Learning About Expedition Routing – Comparing Weather Models

We’ve been using the new (to us) weather routing software to which Troy Bethel introduced us. As cruisers, on an Unsailboat no less, many of the race-oriented features sit idle. But the weather functions are wonderful. This is especially true now that the combination of Sailmail SSB and Iridium are working so well (more on this in a future update).

What we like in particular about the Expedition software is that it allows us to easily compare files from different world wide weather models. In some weather patterns one model may be working better than another, and this new flexibility is a huge boost in our ability to understand what is going on, the risk factors, and how to make the fastest and most comfortable passage. If that sounds enthusiastic it is because we are stoked on this product.

Lets start with the weather models. Using either Expedition connected to an Internet source such as Iridium, or Sailmail (with the SSB radio or Iridium) the first step is to select a model.

Sailmail grib chopper

In the image above the green box represents our present position, about 500 miles from Panama. The blue box is the area of the GRIB file we want to request. Notice at the bottom left “NOGAPS” is highlighted. We can either get this once, or subscribe to it in which case it will be sent automatically over a period of days.


Once you hit the “Request” wrench the dialog above pops up. You then choose the time frame (a certain amount of days at various intervals – in this case three days every 12 hours). You can also select the data (wind, pressure at sea level, and 500mb for this model). Finally, control how often the data points are located (here they are on a one degree grid basis). For SSB connections, which can be slow, we try to minimize area and data.


Now comes the cool part. In Expedition you can run a routing with one model at a time, or a combination of models and Expedition will average their data. Here we are going to run the COAMPS, GFS, and NOGAPS together.


The routing is then displayed on the chart with wind barbs that change as you step through the time frame.


You also have this graphical representation, which shows us true wind speed (TWS) and true wind angle (TWA), both of which are key to our progress and comfort.

Notice across the top are three tabs. One represents the data for the COAMPS model, the next GFS (for which the data is shown) and finally, the average of the two.

For the record, over the last two days GFS and NOGAPS have pretty much agreed with each other, but COAMPS has done the best job of predicting the lumpy uphill conditions of the last 24 hours.

We’ll continue to report on this program as we become more familiar with it.

Posted by Steve Dashew  (April 27, 2008)

6 Responses to “Learning About Expedition Routing – Comparing Weather Models”

  1. stephen greer Says:

    three questions,
    1. in 18 months-june 1, 2011, my wife and i plan to sail to the marquesa’s as the first step around the world for an extended time. is there anyplace to leave the boat safely for the sept 1-feb 1 time frame. also, how does one investigate this type of information as one travels around the world if one would like to leave the sailboat and travel on land for awhile.
    2. someplace, i one of your books, you mention an alternative to a life raft, or at least some form of inflation device that is installed in the interior of the boat. i did not write the name down and cannot find the reference.
    3. do you have an info on the fast flow bilge pump that runs off of the motor shaft and is capable of large flow rates for emergengies. it is always running. does it stress the engine, does it damage the propeller shaft.
    as an aside, do you ever give question and answer seminars. we are beginners and have much to learn.
    stephen greer

  2. Steve Dashew Says:

    Join Seven Seas Cruising Association (SCCA) for many of your answers. The inflatable system which we mentioned is sadly no longer available. Re damage control pumps, these are usually engine mounted, electric, or hydraulic, depending on your boat. It also often makes sense to use a “Y” valve on t he engine intake so the raw water on the engine can be used for dewatering.
    Finally, we don’t have time for seminars, but can heartily recommend those which John and Amanda Neal put on.
    Good Luck

  3. James Peto Says:

    Happy New Year Steve and Linda,
    Seems a while since we met you in Lymington after the Svalbard etc.,.
    Where can I pick up this Weather Program.
    regards james

  4. Steve Dashew Says:

    Look at http://www.iexpedition.org/index.htm

  5. Ben Hines Says:

    Steve, I tried above link but it is not in English. Any updated link and as this posting is 18 months old,any updates as to satisfaction and usability? Thanks

  6. Steve Dashew Says:

    Hi Ben:
    Try http://tasmanbaynav.co.nz/index.htm for Expedition. We have not used it for the past year, and ours is a 2006 version, but we still like it a lot. We’ll see about updating and comment next spring when we have a chance to put it to work/