What this page is about
Saildocs was the first GRIB service designed by sailors for sailors with regard for those with limited bandwidth. Although a little clumsy in use it is the most flexible of all GRIB services and, if counting the kilobytes, the most economical.
Although funded and developed by Sailmail for users of email over HF radio via,, it is freely available to all. .
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On this page
Like most GRIB services, Saildocs. Extracts files on a per request basis from the US NOAA/NCEP global GFS computer model. File size depends upon the amount of data requested and can be from a few tens of kb upwards.
Saildocs was developed for users of Airmail over the radio amateur service Winlink or the SailMail system of user funded marine HF network. For advice on using HF/SSB radio for email, see page produced by Richard Clifford for members of the RCC. for information on the use of Airmail by HF radio..
Output is available up to 15 days ahead although I would only recommend using up to 8 days. Beyond that is of academic interest only. The US NWS runs its computer model 4 times a day using data at 00, 06, 12 and 18 hours UTC. A note concerning the output issued by Saildocs is on another page..
The procedure described using Saildocs may seem somewhat cumbersome to use but extremely flexible. The easiest way to show is by example.
To request a GRIB file send an eail to email@example.com, Type anything you wish as subject - but do not leave it blank.
A simple message reads
That will result in an email with a GRIb file attached that gives Wnd and Pressure values for the area selected, on a 0.5 degree latitude/longitude grid at 0, 24, 48 and 72 hours ahead.
NOTEs. Grid spacing can be multiples of 0.5 degree. Times can be at intervals of 3 hours or multiples of 3 hours. Wind and Pressure are the default elements. Elements can be selected individually or in groups by adding IMMEDIATELY after the separator / with separated by commas with NO spaces.
Elements that the sailor will need are
APCP ------- (for rain)
WAVES ----- (WW3 wave model data)
CAPE ----- (A thunderstorm or lightning risk indicator)
send gfs:40N,60N,0W,20W/0.5,0.5/0,24,48,72/Wind, PRESS, APCP
would be a request for wind, pressure and rain.
To avoid lon strings of time requests, the following convention should be used.
send gfs:40N,60N,0W,20W/0.5,0.5/0,3,..., 72/ . [
(comma dot dot dot comma) to request a forecast every 3 hours from T=0 to T=72 hours.
for a forecasts every 3 hours from T=0 to T=36 and every 12 hours from T=36 tp T=192 hours.
For a daily repeat, use the same format but change the "send" to "sub". For example:
will result in a forecast received daily, shortly after 0615 UTC.
By default you will receive this information daily for 14 days. To change this add a space and days=5 for a 5-day subscription, or days=0 for an indefinite subscription. Examples for a wind only request -
sub gfs:40N,60N,0W,20W/1,1/0,12,...,120/wind DAYS=5
sub gfs:40N,60N,0W,20W/1,1/0,12,...,120/wind DAYS=0
Each GRIB message includes instructions on how to cancel.
Having received the email reply, save the attachment to a folder. Some Viewers are listed on another page of this site. The ‘’’Saildocs Viewfax’’ has crude coastal outlines but is very easy to us. It will look like the lft hand image. The same data using the zyGrib viewer is on the right.:
NOTE. One short feather = 5 knots, one long feather = 10 knots. The arrows "fly" with the wind.
Click on pictures to enlarge