Before releasing the final payment on a new build or major refit in Lombok, insist on a structured sea trial that captures hard numbers: rpm vs speed vs fuel burn, manoeuvring, steering loads, vibration, noise, bilge activity, electrical load and stability behaviour. Document everything in a signed trial report so any defects are rectified before handover documentation is completed.
Why a formal sea trial matters in Lombok
A sea trial in Lombok conditions is not a ceremonial “first cruise”. It is a technical test under controlled loads that either confirms the vessel is ready for commercial or private use, or exposes issues that must be rectified before you release the final instalment.
Local operating areas around Bangsal, Teluk Nara, the Gilis and down to Labuan Bajo involve short, steep seas, seasonal monsoon shifts and varying port approaches. The sea trial must simulate the way the vessel will actually be run, not a light-ship demonstration on flat water.
Your construction or refit contract should link sea-trial acceptance to payment milestones. If you have not yet structured this, review how we typically stage instalments and inspections in the contract payment and supervision framework before committing to a schedule.
Planning the sea trial window and load condition
Agree the sea-trial plan in writing before launch. The plan should state test locations, durations, fuel and water quantities, loading assumptions and what constitutes an acceptable result range for key items such as cruising speed and noise levels.
Typical test loading
- Fuel: 70–100% of service capacity, to reflect typical operating weight.
- Fresh water: at least 50% of tank capacity, unless your trade pattern usually sails fuller.
- Ballast or cargo simulation: sandbags or drums to approximate passenger or cargo weight to a realistic operating displacement.
- Crew and observers: yard crew, owner’s representative, and ideally an independent surveyor.
Weather should be moderate: enough sea to reveal behaviour, but not so rough that you cannot safely execute the test matrix.
Documentation to prepare
- Contract specification and build drawings.
- Engine and gearbox manuals with recommended rpm and load limits.
- Preliminary weight estimate or stability booklet if available.
- Blank sea-trial data sheets for recording each run.
Speed, rpm curve and fuel burn
The most fundamental data from a sea trial is the relationship between engine rpm, vessel speed and fuel consumption. This confirms that the propeller selection, gearbox ratio and hull condition are aligned with the design intent.
How to run speed and rpm tests
- Use measured runs on opposite headings to cancel current and wind as far as practical.
- Hold each test rpm steady for several minutes before recording.
- Record engine rpm from the panel, speed over ground from GPS, and, where possible, real-time fuel flow.
- Do not exceed the engine manufacturer’s recommended continuous rpm limits.
| Test point | Engine rpm (rpm) | Speed over ground (knots) | Fuel burn (L/hr per engine) | Remarks |
|---|---|---|---|---|
| Idle ahead | 600–750 | 2–4 | Record | Check clutch engagement, no knocking |
| Displacement cruise | 1200–1500 | 6–9 | Record | Note vibration and steering effort |
| Economic cruise | 70–80% of rated | Record | Record | Main data point for commercial planning |
| Maximum continuous | Near rated | Record | Record | Watch temperatures, exhaust smoke, alarms |
Compare results against the design speed band discussed at contract signing. Significant underperformance may indicate over-pitching, fouling, excess displacement or hull fairness issues that must be addressed before acceptance.
Manoeuvring, steering and stopping tests
In the tight approaches of Gili Trawangan, Gili Air or Senggigi, predictable manoeuvring and reliable steering are non-negotiable. The sea trial must show how the vessel behaves in slow-speed handling and emergency situations.
Core manoeuvring checks
- Low-speed tracking: Hold a straight course at idle and just above idle. Note any strong helm bias.
- Turning circles: Full-rudder turns both sides at defined rpm. Observe heel angle, turning diameter and response time.
- Crash stop: From service speed, record distance and time to stop when going to full astern (only if safe and within engine/gearbox guidance).
- Astern control: Ability to maintain steerage while going astern, important for tight moorings in Bangsal and Labuan Bajo.
Steering system behaviour
- Hand-wheel turns lock-to-lock and force required at various speeds.
- Hydraulic leaks, hose chafing and ram mounting security.
- Response lag between helm input and rudder feedback.
- Emergency steering changeover procedure and test, where fitted.
Any erratic response or excessive effort should be fixed and re-tested before handover. Adjustments can include rudder angle limiters, hydraulic bleeding, pump replacement or mechanical linkage tuning.
Vibration, noise and structural behaviour
Vibration and noise influence comfort, fatigue and long-term structural life. The sea trial is the time to identify resonances from engines, gensets, shafts and hull panels, especially in timber or composite structures with long spans.
Vibration checks
- Walk the vessel at multiple rpm points, especially near 60–80% of rated rpm.
- Feel for shaft and hull vibration at deck, bulkheads, handrails and window frames.
- Check for loose items: doors latching, deck hatches, ceiling panels and furniture fixings.
- Listen around stern glands, P-brackets and engine foundations for pounding or knocking.
Noise observations
- Measure or at least compare perceived noise levels in the wheelhouse, passenger saloon, cabins and aft deck at idle, cruise and maximum continuous rpm.
- Identify dominant sources: exhaust line, engine room ventilation, deck machinery or structural drumming.
- Record any tonal “hum” at specific rpm that may need isolation or damping.
Corrective work might involve shaft alignment, additional rubber mounts, exhaust lagging, extra insulation or stiffening of lightly supported panels. These should be closed out before you agree that the build is complete.
