Engine sea trial procedures prove that the propulsion plant of a new-build ship meets the contractual performance specification, the class society rules, and the statutory requirements of MARPOL Annex VI before delivery. The sequence runs from the engine maker’s shop test (factory acceptance test, or FAT) through the quay or dock trial to the full sea trial. Each stage is witnessed by the attending class surveyor; no certificates are issued until the relevant test record is signed. This article focuses on the engine-specific demonstrations: the trial hierarchy, the progressive speed trial and MCR endurance run, the maneuvering and crash-stop and astern tests, the governor and safety-device checks, the performance and SFOC measurements, and the ISO 15016 speed-power analysis that feeds the EEDI and EEXI determination. For the broader ship-level program covering manoeuvring circles, zig-zag, and speed trial analysis methods, see sea trials and performance testing.
The Trial Hierarchy: Shop Test, Quay Trial, Sea Trial
The three-stage trial hierarchy exists because each environment can test a different subset of performance claims. No single environment can verify everything.
Stage 1: Factory Acceptance Test (Shop Test)
The factory acceptance test, also called the shop test, runs the bare engine on the manufacturer’s test bed before the engine is shipped to the shipyard. At MAN Energy Solutions and Wartsila, the test bed is a permanent installation with a water-brake or generator dynamometer absorbing the engine’s output, calibrated instrumentation on all fluid circuits, and a certified fuel conditioning system using ISO-standard reference fuel (lower calorific value 42,700 kJ/kg).
The class society surveyor attends as witness. For a two-stroke slow-speed engine going into a vessel classed with Lloyd’s Register, DNV, Bureau Veritas, or any IACS member society, the FAT is a mandatory class hold point. The surveyor checks instrument calibrations before the test, witnesses the full load range, and co-signs the performance test report.
Standard FAT load steps follow ISO 3046-1: the engine runs at 25, 50, 75, 85 (the contractual Continuous Service Rating, CSR), 100 (Maximum Continuous Rating, MCR), and sometimes 110 percent of MCR. At each step the engine stabilizes for a minimum period (typically 1 hour at 25 percent, 3 hours at MCR) and the instrumentation logs: brake power via torque and speed, fuel flow by calibrated Coriolis meters, cylinder indicator cards at all cylinders taken by electronic pressure transducer (PMI), exhaust gas temperatures at each cylinder outlet and after each turbocharger stage, turbocharger speeds, charge air temperature and pressure, scavenge air receiver pressure, and cooling water and lube oil temperatures and pressures on all circuits.
SFOC at each load step is calculated from the measured fuel mass flow divided by measured shaft power, then corrected to ISO 3046-1 reference conditions (25°C inlet air, 1.000 bar, standard fuel LCV). The corrected SFOC curve across the load range constitutes the contractual SFOC guarantee proof. Any individual load-point value that exceeds the guaranteed value plus the agreed tolerance (typically 5 percent above the contractual value for an individual point at MCR) triggers a defect report.
NOx is measured simultaneously by a continuous emission analyzer sampling the exhaust manifold. The measurement follows IMO NOx Technical Code 2008 (as amended), ISO 8178-1, and the E3 test cycle (three mode: 25, 50, 75 percent load with specified weighting factors for slow-speed four-stroke engines, or E2 for constant-speed engines). The weighted average NOx must meet the applicable Tier limit. For ships whose keel was laid on or after 1 January 2016 operating in Tier III Emission Control Areas, the engine must carry Tier III certification; the FAT for a Tier III engine includes demonstration of the selective catalytic reduction (SCR) system or exhaust gas recirculation (EGR) at all E3 load points. See NOx Tier I, II, and III limits for the limit values by keel-laying date.
The FAT also includes mandatory function tests of all safety devices: the overspeed trip (set at 115 percent of rated RPM on most two-stroke engines per IACS UR M45), the low lube oil pressure trip, the high exhaust temperature alarm, the high coolant temperature alarm, and the scavenge fire detector. These are tested by simulated fault injection, not by actually running the engine to failure. The governor is tested for speed regulation bandwidth and droop characteristics. See engine governor systems for the governor theory underlying these tests.
Safety device test results and shop-test performance records form the Technical File lodged with the class surveyor. The Technical File is the documentary basis for the EIAPP (Engine International Air Pollution Prevention) certificate, which certifies the engine’s NOx compliance. Without an EIAPP certificate, the ship cannot trade.
