How to receive grib files when sailing Offshore

Even if a Grib file includes predictions up to 8 days and sometimes even more, the data reliability decrease far before. Updating the weather forecast at sea is a token of safety and better analysis of the best route while racing. 

As soon as you get off a 3G/4G coverage area, it is mandatory to use a satellite internet connection to download Grib files.

Several devices are available in a large price margin going from 2 000€ to 15 000€ for a fast speed dedicated modem like Fleet Broadband at Inmarsat, BGAN at Trane & Trane or Pilot at Iridium.

This kind of device are dedicated to professional use, most of the amateur sailors use a satellite phone as a modem. Indeed those devices are less expensive (between 600 and 2 000€) and allow a data connection whatever the chosen provider.


















At the moment, there are three main satellite communication networks: Iridium, Inmarsat and Thuraya. Iridium and Inmarsat fit the better to navigation as they are the only ones to cover entire world (except the poles for Inmarsat)

Even if every provider offer prepaid cards or subscription, in both cases, it is necessary to choose between a standard SIM Card or Skyfile:

When you will choose your Sim card Iridium or Inmarsat, you will have the choice between the standard format (Iridium or Inmarsat) and the format Skyfile sold by Astrium. If you choose a Skyfile SIM card, you will then have to buy the Skyfile refills.

Skyfiles will allow you to create a dedicated email address. Thanks to its data compression system, it will also increase the downloading efficiency, so time of transfer will be reduced.

As all the communications are charged according to the time spent, this system looks advantageous although the cost per minute is higher.

There are other optimized emails services with subscriptions which are not linked to the SIM card choice, like Teleport from Mailasail.

Sim IridiumSim Inmarsat



To receive Grib files offshore, we can choose in between two methods : direct dowloading or reception by email.


Direct downloading

The direct downloading uses the internet connection at a speed of around 10Kps, so it allows downloading a 60Ko file in a few minutes in theory.  This way, you can use the usual loading interfaces like “NOAA forecast” in Adrena, Ugrib, Navimail, etc…

NOAA forecast

Reception by email

The Grib file request should be done through specialized services like Squid, Saildoc or Mailasail by sending a preset text including the geographical area and data to be included in the Grib file.

Example of a request

A :

OBJET : grib gfs 5N:70W:35N:10W 3,6,9,12,15,18,24,36,48,60,72 GRD,PRMSL

“Retourne les données de vitesses des vents et de pression du modèle GFS pour une zone rectangulaire entre 5°N 70°W et 35°N et 10°W aux échéances indiquées soit toutes les 3 heures le premier jour et à 12 heures d’intervalles pour les 2 jours suivants.”

In response of the request, an email is sent with the Grib file enclosed. You just need to load it via the menu “ Forecast > Load grib” in Adrena to read it.

Load Grib

Thanks to this method, Skyfile Mail, a free software equivalent to Outlook, is going to manage the Grib file request and reception. Skyfile is also managing the opening and closing of the connection and more it manages the download recovering in case of coverage cut.

Do not hesitate to consult our reseller’s specialists of on board computing and communication at sea to evaluate the equipment that will fit you the best.