II—The Passage of Gipsy Moth III

• Published in: Journal of Navigation
• Main Author: Chichester, Francis
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1961
• Subjects: Ocean Engineering; Oceanography; North Atlantic
• Online Access: http://dx.doi.org/10.1017/s0373463300039473; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0373463300039473

Tactics were clearly going to be vitally important in this race, and the first tactical decision was obviously which route to take across the Atlantic. Using a dry-sail method, I worked out the speed at which the boat should sail over about twelve routes or combinations of routes. The method used was to compute from the appropriate monthly Pilot Chart of the North Atlantic (issued by the U.S. Hydrographic Office) the time it would take to cross each area measuring 5° of longitude by 5° of latitude, using the average winds determined over a long period of years. For example, in the first area (Fig. 1), from Plymouth to 5° west, the average wind blows from the west for 18 per cent of the time in June, which should give a rate of advance towards the objective of something like 2½ knots for that period. For the north-westerly and south-westerly winds which, according to the chart have blown for thirty two per cent of the time, at an average of force four, I estimated that I should travel at 4 knots towards the objective: so, similarly with different speeds for beam and following winds, I calculated that I should be able to cross this area in 62 hours. In practice it took 103 hours—more than 4 days instead of 2½—due to head-winds of from force 6 to gale force. However, this wrong estimate did not spoil the value of comparing the routes.