Stage 2: Quay Trial (Dock Trial)
The quay trial, also called the dock trial or mooring trial, runs the engine installed in the ship with the ship moored at the outfitting quay. Power is limited by the mooring arrangement; full ahead power would snap a quay-side mooring wire on most ships. The practical limit is roughly 30 to 40 percent MCR for large two-stroke installations, achieved by running at low RPM against a feathered controllable-pitch propeller, or against limited-pitch on fixed-pitch propeller ships by idling with a brief burst to verify governor response.
What the quay trial can verify, because integration is the purpose of the stage: first firing from cold on starting air, starting-air system air pressure and volume adequacy, bridge telegraph and engine-order telegraph communication, remote control system response from bridge, engine-room automation and monitoring alarms, all auxiliary pump start/stop sequences, lube oil system priming, cooling water system temperature regulation, charge air cooler operation on ship seawater, cylinder lubricator quantity verification (feed rate per cylinder can be checked with the engine rotating slowly), slow turning before the first start (required to clear any hydraulic lock from condensate in indicator cocks), and the full fuel changeover sequence if the ship burns both HFO and MDO or LNG and diesel.
The quay trial is the first demonstration that the engine-to-ship interfaces work. Problems found here (wiring crossed on a bridge telegraph, a cooling water valve aligned for shore supply instead of ship suction, a safety trip that had been jumpered for shop-test and not reinstated) are caught at the quay, where rectification takes hours rather than days at sea.
Stage 3: Sea Trial
The sea trial is the only stage that can demonstrate the engine and propulsion system performing against actual ocean resistance. Ship resistance changes with sea state, wind, water temperature and density, and propeller submergence depth. None of these can be reproduced at a test bed or quay. The sea trial is therefore the definitive acceptance event.
Progressive Speed Trial
The progressive speed trial is the systematic measurement of the speed-power relationship across the engine’s power range.
The progressive speed trial builds the measured speed-power curve from minimum to MCR by running the ship at defined engine power steps, measuring the resulting ship speed and the full engine performance parameter set at each step, then comparing the corrected curve against the contractual prediction.
The standard load steps for a large slow-speed two-stroke main engine are 25, 50, 75, 85 (CSR), and 100 percent MCR. An overload step at 110 percent MCR is demonstrated only where the engine maker and class have approved an overload rating and the engine design permits it; MAN ME engines and Wartsila RT-flex engines have defined overload capabilities, but the overload point is not always contractually required at sea trial. Each step requires a stabilization run of at least 20 to 30 minutes at constant power before measurements begin.
At each load step the trial engineers simultaneously record: shaft power (from a torsiometer on the intermediate shaft, or a torque flange close-coupled to the engine), engine speed (RPM from a tachometer on the flywheel), propeller shaft RPM (from a shaft-mounted proximity sensor), ship speed (from GPS over a defined run length), fuel consumption (from the flow meter set on the HFO supply and return lines, mass balanced for density), and the full cylinder-by-cylinder performance parameter set.
The propeller law relationship means power rises approximately as the cube of RPM on a fixed-pitch propeller in open water: a 10 percent reduction in RPM from 100 to 90 percent corresponds to roughly a 27 percent reduction in power (0.9³ = 0.729, so approximately 73 percent power). This relationship shapes the progressive speed trial run pattern. The engine load diagram and operating envelope shows how the propeller law line, the MCR point, and the layout point interact to define the allowable operating range.
Speed at each step is measured as the average over a defined run length in a constant heading, with corrections applied for current, wind, and (where relevant) shallow water. ISO 15016:2015 defines the correction methodology in detail (section on ISO 15016 and EEDI/EEXI below covers this). The corrected speed-power data points are the contractual performance delivery record.
MCR Endurance Run and CSR Demonstration
The MCR endurance run demonstrates that the engine can sustain full rated power for an extended period without component distress, overheating, or progressive parameter drift. It is a reliability demonstration, not only a performance measurement.
The MCR endurance run runs the engine at 100 percent rated power for a minimum of 4 to 6 hours continuously, with all systems in the sea-going configuration, and verifies that every monitored parameter remains within specified limits throughout the run.
