Background
Sea trials cover a wide range of tests organised into categories: powering and propulsion (speed trials, fuel consumption, endurance), manoeuvring (turning circle, zig-zag, crash stop), seakeeping (motion in waves, where conducted), structural and machinery (vibration, noise, equipment functional tests), and special-purpose trials for cargo systems, gas systems, and military or research equipment. The conduct of trials is governed by a combination of class society procedures, the IMO Standards for Ship Manoeuvrability (Resolution MSC.137(76)), the ISO 19019 standard for speed trials, the IACS Recommendations, and contractual provisions in the shipbuilding contract.
This article describes the principal categories of sea trials, the methods of measuring speed under MSC.137(76) and ISO 15016/19019, the bollard pull trial procedure for tugs, the manoeuvring trials standard package (turning circle, zig-zag, crash stop), the endurance trial, the certification of performance for class and flag, and the post-delivery dry-dock trials and ongoing performance monitoring that maintain the trial results as the operational baseline.
Categories of Sea Trial
Sea trials in a typical newbuilding programme are organised into several events, each with a specific purpose.
Builder’s Trial
The builder’s trial is the first comprehensive test of the vessel under the builder’s control. It is conducted before the formal contractual sea trial and is used by the builder to verify that all systems are functioning, to identify and correct any defects, and to prepare the vessel for the contractual trial. The owner’s representatives may attend as observers but the trial is not contractually binding.
Gas Trial
The gas trial is required for LNG carriers, LPG carriers, and gas-fuelled vessels. It is conducted after the cargo containment system is loaded with cargo or fuel for the first time and verifies the cargo system, gas-handling equipment, dual-fuel propulsion (where applicable), and emergency systems under operating conditions. Gas trials are demanding events typically requiring an experienced gas-trained crew and detailed pre-trial planning.
Pre-Delivery Trial / Contractual Sea Trial
The contractual sea trial is the formal trial that establishes whether the vessel meets the contractual specification. The owner’s representatives, class surveyors, flag State surveyor (where present), and the builder’s trial team are all aboard. The trial programme is fixed in advance, the test results are documented and signed by both parties, and the trial outcome determines contract acceptance and any liquidated damages or bonus payments tied to performance.
Sea Trial Continuation / Repeat Trials
Where the contractual trial reveals deficiencies (e.g. speed below specification), a repeat trial may be required after correction. Repeat trials may be partial (only the deficient items) or full repeats of the affected sections. The repeat is typically scheduled within weeks of the original trial.
Post-Delivery Dry-Dock Trial
After the vessel has been in service for a defined period (typically 6-12 months), a post-delivery dry-dock trial may be conducted to verify ongoing performance and to assess hull fouling effects. Some shipbuilding contracts include a post-delivery performance guarantee with this trial as the basis.
Speed Trial Methods
The measurement of vessel speed at delivery is one of the most economically significant trial outcomes because the delivered speed determines the vessel’s commercial performance, fuel consumption, and the time charter speed warranty. Two principal methods are used.
Measured Mile Method
The measured mile, the traditional method, uses a fixed course of known length (historically one nautical mile, hence the name; modern courses are typically 2-3 nautical miles) marked by transit ranges on shore. The vessel runs the course at constant speed and heading, and the time taken to transit the marked length is measured precisely (originally by stopwatch, now by GPS time-stamp). Multiple runs in opposite directions average out current effects.
The measured mile is conducted at multiple power settings (typically 50%, 75%, 90%, and 100% MCR) to establish the speed-power curve. Each speed point requires several runs (typically 2 reciprocal pairs, total 4 runs) to give a reliable average and to remove tide and current effects.
Measured mile courses exist at a number of locations worldwide: the Skelmorlie measured mile (Firth of Clyde, UK), the Mainland Measured Mile (Goeree-Overflakkee, Netherlands), the Polperro measured mile (English Channel), the SK measured course (South Korea, multiple), and the various measured miles off Japan and China. The choice depends on the builder’s location and the vessel type.
