Vessel Performance Monitoring: Speed, Fuel Consumption and Efficiency Analysis
A ship's speed and fuel consumption are the two numbers that decide whether a voyage makes money — and the two most likely to end up in arbitration. A vessel warranted at about 14 knots on about 35 tonnes a day is not a fixed machine; she is a hull whose resistance climbs as it fouls, driven through water that pushes and pulls her, in weather that shifts hourly, reported by a crew filling in a form at noon. Somewhere inside that noise sits the truth about whether the ship is performing — and both the superintendent trying to time a hull clean and the charterer preparing an underperformance claim are chasing the same signal from the same imperfect data. The stakes are large: the IMO estimates roughly a tenth of the world fleet's fuel burn is down to poor hull and propeller performance, costing owners around $30 billion a year. Yet only about 15% of the fleet carries high-frequency monitoring, and only around 8% uses the data well. This guide breaks down the physics, what actually degrades performance, the ISO 19030 framework, noon reports and their limits, the commercial machinery of speed and consumption claims, and how to build monitoring that earns its keep. Start free trial or book a demo to turn hull and voyage records into decisions and claim defences.
COMMERCIAL & OPERATIONS · VESSEL PERFORMANCE
Speed, Fuel and Fouling: The Signal Hidden in Your Noon Reports
Roughly a tenth of the world fleet's fuel burn is wasted on dirty hulls and worn propellers — about $30 billion a year. The difference between a well-timed hull clean and a lost speed claim is whether you can read performance out of the noise.
Of world fleet fuel burn from poor hull & propeller performance
$30bn
Estimated extra annual fuel cost to owners from that loss
~15%
Of the fleet has high-frequency performance monitoring
~8%
Of the fleet actually uses the performance data well
The Physics You Are Actually Measuring
Everything in performance monitoring rests on one relationship: the power required to push a given hull through water at a given speed. Get the terms straight and most of the confusion in the field disappears. Swipe the table horizontally on mobile.
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Measure
What it is
Why it matters
Speed-power curve
Expected performance in clean, corrected condition
The baseline. Without it there is no analysis, only opinion
STW vs SOG
Speed through water vs over ground; current is the gap
STW is the truth — SOG hides real change
STW at same RPM
Current speed vs history at identical revs
The most revealing trend available without sensors
Slip
Gap between theoretical and actual propeller advance
Tracks propeller condition and fouling over time
Shaft power
Measured engine load, not inferred consumption
Removes the argument from a claim
Hull performance index
Ideal power vs corrected measured power
~100% fresh, <80% degraded
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Always specify STW or SOG when you report a speed. Speed through water is what the hull experiences; speed over ground is what the schedule sees, and the difference is current. For performance analysis STW is what matters, because SOG comparisons are useless — current masks the real change in either direction. Charter party disputes routinely arise from ambiguity over which measurement a warranty clause applies to, and that ambiguity is expensive to resolve after the fact. See how logged voyage data keeps the two straight.
What Actually Degrades Performance
When a ship burns more fuel for the same speed, five candidates are in the frame — and the entire value of monitoring lies in telling them apart. Clean a hull that was fine and the propeller keeps costing you fuel.
Hull Fouling
Marine growth raising frictional resistance — the largest single lever, driven by coating age, water temperature, and above all idle time. A ship sitting warm and stationary fouls fast.
Propeller Condition
Roughness, edge damage, cavitation marks, poor polishing, bent tips, or inefficient propeller-hull interaction — all quietly raise fuel burn, and all are invisible from a noon report.
Weather & Sea State
Wind resistance, wave-added resistance and swell — the dominant short-term noise source, and the reason every serious method corrects for or filters on weather first.
Current
Adverse or favourable, it moves speed over ground without touching the hull's actual performance. Uncorrected, it is the most common source of a false signal.
Loading Condition
Draft and trim change the resistance picture materially — which is why speed-power curves must exist for different loading conditions, not a single laden number.
Engine & Operation
Machinery condition and how the ship is actually run. A shortfall blamed on the hull may be an engine problem — and cleaning the hull will not fix it.
The whole management question in one sentence: is the vessel using more power because the hull is dirty, the propeller is weak, the operating condition changed, or the weather was against her? Noon reports show the symptom; only proper monitoring isolates the cause. That distinction is worth money — the wrong diagnosis means cleaning a hull that was fine while the real culprit keeps burning fuel. And the inputs that separate the causes are not sensor data at all: coating age, cleaning dates, idle periods, and what the last diver found. Book a demo to see hull history behind every performance trend.
The ISO 19030 Framework
Released in 2017, ISO 19030 was the industry's attempt to put a common language under all of this. It defines performance indicators for hull and propeller maintenance, repair and retrofit, measuring change in a vessel's performance over time.
01
A physical model approach
Power-speed curves must be known for different loading conditions — varying draft and trim — with wind resistance corrected for. It specifies sensor accuracy, sampling frequency, reference curves, filtering and correction procedures.
