Fuel Economy Assessment During Passage Planning: Operational Practices for Marine Engineers

By MaritimeHub Chief Engineer Technical Team

Contents

• Introduction
• Fundamentals of Marine Fuel Economy
• Passage Planning and Fuel Economy Link
• Mechanisms Affecting Fuel Consumption
• Key Measurements and Monitoring Tools
• External Factors Impacting Fuel Use
• Failure Modes Affecting Accurate Assessment
• Shipboard Checks and Verification
• Troubleshooting Fuel Economy Problems
• Practical Optimisation Techniques
• Real-World Case Examples
• When and How to Escalate
• Recordkeeping and Documentation
• Future Trends and Innovations
• Review Questions
• Glossary
• Diagrams

Introduction

In the current commercial landscape, maximising fuel economy is a matter of competitiveness, compliance, and safety for marine engineers. Passage planning presents an opportunity to exert control over fuel usage well before lines are let go. Chief engineers must ensure passage plans take full account of all factors impacting fuel consumption, not just for cost efficiency, but also for environmental and regulatory compliance. This article presents a full operational review of fuel economy assessment during passage planning, with practical, actionable methodologies and real-world operational insights for marine engineering professionals. Safety-critical considerations are highlighted throughout, reflecting best shipboard practice and industry expectations.

We cover the full cycle: from mechanisms and measurement to checks, troubleshooting, failure modes, and escalation. Whether you are a cadet learning the ropes or a chief engineer seeking to standardise best practices across your fleet, you will find detailed, practical guidance here.

Fundamentals of Marine Fuel Economy

To assess and optimise fuel economy, the marine engineer must first understand what determines the ship’s fuel consumption profile. At its core, fuel economy is the ratio of work performed (usually in terms of distance covered or cargo carried) to fuel energy expended. Standards such as EEDI (Energy Efficiency Design Index) and EEXI (Energy Efficiency Existing Ship Index) formalise these concepts, while shipowners increasingly track real-time fuel benchmarks.

The principal mechanical drivers of fuel use on board are main engine load, propulsion efficiency, hull resistance, and auxiliary loads. Many vessels spend most time in economical steaming, where marginal gains or losses can have sizeable commercial impacts. Optimising fuel economy means understanding each of these factors, their interactions, and the practical means by which engineers can influence performance.

There is no single magic lever for fuel efficiency; rather, the engineer’s job is to deploy all available information, measurements, and controls. Understanding the vessel’s fuel consumption curve—especially the SFOC (Specific Fuel Oil Consumption) characteristics across varying loads and conditions—is essential. 

Passage Planning and Fuel Economy Link

Passage planning sets the operational envelope for the voyage, including route, speed, waypoints, expected weather, and engine load profiles. Every leg of the voyage offers different challenges—trade winds, currents, expected rough weather, areas of high traffic, and special environmental zones. If the plan is drawn without reference to fuel economy, the ship will burn more fuel than necessary, increasing costs and emissions. 

Effective passage planning is an interdisciplinary task: navigators propose the route, but the chief engineer must assess and advise on engine performance, SFOC curves, maintenance status, and bunker quality. Collaboration at the planning stage is essential. Typical operational tasks include checking the historical fuel consumption rates for similar passages, considering the effect of speed vs consumption for the main engine, reviewing maintenance or engine derating schedules, and checking that all measured data is recent and accurate.

A classic error is to target a passage speed that aligns with charter-party or navigation constraints but ignores the optimum point on the vessel’s SFOC curve. One hour’s gain can cost several tonnes in extra fuel burn. Conversely, running engines consistently at low load to save fuel can increase fouling, reduce efficiency, and cause technical problems if not managed appropriately.

Mechanisms Affecting Fuel Consumption

Numerous mechanisms on board affect fuel use. These mechanisms interact dynamically, and the onboard engineer must recognise both direct and indirect influences:

Main Engine Performance: The load factor, control settings, load distribution (across multiple engines if applicable), and actual vs design condition (pressure, temperature, rpm) all impact net fuel consumption. Indicators such as exhaust gas temperature spread, turbocharger efficiency, and fuel rack position offer real-time insights into health and efficiency.

Propulsion Efficiency: Propeller pitch, condition, and alignment influence how effectively the power generated by the main engine is converted into thrust. Fouled propellers or hulls instantly increase fuel burn for a given speed. Misalignment (for instance, following propeller work) further increases resistance.

Auxiliaries: Power used for electricity, hydraulic systems, and HVAC (heating, ventilation, and air-conditioning) is routinely overlooked. Inefficient auxiliaries create hidden drains on fuel consumption. Careful monitoring and rationalisation, especially in port, can save substantial quantities of fuel.

