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13 new models in NavimetriX

Choosing the right model is half of a good weather decision. Offshore, you want to compare ECMWF and GFS; close to the coast, you want a model at a few kilometres, or even a few hundred metres; and for currents and sea state, you want the best available in each basin. This month, 13 new models join NavimetriX. The library, one of the most extensive on the market, now brings together some thirty models from 14 forecasting services, from the American NOAA to the French Ifremer, available as 87 forecasts to choose from by resolution and area, and all of them are included in the subscription.

What's new in version 1.24

1.24 is one of the biggest updates NavimetriX has ever had. Your boat now has a real logbook, with PDF export. Your trips can be relived with the weather of the day and shared by a simple link, even live from offshore. A barograph keeps an eye on the pressure, and those who work on their performance will find a complete workshop for polars and sail choice. Here is the tour.

What's new in version 1.23

Version 1.23 lifts a limit many of you reported: until now, NavimetriX listened to a single NMEA link. On a boat where the instruments, the GPS and the AIS are three separate boxes, you needed a multiplexer. Not any more.

Six links instead of one

Open Settings › GPS & NMEA and turn on Advanced mode: the page reorganises into six tabs, and your existing link becomes the one on the Instruments tab.

What's new in version 1.21

Version 1.21 is the largest NavimetriX update in a long while: a completely redesigned interface, next-generation instruments, AIS weather station display, and much more. Here is the essence of what changes.

A redesigned interface

• Full-bleed, edge-to-edge chart: the chart fills the whole screen, and the “chrome” (pills, value bar) floats on top with a glass style. It appears on touch and fades away on its own so nothing is hidden.
• Night mode in marine red, designed to preserve your night vision.
• Edge-handle drawers (GRIBs, Charts, Settings…), new typography and a design system that is consistent throughout the app.

Night mode tints the entire interface — chart, gauges, instrument bar and timeline — in a discreet marine red:

GWD, TWA, AWA: Wind in all its forms

Wind: definitions

GWD / GWS

Ground Wind Direction / Ground Wind Speed

This is the direction and speed of the wind in the ground (earth) reference frame. It is the wind from forecasts provided by weather services, received in GRIB files (average wind at 10 metres).

AWA / AWS

Apparent Wind Angle / Apparent Wind Speed

This is the angle and speed of the apparent wind in the boat's sails. The measurements are provided by the boat's wind vane/anemometer sensor. The apparent wind is the instantaneous result of the ground wind combined with the wind created by drift — drift due to wind and drift due to current — and by the boat's speed through water.

How to Perform Effective Routing

Basic Principle

Routing is a navigation aid that can serve two different — but not necessarily contradictory — purposes:

• On passage: comfort and safety, avoiding sea and wind conditions that the boat and crew cannot handle,
• Racing: performance, the best efficiency for the best passage time.

Routing is like a cooking recipe: you first need good ingredients:

• A speed polar containing the theoretical target speeds the boat can achieve based on true wind speed (TWS) and the sailing angle relative to that wind direction (TWA).
• A route with a minimum of waypoints: preferably only departure and destination. Intermediate waypoints should only be used for mandatory passage points.
• Several GRIB files broadly covering the route: wind, waves, currents — the most recent available, with a time horizon sufficient for the approximate duration of the passage.
• A departure date within the temporal coverage of the GRIB files and as early as possible.

The Recipe

The recipe is based on a routing algorithm — a clever calculation whose inner workings are classified top secret. This calculation determines an optimised route by combining wind values and directions, currents and waves with the boat’s speed polar values, along a course from departure to destination.

VMG, VMC, XTE, TAE: a few explanations

Acronyms are used to concisely specify navigation data. This language was originally developed for marine electronic instruments, GPS units and chart plotters. It is now found in digital navigation applications.

These acronyms, in the form of three capital letters, are the initials of English terms defining navigation-specific data and related functions. They make it easy to display information on screens while taking up very little space. Among them, some can be confusing.

Analysis charts to better understand GRIBs

Sailing is about anticipating. When it comes to weather, anticipating means looking far ahead and well in advance, even for short coastal passages. Tracking weather systems coming from the west over the North Atlantic, for instance, helps plan a good weather window for next weekend’s sail. This applies to all parts of the world.

A pedagogical tool

The ability to overlay meteorological analysis charts on GRIB files provides a better understanding of weather phenomena and their evolution. The display of fronts complements the colourised data representation — such as wind strength — and the point symbols like vectors and barbs in GRIB files.