During the endurance run the trial team logs all parameters at 30-minute intervals minimum. The critical watches are the exhaust temperature pattern across all cylinders (a single cylinder showing a rising exhaust above its peers is the first symptom of a deteriorating exhaust valve or a fouled nozzle), lube oil temperatures and pressures at all main bearings and crosshead bearings, cooling water temperatures at each cylinder liner and piston crown cooling outlet, turbocharger inlet and outlet temperatures and speeds (each turbocharger is logged separately on multi-TC installations), charge air receiver pressure and temperature, and scavenge receiver temperature.
The CSR (Continuous Service Rating) is usually set at 85 percent MCR for large slow-speed two-stroke engines, matching the contractual fuel consumption guarantee point and the vessel’s design propulsion point. The CSR run is conducted as a separate step within the progressive trial program, typically as a stabilized 4-hour block at 85 percent. The SFOC at CSR is the most commercially important single measurement, because it is the reference consumption used in the time charter consumption warranty. See specific fuel oil consumption for how SFOC is defined and computed.
For vessels whose EEXI calculation references the 75 percent MCR point (after application of an Engine Power Limitation or Shaft Power Limitation), the trial must also include a stabilized run at the limited power point, with the ship’s speed measured simultaneously. The ISO 15016 correction applied to the trial result then yields Vref, the reference speed used in the EEXI attained formula. This is covered below in the EEDI/EEXI section.
Performance Measurements: Cylinder Indicators, Exhaust Temperatures, Turbocharger
Cylinder Indicator Cards
Cylinder pressure is measured by electronic pressure transducers (PMI, Process Monitoring Indicators, a term also used for the broader online performance system) at each cylinder cover. For large bore engines such as a MAN G95ME-C or a Wartsila X92B, indicator cocks are fitted as standard. The transducer generates a pressure-versus-crank-angle trace (the p-theta diagram) over one complete cycle (720 degrees of crankshaft rotation for a two-stroke).
From the indicator card the trial engineers read: maximum cylinder pressure (Pmax), the compression pressure (Pcomp, the pressure at top dead centre with fuel cut off, derived from the motoring trace), mean indicated pressure (IMEP, the net area of the indicator card divided by the swept volume), and the peak pressure angle (the crank angle at Pmax). These readings, compared across all cylinders, reveal misfueling (a low IMEP cylinder), late injection (a Pmax angle past the target), and worn fuel injection equipment (a soft Pmax compared to specification).
The class surveyor reviews the indicator card set at MCR. IACS Unified Requirements M section M23 requires that cylinder-by-cylinder Pmax variation does not exceed a defined tolerance (typically ±3 bar for large two-stroke engines) relative to the mean. Cylinders outside tolerance must be adjusted before the trial is signed off.
Exhaust Temperature Mapping
Exhaust gas temperature is measured at each cylinder outlet (the temperature at the cylinder exhaust valve outlet, before mixing in the exhaust manifold) and at each turbocharger inlet and outlet. A well-balanced engine shows exhaust temperatures within roughly 20°C cylinder-to-cylinder at a given load point. An outlier typically points to a fuel timing issue, a worn or seized fuel injector needle, or a leaking exhaust valve.
Turbocharger outlet temperature (after the turbine stage) and charge air temperature after the air cooler are measured at each power step. The temperature difference across the turbine stage reflects the energy extracted from the exhaust gases. A turbocharger running with lower-than-design pressure ratio (a sign of deteriorating turbine or compressor wheels) shows up first as a higher-than-expected turbocharger outlet temperature at a given load. See marine engine turbocharging for the thermodynamic relationships.
Turbocharger Speed and Charge Air Pressure
Turbocharger speed is measured by an eddy-current or inductive pickup on the turbocharger shaft. Design speed at MCR for a large ABB or MAN NA/TCA turbocharger on a slow-speed engine is typically 10,000 to 20,000 RPM depending on size. At each load step the trial team confirms turbocharger speed against the maker’s performance map; a speed lower than predicted at a given charge air pressure implies deterioration in the compressor or turbine. Scavenge receiver pressure at each load step is similarly compared against the shop-test record. Departure from the shop-test characteristic points to a change in the combustion air circuit: a leaking charge air cooler, a partially blocked cooler, or a turbine fouled with combustion deposits.
