Streams of data

While the role of a navigator in a big ocean race like the West Coast’s TransPac (sailed every two years from Los Angeles to Honolulu) may seem to have little bearing on the requirements of the average shorthanded voyaging boat, there is actually an important overlap in duties. With all the navigational and weather inputs that he or she must juggle, the racing navigator has become an information manager. Voyaging navigators have also seen an increase in the amount of nav and weather data that can be received on the average voyaging boat.

A look at how a professional racing navigator handles the streams of data acquired during a race can be helpful to the voyaging navigator. Weather, performance analysis, tactics, and communications issues all need to be addressed by the navigator. What information is to be believed and acted upon? What information will require more confirmation? What will those actions be? These are the same questions navigators have faced for centuries, but the type and quantity of information has changed substantially.

Weather has always been a major consideration in yacht racing. The 1999 TransPac Race was no exception. Preparation, as usual, would be a key ingredient to any success stories. In the winter of ’99 Commander’s Weather undertook a survey to try to identify any likely anomalous weather features in the eastern North Pacific that could be associated with a post-La Niña summer. Climatology is the study of average weather conditions, and by identifying anomalies associated with La Niña perhaps an insight could be gained about how to best optimize the boat and sail selection in advance of the race, which was to start in July. La Niña is a period in which the ocean temperature in the eastern South Pacific is unusually cool.

Commander’s Weather’s early study of La Niña conditions provided the following expectations. The Pacific tradewinds would be stronger than usual. That would cause warmer water to "pile up" in the western Pacific, both north and south of the equator. That, in turn, would cause upwelling along the coast of Peru and in the eastern Pacific, off the Central American coast. The upwelling would cause cooler than normal water temperatures in those regions. It also followed that frequently the cooler temperatures extended northward into the north-central and northeast Pacific. That would lead to reduced tropical storm activity in the eastern and central North Pacific and a fairly strong, but westward-displaced eastern North Pacific high pressure system. In short, months before the start of the race to Hawaii, we felt there would be a higher probability of more wind, fewer squalls, and less of a threat from the high.Weather preparations

Meteorological preparationsthe study of real-time weather patternsdidn’t start until June, about a month before the start of the TransPac. To get an understanding of how the weather trends were actually developing, it was necessary to wait until the weather patterns changed from a winter to a summer pattern and the jet stream moved north. This process usually takes place around early June. Every day for three to four weeks information was accessed and printed from a variety of web sites.The daily information gathering started with the NWS (National Weather Service) Marine Charts presented at The weather charts provided at this site are the same charts that are available over HF radio in the form of weatherfaxes. Every morning, the most recent surface analysis, 24-hour, 48-hour, and 96-hour surface forecasts and the 500-Mb analysis were printed out and saved in a three-ring binder.

An effort was made to acquire forecasts with the same valid time (VT) as the surface analysis for later comparison. It would not only be important to understand the weather patterns as they were taking place, it would also be important to build a confidence level in the data that would be acquired during the race. And weatherfaxes were one of the few sources of printed weather information that would be allowed by the race rules during the race. Access to the Internet was not allowed during the race.

To add additional clarification and confirmation in specific areas, near real-time buoy reports were obtained and printed out from the National Data Buoy Center’s web site at: For the TransPac, it would be desirable to have an understanding of how the sea buoys related to the onshore weather conditions, as well as to get an understanding of how closely the surface analysis related to the actual buoy data. That understanding, acquired over time, provides the navigator with a sense of trust in the data. Also linked from the NDBC site is the printed transcript of the verbal coastal forecast provided via radio. During the race, those verbal forecasts could provide useful information about wind shifts to be expected while making landfall in Hawaii or how the California coastal weather varied relative to the offshore weather.

Microwave satellite imagery was also accessed daily and recorded prior to the race; this source provided wind speed and direction for most of the oceans of the world. Low-earth-orbiting satellites send down microwaves that can penetrate cloud cover. Like infrared waves measuring surface temperatures, the microwaves can measure the amount of aeration in the sea surfacea relationship that can provide amazingly accurate wind-speed data over a large area of the ocean. The worldwide data was often less than an hour old and could also be compared to the surface analysis. Available in graphic format from, some of the data is also available as a satellite picture overlay at The wind data depicted over the satellite image is displayed in the form of color-coded wind barbs providing both wind speed and direction information with the pertinent satellite picture in the background. This particular display not only gives a navigator the relevant wind data, it also provides him with a sense of how the surface winds relate to the cloud formations. The pictures provide a very useful way to practice reading satellite pictures and gain an understanding about how they can be interpreted.Color coding the weather charts

The data files began to grow as the start of the race neared. About a week before the start, the surface analyses were color coded. High pressure systems were outlined in red; low pressure systems were highlighted in either blue or green. By organizing the surface analyses and the 24-hour, 48-hour, and 96-hour forecasts separately and in sequence, it was relatively easy to go back and compare the 24- or 48-hour forecast with the surface analysis with the same VT. How accurate had those forecasts been? Were the high pressure systems correctly placed, the fronts in approximately the expected positions and the shapes of the systems similar to those expected in the forecast one or two days earlier? How are these systems compared to more climatologically "typical" patterns? Is the high pressure farther to the north or west than usual? How long does the system take to revert to a more normal position? The answers to these questions began to provide a visceral understanding of how the systems were different in 1999. In fact, they were behaving in a manner that confirmed the long-range "Climatology Study of the Eastern North Pacific during July" undertaken by Commander’s Weather.

