Sea Trial Speed, Power, and Fuel Consumption Validation Project

This project produces a sea-trial speed, power, and fuel-consumption validation package for a vessel after delivery, refit, repowering, propeller repair, or performance dispute. The deliverable is not another resistance formula sheet. It is the engineering evidence file that connects loading condition, trial runs, shaft power, fuel flow, environmental limits, uncertainty, acceptance criteria, and release decision.

Sea trials are useful only when the measured result can be interpreted. A single headline speed does not prove installed performance if displacement, draft, trim, current, wind, wave state, water depth, hull cleanliness, propeller condition, machinery configuration, and measurement uncertainty are not controlled or documented.

This simplified project is for engineering education. Real trials should follow the applicable contract, class and flag procedures, trial standard, owner requirements, calibrated instrumentation, safety plan, and approved correction method.

Project Objective

Prepare a sea-trial validation package for a small coastal service vessel after a propeller replacement and machinery-control update.

The final deliverable must answer:

1. What loading condition, displacement, draft, trim, tank state, hull condition, and propeller condition were tested?
2. Which runs are valid, reciprocal, repeatable, and inside environmental limits?
3. What corrected speed is achieved at the acceptance power?
4. What shaft power is required at the target speed after normalization?
5. What fuel consumption and specific fuel consumption were measured at the reviewed operating point?
6. What uncertainty guard bands apply to speed, power, and fuel results?
7. Does the vessel meet the acceptance criteria, require retest, or need corrective action?
8. What evidence is archived for future service-performance comparisons?

The deliverable should include a trial boundary, test matrix, instrumentation list, environmental log, loading-condition record, run reduction sheet, acceptance comparison, uncertainty statement, anomaly log, and release recommendation.

Trial Boundary

Use this representative project basis.

Quantity	Value
vessel type	twin-screw coastal service vessel
waterline length	54\ \text{m}
trial displacement	620\ \text{t}
target displacement	615\ \text{t}
mean draft during trial	2.85\ \text{m}
trim by stern	0.18\ \text{m}
contract target speed	13.2\ \text{kn}
maximum accepted corrected shaft power at target speed	1.90\ \text{MW}
maximum accepted specific fuel consumption at reviewed point	225\ \text{g/kWh}
maximum allowed wind for valid run set	Beaufort 3 equivalent
minimum water depth	greater than 4T for this simplified screen
hull and propeller condition	clean, documented by diver inspection
shaft power measurement uncertainty	2.0\% of reading
fuel-flow measurement uncertainty	3.0\% of reading
corrected-speed expanded uncertainty	0.08\ \text{kn}

The vessel completes two reciprocal speed runs on the same course. Auxiliary electrical load is held close to the normal trial value, steering is steady, and the propulsion-control mode is fixed for both runs.

Acceptance Criteria

Use these simplified acceptance gates.

Gate	Criterion
valid trial condition	loading, draft, trim, water depth, weather, hull and propeller condition documented
corrected speed	guard-banded corrected speed is at least 13.2\ \text{kn}
normalized shaft power	guard-banded power at 13.2\ \text{kn} is not above 1.90\ \text{MW}
fuel performance	guard-banded SFOC is not above 225\ \text{g/kWh}
repeatability	reciprocal runs are consistent and no machinery alarms occur
release evidence	instrumentation calibration, run logs, weather, loading condition and anomaly log are archived

These are teaching criteria. Contract trials may specify a different speed correction method, confidence basis, environmental limit, loading correction, endurance run, or fuel-measurement procedure.

Step 1: Check Trial Condition

The trial condition is valid only if the measured vessel state is close enough to the required state for the selected correction method.

Item	Trial observation	Comment
displacement	620\ \text{t}	5\ \text{t} above target
mean draft	2.85\ \text{m}	recorded before and after runs
trim by stern	0.18\ \text{m}	inside planned trial band
water depth	14.0\ \text{m}	depth ratio 14.0/2.85=4.91
hull condition	clean	diver inspection recorded
propeller condition	clean and recently repaired	repair certificate and visual check recorded
wind and sea	inside limit	accepted for simplified trial

Depth ratio:

Since:

the simplified shallow-water screen is acceptable.

Engineering Comment

This does not prove shallow-water effects are zero. It only says the run set is not rejected by the simplified depth gate. A formal standard may still require more detailed correction.

