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Different Types of Marine Diesel Engines

Different Types of Marine Diesel Engines

Most contemporary boats run on diesel engines. In fact, diesel engines have been the powerhouses of boats for over 100 years. The first one was installed in a Danish ship Selandia in 1912. If you are looking to buy a boat, or are thinking of rebuilding your boat, one of the most important things on board is the engine. There are several different types of marine diesel engines to choose from. All have some advantages and some drawbacks. Listed below is a brief description of all types.

Why are they so popular?

All diesel engines (including marine diesel engines) are very reliable and extremely durable machines. This is an important thing you want in an engine when you spend a lot of time away at sea where help can be days away. What’s more, diesel engines are fairly economical. They provide decent mileage for the fuel they spend. However, they are rather large and expensive. Additionally, repair and maintenance need to be handled by skilled professionals to ensure long work life of the engine.

How do they work?

Diesel engines were invented by a German engineer Rudolph Diesel in 1892. Essentially, a diesel engine contains chambers called cylinders. They are filled with a mixture of gas and fuel, which is then ignited. The explosion sends the piston downwards. The piston cranks the crank, creating effective work which is then transferred to the propulsion (in the case of marine engines, the propeller).

Outboard/inboard engines

The first distinction you can make between different types of marine diesel engines is whether they are attached on the outside of the boat, or if they are set inside. With larger boats like yachts, all engines are inboard, and cannot be substituted for an outboard. However, many smaller boats have an option. 

The outboard is fairly practical when it comes to moving the engine. During the winter, most boat owners do not use their vessels. If you have an outboard, you can easily remove it and prevent any damage or buildup on the propeller. Inboard engines, on the other hand, cannot be moved easily. However, they do offer some perks. Better fuel efficiency, being a lot quieter and creating fewer waves are probably the most commonly cited ones.

Four stroke/ two stroke engines

Once you’ve settled on a style of the engine, you come to the other big decision, four or two stroke engine. What this means is actually how many steps does it take to complete a full cycle.

Four stroke engines are usually larger, reserved for bigger boats. Essentially, it uses a four-step process for power. Injection of the fuel, followed by compression to increase the efficiency, followed by combustion when the fuel is exploded, sending the piston down. The final step is exhaust when the expended fuel and gasses are expelled from the cylinder. Due to the compression, the quality of the fuel used in these engines is not as important as with other kinds of engines. 

Two stroke engines considerably reduce the complexity of the cycle. There are only two steps: intake, when the air is inserted, simultaneously expelling the used up gasses. The second step happens when the piston moves to the top of the cylinder. In that moment, fuel is added. As the fuel explodes, it pushes the piston downwards, creating work. As the piston starts going forward, the cycle starts again. Two stroke engines are usually more fuel efficient and more compact than the four stroke ones.

Once you have decided which of the different types of marine diesel engines is right for you, the next step is to find a reliable partner with plenty of experience in boat maintenance and boat repairs. PCE has been around for over four decades and has been named a trusted partner by the US Navy for almost any type of vessel repair. Contact PCE today to learn more.

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