Improving Fuel Efficiency in Marine Engines

As a marine operator or owner, you are likely interested in reducing your operational costs, increasing your profit margins, and complying with environmental regulations. One way to achieve these goals is by optimizing your fuel consumption. In this article, we will explore the concept of Specific Fuel Oil Consumption (SFOC), which is a key performance indicator of marine engines, and provide you with practical tips on how to improve it.

Table of Contents

What is SFOC?

SFOC is a measure of the amount of fuel consumed by a marine engine to produce a unit of power output, usually expressed in grams per kilowatt-hour (g/kWh). It is a function of the engine design, operating conditions, fuel quality, and maintenance practices. A lower SFOC indicates a more fuel-efficient engine, which translates into lower fuel costs, fewer emissions, and longer engine life.

Factors affecting SFOC

Several factors can influence SFOC, including:

Engine load

The SFOC of a marine engine varies with the power demand, or load, placed on it. At low loads, the engine operates less efficiently, as it has to overcome internal friction and pumping losses that become a larger proportion of the total energy output. At high loads, the engine may suffer from incomplete combustion, excessive heat, or mechanical stress, which reduce its efficiency and reliability.

Engine speed

The SFOC of a marine engine also depends on its rotational speed, or RPM. At low RPMs, the engine may not be able to achieve the required power output, and may consume more fuel than necessary. At high RPMs, the engine may produce more power than needed, and waste fuel through excess heat and friction.

Fuel quality

The SFOC of a marine engine is affected by the quality and composition of the fuel it uses, such as the viscosity, density, sulfur content, and calorific value. Higher-quality fuels generally have a lower SFOC, as they produce more energy per unit of volume and burn more cleanly.

Maintenance practices

The SFOC of a marine engine is influenced by its maintenance practices, such as the frequency and quality of inspections, repairs, and cleaning. A poorly maintained engine may suffer from fouling, corrosion, leaks, or wear, which increase its fuel consumption and emissions.

How to improve SFOC

To improve the SFOC of your marine engine, you can consider the following strategies:

Optimize engine load

By optimizing the engine load, you can reduce the SFOC of your marine engine. You can do this by adjusting the propeller pitch, the throttle position, or the vessel speed, depending on the operating conditions and the power demand. You can also avoid unnecessary idling or overloading, and plan your routes and cargo to minimize the time and distance spent at low loads.

Adjust engine speed

By adjusting the engine speed, you can optimize the SFOC of your marine engine. You can do this by selecting the appropriate RPM range for your operating conditions, and avoiding excessive or insufficient speeds. You can also use the governor or the fuel injection system to control the speed and fuel supply, and avoid sudden changes or fluctuations.

Use high-quality fuels

By using high-quality fuels, you can reduce the SFOC of your marine engine. You can do this by selecting fuels with lower viscosity, density, sulfur content, and contaminants, and by avoiding mixing or diluting fuels of different grades or origins. You can also monitor the fuel quality and quantity regularly, and clean or replace the fuel filters and separators as needed.

Optimize vessel design

The SFOC of a marine engine can also be influenced by the vessel's design and operation. A well-designed vessel can reduce the drag, resistance, and wave-making of the hull, and thus lower the power demand and fuel consumption of the engine. You can optimize the vessel's design by selecting the appropriate length, beam, draft, and shape, and by using hydrodynamic modeling and testing. You can also use technologies such as bulbous bows, hull coatings, and air lubrication to further reduce the friction and drag.

Implement energy-saving devices

The SFOC of a marine engine can also be improved by implementing energy-saving devices that can capture, store, or reuse the waste energy from the engine or the vessel. Some examples of energy-saving devices are:

  • Turbochargers and intercoolers, which can increase the air intake and combustion efficiency of the engine.
  • Exhaust gas heat exchangers and economizers, which can recover the heat from the exhaust gases and preheat the fuel or the water.
  • Waste heat recovery systems, which can convert the waste heat from the engine or the exhaust gases into electricity or steam.
  • Hybrid propulsion systems, which can combine the use of electric motors and batteries with the engine to reduce the fuel consumption and emissions.
  • Wind-assisted propulsion systems, which can use sails, rotors, or kites to harness the wind power and reduce the engine load.

Monitor and optimize SFOC

To ensure that you are achieving the best possible SFOC for your marine engine, it is important to monitor and optimize it regularly. You can do this by:

  • Installing a fuel flow meter and a power meter to measure the fuel consumption and power output of the engine in real-time.
  • Recording the SFOC values and comparing them with the manufacturer's specifications or the industry benchmarks.
  • Analyzing the SFOC data and identifying the trends, patterns, and anomalies that may indicate the need for further optimization or maintenance.
  • Adjusting the operating conditions, the fuel quality, or the maintenance practices based on the SFOC data and the optimization goals.