Step 2: Reduce Reciprocal Speed Runs

Measured speed over ground for two reciprocal runs is:

Run	Direction	Speed over ground
1	outbound	13.80\ \text{kn}
2	reciprocal	12.90\ \text{kn}

For a simplified current-cancellation screen, average the reciprocal speeds:

Speed margin before uncertainty:

Guard-banded speed margin:

Engineering Comment

The corrected speed passes the simplified target after guard band. The result depends on the two reciprocal runs being close enough in time and condition that current, wind and machinery settings are reasonably paired. If wind, sea state, rpm or steering changed materially between runs, the average would not be strong evidence.

Step 3: Average Shaft Power

Measured shaft power for the same two runs is:

Run	Shaft power
1	1.82\ \text{MW}
2	1.86\ \text{MW}

Average shaft power at the corrected speed:

The power readings are consistent enough for a screening reduction:

Relative difference from the average:

Engineering Comment

Power repeatability is plausible for a simplified trial, but this is not a calibration statement. The trial package should include shaft-power meter calibration, torsion-meter configuration, rpm signal quality, gear ratio, and whether power is measured per shaft or total propulsion.

Step 4: Normalize Power to Target Speed

For a narrow speed band near the trial point, use a cubic speed-power screen:

Substitute:

Power uncertainty at the normalized point, using 2.0\%:

Guard-banded power margin:

Engineering Comment

The vessel passes the simplified shaft-power gate. The cubic law is a local correction, not a universal model. It is acceptable here only because the speed correction is small. A larger correction should use the agreed speed-power curve or trial standard.

Step 5: Calculate Fuel Performance

The measured total fuel flow during the two reviewed runs is:

Specific fuel consumption on total shaft-power basis is:

Use:

Then:

Fuel-flow uncertainty:

Guard-banded SFOC margin:

Engineering Comment

Fuel performance passes the simplified gate. The boundary must be stated: this is fuel flow divided by measured shaft power at the trial operating point. It is not generator electrical efficiency, whole-vessel energy per nautical mile, endurance fuel rate, or annual fuel consumption.

Step 6: Interpret the Result as an Engineering Decision

The reduced evidence is:

Check	Result	Decision
depth screen	h/T=4.91	accepted for simplified screen
corrected speed	13.35\ \text{kn}	above target
guard-banded speed margin	0.07\ \text{kn}	pass
normalized shaft power	1.779\ \text{MW}	below limit
guard-banded power margin	0.085\ \text{MW}	pass
SFOC	212\ \text{g/kWh}	below limit
guard-banded SFOC margin	6.64\ \text{g/kWh}	pass

Engineering Comment

The trial can be released for the simplified acceptance statement. The strongest evidence is not that every number is favorable; it is that speed, power and fuel margins remain positive after uncertainty guard bands. The release should still be limited to the documented condition: clean hull, clean propellers, trial displacement, accepted weather, accepted water depth, and fixed machinery configuration.

Step 7: Required Trial Evidence

The release package should include:

1. loading condition, displacement, drafts, trim, tank state, fuel state and ballast state;
2. water density, depth, wind, wave, current observation, route and run timing;
3. hull and propeller condition evidence;
4. shaft rpm, shaft power, torque, fuel flow, auxiliary load and machinery configuration;
5. reciprocal run logs with start and end times, headings, steering state and rejected run notes;
6. correction method and calculation worksheet;
7. instrumentation calibration and uncertainty statement;
8. comparison with contract, design prediction or previous baseline;
9. anomaly log covering alarms, steering corrections, vibration, cavitation signs or fuel-system issues;
10. release statement and any operating restrictions.

Common Failure Modes in Sea-Trial Validation

1. Reporting speed over ground without current correction or reciprocal pairing.
2. Comparing measured shaft power with brake-power or generator-power limits.
3. Ignoring displacement, draft and trim differences from the target condition.
4. Accepting a run set with changed wind, current, water depth or steering effort.
5. Treating fuel flow as comparable when auxiliary load, generator loading or fuel temperature changed.
6. Omitting hull and propeller condition, then using the result as a long-term performance baseline.
7. Reporting a pass without uncertainty guard bands when the margin is small.
8. Releasing the vessel after a favorable speed result while vibration, cavitation or machinery alarms remain open.

Final Release Statement

For this simplified trial, the vessel meets the speed, shaft-power and fuel-consumption acceptance gates with positive guard-banded margins. The recommended decision is:

Release the sea-trial speed-power and fuel-consumption result for the documented clean-hull, clean-propeller, trial-displacement condition, with the calculation worksheet, instrument calibration, reciprocal run logs and uncertainty statement archived as the performance baseline.

The release should not be generalized to fouled hull service, heavy displacement, shallow water, high sea state, damaged propellers, different control modes, or untested machinery configurations. Future service-performance comparisons should use the same boundaries or explicitly correct for the differences.