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Sun sights on the Marion-Bermuda Race

Jul 19, 2007

It has been a long time since I taught a celestial navigation seminar for Ocean Navigator, but occasionally I still run into students I have had the pleasure to teach.

I ran into Bob Dreyer recently. He was one of my students, and I met him when he and his family sailed into Greenport, where I call home. After reacquainting ourselves, Dreyer told me he had been the navigator aboard Shearwater, a yacht that competed in the 2005 Marion to Bermuda race. I was delighted that he had put his studies to practical use and I asked him to send me some information about the race so I could write about it. Here is some of what he told me:

"It is the navigator's responsibility to inform the skipper of the boat's position at all times in order for him to make strategic decisions. Prior to the race we were briefed on weather conditions and the Gulf Stream position. Warm and cold eddies often carry significant counter currents, which could retard the average boat speed significantly. Sometimes these currents can be as fast as 4 knots. Another variable is entering the Gulf Stream at the right point to catch a favorable meander in a southerly direction. This point is dubbed €˜point alpha,' and that entrance into the Gulf Stream will make the difference between a finish with honors versus just finishing.

Another component of a successful race is gauging weather conditions accurately in order to find favorable wind direction and speed. High-pressure areas can lead to windless days. The navigator is constantly aware of these issues and through accurate determination of the vessel's position he informs the skipper of any opportunity to increase the VMG."

Shearwater departed Marion on June 17. The vessel was entered into the cruising class division sailing against 13 others, including two Navy boats. On June 19 Shearwater was at a DR of 38° 10' N by 69° 05' W. Dreyer and the skipper took a sun shot at 13:36:25 GMT. The height of eye was 10 feet and there was no watch error or sextant error. A lower limb shot of the sun was taken. The Hs was 48° 39.8'.

Calculate the Ho, and then plot the sun line in relation to the DR. We will be using the 2006 Nautical Almanac and Vol. 2 of HO 249 for our solutions. For those who don't have this volume, the numbers are as follows: Hc 48° 54, d +31, Z 98°. The Table 5 correction for minutes of declination is +13. Remember to round off tenths of minutes of declination to the highest number of minutes.

By the way, Shearwater finished 6th in class, beating the Navy boat, which made the crew very happy!

A. What is the Ho?

B. What is the LHA?

C. What is the Intercept?

D. What is the EP after plotting?  

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