What this page is about
The definitive service, SailDocs is a source of GRIB (and other) services generated by sailors for sailors and with an acute awareness of the needs of those with limited bandwidth. Although a little clumsy in use, it provides a standard by which to judge other services.
Not the easiest to use but the most flexible and, for those with limited bandwidth, the most economic being developed for users of email over HF radio via Sailmail.
Saildocs GRIB code service
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A good GRIB data service is available from Saildocs. Files are extracted on a per request basis from the US NOAA/NCEP global GFS computer model and can cover any requested area, worldwide. The resulting file size depends upon the amount of data requested but can, in principle, be anywhere from 1 kb to megabytes. For most normal cruising requirements, file sizes of a few kb may be sufficient and need not exceed 10 - 15 kb. Radio email services are available using Airmail software on one's laptop in conjunction with either the Winlink or SailMail systems, or even both. (Currently, SailMail will now handle GRIB files up to 10 kb for Pactor-2 users, and 30 kb for Pactor-3 users.) For detailed information for use with Airmail see the Notes on receiving SailDocs over HF provided by Allan Riches of Brunei Bay Radio. | Also see the 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 5 to 7 days which I regard as a reasonable limit for useful (rarely accurate) forecasting although this limit is slowly being pushed out beyond that time. 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.. |
Requesting a GRIB file
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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 query@saildocs.com, Type anything you wish as subject - but do not leave it blank. A simple message reads send gfs:40N,60N,0W,20W/1,1/24,48,72/PRMSL,wind Between those latitudes and longitudes, you will get forecasts of wind and pressure at 24 hour intervals on a 1-degree grid. Available elements are PRMSL or PRESS for mean sea-level pressure, WIND for the gradient surface wind ((10-metre), SEATMP for sea-surface temp, AIRTMP for air temperature (2M altitude), and WAVES for wave-height (from the WW3 model). The default is pressure and wind. Grid spacings can be 0.5, 1, 2. |
Times can be 0, 3, 6, 9, 12 etc to 192. This would be tedious to write, so send gfs:20N,60N,160W,120W/1,1/0,6,...,36,48,...,144 will give data at 6 hour intervals fro 0 to 36 hours and every 12 hours to 144 hours. It must be comma dot dot dot comma between the times. The model data are updated shortly before 06:00z for the 00z model-run and every 6 hours. IMPORTANT: Do not insert any spaces, Saildocs uses spaces to delimit parameters. For simplicity, copy and paste the above message, then put in your own values for Lat, Lon, the times and the spacing - ie I often use 1,1. Data from other NOAA and US Navy models are available, send a (blank) email to: gribmodels@saildocs.com for details. |
Repeat Requests and Cancellations
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For a daily repeat, use the same format but change the "send" to "sub". For example: sub gfs:40N,60N,0W,20W/1,1/24,48,72,96,120 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. |
For example: sub gfs:40N,60N,0W,20W/1,1/24,48,72,96,120 days=5 sub gfs:40N,60N,0W,20W/1,1/24,48,72,96,120 days=0 Each GRIB message includes instructions on how to cancel. |
NOTE re Word-Wrap
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It is essential that the whole message is on one line of the email message. This is because the CR/LF acts like a space and is a delimiter. This is particularly important to note if you ask for a large number of times and use requests for repeat messages. In Outlook Express - use Tools - Options - Send - Mail Sending Format - Plain text settings. Ensure that the automatic Wrap text figure exceeds the number of characters in the request. |
A long request-line can be broken with a "=" character as follows: Best is to avoid a long list of times as shown above. |
Loading and Viewing
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Having received the email reply, save the attachment to a folder. Open Viewfax by double clicking on the attachment icon in the email. This will open the GRIB file in whatevr is your default viewer - in this case Viewfax. It is then possible to view the charts in sequence or at random. A chart viewed using Viewfax will look like this: If you leave the mouse pointer on the chart it will show a sequence of winds at that point. Click on picture to enlarge NOTE. One short feather = 5 knots, one long feather = 10 knots. The arrows "fly" with the wind. |
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