How Knotworth builds its cost ranges
Where the ranges come from
Every band below lists the references it was built from, each labelled by what kind of evidence it is - a published price list, an owner's reported cost, or our own modelled estimate - with the date it was checked, the geography it was observed in and the exact scope that was priced. A buyer's own pasted quote is a fourth kind and outranks all three. Bands are planning figures for a typical production cruiser in sail-away condition, not quotes: rows marked local quote advised should be replaced by a current figure from your yard before they anchor a decision. Ranges are stored in USD and converted to your currency at the daily ECB rate, stamped into each report along with this table's version.
Size scaling
Bands are anchored at 30 / 40 / 47.5 ft and interpolated linearly between anchors (clamped outside), so a 34.5-footer gets a value between the 30 ft and 40 ft anchors rather than jumping a size class. When a boat's length is unknown, the ~40 ft reference applies and the line says so at low confidence.
Labor and region
Labor-heavy jobs (rigging, bottom work, engine) scale by a coarse country-level factor for where the work will be done - by default the boat's location, overridable per deal - from ~0.8 in low-cost regions to ~1.2 in the US and northern Europe. Each row shows its rough labor share; parts-dominated items (sails, life raft, EPIRB) don't scale. This is deliberately coarse: it localizes a planning band, it does not price a yard.
The reference table
| System | ~30 ft | ~40 ft | ~47.5 ft | Interval | Labor share | Confidence / notes |
|---|---|---|---|---|---|---|
| Standing rigging (re-rig) local quote advised | $3,000–$6,000 | $6,000–$10,000 | $10,000–$18,000 | ~12 yr | 45% | medium confidence - Wire + swage/mechanical terminals, mast in; add 30–50% for rod or mast-out yards. |
| Running rigging local quote advised | $1,700–$2,500 | $2,500–$4,500 | $4,000–$7,000 | ~6 yr | 30% | medium confidence |
| Sails | $3,000–$5,500 | $5,000–$9,000 | $8,000–$15,000 | ~10 yr | 10% | medium confidence - Band prices a working wardrobe (main + genoa), cruising dacron, loft-made; laminates cost more. When individual sails are known, each line carries its rough share of the band. |
| Bottom antifoul local quote advised | $800–$1,800 | $1,500–$3,000 | $2,500–$4,500 | ~2 yr | 60% | medium confidence - Haul, prep, two coats ablative; excludes barrier work. |
| Barrier coat + paint local quote advised | $3,000–$6,000 | $5,000–$10,000 | $8,000–$15,000 | ~12 yr | 70% | medium confidence |
| Life raft | $1,700–$3,700 | $1,700–$3,700 | $2,500–$4,000 | ~3 yr | 0% | medium confidence - Purchase; a recert cycle runs $300–800. |
| Ground tackle | $850–$2,000 | $1,500–$3,100 | $2,400–$5,000 | – | 0% | medium confidence |
| EPIRB | $680–$1,100 | $680–$1,100 | $680–$1,100 | – | 0% | medium confidence |
| Dinghy + outboard | $3,000–$7,000 | $4,000–$8,000 | $4,000–$9,000 | – | 0% | medium confidence |
| Engine - repower local quote advised | $15,000–$25,000 | $18,000–$30,000 | $20,000–$35,000 | – | 40% | medium confidence - New auxiliary diesel, mounts, alignment; saildrive higher. |
| Engine - rebuild local quote advised | $8,000–$12,000 | $10,000–$14,000 | $12,000–$18,000 | – | 60% | medium confidence |
| Engine - major service local quote advised | $1,500–$3,000 | $2,000–$4,000 | $3,000–$5,000 | – | 70% | medium confidence |
References behind each band
The kind label is the point: a published price is a list price you can check, a reported owner cost is what someone actually paid, a modelled estimate is our compilation. Where a reference has a public page we link it; where it is a compiled internal record we say so rather than link to something generic. Geography tells you whether the figures were observed where your boat will be worked on.
