Do All Big Ships Have Two Engines? Debunking Misconceptions About Merchant Vessels

Many people assume that all large merchant vessels require two engines to function. However, the reality is quite different from this popular myth. In this article, we explore the truth behind ship propulsion and debunk the common misconception that all big ships must have two engines.

The Reality of Merchant Vessels Propulsion

Large merchant ships, such as Panamax bulk carriers, typically have a single large slow-speed diesel engine to power them. These engines are designed to generate a substantial amount of power with a slower rotational speed, allowing for more efficient fuel consumption and reduced maintenance costs. For instance, each of the seven Panamax bulk carriers I've been on, ranging from 70,000 to 70,000 tons, featured a single engine of approximately 17,000 bhp (brake horsepower).

Why the Shift to Single Engines?

The transition to single engines in large merchant vessels can be attributed to several factors. First, the efficiency of modern slow-speed engines has significantly improved. These engines are optimized for large efficiency gains when run at their designed speed and load, leading to reduced fuel consumption and lower operational costs. Additionally, the single-engine design simplifies ship construction and maintenance, further justifying the choice over twin engines.

Exceptions: Multiple Engine Configurations

While the majority of large merchant ships opt for a single engine, there are indeed exceptions. In particular, some specialized ships, such as Roll-on/Roll-off (RoRo) vessels, may require dual engines for various reasons. RoRo vessels are designed to transport wheeled cargo, such as cars, trucks, and construction equipment, both on deck and in the open bottom of the vessel. Given the need for power fluctuations throughout various loading and unloading operations, multiple engines can provide more reliability and flexibility.

Considerations for Dual Engine Ships

For ships that do employ dual engines, such as the 20 vessels I've been aboard, ranging between 5,000 and 145,000 tons, the configuration is often chosen based on specific operational needs. For example, smaller ships might use twin engines to offer more flexibility in engine shutdown and restart during maneuvers. Larger ships may opt for dual engines to ensure redundancy in critical safety systems, thereby maintaining crew and cargo safety during extreme weather conditions or mechanical failures.

Conclusion: A Critical Overview of Merchant Vessels’ Propulsion

To summarize, it is not accurate to claim that all big ships must have two engines. The design and choice of engines in merchant ships are heavily influenced by the specific needs, operational requirements, and fuel efficiency standards. While many large vessels opt for single engines due to their inherent efficiency and cost-effectiveness, other specialized ships, like RoRo vessels, may benefit from a dual engine configuration.

The world of shipping is complex and dynamic, with ongoing advancements in technology continually shaping contemporary practices. As such, it is crucial to stay informed about these developments to grasp the current state of modern maritime transport.