Logging Weather Data

Those of you who have been with us for a while know we have a passion for and about weather. Weather affects everything we do when cruising: our comfort, passage speed, security. Obviously this applies at anchor as well as on passage.

Although the latest generation of weather models are better, they still have problems resolving the data on a micro basis, where it affects all of us. That’s why there are still so many weather-related “surprises” when cruising.

Over the years we have worked with various computer folks to develop weather tools. A recent convergence of technology and serendipity has put us in that position again. We are putting our heads together with Troy Bethel, a yachting techie with extensive weather and navigation experience over hundreds of thousands of ocean miles, to adapt a top-end racing program to the needs of cruisers. We get nothing out of this besides friendship, and a chance to have a really cool program for our own use.

We’re working with a beta version now and over the next six months we’ll update you on how this is going.

If you log the trends for barometric pressure, true wind direction, and true wind speed, you will have most of the information you need to know where your current winds are coming from and what they are likely to do. You can use this data to:

  • Plan better routes.
  • Prepare for heavy going, or avoid it.
  • Know when to heave to and when to proceed.
  • Stay away from the worst quadrants of a given weather system.
  • Find better wind strength and angles.
  • Analyze GRIB and fax to see how accurate it is, and understand if the forecast is going to be late or early.

In short, logging those three items are the key to everything. You can do this in your log book – which is what we usually do. But how much better would it be to have a graphical interface!


How about something like the data above? Barometric pressure, True Wind Direction, True Wind Strength, Speed Over Ground, and Air Temperature.


Having a mean average to smooth out the local oscillations would also be good. That is what the straight line in each set of data represents.

The ability to view the graph and mean averages over different time spans is also a help. Is this a short-term wind shift over the last half hour, or is it part of a three- to six-hour trend?

This sort of information is is easy and fun to use.

We’ve got the processing power now on just about every cruising boat to do this. What has been missing are the sensors, in particular barometric pressure. Well, we are happy to tell you that this problem has been solved. We’ll get into more detail in subsequent articles. For now, know that the system about which we have been dreaming will be available for substantially less than it would cost to replace our lovely old barograph – which is showing the affects of age – and for which parts are no longer available.

Stay tuned…

Posted by Steve Dashew  (April 15, 2008)

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