined to operate the same way as an automobile's motor by the 1920s. The inboards operating on diesel work by using a stern-drive propulsion leg that attaches to the propeller at the back of the boat. Diesel is combusted in the same process as it is in an automobile's engine. The diesel drives the inboard engine, generating steam that moves pistons and the propelling leg to cause the vessel to move forward or backward. Diesel powers one cylinder to v12 equipment.

How are marine inboard engines cooled?
  • Freshwater: A constant flow of freshwater may be used to keep the engine cooled. Inboards that do this are typically one-cylinder or two-cylinder engines.
  • Sea water: In some cases, the inboards make use of raw or saltwater cooling setups. Because the saltwater contains salts that are potentially corrosive to the engine and could interact with any leaking diesel fuel, these cooling systems usually use zinc anodes to capture the reactive salts so they do not cause any corrosion on the diesel-fueled engine.
  • Heat exchanger: A powered heat exchanger can also be used to cool engines of boats. The power heat exchanger works by indirect cooling with a chemical refrigerant, much like an air conditioner or a refrigerator. It absorbs heat from the engine block and dissipates it to the exterior of the hull with the use of a fan that is powered with electricity from the boat's battery.
What kind of steering pairs with inboard engines?

Boats that have inboard motors will have a number of different configurations to offer different steering options. The size of the boat and the configuration of the hull help to determine which steering and propulsion method works best for the boat.

  • Single screw: This refers to a boat that has a single inboard engine and one propeller. It is typically steered exclusively with a steering wheel. This kind of steering requires some practice when it comes to docking and maneuvering in tight places. It is relatively fuel efficient.
  • Twin screw: This refers to an inboard engine, or more likely a pair of inboard motors, that are each attached to their own propeller. Additional maneuverability comes with a second propeller, and you can pivot a boat by putting one propeller in forward and the other in reverse.
  • Bow and stern thrusters: These are jet drives that run perpendicular to the direction of travel for the boat's inboard propellers. They are found mainly in large boats and help inboards to maneuver sideways when docking.
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