Formula and Calculation of SFOC

The Specific Fuel Oil Consumption (SFOC) of a marine engine can be calculated using the following formula:

SFOC = MFO / (P x n)


  • SFOC is the Specific Fuel Oil Consumption, measured in grams per kWh or kilograms per metric horsepower hour (g/kWh or kg/kWh)
  • MFO is the Mass Flow of Fuel Oil, measured in kilograms per hour (kg/h)
  • P is the Power Output of the engine, measured in kilowatts (kW) or metric horsepower (MHP)
  • n is the Engine Speed, measured in revolutions per minute (RPM)

To convert the SFOC values from grams per kWh to kilograms per metric horsepower hour, you can use the following conversion factor:

1 g/kWh = 0.7355 kg/MHP h

To calculate the SFOC of a marine engine, you need to measure or estimate the MFO, P, and n values under the operating conditions of the engine. The MFO can be measured using a fuel flow meter or estimated using the fuel consumption rate and the density of the fuel. The P and n values can be measured using a power meter and a tachometer or estimated using the load and speed of the engine.

For example, let's assume that a marine engine consumes 250 kg/h of fuel oil and produces 2000 kW of power at 100 RPM. The SFOC of this engine can be calculated as follows:

SFOC = 250 kg/h / (2000 kW x 100 RPM / 60) = 0.208 kg/kWh

This means that the engine consumes 0.208 kg of fuel oil per kilowatt-hour of power produced, or 208 grams of fuel oil per kWh. The SFOC value can be used to compare the fuel efficiency of different engines or to evaluate the performance and optimization of a specific engine.

Frequently Asked Questions (FAQ)

What is Specific Fuel Oil Consumption (SFOC)?

Specific Fuel Oil Consumption (SFOC) is a measure of the fuel efficiency of a marine engine, expressed as the mass of fuel oil consumed per unit of power output. SFOC is typically measured in grams per kilowatt-hour (g/kWh) or kilograms per metric horsepower hour (kg/MHP h).

Why is SFOC important for marine engines?

SFOC is important for marine engines because it directly affects the operating costs, environmental impact, and reliability of the engine. A lower SFOC value indicates a more efficient use of fuel and a lower fuel consumption rate, which can reduce the fuel costs and emissions of the engine. A higher SFOC value indicates a less efficient use of fuel and a higher fuel consumption rate, which can increase the fuel costs and emissions of the engine and shorten the service life of the engine components.

How can SFOC be improved in marine engines?

SFOC can be improved in marine engines by optimizing the engine design, operation, and maintenance. Some common ways to improve SFOC include:

  • Using more efficient combustion technology, such as high-pressure fuel injection and electronic control systems.
  • Using lower viscosity and higher-quality fuel oil, such as marine gas oil (MGO) or distillate marine fuel.
  • Maintaining the engine components, such as the injectors, pumps, filters, and turbochargers, to ensure optimal performance and minimize fuel waste.
  • Monitoring the engine parameters, such as the fuel consumption rate, exhaust gas temperature, and air-fuel ratio, to identify and correct any deviations from the optimal values.

What is the typical range of SFOC values for marine engines?

The typical range of SFOC values for marine engines depends on the type, size, and age of the engine, as well as the operating conditions and fuel quality. However, as a general guideline, the SFOC values for modern marine engines can range from 150 to 300 g/kWh or 1.1 to 2.2 kg/MHP h, while the SFOC values for older and less efficient engines can range from 400 to 600 g/kWh or 3.0 to 4.4 kg/MHP h.

How can SFOC be measured in marine engines?

SFOC can be measured in marine engines using various methods, such as fuel flow meters, power meters, tachometers, and engine monitoring systems. The measurement accuracy and reliability of these methods depend on the type and quality of the equipment and the expertise of the operators. To ensure accurate and consistent SFOC measurement, it is recommended to follow the relevant international standards and guidelines, such as ISO 3046 and MEPC.1/Circ.736.


By implementing the strategies and technologies described in this article, you can improve the Specific Fuel Oil Consumption of your marine engine, reduce your fuel costs and emissions, and enhance your operational efficiency and competitiveness. Remember to monitor and optimize your SFOC regularly, and to consult with experts and manufacturers if you have any questions or concerns. Thank you for reading!