Boiler Operations: In cold climates or where cargo heating is required, auxiliary boilers can become a major consumer. Assessing requirements in advance and running boilers at their design loads prevents oversized use and cycling losses.

Key Measurements and Monitoring Tools

To manage fuel economy, engineers must rely on the right measurements and tools. This begins with accurate daily tank soundings and bunkering records. Modern vessels increasingly have fuel flow meters with remote monitoring. Where fitted, these should be diligently checked for calibration and maintained accordingly.

Other essential measurements include main engine rpm, load, scavenging air pressure, exhaust gas temperatures (all units), turbocharger rpm, and propeller pitch. Spot checks must be reconciled against remote monitoring readouts and engine logbook values. Unexpected drifts—such as rising fuel consumption at fixed rpm or a growing exhaust temperature spread—usually signal emerging problems before alarms are triggered.

Draught and trim measurements also have a significant bearing. Incorrect or untrimmed vessels impose substantially greater resistance, especially at higher speeds. Regular hull and propeller inspections (visual or via ROV) ensure physical condition is being accounted for in planned passage parameters.

Environmental monitoring tools offer increasingly sophisticated routing suggestions, factoring in currents, wind, and satellite weather. However, such intelligence is only as valuable as the accuracy of shipboard measurements used to set the model’s baseline. No system can correct for poor tank sounding or a missing manifold log.

External Factors Impacting Fuel Use

Engineers must account for a variety of external factors when advising on passage planning fuel assessments. These include weather, sea state, currents, traffic density, ECA (Emission Control Area) requirements, and port congestion risks. The impact of weather routing can be dramatic, particularly on containerships and bulkers exposed to ocean swells or headwinds. 

For example, a 30,000 DWT bulk carrier heading into a strong head current will burn significantly more fuel per mile than running with the same current astern. This is compounded by windage—high-sided vessels suffer more from wind than low-slung ships. Seasonal variation in trade patterns should also be checked, both for safety and economy; poorly planned avoidance routes may increase passage distance by hundreds of miles.

The prudent engineer engages actively with the bridge team, requesting early warning for significant course or speed changes. For longer passages expected to traverse ECAs or SECA zones, switch-over times for compliant fuel and engine adjustments (possibly including derating or NOx abatement activation) must be built into the fuel estimate and the passage plan.

Pilots, port restrictions, and even canal transits (such as the Suez or Panama Canal) should be analysed for their fuel implications. Waiting time, required propulsion modes, and auxiliary loads in these high-consequence areas are often under-appreciated, yet can dramatically shift real fuel burn away from estimates if not considered from the outset.

Failure Modes Affecting Accurate Assessment

Several failure modes can compromise both the assessment and execution of fuel economy during passage planning. These failures can be technical, procedural, or people-centric.

One of the most serious technical failures is inaccurate tank soundings or defective flow meters. A single missed error here can skew fuel consumption reporting for a whole voyage. Incorrect calibration, stuck floats, or poorly mixed tank strata following bunkering are common sources of error.

Hull fouling is the classic silent killer of fuel economy. Even a moderate coating of marine growth increases resistance dramatically. If not addressed at dry-dock or checked during regular vessel underwater inspections, no amount of careful planning will restore expected fuel performance. Propeller and hull roughness are frequently underestimated in passage fuel calculations.

Planning errors—such as not accounting for heavy weather deviation, underestimating auxiliary boiler consumption, or failing to factor ECAs—are too often discovered mid-voyage, when mitigation is costly or impossible. A lack of interdisciplinary communication (typically bridge and engineering) exacerbates these oversights.

Shipboard Checks and Verification

Proactive shipboard checks underpin the engineer’s ability to validate and improve passage planning fuel assessments. Chief among these is the validation of baseline consumption rates through daily performance monitoring. If the actual fuel use begins to depart from planned consumption by more than 2–3%, an immediate review is required.

Routine checks must include:

– Comparing total daily bunker consumption figures against main engine logbook data, auxilliary logs, and tank soundings. Unexplained discrepancies typically indicate measurement or reporting errors, leaking valves, or even potential loss due to theft or cross-connection.
– Checking that all calibrated instruments—including fuel flow meters, pressure gauges, and temperature sensors—remain within date and pass regular spot checks. Where the equipment allows, engineers should conduct calibration cross-checks against manual readings at least monthly.
– Engine room walkarounds at varying loads and weather conditions. This promotes early detection of leaks, abnormal vibrations, or running conditions that could elevate fuel consumption stovepipe-style, outside of remote monitoring boundaries.