To further confirm the accuracy of the marine weatherfaxes and satellite data, buoy and ship reports were compared to the graphic data. I had undertaken similar studies and cross-checking during the Whitbread Round the World Race in 1989-’90. Those earlier results were frequently somewhat less than impressive. Forecasts occasionally didn’t look even remotely like the surface analysis issued days later. Satellite imagery was often difficult to interpret and seldom had easy-to-understand barbed arrows to explain the surface winds. Much time was spent obtaining information that was often incorrect. Things have changed. In most cases leading up to the ’99 TransPac, even the 96-hour forecasts were remarkably close to the mark, while 24-hour and 48-hour marine weatherfaxes were quite often spot on.

A high degree of confidence could be placed in the forecasts that would be available during the race. The only way to really know that was to confirm it repeatedly or discover the information’s limitations beforehand. If the data was going to be wrong 50% of the time, as an example, more care would be required to guard against the unexpected or "unforecast." If the data and anomalous features were better understood and forecast correctly 90% of the time, decisions could be made with a higher degree of confidence. Even setting up for an atypical approach to Hawaii might be undertaken if the expected weather patterns suggested such a course of action.

As navigational tools have gone from sextant to DGPS, navigation has gone from being an "art/science" to being almost a pure science. It’s still necessary for the navigator to take subjective precautionsan art based upon experience. But weather routing is still an "art/science" in that much of the endeavor is still based on subjective analysis of a group of variables that have different levels of reliability. "The weather forecast is probably pretty good." "The polars for the boat are pretty close." "The downwind calibrations are a little off." "We’re starting to break into surfs more easily and may be able to stay with that cloud line longeror get into a more favorable weather pattern." As each variable becomes more accurately refined, the results are more easily predicted.Reliable service

In light of that, navigation instruments are interfaced, leading to more complete data that provide more information. The data can be shown on deck through a variety of displays. The on-board computers will log every detail, but in the event of an electrical failure it is only prudent to maintain a log, carry the correct paper charts, and, as always, prepare for the unexpectedit will happen. Displays develop loose connections. Computers crash, and programs refuse to run. Aboard our boat, Magnitude, thanks to a great deal of preparation by Steve Dodd, most of the equipment worked quite well and provided reliable service. Had the equipment failed, the dividers, parallel rules, and barograph would have continued to work quite nicely.

Integrated, computerized navigational systems are, without a doubt, a huge boon to the racing navigator. But they do not provide him with an overabundance of spare time. More information requiresand deservesmore analysis. Weather satellite picture receivers are an example of this. They are also perhaps one of the most misunderstood tools in the modern nav station. Some of the most common uses of these receivers is to locate fronts and storm cells, determine the shape of weather systems and approximate location of high pressure systems, identify the location and intensity of ocean currents, and detect the presence of a sea breeze along a coastline or a wind shift surrounding an island group. By comparing the satellite pictures to weatherfaxes or other pictures, one can further determine the rate of a system’s advance or how the shape and intensity of a system is changing.

During the ’99 TransPac, little or no time would be spent under the influence of low pressure or frontal passages. The Commander’s Weather’s climatology study implied that, with colder sea temperatures, there would be fewer squalls than normalfewer high-altitude cloud formations and storm cells. The high pressure system would be stronger than usual and possibly be located farther to the north or west than during a "typical" year. Compared to the Bermuda Race, which crosses the Gulf Stream, the TransPac is little influenced by ocean currents. The presence or lack of clouds over Hawaii would determine whether or not the wind shift surrounding the islands could be determined by satellite.

In other years, with storm cells more prevalent, satellite pictures can be of significant benefit, but their greatest value is in extra-tropical regions affected by low pressure systems or frontal passages. Regardless of location, however, in order for satellite pictures to be of any value, they must be analyzed. And the analysis takes time and understanding. For the tool to be of benefit, the navigator can spend up to an hour on a good picture. Check out the rate of advance for a system. Look for the highest clouds in the front to determine the greatest winds. Look for wind shifts. Figure out how to best position yourself for the coming weather.Routing software

Weather routing software has come a long way over the last 10 years. Three of the first four boats to finish had KiwiTech software on board. The gridded binary (GRIB) weather files that this type of route-planning software uses can be modified during the race to update files created prior to the start. "What-if" games can be played to help analyze the optimal route. And numerous variables can be displayed as time graphs to help in monitoring changing conditions and performance. Aboard Magnitude, we used software to plot other boats’ positions from the daily radio schedules’ position reports. Range and bearings could be quickly determined, distances to go to waypoints, distances run, and so forth. The plots could be overlaid on a Maptech digitized National Imagery and Mapping Administration (NIMA) chart with the GRIB weather displayed on the same chart. Quickly one could see who was digging deeper on the course, who was heating up, and how much distance the moves had gained or lost for them. From the computer screen instruments could be monitored, weatherfaxes received, performance analyzed, and results quantified. The ingredient that was added to the navigational mix that was not on the computer screen was the "human factor"the knowledge and experience of the crew.

Numerous articles have been written about racing the TransPac. Many of them are by Stan Honey, the navigator on Pyewacket, the only boat in front of us at the finishboth Pyewacket and Magnitude broke the existing course speed record. Aboard Magnitude we had a wealth of sailing experience in the crew. Many had competed in a multitude of TransPacs, Kenwood Cups, and other events in and around Hawaii. Several had done extensive plotting of wind shifts in varying conditions for earlier events. Combining their knowledge with the interpreted weatherfaxes and VHF coastal weather reports, we were able to shave miles off our route on the final approach while optimizing our performance down the track.

The navigator is an information manager. He always has been. Only now, the type, volume, and sources of that information are undergoing significant changes. It’s still a matter of collecting, collating, understanding, and acting upon data.

By Ocean Navigator