GPS Method
GPS-based speed trials use precise GPS position measurement (now typically RTK-GPS or differential GPS with sub-metre accuracy) to measure speed-over-ground continuously over a long run. The vessel runs at constant power for a period (typically 20-30 minutes per run) and the average speed is calculated from the GPS position track.
GPS trials avoid the need for shore reference marks and can be conducted in any suitable open water area. They are now the dominant method for speed trials of large commercial vessels, with measured mile retained for some smaller vessels and naval applications.
ISO 15016 (Ships and marine technology, Guidelines for the assessment of speed and power performance by analysis of speed trial data) and the more recent ISO 19019 (revision of 15016 and now the principal reference) standardise the GPS-based trial procedure. The procedures address: number and duration of runs, environmental corrections (wind, waves, current, depth), power measurement, and statistical analysis of results.
Speed Trial Corrections
The raw speed measured at trial must be corrected to standard conditions to allow comparison with contractual speed and design predictions. The principal corrections are:
Wind correction: actual wind force and direction during trial vs design (calm) condition. Wind force on the vessel is calculated from OCIMF or vessel-specific wind coefficients applied to the measured wind. Above-water area resistance is then deducted from the measured power.
Wave correction: actual wave conditions vs design (calm water) condition. Wave-added resistance is calculated using the vessel’s wave-resistance characteristics from model tests or numerical analysis. Trials conducted in wave conditions above a defined threshold are normally cancelled.
Current correction: trials in moving water (tide, ocean current) bias speed-over-ground. The reciprocal-run method (averaging runs in opposite directions) cancels current to first order; further corrections may be applied for higher-order effects.
Shallow water correction: speed trials in water less than approximately 5-6 times the draft are subject to “shallow water effect” (increased resistance and squat). Trials are conducted in deep water, but where this is impossible, the Lackenby formula or equivalent correction is applied.
Air density correction: engine power output depends on inlet air density, which varies with temperature and pressure. Power is corrected to ISO standard conditions (25 deg C, 1.013 bar).
Hull fouling correction: a recently dry-docked hull has lower resistance than a hull with weeks of service. Trials are conducted with a clean hull, ideally within a defined period after dry-dock.
The corrected trial speed and power are then plotted against the contractual specification. Deviations are subject to the contract’s tolerance band (typically 0.2-0.5 knots) and any liquidated damages provisions.
Bollard Pull Trial
The bollard pull trial is the standard performance test for tugs. The trial measures the static thrust the tug can develop against a fixed bollard at maximum continuous engine output.
The trial procedure follows IACS Recommendation 16 and various class society procedural notes:
- Wire length at least 3 times the tug’s length to ensure thrust acts in line.
- Water depth at least 2 times the tug’s draft and clear of bottom interference.
- Wind not exceeding Beaufort 3-4.
- Continuous bollard pull measured by averaging dynamometer readings over 5-10 minutes at peak power.
- Maximum bollard pull (5-30 second peak) recorded separately if specified.
A typical bollard pull certificate states the continuous and maximum bollard pull at full ahead and (for ASD/azimuth tugs) at full astern. The certificate is issued by the attending class surveyor and is valid for the trial conditions.
Manoeuvring Trials: Turning Circle
The turning circle trial measures the vessel’s response to maximum rudder angle from a constant initial speed. The trial is conducted at the deepwater test area in calm conditions.
The standard manoeuvre is: vessel at full ahead at the trial speed (typically the contracted approach speed, often 90-95% MCR), rudder put hard over (35 degrees in most cases) and held until the heading has changed by 540 degrees (one and a half revolutions). The trial is conducted in both directions (port and starboard).
The principal turning-circle parameters measured are:
- Advance: the distance moved in the original direction of motion when the heading has changed by 90 degrees.
- Transfer: the distance moved perpendicular to the original direction of motion at heading change of 90 degrees.
- Tactical diameter: the diameter of the turning circle when heading has changed by 180 degrees.