SFOC Measurement at Sea Trial
SFOC at sea trial is measured by the same mass-flow-meter method as at shop test, but with ship-grade fuel rather than ISO reference fuel, and against the propeller load rather than a dynamometer.
SFOC at sea trial equals the measured fuel mass flow rate in grams per hour divided by the simultaneously measured shaft power in kilowatts, then corrected to ISO 3046-1 reference conditions for inlet air temperature and pressure, fuel lower calorific value, and cooling medium temperature.
The correction to ISO reference conditions is important because the sea trial may be conducted in ambient conditions different from the standard: hot tropical air increases specific fuel consumption relative to a cool temperate test, because the air density is lower and the engine is aspirating less oxygen mass per stroke. ISO 3046-1 Annex D defines the correction procedure. For modern slow-speed two-stroke engines, the total ambient correction from, say, 38°C and 1.013 bar to ISO 25°C and 1.000 bar moves the SFOC by 2 to 4 g/kWh, well within the measurement uncertainty of the trial if not applied.
The fuel flow meters used at sea trial must be calibrated before the trial and their calibration certificates presented to the class surveyor. A Coriolis mass flow meter measuring on both the supply and return lines (with the difference being the net consumption) is the preferred arrangement. Older installations may use positive-displacement meters. Measurement accuracy should be within 0.5 percent of reading.
The SFOC guarantee is quoted at ISO reference conditions. The trial team applies the ISO correction, calculates the corrected SFOC at each load step, and compares it to the contractual values in the engine specification sheet. A corrected SFOC at MCR more than 5 percent above the guaranteed value constitutes a contractual non-conformance; the builder and engine maker must investigate before delivery.
The specific fuel oil consumption curves article describes how SFOC varies across the engine load range and why the curve shape matters for vessel economics.
Maneuvering, Crash-Stop, and Astern Trials
Maneuvering: Order-to-Response Time
The maneuvering trial sequence begins with verification that the engine responds to bridge orders within the time limits specified in the engine operating manual and the class rules. For a large MAN ME or Wartsila RT-flex engine, the time from an “All stop” order at the bridge telegraph to the engine beginning to decelerate is specified in seconds: typically less than 10 seconds end-to-end including telegraph transmission, electronic governor response, and fuel rack actuation.
Astern power is achieved by reversing the engine direction in two-stroke engines (the camshaft shifts to the astern timing position and starting air is admitted in the opposite sequence to spin the engine backwards). The time to go from full-ahead rotation to stable astern rotation, confirmed by tachometer, is a key maneuvering parameter. The engine maker specifies the maximum allowable time for each engine model.
Reversing Test
The reversing test demonstrates the complete direction reversal sequence: engine running ahead at a defined speed (typically 40 to 60 RPM for a large slow-speed engine), an astern order given, engine stopping on starting air in astern mode, and then running stably astern. The test is conducted multiple times to confirm repeatability. See engine reversing system for the mechanical and control systems involved.
A controllable-pitch propeller ship has a different reversing test: the test verifies pitch reversal response time rather than engine direction reversal. The engine continues running ahead while the CPP blades swing through zero pitch to astern pitch. Some configurations allow CPP ships to achieve astern thrust from a forward-running engine within 15 seconds of the order, faster than a fixed-pitch reversing engine.
Starting Air Test
The starting air test verifies the starting air system can start the engine a defined number of times from cold without recharging. SOLAS Chapter II-1 Regulation 26 requires that the compressed air system can provide at least 12 consecutive starts for a reversible main engine, or 6 starts for an engine with a separate reversing mechanism. The test is conducted with the starting air receiver at normal operating pressure (typically 25 to 30 bar) and the valve train in the start-ahead position, then repeated for astern starts. See engine starting air system for the system architecture.
Minimum Stable Speed Test
The minimum stable speed test determines the lowest RPM at which the engine can maintain stable combustion without misfiring or hunting. For large slow-speed two-stroke engines the minimum stable speed is typically 10 to 15 percent of MCR RPM (roughly 10 to 15 RPM for engines rated at 80 to 100 RPM MCR). Below minimum stable speed, the long piston stroke means individual injection events become so widely spaced in time that combustion stability degrades. The test runs the engine at progressively lower RPM, checking for stable indicator card shape and uniform exhaust temperatures, until the stability limit is identified.
