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Module 1 Batteries
Module 2 Wiring

Module 4 Lightning
Module 5 DC Systems
Module 6 Electronics
Module 7 Radios
Module 8 Water
Module 9 HVAC
Module 10 AC Power

Marine-Engine and Electrical Systems

check out the Marine Electrical School swicki at eurekster.com

Module 103 Marine-Engine Systems, Electrical and Control Systems

At the completion of this subject module you will understand basic diesel systems, Electronic engine control systems, engine starting systems, engine instrumentation, pre-heating systems, basic ignition systems, outboard engines and charging systems and how to perform basic maintenance and troubleshooting on all of the marine diesel engine systems


The diesel engine is the main propulsion source for most motorboats and power vessels, and an auxiliary one for sailing boats, and therefore the basics will be covered so that the relationship and context between the various electrical systems is understood.

The diesel was invented in the late 19th century, and named after the pioneer engineer Rudolph Diesel. The diesel engine works on the principle of compression-ignition, where air is compressed to a point where fuel combustion will occur spontaneously.

This manual deals with 4 stroke compression-ignition engines. The 4-stroke cycle comprises the air intake, compression, power and exhaust. While there is much talk about bio-diesel in these times of high oil prices, in fact the diesel was originally invented to run on peanut oil.

The Marine-Engine Starting System

The marine-engine requires a number of other systems to support it. The principle system to turn over the engine and start combustion is the starter motor and related control systems. Marine Diesel Engine Starting Systems Part 1 All about electric starting systems for marine diesel engines. Marine Diesel Engine Starting Systems Part 2 All about electric starting systems for marine diesel engines. To monitor the basic parameters such as oil pressure, water temperature and speed various sensors and related instrumentation is used.

The Air Intake (Suction) Stroke

At (Top Dead Center) TDC the air inlet valves open, the exhaust valves are closed and the air required for fuel combustion is drawn in (via turbocharger and air filter) as the piston moves downwards. This creates a partial vacuum to "suck" the air in to the cylinder. At the bottom of the stroke, Bottom Dead Center (BDC) the inlet valves close.

The Compression Stroke

In the compression stroke the piston moves upwards to compress the air, and raises the temperature within the engine cylinder, typically to around 550 Deg C. At just before TDC fuel injection takes place and after an interval ceases.

The Power Stroke

When the fuel is injected it ignites spontaneously, and once ignited, increased pressure is then generated in the cylinder, driving the piston down to BDC.

The Exhaust Stroke

At BDC the exhaust valves open to expel exhaust gases, and at the end of the stroke the valves close at TDC. The process of expelling exhaust gases and replacing them with new fresh air is called scavenging.

Each cylinder typically has 2 or 4 valves, one or two for inlet and the same for exhaust. The valves are actuated by rocker arms. These are controlled by pushrods that are controlled by the camshaft lobes. The camshaft is gear driven from the main crankshaft. This arrangement ensures the correct timing in each stage of the 4 stroke cycle. These parts are lubricated by the lube oil system

The Marine-Engine Combustion Air System

The air for fuel combustion is drawn in through an air filter and compressed. The amount of fuel that can be burnt, and therefore the amount of power of the engine are limited by the air mass within the cylinder. The options are to pre-cool the air to increase the air density, or to use turbo-charging. This raises the air density by increasing the pressure at which the cylinder is filled with air during the air intake stroke, and increases the engine power for the same cylinder size.

The turbocharger is essentially a small air compressor, which is driven by a turbine placed in the exhaust line. As the marine-engine load increases, the exhaust gas output velocity also increases, which increases the turbine speed to drive the air compressor faster, which increases the air pressure into the cylinders. As the air is compressed into the engine cylinders, the air temperature also increases which reduces available oxygen, so some engines may have intercoolers installed. These cool the compressed air, which improves combustion

All you need to know about the marine-engine and alternator-generator-starter systems on boats

Useful Resources

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All about the marine-engine and more

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