- Steady turning radius: the radius of the steady-state circular path.
IMO Resolution MSC.137(76) Standards for Ship Manoeuvrability sets criteria for these parameters, expressed in ship lengths. The advance must not exceed 4.5 ship lengths and the tactical diameter must not exceed 5.0 ship lengths. Failure to meet these criteria is reported to the flag State and may require remedial action.
Manoeuvring Trials: Zig-Zag
The zig-zag trial (also called the Kempf zig-zag) measures the vessel’s directional response to alternating rudder commands. The trial is the principal test of yaw response and overshoot characteristics.
The standard 10-10 zig-zag manoeuvre is: vessel at full ahead, rudder put 10 degrees to starboard until the heading changes by 10 degrees, then rudder put 10 degrees to port and held until heading changes by 10 degrees in the opposite direction (now passing through original heading and going to 10 degrees the other way). This is repeated for several cycles.
The principal zig-zag parameters are:
- First overshoot angle: how far the heading swings past the rudder reversal point on the first reversal.
- Second overshoot angle: how far the heading swings past on the second reversal.
- Initial turning time: time from rudder application to the heading reaching 10 degrees.
MSC.137(76) sets criteria for first and second overshoot angles based on ship length and speed. A 20-20 zig-zag is also conducted for some vessels with the same overshoot criteria but at larger amplitude.
Manoeuvring Trials: Crash Stop
The crash stop trial measures the vessel’s stopping distance under emergency astern propulsion. The trial is the principal test of emergency stopping capability and is critical for safety in confined waters.
The standard manoeuvre is: vessel at full ahead at the trial speed, all-back full ordered, and the vessel allowed to come to a complete stop. The trial measures:
- Track reach: the total distance travelled from the moment of the all-back order to complete stop.
- Time to stop: the elapsed time from order to stop.
- Heading change during stop: most vessels veer significantly during the stop because of asymmetric propeller effects.
MSC.137(76) sets the track reach criterion at not exceeding 15 ship lengths under good conditions for normal merchant ships. Some vessels (particularly large oil tankers and bulk carriers) have track reach approaching this limit and the trial result is a critical safety parameter.
The crash stop is hard on the propulsion plant. The reversal of a large two-stroke main engine from full ahead to full astern stresses the engine, the shafting, and the propeller. Repeated crash stops are not normally conducted, and the trial is performed only as required by class and contract.
Endurance Trial
The endurance trial verifies that the vessel can operate at design conditions for an extended period without overheating, fuel exhaustion, or other failure. The trial is typically 4-6 hours at full continuous output, with all systems operating in their design configuration.
During the endurance trial, the engineering team monitors:
- All engine and machinery temperatures and pressures.
- Fuel consumption (mass and volume) integrated over the run.
- Lubricating oil and cooling water flow rates.
- Vibration levels at multiple locations.
- Noise levels (where contracted).
- Auxiliary power consumption and balance.
- Emissions (where required by contract or regulation).
The endurance trial provides the formal Specific Fuel Consumption (SFC) certification that becomes the baseline for engine performance monitoring over the vessel’s service life. SFC is typically expressed in g/kWh of fuel consumed per unit of engine output. The trial-certified SFC corrected to ISO conditions is the contractual baseline.
IMO Resolution MSC.137(76)
IMO Resolution MSC.137(76), Standards for Ship Manoeuvrability, was adopted in 2002 and is the international standard for manoeuvring trials. It applies to ships of 100 metres or more in length and to chemical tankers and gas carriers irrespective of length.
The standards specify quantitative criteria for:
- Turning ability (advance, tactical diameter).
- Initial turning ability (10-degree heading change in 1.5 ship lengths or less).
- Yaw checking and course-keeping ability (zig-zag overshoot angles).
- Stopping ability (crash stop track reach).
Compliance with MSC.137(76) is mandatory under SOLAS Chapter II-1 Regulation 29. The trial results are documented in a Manoeuvring Booklet and a Pilot Card (used by the pilot) that are provided to the bridge. The Wheelhouse Poster summarises the manoeuvring data for ready reference.