Crash Stop
The crash stop trial is the highest-stress test in the engine sea trial program. From full-ahead speed, an “All stop, all back full” order is issued simultaneously. The engine must stop ahead rotation, reverse direction using starting air in the astern admission mode, and develop full astern power as rapidly as possible.
The crash stop demonstrates the propulsion plant’s emergency stopping capability. The stopping distance (track reach) is measured from the moment of the astern order to the moment the ship’s speed reaches zero, and must not exceed 15 ship lengths under MSC.137(76) for normal merchant ships.
The stress on the engine during a crash stop is high. The propeller, still turning ahead due to the ship’s forward momentum, is fighting a reversed engine. The resulting axial thrust shock loads the crankshaft thrust bearing and the shafting. This is why crash stops are conducted only as many times as required by class and contract (usually once, occasionally twice if the first is invalid due to environmental conditions). The engine maker’s service engineer monitors critical parameters during and after the crash stop to confirm no permanent damage.
Astern power for a large two-stroke engine is typically 70 to 75 percent of ahead MCR: the Wartsila RT-flex engines and MAN ME engines both specify this reduced astern power limit in their engine instruction manuals, because combustion on the astern stroke uses different fuel valve timing and the exhaust valve timing is not fully optimized for astern running.
Astern Running
After the crash stop, a separate astern-running test verifies sustained astern operation. The engine runs at full astern power for a defined duration (typically 30 minutes per class requirements) to confirm thermal stability, lube oil delivery adequacy, and exhaust temperature patterns in astern mode. Some class societies require the engine to demonstrate astern endurance at MCR-equivalent astern output; others accept a lower sustained astern power demonstration.
Governor and Safety Device Tests
Governor Test at Sea
The governor test at sea repeats and extends the shop-test governor checks in the fully integrated condition. With the engine running at MCR, the trial team steps the fuel lever to an intermediate setting and checks that the governor holds steady speed (speed regulation, or droop characteristic) within the specified tolerance. A well-tuned Woodward or electronic governor on a modern MAN ME/GI or Wartsila RT-flex engine holds steady-state RPM within 0.5 percent of setpoint across load swings that represent the effect of a wave train passing under the hull (propeller loading varies substantially cycle-by-cycle in a seaway).
For network-connected generator engines, the governor and load-sharing test verifies that the governor droop setting allows two or more generators to share load stably on the busbar. Generator governor droop is typically set at 3 to 5 percent (meaning a 100 percent load swing from no-load to full-load produces a 3 to 5 percent drop in frequency). This test is part of the auxiliary engine sea trial sequence run in parallel with the main engine tests.
Overspeed Trip
The overspeed trip is tested by running the engine at MCR and then simulating an overspeed condition by a controlled test input to the governor circuit (not by actually accelerating the engine to overspeed, which would be destructive). On electronic governor systems (MAN ME, Wartsila RT-flex), the test is performed by injecting a simulated speed signal above the trip threshold into the protection system. The trip must activate the fuel cutoff and the starting air shut-off valve within the prescribed response time, and the engine must decelerate and stop.
IACS Unified Requirements M section M45 sets the overspeed trip threshold at 115 percent of rated RPM for the main engine and 115 percent for generator engines. DNV class rules additionally require a secondary mechanical overspeed device independent of the electronic system on all main engines above 375 kW. Both the primary and backup trips are tested at the sea trial.
Other Safety Trips
The full safety-device test list for the main engine sea trial includes: low lube oil pressure trip (activated by closing the supply valve momentarily to drop pressure below the trip setpoint while monitoring shutdown response), high bearing temperature trip (simulated by a test input), high exhaust temperature alarm and trip (simulated), scavenge space fire detection (simulated by test aerosol at the detector), and bridge control failure transfer to engine-room control (tested by removing bridge control while the engine is running at a low stable load). Each trip event is logged with time-to-response and shutdown sequence.
ISO 15016 Speed-Power Analysis and EEDI/EEXI
ISO 15016 Corrections
Raw trial data (ship speed over ground and shaft power at each load step) must be corrected to a standard set of conditions before comparison with the contractual speed-power prediction. ISO 15016:2015 defines the methodology. The principal corrections are:
Wind resistance correction: the trial team measures apparent wind speed and direction at the masthead anemometer throughout each load step. Transverse and longitudinal wind force components are calculated using the vessel’s above-water wind resistance coefficients (from the design yard’s CFD model or tank test). The wind-added resistance is converted to an equivalent ship speed correction.
