MarineNav — Offline Chart & Weather Navigator

SOG

–kt

COG

–°T

Position GPS

– –

True Wind

–kt

Depth

–m

Next WP

–

ETA

–

Route Planning

Click the chart to drop waypoints. Drag them to adjust. Distances use rhumb-line by default.

Route name

WP	Brg	Dist nm

Boat speed (kts, for ETA)

Method

Import GPX route

Weather (GRIB)

Load GRIB2 wind-component files (U & V, e.g. UGRD/VGRD 10 m) downloaded from NOAA NOMADS. Files decode entirely on this device — nothing is uploaded.

Get files from NOMADS GFS filter: pick a region + level "10 m above ground", variables UGRD & VGRD, and download the two resulting .grib2 files while you have a connection. Then load them here for fully offline use afterward.

U-component GRIB2 (UGRD)

V-component GRIB2 (VGRD)

Display mode

🎏 = 50kt ╱ = 10kt ╱ (short) = 5kt ○ = calm

Boat Polar & VMG

Predicted boat speed vs. true wind angle/speed. The bundled table is a generic example — load your boat's real polar (VPP output or Expedition-style CSV) for accurate numbers.

Polar file (CSV)

Currently loaded: Example generic 36ft cruiser-racer (not a real boat — for demonstration only)

TWS for diagram / VMG (kts)

Isochrone Weather Routing

Computes the fastest route to a destination using your polar + loaded GRIB wind field (true isochrone method — same family of algorithm as Expedition/qtVlm). Requires wind data loaded in the Weather panel first.

Time step (minutes)

Heading resolution (degrees)

Max routing horizon (hours)

No land/depth avoidance — this is open-water performance routing only. Always sanity-check the plotted route against the chart.

AIS Targets

Decodes AIVDM/AIVDO messages arriving over the NMEA bus (from an AIS receiver/transponder on your boat's network — connect it under the NMEA panel first). This app does not fetch AIS from any internet aggregator.

No targets yet — connect an AIS-capable NMEA source.

NMEA0183 Bus

Connects to your boat's actual instrument bus — GPS, wind, depth, AIS — over a direct serial link or a network bridge that speaks WebSocket.

Serial (USB-NMEA adapter, Chrome/Edge only)

WebSocket bridge URL

Plain TCP/UDP NMEA bridges (Yacht Devices, Digital Yacht, etc.) can't be reached directly from a browser — point this at a WebSocket-speaking source, e.g. a SignalK server's NMEA-over-WS endpoint, or a small local ws↔tcp relay.

Status: not connected

Use NMEA bus for position/instruments when connected

Live sentence feed

Offline Charts

Pan and zoom over an area while connected — tiles you view are cached automatically by the service worker. Or use "Download this view" to prefetch the visible area + 2 zoom levels in.

Base layer

Show OpenSeaMap buoys/marks overlay

NOAA discontinued its old raster chart tile service in 2022. This app uses NOAA's current Chart Display Service, which renders the same up-to-date chart data (ENC) with traditional paper-chart symbology — functionally the raster-chart look, kept current. Not for primary/legal navigation — always carry official charts and cross-check position.