ISO 19019
ISO 19019 (Sea trials of ships, originally part of the 15016 series) provides the standardised procedure for speed trials. It addresses:
- Trial site selection (water depth, current, traffic).
- Environmental conditions limits (wind, waves).
- Run procedures (number of runs, run duration, course-keeping).
- Measurement requirements (GPS accuracy, power measurement, environmental sensors).
- Data analysis and corrections.
- Reporting format.
ISO 19019 is referenced in most modern shipbuilding contracts and class society trial procedures. Compliance with ISO 19019 is generally accepted as evidence of a properly conducted speed trial.
Certification of Performance
The output of the sea trial programme includes formal certification of various performance parameters:
The Speed Trial Certificate, signed by the owner, builder, and class surveyor, certifies the corrected trial speed at the agreed power settings. This is the primary commercial document for the vessel’s speed warranty.
The Manoeuvring Booklet, certified by class, contains all manoeuvring trial data and is required to be kept on board under SOLAS Chapter V Regulation 28.
The Bollard Pull Certificate (for tugs) certifies the continuous and maximum bollard pull.
The Specific Fuel Consumption Certificate, derived from the endurance trial, certifies the engine’s fuel consumption baseline.
The Class Certificate of Trial, issued by the classification society, confirms that the trial programme was conducted in accordance with class rules and that the vessel is fit for service.
Post-Delivery Performance Monitoring
After delivery, the trial-certified performance becomes the baseline against which the vessel is monitored throughout service. Performance monitoring serves several purposes:
Charterparty performance: under time charter, the speed and consumption warranty must be maintained. Significant deviations may give rise to performance claims under the off-hire and performance claims framework.
Hull and propeller fouling: as the hull fouls, resistance increases and speed at constant power falls (or fuel consumption at constant speed rises). Comparison with the trial baseline indicates fouling progression and informs hull cleaning or dry-dock decisions.
Engine condition: as the engine ages, SFC tends to drift upward. Monitoring against the trial baseline indicates the need for major overhaul or component replacement.
Regulatory compliance (CII, EEXI): the IMO Carbon Intensity Indicator and Energy Efficiency Existing Ship Index require annual reporting of operational efficiency. The trial baseline informs the EEXI calculation; the actual operational data informs the CII rating.
Related Wiki Articles
- Marine Engine Performance Monitoring
- Tug Operations and Bollard Pull
- Marine Bridge Equipment and Integrated Bridge Systems
- Marine Voyage Planning and Routing
- Time Charter Party
- Off-Hire and Performance Claims
- Classification Society
- SOLAS Convention
- Marine Stabilisers
- Pilotage Operations
- Heavy Weather Operations
References
- IMO Resolution MSC.137(76), Standards for Ship Manoeuvrability, 2002
- IMO Resolution MSC.1/Circ.1053, Explanatory Notes to the Standards for Ship Manoeuvrability
- SOLAS Chapter II-1, Regulation 29 (Manoeuvring information), and Chapter V, Regulation 28 (Records of navigational activities)
- ISO 19019:2005 (and subsequent revisions), Ships and marine technology, Sea trials of ships
- ISO 15016:2015, Ships and marine technology, Guidelines for the assessment of speed and power performance by analysis of speed trial data
- ITTC Recommended Procedures and Guidelines, Speed and Power Trials, current edition
- IACS Recommendation 16, Towing and Mooring Arrangements (Bollard Pull aspects)
- ABS Guide for Sea Trials
- DNV Class Programme for Sea Trials
- Lloyd’s Register Procedure for Speed Trial Analysis
- ICS Bridge Procedures Guide, current edition
- IMO Resolution MEPC.328(76) and the EEXI/CII regulatory framework
- The Nautical Institute publications on ship manoeuvring
- The Society of Naval Architects and Marine Engineers (SNAME) Technical and Research Bulletins on trial procedures