to GRIB formatted data showing raw wind strength and direction data without interpretation. GRIBs are at http://passageweather.com/ and on the National Weather Service website. Evaluations of the accuracy of the GRIB results are particularly valuable if these strictly model-based data are to be used in routing software such as Expedition, Deckman, and MaxSea. Beyond developing confidence in the models (and knowledge of their weaknesses), this pre-start exercise is the best way to become familiar with the weather conditions most likely to prevail during the race. This knowledge adds greatly to the value of information provided by professional weather services, and it facilitates onboard decision-making should conditions turn out to differ from the forecast.
selected race strategy and the reasons for it before the start, and be informed of changes during the race. The navigator’s instructions must be clear, in easily understood language, and discussed at each change of watch, and possibly more often. This is not a time to be a “riddler!”
Predicting Sea State
In addition to their individual value, the wind and current data you acquire and analyze will help you make accurate estimates of sea state, which is a very important factor in race strategy. The amplitude and steepness of ocean wind-driven waves can be altered by interactions between wind and current. Wind blowing against the current results in a significantly larger wave amplitude and shorter wavelength than what appears when wind blows with current or when there is no current. Steep conditions with breaking waves are often observed in the Gulf Stream and in areas of strong tidal currents. US Sailing’s Performance Package does not include consideration of the wind-current interaction. There are, however, several graphical methods that can be used to correct wind/wave estimates to account for this effect. A good aid here is William G. Van Dorn’s book Oceanography and Seamanship.
Communicate ClearlY Acquisition and analysis of these data allows the development of an initial strategic plan. By combining the probable position of the Gulf Stream and associated eddies with anticipated wind conditions with an estimate of the boat’s and crew’s capabilities, the skipper and navigator can select one or more routes to take. Some navigators use a routing program to assist in this process, but others find this unnecessary given the short duration of the race and the sometimes less than adequate model representations of winds and currents, particularly in the vicinity of the Gulf Stream. Whichever method you employ, your strategy should be continually refined right up to the start, and to some extent during the race. The success of the process depends on clear communications 23 among the entire crew, who should understand the
Race Strategy, Suggested Timeline Fall-Winter Before Race Boat Preparations - Check of hull, rig, sails and systems (including all navigational instruments) January - February Review past race conditions, see http://nomads.ncdc.noaa. gov/ncep/NCEP Obtain polars and consider optimization http://offshore.ussailing.org/ORR/Performance_Products.htm March - April Launch Boat Initial tests of polar predictions Finalize Instrument calibrations and Finalize Sail Selection May Crew training trials and races Begin analyses of Gulf Stream conditions see http://bermudarace.com for Tutorials June Continue Gulf Stream analysis Begin analysis of probable race weather conditions. http:// www.nws.noaa.gov/om/marine/home.htm Develop initial routing strategy - revise as forecasts improve within 96hrs of race start Finalize strategy following Skipper’s Meeting and Weather/ GS briefings - present to crew with details June 20 - Race Start