Understanding Marine Engine Operation and the Consequences of Non-Starting

Marine engines, whether they are part of naval ships or commercial vessels, operate on principles very similar to those of automobile engines. They work in a way that their output shaft goes into a gearbox, and from there, the drive powers the propeller. However, the critical nature of their operation means that if the engine fails to start, the vessel remains stationary.

The type of engine used in a ship depends on the vessel's size and primary trade. Naval ships use nuclear steam plants, gas turbines, and diesel engines, each operating on different principles. Ferries, passenger ships, and tugs typically use high or medium-speed diesel engines, while most merchant vessels use single, large, low-speed diesel engines. These engines are much bigger than those found in cars or trucks but functionally operate on the same basic principles.

Reliability and Functionality of Marine Diesel Engines

Marine diesel engines are incredibly reliable and can continue to function even if one or more cylinders fail. Each cylinder in a marine diesel engine is designed to be a complete, independent unit. For instance, a large marine diesel engine with six cylinders can ignite and start due to the compressed air injection into the cylinders pushing the pistons down and injecting fuel as they rise, ultimately igniting and starting the engine.

The engine is attached directly to the shaft and propeller, with no gearbox or clutch in between. When the engine starts, the propeller rotates, and the ship moves forward. To move the vessel in reverse, the engine is stopped, and the camshaft is moved axially to reverse the valve opening sequence, after which the engine is restarted. This reversal can only be performed at very low speed.

The propeller and engine array are generally designed to operate in this direct connection to ensure maximum efficiency. Figure 1 shows a marine diesel engine with a large six-cylinder setup for high power output. (Figure 1: Larger six-cylinder 13,600kw marine diesel engine courtesy of Wartsila)

However, if the main engine doesn't start, it can be a serious issue. Such failures are rare but can occur due to various reasons such as fuel supply issues, electrical malfunctions, or mechanical failures. In such cases, the ship may need to be towed back to port for repairs. It is, in essence, similar to what would need to be done if your car refuses to start.

The Role of Tugs in Marine Operations

Given the size and importance of these vessels, it's not uncommon for large merchant ships to require towing assistance when entering or leaving ports. They may need tugs to help them move forward until they are cleared to start their engines. This is due to the fact that the engines may not have started up yet and need the additional power of a tug to get underway.

Engine shaft and propeller array courtesy Wartsila.

Conclusion

In conclusion, understanding how marine engines work and the consequences of non-starting is crucial for both professionals in the maritime industry and for anyone interested in boats and cargo transport by sea. Marine diesel engines, while powerful and reliable, can pose serious issues if not maintained properly or in the event of a malfunction. Always ensure proper maintenance and checklists are followed to prevent such issues from arising.

References:

Wartsila Engine Documentation. Larger six-cylinder 13,600kw marine diesel engine courtesy Wartsila.

Figure 1: Larger six-cylinder 13,600kw marine diesel engine courtesy Wartsila.