02
Filtering is the method
Data is filtered before analysis, keeping only points in calm weather, stable course and speed, and deep, unconfined, ice-free water. The discipline is in what you throw away.
03
A tiered structure
Three tiers by accuracy — noon reports at the lowest, continuous automatic monitoring at the highest. The tiering exists so the whole industry can take part, not just the sensor-equipped minority.
04
The vessel against herself
The standard compares a ship to her own performance between a reference and an evaluation period. It is a change-detection tool, not a way to rank one ship against another.
Its limits are worth knowing, because practitioners hit them constantly. The Part 2 standard method needs high-frequency auto-logging data most vessels do not have — one estimate put Part 2's applicability at around 10% of the fleet. The computation can show a dependency on speed, with faster sailing producing lower computed degradation, and the computed hull condition can shift with the weather, which in reality it does not. Part 3's tiered methods, including noon reports, exist precisely so the majority can demonstrate compliance. The pragmatic answer the market found is snapshot reporting — capturing speed, draft, trim, power and weather at the same instant as the noon average — plus smarter filters that keep more data than the strict norm allows.
The analysis is only as good as the record beneath it.
Marine Inspection holds inspection reports and underwater survey findings, tracks maintenance and defect history per vessel, and keeps the coating, cleaning and drydock record that turns a performance chart into a decision — or a defence.
For most of the fleet the noon report remains the primary data source — and it deserves neither the contempt nor the trust it typically gets. The weakness is averaging, not the fact that a human wrote it.
What Noon Reports Do Well
Exist on virtually every ship, cheaply, fleet-wide
Contemporaneous — written during the voyage, not after
ISO 19030's lowest tier is built on them deliberately
Detect trends reliably with filtering and enough history
Proven at fleet scale for hull and propeller optimisation
Where They Fall Down
One data point per day, averaged over changing conditions
Manually entered, with weather observed by eye
Tribunals have found deck-log figures exaggerated
Consumption is claimed, not measured
A daily average hides everything that happened between
The upgrade path is not necessarily a sensor refit. Snapshot reporting — recording speed, draft, trim, power and weather at the same moment as the noon data rather than as a 24-hour average — materially improves low-frequency data at almost no cost. Fix the averaging and a noon report becomes a usable measurement.
Speed and Consumption Claims
This is where performance monitoring stops being engineering and becomes money. The structure of a performance warranty is remarkably consistent, and every word in it is load-bearing. Swipe the table horizontally on mobile.
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Warranty element
What it means
The catch
The warranty
e.g. laden about 13.0 kn on about 23.5 mt VLSFO + 0.2 mt LSMGO
Applies only on a good weather day
Good weather
Wind ≤ Beaufort Force 4, sea ≤ Douglas Sea State 3
0.5–1.25 m significant, no adverse current
Duration
A continuous period, generally 24 hours
One arbitrator held it must run noon to noon
"About"
A defined tolerance on the figures
Commonly ±5% or 0.5 knots
Current
Adverse current disqualifies the period
Owners keep the benefit of positive currents
Evidence
Logs plus weather-service reports
On consistent discrepancy, weather service rules
The arbitration record shows how sharply this bites. In one dispute the charterers' weather routing company calculated a good weather speed of 9.88 knots against a warranted about 12.50, while owners rejected the calculation on the ground that there had been no good weather days at all under the charter's own definition. In another, the fight was over whether "significant" wave height should be read at all, with charterers relying on a 2011 arbitration in which swell up to 2 metres was held to fall within Douglas Sea State 3, and a separate 2014 award treating a total sea-plus-swell significant height of 2 metres or less as a good weather day.
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Warranties are given "in good faith and without guarantee." Owners warrant a speed and a daily consumption but only on a good weather day — they do not wish to be exposed when the vessel meets heavy weather. The word "about" carries a defined tolerance, commonly ±5%, or in one case an allowance of 0.5 knots, so a 13.5-knot warranty became a 13.0-knot minimum. Every one of these words is argued over in a claim, which is why the fixture wording and the ship's records have to line up exactly. See how voyage records support a warranty position.
Why Owners Increasingly Win These
A discernible trend has emerged in recent awards, and it runs against the reflexive assumption that a weather routing report settles the matter.
The Clause Governs, Not the Report
In a 2024 award a routing company's report could not found the charterers' claim because it did not assess performance in line with the contractual warranty — the deductions were unlawful. Commentators noted routing reports straying too far from the charter's own parameters.
Deck Logs Still Matter
In the same award the tribunal found deck-log figures exaggerated on sea state and swell — yet still held that due regard must be given to the deck logs alongside the routing data. Neither source wins automatically.
Strict Adherence to the Charter
Across London Arbitrations 15/07, 26/19 and beyond, tribunals have endorsed strict adherence to what the charter provides. If the parties defined good weather a certain way, that definition applies — however inconvenient.
The Reasonable Reader
Where a clause was ambiguous, one tribunal read it as a reasonable person with all the background would — concluding it was inconceivable that bad weather would be left undefined. Sensible intent beats a literal reading that produces absurdity.
