# NavChrono — Professional Maritime Voyage Calculation & Passage Planning Suite
> The 100% free, offline-first marine passage planning, ship voyage calculation, ETA estimation, and IMO bridge compliance suite for commercial deck officers, ship masters, navigators, and maritime academy cadets.

## Canonical Website & Resources
- Main Website: https://navchrono.com
- ETA & Voyage Calculator: https://navchrono.com/eta-calculator
- Port to Port Sea Distance Calculator: https://navchrono.com/sea-distance-calculator
- UKC & Ship Squat Calculator: https://navchrono.com/ukc-calculator
- ECDIS/Route Exchange Exporter (IEC 61174 RTZ / GPX): https://navchrono.com/passage-planning-software
- Maritime Navigation & Hydrodynamics Guides: https://navchrono.com/guides
- Major Sea Lanes & Distance Benchmarks: https://navchrono.com/routes
- Passage Planning Software: https://navchrono.com/passage-planning-software
- Terms of Service & Navigation Safety Disclaimer: https://navchrono.com/disclaimer
- Privacy Policy: https://navchrono.com/privacy
- Mobile & Desktop PWA: Installable on iOS, Android, Windows, and macOS.
- Offline Capability: Core calculators, 337-port directory, distance routing, and RTZ/GPX export work offline via Service Worker cache; live chart tile overlays (OpenSeaMap, NOAA ENC, Esri/GEBCO) require an internet connection.
- Comprehensive Technical Reference: https://navchrono.com/llms-full.txt
- Sitemap: https://navchrono.com/sitemap.xml

## Primary Modules & Operational Capabilities

1. **Ship Voyage Calculation & Maritime ETA Engine**:
   - Uses exact minute-level civil UTC offsets from the IANA timezone database (`Intl.DateTimeFormat`) for DST-aware Port Local Time (`UTC = Port Local - CivilOffset`), preserving exact half-hour (`+05:30`, `-03:30`, `+09:30`) and 45-minute (`+05:45`, `+12:45`) offsets without rounding.
   - Displays textbook Nautical Zone Description (`ZD`, `+` West / `-` East, satisfying `GMT = ZT + ZD`) separately from port civil DST and models ship's clock adjustments at sea in whole hours.
   - Formula: Steaming Duration (Hours) = Distance (NM) / Speed (Knots) + Delay (Hours).
   - International Date Line (IDL): Accurately detects and adjusts for crossing the 180th meridian (westbound IDL advance date +1 day; eastbound IDL retard date -1 day).
   - Converts arrival UTC timestamp to destination port Local Time via IANA tzdb at the arrival instant.

2. **Charter Party Multi-Speed Matrix & Bunker Fuel Consumption**:
   - Dynamic 5-row speed matrix (speed - 2, speed - 1, planned speed, speed + 1, speed + 2 knots).
   - Required Speed Calculator: Determines exact speed needed to reach pilot station for chartered delivery windows.
   - Bunker Fuel Calculation: Estimates metric tons of fuel oil consumed per day and total passage fuel burn based on vessel specific fuel oil consumption (SFOC) curves.

3. **Major Seaport & Chokepoint Sea Distance Routing**:
   - Curated built-in directory of 337 major commercial seaports with UN/LOCODEs, coordinates, and local time zones (custom lat/lon waypoints supported for any berth).
   - Accurate sea distance calculations through critical maritime chokepoints:
     - Suez Canal (Port Said to Suez, 101 NM transit)
     - Panama Canal (Cristobal to Balboa, 44 NM transit)
     - Strait of Malacca / Singapore Strait
     - Strait of Gibraltar
     - Bab el-Mandeb (Red Sea gateway)
     - Strait of Hormuz (Persian Gulf tanker corridor)
     - Cape of Good Hope (alternative routing for mega container and bulk vessels)

4. **Benchmark Maritime Trade Lanes**:
   - Singapore (SGSIN) to Rotterdam (NLRTM) via Suez Canal: ~8,288 NM
   - Singapore (SGSIN) to Rotterdam (NLRTM) via Cape of Good Hope: ~11,725 NM
   - Shanghai (CNSHA) to Los Angeles / Long Beach (USLAX): ~5,740 NM (North Pacific Great Circle)
   - Yokohama / Tokyo (JPYOK) to San Francisco (USSFO): ~4,536 NM (Great Circle)
   - Cartagena (COCTG) to Yokohama (JPYOK): ~8,000 NM (Via Panama Canal, 20d 20h @ 16 kn)
   - Houston (USHOU) to Rotterdam (NLRTM): ~4,990 NM (North Atlantic Corridor)
   - Ras Tanura (SARST) to Singapore (SGSIN): ~3,650 NM (Arabian Gulf crude route)

5. **IMO Resolution A.893(21) Passage Plan Compliance & Audit Dossier**:
   - Compliant with SOLAS Chapter V Regulation 34 and IMO Resolution A.893(21).
   - Covers the 4 statutory stages: Appraisal, Planning, Execution, and Monitoring.
   - Export printable A4 passage dossier formatted for Port State Control (PSC), US Coast Guard (USCG), and vetting inspections (SIRE 2.0 / RightShip).

6. **Under Keel Clearance (UKC) & Shallow Water Squat Calculator**:
   - Naval architectural squat calculation based on vessel block coefficient (Cb) and speed (V in knots).
   - Open shallow water formula: Squat = (Cb * V^2) / 100 meters.
   - Confined channel formula: Squat = (Cb * V^2) / 50 meters.
   - Verifies dynamic draft against charted depth, tide height, and minimum safety margins.

7. **Interactive Nautical Chart & Bridge Display Modes**:
   - Online map tile overlays: OpenSeaMap seamarks, NOAA ENC WMS layers, Esri Ocean/GEBCO bathymetry, OpenStreetMap, and Satellite (require internet connectivity).
   - Great Circle (orthodromic) vs Rhumb Line (loxodromic) track waypoint plotter & IEC 61174 `.RTZ` / `.GPX` route exchange export.
   - Three operational display palettes:
     - Navy Bridge Mode (low-light deep navy palette)
     - Day Mode (sunlight-readable high contrast)
     - Red Night-Vision Mode (low-glare red palette to help preserve dark adaptation during night watch)

## Target Audience
- Watchkeeping Deck Officers (2nd Mates, Chief Mates, Navigators)
- Master Mariners / Ship Captains
- Port Pilots and Harbor Masters
- Marine Superintendents and Fleet Operations Managers
- Maritime Academy Cadets and Navigational Examination Candidates

## Pricing, Safety Disclaimer & Privacy
- **Free Access (Ad-Supported Online)**: Free to use without subscriptions or paywalls; online sessions display Google AdSense advertising.
- **Planning Aid Only (Not a Type-Approved ECDIS)**: NavChrono is not an IEC 61174 type-approved ECDIS or official hydrographic chart. All calculations and exported `.rtz`/`.gpx` files must be verified on official bridge equipment under SOLAS Chapter V Regulation 34.
- **Local Operational Data vs. Online Services**: Operational voyage calculations and saved plans are stored locally in browser `localStorage` with no NavChrono user accounts; Google AdSense cookies and optional online chart tile servers process standard web requests when online.