It is also vital to maintain a good working relationship with the bridge team during passage, ensuring continual sharing of real system performance and upcoming operational changes. The best-planned voyage can rapidly unravel when uncommunicated ballast movements, course alterations, or unexpected holds in port are imposed on the plant.

Troubleshooting Fuel Economy Problems

When actual fuel consumption exceeds passage plan forecasts, a structured approach to troubleshooting is critical. The first step is always to verify measurement integrity: check all tank soundings, flow meters, and daily engine logs for consistency and plausibility. If the data makes sense, move outward through the engine systems.

Look for signs of inefficiency within the main propulsion plant: increased exhaust gas temperatures, unbalanced cylinder loads, turbocharger lag, or unusual vibration all point to emerging technical faults. A growing SFOC at a constant rpm can indicate injector fouling, air filter clogging, or turbocharger underperformance.

If all propulsion variables check out, shift focus to the hull and propeller. Small changes in resistance make major differences at sea. During the voyage, increased vibration, noise, or speed drop-off at constant rpm often signal propeller or hull fouling. Post-arrival, check underwater for damage or marine growth, and reference against satellite weather logs to see if underestimated currents or winds were encountered.

Auxiliary loads, particularly during extreme weather (cold spells or heatwaves), can escalate unnoticed. Look for signs of unplanned generator loading, boiler usage, or HVAC demand. Review all relevant machinery logs and investigate discrepancies quickly before the root cause becomes obscured by events.

Practical Optimisation Techniques

Optimising fuel economy during passage planning and execution is a continual process. Chief engineers should treat this as a cyclical rather than one-off activity. Begin by working closely with the navigation team to select a passage plan that considers minimal resistance (calmer waters, more favourable currents) and the vessel’s most efficient speed range, typically found just below the knee of the SFOC curve.

Once underway, monitor real-time consumption versus planned benchmarks. Adjust speed or propulsion settings proactively if external factors (weather, currents) deviate from forecast. Where safe and compliant, employ engine derating, variable frequency drives, and waste heat recovery to squeeze further efficiencies from the plant.

Encourage the habit of running all auxiliary systems as close to design conditions as practicable. For example, run air compressors and boiler burners for longer at lower loads, rather than short cycling at maximum capacity. Maintain equipment in optimum condition: poorly maintained separators, pumps, or heat exchangers degrade plant efficiency incrementally.

Prioritise hull and propeller cleaning, both at dry-dock and by in-water cleaning where feasible and permitted. Even a small investment in proactive cleaning can return an order-of-magnitude improvement in passage fuel economy, especially for vessels on long hauls.

Real-World Case Examples

A chief engineer on a panamax bulker discovered on westbound Atlantic passage that real fuel consumption was running nearly 15% above planning estimate. Initial suspicion fell on poor weather, but detailed review revealed the forward starboard peak tank had not been fully ballasted, inducing excess trim by the stern and elevated hull resistance. Correction restored consumption to within 3% of plan for the remainder of passage.

On a large container vessel, a sudden spike in SFOC was traced to inaccurate tank soundings due to defective measuring tape calibration after routine maintenance. The issue would have gone undetected had cross-checking with engine flow meters not been rigorously practised.

A product tanker transiting from Singapore to Durban was able to shave 5% off planned fuel use by integrating updated weather routing data with real-time hull performance trends. By dynamically adjusting speed and engine load in tandem with weather shifts, the passage maximised efficiency without risking delays. In all cases, operational vigilance by the shipboard engineering team made the difference.

When and How to Escalate

The hallmark of a competent chief engineer is knowing when to escalate issues beyond the shipboard team. Escalation is essential when:

– Systemic measurement failures (suspected theft, flow meter tampering, repeated tank sounding anomalies) are detected.
– Condition of hull or propeller cannot be properly assessed or remedied during the voyage, and persistent excessive consumption is observed.
– Repeated divergence between passage plan and actual consumption indicates a potential design, maintenance, or performance deficiency beyond routine correction.
– Commercial, regulatory, or environmental reporting thresholds (e.g. excessive ECA fuel use) risk being breached.

The escalation process typically starts with a detailed written report to the master, supported by logs, daily consumption tables, and spectrum evidence from all relevant plant measurements. Ship management and owners’ technical departments may then commission additional troubleshooting, hull inspection, or bunker quality analysis depending on the nature of the problem.

Safety, commercial risk, and environmental compliance are all at stake. Escalate early when in doubt—late detection can mean substantial financial exposure.

