There are several categories of decisions each Winlink/Saildocs user must deal with to gain effective use of this data:

1. Which weather documents to retrieve.  This decision is a function of both the bandwidth available when connected (how many files and of what size can be downloaded) and the ability of the sailor to use the reports.  The limited bandwidth of both the networks and the sailor's brain make it necessary to restrict the number of documents requested to those that are most important to the voyage.
2. When to acquire specific weather documents.  This decision is a function of both the existing propagation conditions (what time of day can you reliably connect) and the scheduled availability of the requested documents.  The later issue is very important as weather data is very perishable.  A forecast that was prepared 6 hours ago may no longer represent the current outlook of the forecaster. 

The purpose of this web page is to document how I deal with the decisions in the second category.

• GRIB file twice each day to cover the next 72 hours
• Ship and Buoy reports at least once each day
• Surface Analysis once each day
• Met Area II Text Forecast for the first half of the voyage (east of 40 deg W. Lon)
• NOAA Forecaster Map Discussion for the second half of the voyage (west of 40 deg W. Lon.), twice each day.  This is actually a text message from the duty NOAA forecaster explaining how he/she intends to adjust and reconcile the various numerical models used by NOAA and other meteorological organizations.  It is an amplification on the information contained in the GRIB files.  Unfortunately the discussion is limited to the NOAA area of responsibility in the Atlantic Ocean (west of 40 deg W. Lon.).

In the process of determining a document's availability we need to take into account the different ways Saildocs and Winlink acquire the documents from the Internet.  While I've not seen anything documented for either system, it appears that Saildocs has a scheduled retrieval time for most documents in its library.  At a scheduled time the Saildocs server will download the document from its URL.  When Saildocs receives a request for some documents that are downloaded frequently (every hour or less), the request may be held until the next schedule retrieval of the document.  Then when that retrieval takes place the weather document is forwarded back to the requestor.  For other documents with less frequent retrievals (e.g., every 6 hours) Saildocs may immediately send what ever version of the document is currently stored on the server.

Again, the Saildocs retrieval methodology I described above is just based on my experience using this service.  The actual methodology might be different, and of course could change at any time.

Winlink appears to retrieve the document from the Internet at the time of the request and sends it to the requestor within minutes.

So, if my understanding of these systems is correct, with Saildocs you are assured of getting a recent version of the requested document, but you may have to wait up to an hour after your request for some documents to be available.  With Winlink you can expect to receive the document within a few minutes of your request, but that document may be updated shortly after you receive it and your copy may be obsolete before you even have a chance to download it.

Usually you can find the document availability information in Winlink or Saildocs message to which the document is attached.

Therefore to get the latest version of a given GRIB file it is best to request it be delivered between 5 and 6 hours after one of the base times (00z, 06z, 12z, and 18z) for the document.

I believe this document is generated at least every 6 hours by the NOAA duty forecaster, but the schedule is not very  precise.  It appears to be posted anywhere from 1 to 2 hours after the GRIB under discussion is available from Saildocs.  So the discussion of the model output contained in the 00z GRIB forecast is posted between 06 - 07z (the GRIB itself being available around 05z).  If I wanted to acquire both this discussion and the associated GRIB in a single connection I would wait until 07z to make that connection.

The 18z document in the screen capture above discusses the data in the 12z GRIB, and the 06z document discusses the 00z GRIB.  So it would be of benefit to download these documents at the same time as the associated GRIBs.  Therefore I would schedule my retrieval of these document pairs at 19z and 07z, respectively.

In this case WL2K retrieved the document from the Internet at the time it generated this message.  That is, WL2K does not store this document on its server, but retrieves it at the time the system receives the request.  This document was retrieved from the NOAA web server at 07:50z (green highlight), the same time this message was sent to my email address.  The document was published on the NOAA server at 04:04z (yellow highlight).  This is the 00z Surface Analysis.

So it would appear that the Surface Analysis is available a little over 4 hours after the valid period of the data and about 50 minutes prior to the availability of the GRIB file based on the same data.

So if I want to have a Surface Analysis and GRIB file based on the same data I should plan to retrieve this document at the same time as the GRIB file, or around 5 hours after base time.  For a 00z Surface Analysis and GRIB I should request those files be delivered around 05:00z.  If I wanted the NOAA Map Discussion document as well, I might wait until 07:00z and retrieve all 3 documents at one time.

Once again WL2K has retrieved this document from the French Meteo web site at the time of my request (green highlight).  The forecast valid time is 09z and was last updated on the Meteo web site at 08:30z.

So the latest MET Area II Forecast should be available every 6 hours starting at 00z.

Therefore early in the voyage I will be looking to connect to Winlink or SailMail between 02:00z and 04:00z in the morning and between 22:00z to 00:00z in the evening.  As we progress further west those connection times will shift to later hours.  As we near the East Coast of the USA the connection times will likely be between 07:00z and 09:00z in the morning and 03:00z and 05:00z in the evening.  Therefore the likely connection times during the entire voyage will be somewhere between 22:00z and 09:00z.  The following table summarizes the document availability during those connections times.

In developing a connection and document retrieval schedule, one other thing needs to be kept in mind - the difference between a subscription for a Winlink document and a Saildocs document.  A document subscription is one of the best ways to implement a document retrieval schedule.  However, the differences between Winlink and Saildocs have implemented document scheduling have an effect on not only how you set up those subscriptions, but also on when and how often you must connect to the network.

These differences reflect the basic differences that exist in many client-server applications, whether to put the application on the server or the client.  There is seldom one best choice and the differences between Winlink and Saildocs demonstrate this.  Winlink uses a client-driven subscription process and Saildocs is server-driven.  Each approach has its advantages and disadvantages for the cruising sailor.

Document subscription is a useful tool for scheduling document retrieval, but these subscriptions behave very differently depending on from which library the document is retrieved and which network is used for the connection.  These differences and the associated Advantages and Disadvantages are summarized below.

So Winlink has the advantage when connections are frequent or when the schedule changes often.  Saildocs has the advantage of requiring minimal connections to acquire the required documents.  Of course subscriptions are not necessary to manage a document retrieval schedule, they just automate the process.  Sometimes that automation is of significant benefit, but sometimes it gets in the way.  I use subscriptions sparingly, primarily for the GRIB and ship reports from Saildocs, where there is a specific time I want the document captured.

The documents I request for a given connection time will be based on the document availability table above.  For example, if the earliest propagation will allow a good connection is 22z, I will likely wait until 23z to get the latest GRIB file on the same connection.

• GRIB files via a SailDocs subscription twice each day at 06Z and 12Z
• East and Central Atlantic Buoy Reports once each day at 0030Z
• Met Area II Forecast twice each day at 06Z and 12Z

As we neared 40W Longitude I dropped the East Atlantic Buoy reports and MetArea II forecast and added the West Atlantic Buoy Reports, the Met Area IV forecast and the NOAA Map Discussion.

So I depended primarily on the GRIB files for my weather data and they proved to be very accurate, particularly in predicting the formation of minor storm systems in the Western Atlantic.  We were able to navigate around these storm systems during the final week of the voyage from Madeira to Bermuda.  During this period I increased my acquisition of the GRIBs from twice each day to four times each day.  Of course the daily input from Herb Hilgenberg was of equal value to the GRIBs for this navigation.

Below are links to the two Excel Workbooks I used as logs of my connections to Winlink and SailMail.

• Winlink Log
• SailMail Log