Wave-added resistance: the wave spectrum is measured by a wave buoy or the ship’s own motion sensors. Wave added resistance is calculated from the vessel’s response amplitude operators (RAOs), which describe how the hull converts incident wave energy into added propulsive resistance. ISO 15016 provides an ITTC-recommended method for this calculation. Trials conducted in sea states above Beaufort 5 (significant wave height above approximately 3 meters) are generally accepted only with explicit class agreement, because wave correction uncertainty increases rapidly above this threshold.
Current correction: the double-run method (runs in opposite directions at each load step) removes constant current to first order. ISO 15016 requires a minimum of four reciprocal runs per load step for statistical validity.
Shallow water correction: the Lackenby or Schlichting method adjusts for the speed reduction in water depth less than approximately 20 times the draft. Trial sites for large vessels are selected to be at least this depth; where unavoidable corrections exceed the tolerance in the contractual specification, the parties must agree on acceptance.
Air density correction: ISO 15016 corrects engine power output to a standard ambient condition. The correction for air temperature and pressure on a two-stroke engine power output is on the order of 0.4 percent per 1°C deviation from the 25°C reference.
EEDI and EEXI Connection
The Energy Efficiency Design Index (EEDI) and the Energy Efficiency Existing Ship Index (EEXI) both require a reference speed (Vref) at a defined power point. For EEDI, Vref is the speed at 75 percent MCR of the propulsion plant, corrected to calm water by ISO 15016. The EEDI attained value is computed as the CO2 emission per tonne-nautical mile at this reference condition. MARPOL Annex VI Regulation 21 mandates EEDI compliance for new ships; the sea trial data is the primary evidence.
For EEXI (MARPOL Annex VI Regulation 23, in force since 1 November 2022 for existing ships above 400 GT on international voyages), the reference speed is computed at the engine’s limited MCR after any Engine Power Limitation (EPL) or Shaft Power Limitation (ShaPoLi). The sea trial for an EPL-fitted vessel must demonstrate actual ship speed at the limited power, and the ISO 15016-corrected result becomes the Vref submitted to the flag state and class for the EEXI verification. See what is EEXI for the regulatory framework and EEXI EPL and ShaPoLi for the limiting mechanism.
Class societies accept ISO 15016-corrected sea trial data or tank-test-derived predictions, with sea trial data preferred where available. DNV and Lloyd’s Register both publish procedural notes confirming that a sea trial conducted and analyzed per ISO 15016 satisfies the EEXI reference speed verification requirement.
| Speed-power analysis item | ISO 15016 section | Notes |
|---|---|---|
| Trial site selection | Section 4 | Minimum depth, current, traffic criteria |
| Number of runs per load point | Section 5.3 | Minimum 4 reciprocal runs (2 pairs) |
| GPS measurement accuracy | Section 5.4 | DGNSS or RTK preferred, <0.5 m |
| Wind correction method | Annex B | ITTC recommended coefficients |
| Wave correction method | Annex C | RAO-based or ITTC standard method |
| Current correction | Section 6.2 | Double-run, higher-order correction optional |
| Shallow water correction | Section 6.4 | Lackenby method above specified depth ratio |
| Engine power to ISO reference | Section 6.5 | ISO 3046-1 ambient correction |
| Reporting | Section 7 | Format for corrected speed-power curve |
The Trial Sequence: End-to-End Table
| Trial stage | Location | Key engine tests | Class hold point? | Primary output |
|---|---|---|---|---|
| Factory acceptance test | Engine maker’s works | MCR + load range SFOC, Pmax, NOx, safety devices, governor | Yes (surveyor witness required) | EIAPP certificate basis, Technical File |
| Quay trial | Shipyard quay | First start from cold, telegraph comms, auxiliary systems, slow-turning | Usually a class attendance point | Commissioning sign-off |
| Builder’s trial | At sea | System integration check, engine running-in, preliminary speed data | Class attendance only | Internal defect list |
| Contractual sea trial | At sea | Progressive speed trial, MCR endurance, SFOC at CSR, crash-stop, astern, governor/overspeed, safety trips | Yes (class certificates issued) | Speed trial certificate, SFOC certificate, delivery |
Attendance and Certification
Class Society Surveyor
The class surveyor’s role at the engine sea trial is dual: technical witness and certifying authority. The surveyor checks that the trial program covers all items required by the class rules (typically listed in the class society’s ship survey procedure), that instrumentation is calibrated, that measurements are taken and recorded correctly, and that the results meet the class approval criteria. For two-stroke main engines, IACS Unified Requirements M Section M23 defines the minimum test scope; individual class societies add requirements on top.
