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Text Box: Preface The Problem : Crossing oceans in a sailboat is a complex dynamic problem with the boat’s progress depending on the evolving wind field and the current. In the past, sailors have had to plan voyages based on pilot charts which indicate the prevailing conditions and for the prudent sailor the range of expected conditions. Unfortunately, prevailing or climatological patterns never occur . On a given day, the variety of conditions across an ocean are defined by the weather for that day - the individual highs, lows, clouds, rain etc. This daily weather does not look like the pilot chart climatology which is the aggregation of these weather events. As another thing that Mark Twain probably didn’t say “climate is what you expect - weather is what you get”. Climate statistics were put together as a means to summarize expected conditions and are invaluable in understanding the distribution of weather conditions at a point. In sailing, however, you are never at one point long enough to enjoy the climatology for that point. You sail in the evolving daily wind field. In the past, pilot chart type climate statistics were the only way one could comprehend the thousands of hours of different weather events. Today, however, relatively powerful computers available to most sailors at home coupled with a sail boat simulator allow the sailor to experience the historical weather data from a quite different but practical point of view. The following describes what appears to be the first sailboat simulator tied to a 40 year world weather data set that allows the sailor to sail across an ocean experiencing actual winds as the boat sails through the evolving wind field. For example, a sailor planning to sail from Boston to Gibraltar in late May can select a year, a weather window to start the voyage, then sail through the weather systems experiencing the head winds, following winds, calms, gales etc. that all occur that year on the voyage. The sailor may make this sail forty different years, if he desires, to see the best and worst the Atlantic has to offer. This is a totally different way of viewing the climatology of a voyage. Weather Data : In the relatively recent past, accessing large