In the maritime industry, performance is currency. When a vessel fails to meet its warranted speed or consumes more fuel than specified in the charter party, the financial repercussions are immediate. Yet, for many ship owners and operators, identifying the root cause of underperformance is rarely straightforward.

While external factors like adverse weather and currents are often the first to be blamed for speed loss, the reality is frequently found within the vessel itself. As environmental regulations such as the CII (Carbon Intensity Indicator) and EEXI (Energy Efficiency Existing Ship Index) tighten, the tolerance for technical inefficiency is shrinking to zero.

A ship is a complex ecosystem of hydrodynamic and mechanical systems. When one component falters, the entire efficiency profile degrades. Understanding the technical reasons behind speed loss and excessive fuel consumption is not just about engineering; it is about protecting the commercial viability of the asset.

Here are the primary technical factors that lead to underperforming vessel speed and fuel efficiency.

1. Hull Roughness and Biofouling

The most significant technical factor influencing a ship’s performance is the condition of its hull. The relationship between the hull and the water defines the vessel’s hydrodynamic efficiency.

Biofouling—the accumulation of microorganisms, plants, algae, or small animals on the hull—drastically increases frictional resistance. Even a light layer of slime, which may be barely visible to the naked eye during an inspection, can increase fuel consumption by up to 10% to maintain a specific speed. Heavier growth, such as barnacles or tubeworms, can push this penalty significantly higher, sometimes exceeding 30%.

However, it is not just biological growth that causes drag. Physical hull roughness, caused by corrosion, pitting, or poor coating application during dry dock, also disrupts water flow. As the hull surface degrades over time, the boundary layer of water against the ship becomes turbulent rather than laminar, acting as a brake on the vessel’s momentum.

2. Propeller Surface Degradation

While the hull creates resistance, the propeller provides the thrust to overcome it. Any degradation in propeller condition has a multiplier effect on inefficiency.

A rough propeller surface, whether due to fouling, cavitation damage, or corrosion, cannot slice through the water efficiently. This forces the engine to work harder—burning more fuel—to achieve the same Revolutions Per Minute (RPM) and thrust.

Furthermore, physical damage to the propeller blades, such as bent tips or edge modification, can lead to severe energy loss. This damage disturbs the wake field and can cause vibration, which wastes energy that should be converted into forward motion. Regular polishing and inspection are critical, as a polished propeller can yield fuel savings of 3-4% almost immediately.

3. Main Engine Inefficiencies

If the hull and propeller are in pristine condition but the vessel still lags, the focus must shift to the engine room. The main engine is the heart of the vessel, and even minor deviations from optimal settings can result in poor specific fuel oil consumption (SFOC).

Common technical issues include:

• Fuel Injection Systems: Worn fuel valves or incorrect injection timing can lead to poor combustion. If the fuel is not atomised correctly, it does not burn completely, reducing power output and increasing emissions.
• Turbocharger Performance: A fouled turbocharger cannot provide the necessary air mass for efficient combustion. This often results in higher exhaust gas temperatures and reduced engine power for a given fuel setting.
• Charge Air Coolers: If these are blocked or fouled, the air density drops, starving the engine of oxygen and reducing efficiency.

Proper technical management of ships plays a pivotal role here, ensuring that planned maintenance systems are rigorous enough to catch these degradation issues before they impact commercial performance.

4. Inaccurate Sensor Calibration and Data Logging

Sometimes, the vessel is performing correctly, but the data says otherwise. In the era of performance monitoring, a ship is only as efficient as its sensors say it is.

Speed logs are notoriously unreliable. If a speed log is miscalibrated, it might report a speed through water that is lower than reality, making the vessel appear inefficient in performance reports. Similarly, torque meters (used to measure shaft power) and fuel flow meters can drift over time.

If a flow meter reports 2% more fuel than is actually being consumed, the vessel is technically performing well, but commercially, it appears to be failing. Regular calibration of these instruments is essential to distinguish between a phantom sensor error and a genuine mechanical fault.

5. Rudder and Autopilot Settings

Steering a ship requires energy. Every time the rudder moves, it creates drag. While necessary for course keeping, excessive rudder movement is a silent killer of fuel efficiency.

An improperly adjusted autopilot system can cause a vessel to “hunt” for its course, resulting in constant, large rudder angles. This increases the distance the vessel actually travels (cross-track error) and creates significant hydrodynamic drag.

Optimising autopilot settings for the specific sea state and loading condition is a technical nuance often overlooked. In calm seas, a “tight” setting is appropriate, but in rough weather, allowing a slightly wider yaw band prevents the steering gear from fighting the ocean unnecessarily, preserving momentum and fuel.

6. Thermodynamics and Waste Heat Recovery

For modern vessels, efficiency is not just about propulsion; it is about total energy management. Waste Heat Recovery Systems (WHRS) are designed to capture thermal energy from exhaust gases and convert it into electricity or steam.

If the economiser (exhaust gas boiler) is fouled with soot, heat transfer efficiency drops. This forces the vessel to fire up auxiliary boilers to generate steam for heating fuel or accommodation, consuming additional diesel oil. While this doesn’t directly slow the ship down, it drastically impacts the overall fuel efficiency rating of the voyage.

Ensuring Peak Performance

Identifying the cause of underperformance requires a forensic approach. It is rarely a single catastrophic failure but rather a combination of small technical degradations—a slightly fouled hull, a rough propeller, and a turbocharger running at 90% efficiency.

For ship owners, the pathway to restoring speed and efficiency lies in data-driven maintenance. By moving from reactive repairs to condition-based monitoring, operators can address hull roughness and engine parameters before they become commercial claims. In a market defined by tight margins and strict environmental targets, technical precision is the only safety net.