Methodology

Observed means an AIS message was received: position, speed over ground, timestamp. Published specification means a static figure from builder, registry or class records — length, tonnage, engine configuration, maximum guest berths. Estimated means a model output with an uncertainty range: fuel burn, CO₂, market value.

Ranges are never replaced by a single tidy number. If the range is wide, the underlying uncertainty is wide.

AIS reception is uneven. Terrestrial receivers cover coastal areas densely and open water poorly; satellite passes leave gaps of minutes to hours. Transponders can be switched off, misconfigured, or report stale static data.

Positions published here are delayed by at least 15 minutes and the snapshot refreshes at most once per hour. This is deliberately not a realtime tracker.

Gaps are shown as gaps. We do not draw a route through unobserved water, and we do not infer a port call from an absence of signal.

For each observed interval, the model takes the vessel's installed power, hull type and published speed profile, and derives a load factor from the observed speed over ground. Fuel burn per hour follows from that load factor and a specific fuel consumption band for the engine class, producing a low and a high figure rather than a point value.

Stationary time is modelled separately at auxiliary/hotel load, which is why an anchored vessel still carries a non-zero estimate.

Method tiers describe the quality of the inputs: tier A uses vessel-specific published consumption data, tier B a class-level curve, tier C a length-and-tonnage fallback.

Litres are converted to mass using the density of the reported fuel type, then to CO₂ with a fixed well-recognised emission factor per tonne of fuel (MGO and HFO differ). The conversion adds no uncertainty of its own; the range you see is inherited from the fuel estimate.

Flight comparisons are computed from the great-circle distance between two airports, multiplied by a 1.08 route uplift, and a fixed 0.000158 tonnes CO₂ per passenger-kilometre factor for an economy seat. The default route is Amsterdam (AMS) to New York JFK, but both origin and destination can be changed. The result is an illustration of scale, not part of the emissions calculation.

The snapshot reports three independent metrics and never merges them:

• provider_availability_pct — how much of the window the upstream AIS providers were actually delivering data.
• target_detection_rate_pct — the share of vessels in the target population that were detected at all.
• emissions_temporal_coverage_pct — the share of the window for which a given vessel had usable observations. This is the one the public 24h headline depends on.

Below 70% emissions temporal coverage, no emissions figure is published for that vessel. It appears as insufficient observational coverage instead of a confident-looking estimate.

Fuel in litres is the source datapoint, split into propulsion and onboard services. CO₂ is derived from it: fuel_mass_kg = litres × fuel_density_kg_per_liter and co2_kg = fuel_mass_kg × 3.206 (EU MRV factor for diesel / gas oil). Density is an explicit per-vessel parameter, sourced where published, with a stated default of 0.84 kg/L (source: superyacht_master_batches_1-5_fuel_speed.xlsx, sheet “Methodology”, row “Default diesel density” — modelling assumption only, to be replaced with a fuel-specific density when available) — never a silent constant. Each source datapoint also carries a fuel scope (main engines only, total onboard, or unknown) so generator consumption is not double counted.

Emissions are reported per operational state — underway, at anchor, in port — as time actually spent in that state × the best available state-specific fuel rate × the fuel CO₂ factor. The anchor rate comes from a strict preference order: vessel-specific published generator consumption, then a vessel-specific generator/load model, then a calibrated class model, then a broad fallback. It is never calculated as a percentage of the underway rate; published fleet splits (YETI 10/34/56, Heesen 42–58%) are sanity checks only.

Every estimate carries a status — Observed, Estimated — vessel specific, Estimated — class model, Estimated — broad benchmark — and a method tier. A broad benchmark is never shown with the same visual certainty as a vessel-specific datapoint, and low-confidence figures appear as ranges rather than falsely precise single numbers.

The cruise comparison uses the ICCT figure of 250 g CO₂ per passenger-kilometre for the most efficient cruise ships, derived from EU MRV-verified reporting (for one specific ship, 317 g CO₂ per passenger-nautical-mile). Both sides of the comparison use the same unit: kilograms of CO₂ per passenger over the same observed distance in the same 24h window.

AIS does not report persons on board. The yacht side therefore divides total CO₂ by a charter-certified guest capacity taken from published charter data — 12 guests for the reference vessel, not the 22–24 cabin berths some sources quote — and is labelled Estimated — vessel specific, never observed.

The bottle-cap context card sits deliberately outside the methodology surface. It compares the annualised observed CO₂ of the tracked fleet with the 2.6 million tonnes CO₂-eq attributed to the single-use plastics scope of the EU directive. The wider 3.4 Mt estimate also covers fishing gear and is not used here.

Whether that 2.6 Mt is an annual saving reached by 2030 or a cumulative total up to 2030 is not yet confirmed from the primary source, so the card carries a visible placeholder instead of definitive framing. The annualisation is a fixture-grade placeholder until coverage-adjusted observations exist.

European Commission, COM(2025) 109 final, Table 1 (18 March 2025) — review of Regulation (EU) 2015/757 on the potential inclusion of ships below 5,000 GT but not below 400 GT. Source of the quoted 2023 figures: 896 yachts of 400–4,999 GT calling at EU ports, an estimated 1.45 million tonnes CO₂, equal to 1.1% of all shipping emissions monitored under EU MRV that year. Quoted verbatim on the Impact page and labelled as EU Commission data, never as an output of this model. That population (400–4,999 GT, EU port calls) is not the ≥60 m LOA fleet tracked here, so the two sets of figures are never combined.

Gross tonnage thresholds shown on vessel pages — 300 GT (EU Vessel Traffic Monitoring Directive), 400 GT (proposed MRV/ETS extension) and 5,000 GT (current MRV/ETS scope) — are regulatory reference points, not an inclusion criterion of this tracker. Length alone (≥60 m LOA) decides which yachts are followed here.

No person tracking, no ownership claims, no statements about who is aboard. Capacity is always described as maximum guest berths. The dataset is described as observed superyachts, never as all superyachts.

The figures currently shown are fixture data for product validation: fictional vessels, fictional observations, real schema.