The lesson cuts both ways. A charterer whose claim rests on a routing report that applied its own parameters rather than the charter's will lose. An owner whose deck logs are demonstrably exaggerated on sea state hands the other side a weapon, even in a case they win. And a superintendent who cannot produce hull cleaning dates, coating history, propeller polishing records and underwater inspection findings has no way to rebut an allegation that the ship was simply dirty. Precision in the fixture and rigour in the records decide these — nothing else. Book a demo to keep that record defensible.
Clean hull
A well-timed hull clean, decided on data...
vs
$30bn
...against the industry's annual bill for hulls left too long
Building Monitoring That Pays
The final question is what a performance programme should actually deliver. The test is blunt: a hull performance programme should not end with a chart.
01
Establish the baseline
A speed-power curve for each relevant loading condition, in clean corrected condition. Pre-drydock baseline and post-drydock curve are what prove whether a coating worked or the ship just benefited briefly from a fresh bottom.
02
Get power, not just consumption
Shaft power or engine-load data removes the dependence on noon-report consumption claims. It is the single highest-value technical upgrade for a performance programme.
03
Rank the fleet, not the ship
Normalised speed loss, excess fuel, cleaning payback, idle exposure, coating age, ship type and route profile answer the real question: which five hulls are costing the fleet the most fuel this quarter?
04
Isolate the cause before spending
Monitoring should tell you whether the loss is hull fouling, propeller condition, weather, loading, or engine operation — so you clean, polish, inspect or investigate the right thing rather than the habitual one.
05
Drive a decision
The programme should tell the owner whether to clean, inspect, polish, change coating, challenge a performance claim, adjust speed, or protect a charter clause. Anything short of that is instrumentation, not management.
06
Keep the evidence trail
Underwater photographs, cleaning records, idle patterns, coating age, inspection findings and drydock scope — the inputs that support coating-warranty talks, next drydock planning, and defending fuel performance to charterers.
Turn Hull History Into Decisions and Defences
Marine Inspection holds coating age and type, cleaning and polishing dates, idle periods, underwater inspection findings, drydock scope and defect history per vessel across the fleet — the inputs performance analysis actually runs on, timestamped and retrievable. Time a hull clean, negotiate a coating warranty, or rebut a consumption claim with evidence instead of assertion.
Measuring a ship's speed and fuel consumption against her expected speed-power curve — corrected for weather, current and loading condition — to detect degradation in hull and propeller performance over time. The IMO estimates about a tenth of the world fleet's fuel burn is attributable to poor hull and propeller performance, costing owners around $30 billion a year. Book a demo.
What is ISO 19030?
A standard released in 2017 defining indicators for measuring changes in hull and propeller performance over time. It uses a physical model needing power-speed curves for different loading conditions, corrects for wind resistance, filters data to calm stable conditions, and works in three tiers — noon reports at the lowest, continuous automatic monitoring at the highest. It compares a vessel to herself between periods rather than ranking ships against each other. Book a demo.
What is the difference between STW and SOG for performance?
Speed through water is what the hull experiences; speed over ground is what the schedule sees, and current is the difference. For performance analysis STW is what matters — SOG comparisons are useless because current masks actual performance changes. Always specify which you are reporting, because charter party disputes frequently arise from ambiguity over which measurement a warranty applies to. Book a demo.
What counts as a good weather day?
Typically defined in the charter as wind not exceeding Beaufort Force 4 (maximum 16 knots) and total combined sea and swell significant wave height within Douglas Sea State 3 (0.5 to 1.25 metres), with no adverse currents and no negative influence of swell — and generally requiring a continuous period of at least 24 hours, which one arbitrator held must run noon to noon. The exact wording in the fixture governs. Book a demo.
What does "about" mean in a speed warranty?
It carries a defined tolerance, commonly ±5%, or in some fixtures an express allowance such as 0.5 knots — so a warranted about 13.5 knots became a 13.0-knot minimum in one case. Performance details are also frequently given "about, in good faith and without guarantee," which further qualifies the obligation. Book a demo.
Is a weather routing company's report binding?
Only if the charter says so, and only if it applies the charter's own parameters. Some clauses make an independent routing service's data binding on both parties. But in a 2024 award a tribunal held a routing report could not found the claim because it did not assess performance in accordance with the contractual warranty, making the deductions unlawful — part of a noted trend of routing reports straying from the charter's parameters. Book a demo.
What is the hull performance index?
The relationship between ideal power and corrected measured power, expressed as a single indicator of added resistance from hull and propeller fouling. It sits at roughly 100% for a vessel with fresh paint and falls below 80% for a degraded hull, giving a simple KPI for deciding when cleaning or coating work is justified. Book a demo.
Read Performance Out of the Noise — and Prove It When It Counts.
Marine Inspection keeps coating age, cleaning and polishing dates, idle periods, underwater inspection findings, drydock scope and defect history per vessel across the fleet — the record that lets you time a hull clean, negotiate a coating warranty, or rebut a consumption claim with evidence rather than assertion. Timestamped, searchable, and ready when the claim lands.