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: re-rig, wire + swage/mechanical terminals, mast in
- published priceTrade price lists, compiled · checked 2025-11 · US rigger, sailmaker and chandlery price lists · scope: 1x19 wire, terminals and rigger labor per stay
- reported owner costOwner-reported refit costs, compiled · checked 2025-11 · US and EU owner-reported refit costs · scope: full re-rig invoices, 30–48 ft
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: halyards, sheets, reefing lines - full set
- published priceTrade price lists, compiled · checked 2025-11 · US rigger, sailmaker and chandlery price lists · scope: line per metre + splicing
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: working wardrobe: main + genoa, cruising dacron
- published priceTrade price lists, compiled · checked 2025-11 · US rigger, sailmaker and chandlery price lists · scope: loft list prices, dacron main and genoa by size
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: haul, prep, two coats ablative
- reported owner costOwner-reported refit costs, compiled · checked 2025-11 · US and EU owner-reported refit costs · scope: yard antifoul invoices incl. haul
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: strip, barrier coat, repaint
- reported owner costOwner-reported refit costs, compiled · checked 2025-11 · US and EU owner-reported refit costs · scope: barrier-coat job invoices
- published priceTrade price lists, compiled · checked 2025-11 · US and EU chandlery list prices · scope: 4–6 person coastal/offshore raft, purchase
- published priceTrade price lists, compiled · checked 2025-11 · US and EU chandlery list prices · scope: anchor + chain + rode sized to LOA
- published priceTrade price lists, compiled · checked 2025-11 · US and EU chandlery list prices · scope: 406 MHz EPIRB, purchase
- published priceTrade price lists, compiled · checked 2025-11 · US and EU chandlery list prices · scope: inflatable tender + small outboard
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: new auxiliary diesel installed, shaft drive
- published priceTrade price lists, compiled · checked 2025-11 · US and EU dealer list prices · scope: engine list prices by HP
- reported owner costOwner-reported refit costs, compiled · checked 2025-11 · US and EU owner-reported refit costs · scope: repower invoices incl. mounts and alignment
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: in-frame rebuild, marine diesel 20–60 HP
- reported owner costOwner-reported refit costs, compiled · checked 2025-11 · US and EU owner-reported refit costs · scope: rebuild invoices
- modelled estimateKnotworth cost reference (PRD §10.1) · checked 2025-11 · US baseline; EU/UK via the regional labor factor · scope: major service: injectors, heat exchanger, mounts, fluids
- reported owner costOwner-reported refit costs, compiled · checked 2025-11 · US and EU owner-reported refit costs · scope: major service invoices
Replacement intervals are risk windows, not cliffs
An interval is a typical service window, not an expiry date. A component at or past its window creates a reserve or a verification question - never a "confirmed defect". Documentation, inspection or a survey can move any line in either direction, and age-based items are always labeled AGE-BASED in the negotiation evidence, separate from confirmed problems.
Confidence, contingency and taxes
Every line carries a confidence level: high for deterministic transaction math, medium for banded work with known age, low for unknowns and unverified claims. Contingency runs 10–25% by boat age and how much of the big-ticket picture is verified. Tax lines (EU VAT by country, EU/US import duty, US state boat taxes with their caps) are estimates with the applicable rule named in the assumption - they are never certain without the paperwork, cross-border cases deserve a customs broker, and nothing here is tax or legal advice.
Your figures beat ours
Any line can be overridden with a real quote, and the override propagates to the total, the ceiling comparison and the verdict. A professional survey supersedes the whole Stage-1 estimate - Knotworth is a research aid for deciding whether a boat is worth the survey, as described here, not a replacement for one.
Methodology questions
Why do my yard's quotes differ from your ranges?+
They should - a range is a planning band, not a quote. Labor rates, yard access, and what the work uncovers all move the number. That's exactly why every line in a report can be replaced with your real quote, which then beats our estimate everywhere, including in the verdict.
When does a professional figure supersede Knotworth?+
Always. A surveyor's finding, a rigger's invoice or a yard quote outranks every model estimate. Enter it on the line and the report recomputes around it; after purchase, the survey supersedes the whole Stage-1 estimate.
How accurate is the AI condition read?+
The extraction is designed so the model can only quote, never invent: every 'work done' claim must cite a verbatim phrase from the listing or seller reply, with deterministic validation behind it. We score it continuously against a labeled test set covering hedges, partial work, contradictions and absences - and we treat that as an ongoing measurement, not a one-time proof.