After a satisfactory trial, the surveyor signs the trial protocol and issues or recommends issuance of: the engine-specific entries in the Classification Certificate, the EIAPP Certificate (countersigned with the flag state authority), and the entries in the Certificate of Registry relating to propulsion. A classification society overview describes how these certificates sit within the broader survey system.
Shipowner’s Representative
The owner’s representative (or the owner’s designated inspection company, such as an independent surveyor) attends to verify the contractual specification is met. The owner signs the acceptance protocol at the end of a successful trial. If any parameter is out of specification, the owner may withhold signature pending rectification. The shipbuilding contract’s commercial terms govern the consequences: most contracts allow a defined number of days to remedy a trial deficiency before liquidated damages or rejection clauses activate.
Manufacturer Service Engineers
The main engine maker’s service engineer monitors the engine throughout the trial, particularly during the MCR endurance run and the crash stop. They carry authority to stop the trial if a parameter indicates impending damage. They also take their own set of measurements for the maker’s field record, which feeds back into the engine model’s performance calibration data.
Turbocharger makers (ABB Turbocharging, MAN Turbocharger, Mitsubishi Turbocharger and Engine Europe) may also attend when a new turbocharger type is being commissioned for the first time or when the turbocharger performance test is a contractual requirement.
SFOC as the Commercial Performance Baseline
The ISO-corrected SFOC curve measured at the sea trial becomes the performance baseline that follows the vessel through its commercial life. The time charter party’s consumption warranty references the trial-certified SFOC: a vessel warranted to consume 38 tonnes per day at 14 knots CSR is expected to maintain that figure in calm water at equivalent displacement, within the contractual tolerance.
The SFOC baseline also feeds the CII calculation. The IMO Carbon Intensity Indicator under MARPOL Annex VI Regulation 28 rates a ship annually based on its CO2 per capacity-nautical mile. The ship’s energy model uses the trial SFOC curve to estimate the fuel consumption component of CII at different speed and load settings. A vessel with better (lower) trial SFOC enters service with a higher initial CII rating. See what is CII for the operational implications.
In practice, SFOC in service tends to increase from the trial baseline as the engine accumulates running hours and components wear. Engine performance monitoring using online PMI systems tracks the cylinder pressure data and exhaust temperatures against the trial baseline. A cylinder Pmax drifting 5 bar below the baseline alongside a rising exhaust temperature in that cylinder typically signals injector nozzle wear or valve seat erosion. See engine performance monitoring PMI for how the trial data becomes the reference for in-service condition monitoring.
Auxiliary Engine Trials
Main propulsion trials attract most of the attention, but the auxiliary engine trials run in parallel and are equally required for delivery.
Auxiliary diesel generator engines are tested at the shipyard quay and at sea through: the load acceptance test (sudden application of full generator load from no-load to verify the governor does not cause an unacceptable frequency transient), the voltage and frequency regulation verification, the emergency generator start from dead ship (the emergency generator must start and accept full emergency load within 45 seconds of a total blackout per SOLAS Chapter II-1 Regulation 42), and the sequential load-shedding and restarting demonstration in the event of a bus fault.
For LNG-fuelled vessels and LNG carriers, the dual-fuel generator engines and the gas combustion unit are additionally tested for gas mode operation, pilot fuel quantity verification, and gas valve response time. See marine auxiliary engines and generators for the auxiliary engine technical background.
Post-Trial Documentation
A complete engine sea trial generates a substantial documentation set. The core documents are:
The Engine Performance Test Report covers the FAT data: all load-step parameter tables, indicator card plots, SFOC curve, ISO corrections, NOx measurement record, and the surveyor’s witness certificate.