Recordkeeping and Documentation

Robust documentation underpins all aspects of fuel economy management. Ship-specific documentation must include regular, signed entries for bunker receipt, daily soundings, fuel transfer operations, and consumption breakdowns for all relevant machinery. These records underpin later analysis, troubleshooting, and regulatory reporting, and often provide the first forensic evidence when discrepancies arise.

A best practice is to maintain a centralised set of digital records where possible, supplemented by rigorously completed hard-copy logbooks. Each chief engineer should periodically review the standard of documentation on board and run spot checks on historical entry accuracy. If a culture of meticulous recordkeeping is not instilled at an early stage in the engineering team, both operational and compliance vulnerabilities will emerge sooner or later.

When submitting fuel consumption or passage reports ashore, provide clear context regarding assumptions, weather encountered, and uncontrollable deviations. An engineer’s demonstrable attention to documentary integrity is often the decisive factor in resolving commercial disputes over fuel reconciliations or emissions limit breaches.

Future Trends and Innovations

The fuel economy landscape is rapidly evolving, with digitalisation, new fuel types, and advanced propulsion technologies transforming operational practice. For the marine engineer, this presents both new opportunities and challenges. Remote monitoring, big data analytics, and AI-based voyage optimisation offer unprecedented detail and predictive capability, but only when implemented alongside robust shipboard practices and data hygiene.

New marine fuels—such as LNG, biofuels, and synthetic alternatives—bring different combustion characteristics and engine optimisation parameters. Chief engineers must stay abreast of changing technical guidance, both from manufacturers and regulatory bodies. Hybrid propulsion technologies, including battery and waste heat recovery integration, are increasingly standard for newbuilds, requiring further adaptation of passage planning assessment methods.

Despite these advances, the role of the shipboard engineer in critically assessing, validating, and acting on passage planning data remains irreplaceable. Technology is a force multiplier, not a panacea; best practice in fuel economy assessment is always rooted in vigilant operator intervention.

Review Questions

1. What are the main contributors to vessel fuel consumption during passage?
2. How does hull fouling impact fuel economy, and how can it be detected?
3. What is Specific Fuel Oil Consumption (SFOC), and why is it important in passage planning?
4. Describe the main measurements required to assess fuel use on board.
5. How can inaccurate tank soundings distort fuel economy calculations?
6. Explain how external weather routing affects passage fuel assessment.
7. What shipboard practices help maintain reliable fuel flow meter readings?
8. When should the engineering team escalate passage plan fuel discrepancies to shore?
9. How should auxiliary loads be considered during passage planning?
10. What operational checks verify passage plan assumptions during the voyage?
11. Why is interdisciplinary collaboration between bridge and engine departments essential?
12. List the common failure modes affecting accurate fuel consumption reporting.
13. How can ships optimise engine load distribution for best fuel economy?
14. What should be done if measured main engine fuel consumption suddenly increases?
15. Describe best documentation practices for passage planning fuel assessment.
16. How do alternative fuels impact the traditional passage planning fuel assessment process?
17. What troubleshooting steps should be taken following significant fuel consumption divergence?
18. How are emission control area transits factored into fuel economy assessments?
19. What are the implications of underestimating port standby fuel use during planning?
20. How does maintaining correct vessel trim support fuel efficiency?

Glossary

• SFOC (Specific Fuel Oil Consumption): A measure of fuel used per unit of work; usually grammes per kWh.
• EEDI (Energy Efficiency Design Index): IMO metric for new ship fuel efficiency.
• EEXI (Energy Efficiency Existing Ship Index): Similar to EEDI but for existing tonnage.
• Passage Planning: The process of creating a voyage blueprint, including route, speed, and timing.
• Bunker: Shipboard fuel oil storage.
• Trim: The longitudinal balance of a vessel, affecting resistance.
• Derating: Operating an engine below its maximum continuous rating to optimise efficiency.
• ECAs: Emission Control Areas where stricter fuel requirements apply.
• Auxiliary Load: Power consumed by machinery aside from main propulsion (e.g., generators, HVAC).
• Weather Routing: The practice of choosing a passage route to minimise fuel use and risk via weather forecasts.

Diagrams

Simple Representation: Passage Planning Fuel Assessment Cycle

[ Voyage Plan ]
      |
      v
[ Engine Performance Checks ]
      |
      v
[ Fuel Consumption Estimates ]
      |
      v
[ Real-life Measurements ]
      |
      v
[ Troubleshooting & Optimisation ]
      |
      v
[ Documentation & Reporting ]
      |
    (cycle/repeat)

SFOC Curve Example

| 
|\
| \
|  \
|   \
|    \
|     \_____
|          \
|___________\____________

  <-- Main Engine Load -->

(SFOC minimum at optimal medium load, rises steeply at low/high loads)