What the Index measures, and what it does not.
Blue Water Index estimates what a recreational boat is worth by measuring the market's own evidence. This page sets out where that evidence comes from, how it becomes a number, and the limits of what that number can tell you.
If you want the story rather than the terms, start with How It Works.
Advertised asking prices, and how they change.
The Index observes the life of a listing rather than a snapshot of it: the price a vessel is advertised at, every change the seller makes to that price, how long it stays on the market, and the point at which it stops being advertised.
Movement is measured in the currency of the original listing, on vessels observed at both ends of the period being reported.
Public listing pages, collected under each site's own rules.
Evidence comes from pages that brokers, dealers, marketplaces and portals publish in order to advertise a vessel. Collection honours the access rules each site states, and no listing is republished: what the Index keeps is the measurement, not the page.
Coverage grows and occasionally contracts as sources change. It is restated in the Market Pulse rather than kept as a running claim here.
The rules that collection runs under, and what happens when a site declines, are set out in full in our Data Collection Policy.
One vessel, however it was described.
The same boat is advertised under different builder and model spellings, in different languages, in different currencies, with different tax treatment and different units. Before anything is compared, each listing is resolved to a canonical vessel — builder, model, year and variant — and its price expressed on consistent terms.
Each market calibrated on its own evidence.
Statistical models measure how characteristics such as age, length, configuration, region and equipment relate to advertised values. A market is calibrated on the evidence from that market: a 12–16m sail boat in Great Britain is not priced from what similar boats are advertised at in another region.
Uncertainty is part of the answer.
Every estimate carries a confidence grade and a range, both derived from the evidence actually available for that vessel in that market. Thin evidence produces a wider range, and says so.
Where the evidence is too thin to support an estimate at all — a rare vessel, a heavily modified one, a market the Index does not yet cover — it refuses, and names what is missing.
What the Index does not claim.
These limits are not caveats added at the end. They are the reason the rest of it is worth reading.
An advertised price is what a seller is asking, not what a buyer paid. The Index measures the first and does not claim to observe the second.
A listing can disappear because it sold, because it was withdrawn, or because a broker reorganised a website. We record that it left, and do not record why.
A tracked sample, however large, is not the whole of any national market. Figures describe the vessels the Index observes.
A valuation from the Index is market evidence. It is not a survey, not a condition assessment, and not a substitute for either.
Where the Index estimates what a boat may sell for, it reads condition from the listing. Tested against 40 boats that brokers had graded themselves, it identified none of the 21 they judged to need a refit: their listings did not say so. A boat that needs work will be worth less than the estimate, and only a survey can establish its condition.