The Sea Trial Protocol is the master document produced at sea. It contains all progressive speed trial data tables, the MCR endurance run log (parameter tabulated at 30-minute intervals), the crash-stop track chart and timing record, the governor and overspeed test records, all safety-device test records, and the SFOC and performance measurement tables at each load step.
The ISO 15016 Analysis Report presents the raw run data, the environmental corrections applied at each run, the corrected speed-power curve, and the comparison with the contractual speed-power prediction. This report is reviewed and countersigned by the class surveyor.
The EIAPP Certificate (or the Technical File amendments if the engine already holds an EIAPP) is finalized from the FAT NOx data and lodged with the flag state.
The Delivery Protocol (signed by builder, owner, and class) records acceptance of the vessel and references the trial documents as the contractual performance proof.
Limitations
Engine sea trial results carry inherent measurement uncertainty, and users of the trial data should understand the bounds:
SFOC measurement uncertainty is typically ±1 to ±2 percent at a well-instrumented trial. This means a trial result of 165 g/kWh at MCR has a realistic uncertainty band of roughly ±2 to ±3 g/kWh. Contractual SFOC guarantees are written with this in mind; most shipbuilding contracts allow the engine to exceed the guaranteed SFOC by up to 5 percent before a deficiency is triggered.
ISO 15016 speed-power corrections introduce their own uncertainty, particularly the wave correction. In sea states above 2 meters significant wave height, wave correction uncertainty alone can approach ±0.2 to ±0.3 knots, which is the same order of magnitude as the contractual speed tolerance. Trials in marginal weather are a known source of commercial disputes.
The trial measures performance at a specific displacement and hull condition. The trial hull is clean (typically freshly dry-docked for anti-fouling paint application). In service, hull roughness increases resistance within months; any charter speed warranty must account for the fouling allowance separate from the trial result.
Engine sea trials are conducted on a finite number of runs. Statistical averaging reduces current and wind error but doesn’t eliminate them. For vessels where the speed guarantee carries large liquidated damages (a VLCC or large containership where 0.1 knot deviation represents millions of dollars annually), parties sometimes agree to additional trial runs or third-party analysis of the ISO 15016 dataset.
Engine trial results do not predict future reliability. The MCR endurance run confirms 4 to 6 hours at full load; it cannot demonstrate 10,000 hours between major overhauls. In-service performance monitoring, as described in marine engine performance monitoring, bridges the trial baseline and the actual operational record.
Finally, sister-ship comparisons are useful but imperfect. Systematic differences in propeller pitch setting, hull form variations within the class tolerance, and differences in auxiliary loading between sister ships can create apparent performance differences that aren’t actual engine differences. Trial teams conducting sister-ship comparisons should standardize displacement and trim before interpreting deviations.
See Also
Related wiki articles
- Sea Trials and Performance Testing: the broader ship-level trial program covering turning circles, zig-zag, measured mile, and ISO 19019
- Specific Fuel Oil Consumption: SFOC definition, units, and commercial significance
- Specific Fuel Oil Consumption Curves: how SFOC varies across the load range
- Engine Load Diagram and Operating Envelope: propeller law, layout point, MCR/CSR relationship
- Engine Governor Systems: governor theory underlying the sea trial governor tests
- Engine Reversing System: mechanical and control detail of the reversing test
- Engine Starting Air System: starting air system and the SOLAS 12-start requirement
- Engine Performance Monitoring PMI: how trial baseline data becomes in-service condition monitoring
- Marine Engine Turbocharging: turbocharger performance and the TC speed test
- Marine Auxiliary Engines and Generators: auxiliary engine trial requirements
- What Is EEXI: EEXI regulatory framework and the role of sea trial Vref
- EEXI EPL and ShaPoLi: engine power limitation and how it changes the trial power point
- NOx Tier I, II, and III: NOx limit values by keel-laying date
- What Is CII: how trial SFOC feeds into the operational CII calculation
- Classification Society: how class certificates fit the broader survey hierarchy
Related calculators
- Specific Fuel Oil Consumption: SFOC calculation with ISO 3046-1 corrections
- Engine Scavenge Air Pressure Estimate: charge air pressure at load points
- System: Main Engine Slow-Speed 2-Stroke: integrated slow-speed engine system parameters