Bilge, dewatering and watertight integrity
Lombok and Nusa Tenggara trades involve frequent loading, beach landings in some cases and heavy rain. Bilge and dewatering systems must be validated under real operating conditions.
Bilge system trial
- Simulate water ingress by adding controlled quantities of clean water to each bilge compartment where safe and permitted.
- Confirm automatic float switches activate and deactivate pumps correctly.
- Check manual override switches, indicators and audible alarms at the control positions.
- Inspect discharge overboard points for clear flow and correct routing above waterline.
Watertight doors, hatches and scuppers
- Hose-test deck hatches and door seals in key areas such as foredeck lockers and machinery spaces.
- Verify scupper capacity in heavy spray or simulated rain.
- Confirm that any non-return valves are accessible and operating.
Record pump model, rated capacity and observed performance. Any slow-acting or air-locked bilge pump needs rectification before commercial service, as this will be critical during inspections by the Syahbandar and other authorities.
Electrical load and redundancy under way
Many problems only appear when the electrical system is loaded under way: voltage drops, nuisance breaker trips or overheating connections. The sea trial is the correct time to apply realistic demand.
House and navigation loads
- Run all navigation electronics, communication systems, lighting and critical pumps simultaneously for a sustained period.
- Monitor voltage at key distribution boards and at the main battery bank.
- Test inverter/charger changeover behaviour where fitted.
Genset and shore-power changeover
- Operate each genset at planned continuous load (often 60–80% of rating).
- Switch between shore power and genset under controlled conditions to confirm no unexpected blackouts.
- Check thermal performance of switchboards and cable runs by hand-feel or thermal imaging where available.
Any hot smells, discolouration or repeated trips suggest undersized cables or poor terminations. These must be corrected before you sign off the build, as retrofitting later is more disruptive.
Stability behaviour and seakeeping
Formal stability approval for Indonesian-flagged passenger and cargo vessels is governed by Kemenhub and, in many cases, BKI. A sea trial does not replace those calculations and inclining tests, but it does give practical confirmation of how the vessel behaves in live seas and during passenger movements.
Operational stability observations
- Note roll period and comfort in beam seas at different speeds.
- Simulate passenger movement across decks and observe heel response and recovery.
- Test turning at cruising speed in moderate seas, watching heel angle and deck wetness.
- Observe bow immersion in head seas and stern behaviour in following seas where conditions permit.
For commercial vessels, confirm that the observed behaviour aligns with Kemenhub requirements and any BKI class assumptions. Any unexpected tenderness or excessive stiffness warrants further technical assessment, usually in cooperation with an independent naval architect or surveyor.
Recording, sign-off and dealing with defects
Sea-trial value depends on the quality of the records you keep. Numbers, conditions and observations must be clear enough that both yard and owner can agree which items are defects, which are adjustments, and which fall within tolerance.
Practical recording methods
- Use pre-printed data sheets for each test run with fields for rpm, speed, fuel burn, temperatures, noise notes and comments.
- Capture GPS screenshots for speed runs and track logs for manoeuvring tests.
- Photograph engine displays showing load, temperature and alarm status.
- Ask all parties to initial each completed page at the end of the trial day.
Any issues discovered should be logged as punch-list items with agreed rectification actions and dates. Your build agreement and the typical sequencing outlined in the build process timeline should define how these items impact final acceptance and payment release.
Role of independent surveyors
Many owners appoint an external professional to attend sea trials and support the technical sign-off. This can reduce disputes and provide an independent view on performance and safety. For more detail on that process and what to expect, see the discussion on appointing an independent marine surveyor before handover.
Frequently asked questions
Who should attend the sea trial in Lombok?
At minimum, the yard’s captain or helmsman, engineering representative and an owner’s representative should attend. For commercial vessels, many owners also include an independent surveyor. This group allows real-time discussion of engine data, manoeuvring behaviour, safety systems and any items that need rectification before final payment is released.
How long should a proper sea trial take?
A meaningful sea trial for a new build or major refit usually requires several hours underway. You need enough time to stabilise at each rpm point, conduct repeated speed runs, complete manoeuvring tests, check bilge and electrical systems under load and run in at least moderate sea states. Rushing the trial increases the chance of missing important defects.
Can we conduct a sea trial with partial loading?
Yes, but it should approximate realistic operating displacement. If you test too light, speed results will look optimistic and stability behaviour may not represent daily service. Use water ballast, fuel and temporary weights to simulate passengers or cargo. Document the exact loading during the trial so performance expectations are interpreted correctly in future operations.
What if performance numbers are below the design expectations?
If the vessel does not achieve the expected speed or fuel burn bands, treat the sea-trial report as the starting point for diagnosis. Common causes include propeller mismatch, excess displacement, hull fouling, alignment issues or engine tuning. The builder should propose corrective actions, implement them and repeat targeted tests before you sign acceptance and release the final instalment.
Is a sea trial still needed after a refit, not a full new build?
Yes. Any significant refit affecting propulsion, steering, electrical systems, weight distribution or structure warrants a sea trial. Even if the hull is unchanged, new engines, propellers, tanks or superstructure can alter performance and stability. A structured test confirms that the modified vessel remains safe, efficient and compliant with local operating and regulatory requirements.