It had been six years since Richard Imrie had been offshore; he wasn’t bothered by that given that he is perfectly content to stay at home on the east end of Long Island windsurfing in the Atlantic swells. It was his 29-year-old son, Max, who wanted to make an offshore passage with his dad. “He wanted,” Imrie said, “to do a trip before I got too old.”
It’s not like the man has no experience. Raised in Scotland, Imrie cut his sailing eyeteeth sailing gaff-rigged clinker boats in the Firth of Forth. When he grew into manhood he purchased a Columbia 50, and with his family, lived in the British Virgin Islands for a year before taking off to the Azores and ultimately the Mediter-ranean, where they cruised for four years. Those were in the pre GPS days and Imrie recalls that “we navigated across the Atlantic with sextant and RDF.”
Last year he bought Thula (which means peace in Swahili), a 1980 built Baltic 39, and after sailing coastal for a season he thought he was ready to see how the boat handled offshore. So in June of this year, father, son, and two friends decided to test themselves and their boat on a voyage to Bermuda.
From the moment they departed the dock in Greenport, Long Island, N.Y., they battled the elements. First it was the opposing currents that delayed them all day when trying to round Montauk Point. Once into the Atlantic they didn’t get much relief, having to constantly reef down trying to figure out how to sail the rhumb line buffeted by squirrelly, heavy winds. “The winds were from all over the place,” Imrie said. The wind finally settled down into a southeasterly, which put them close-hauled as they approached the island of Bermuda. Not just the winds bedeviled them, but the currents as well. “It seemed that the Gulf Stream went on forever from New York all the way to Bermuda.” Counter currents slowed them down, it seemed they couldn’t escape them. Finally, before another ferocious front could nail them, they made Bermuda after five days. They hunkered down for five days awaiting a weather window to return home, which they did in another five days.
Imrie found his old Davis Mark 3 sextant stowed aboard and decided to see if he could still take a sight. He admits to being rusty after having not used one in 25 years. He reviewed the procedure using Mary Blewitt’s book, Celestial Navigation for Yachtsmen. He adjusted the mirrors, and began taking sun sights. “I had to remember to point it exactly at the sun,” Imrie said, “but basically after a couple of minutes it was self-explanatory.”
Let’s join the amateur navigator, sextant in hand at a DR of 32° 47’ N by 65° 08’ W on June 20, 2009. His height of eye is 10 feet and there is no sextant error and no watch error. He takes two shots of the sun in the morning shooting the lower limb. The first shot is taken at 13 hours, 32 minutes and 6 seconds. The Hs is 51° 39’. The second shot is taken at 13:35:02. the Hs is 52° 22’.
A. Reduce both shots to the Ho
B. Using H.O. 249 Vol. 11 find the intercepts
C. Plot and calculate the estimated position
Extended solution
Richard Imrie and his son are on their way to Bermuda. It has been years since Imrie had done a sun sight but he was game to try his hand again. He decides, using his Davis plastic sextant to get some sun sights. His DR at the time of his sights is 32° 47’ N by 65° 08’ W. The day in question is June 20, 2009. Height of eye is 10 feet. There is no sextant error nor any watch error. Imrie takes two lower limb sights of the sun. The first observation is at 13 hrs 32 min 06 sec. The Hs is 51° 39’. The second shot is at 13 hrs 35 min 02 sec. And the Hs is 52° 22’
First we reduce both sights to find the Ho:
The GHA for the first sight is 22° 37.5’. To that we add 360° thus
382° 37.5’
-65° 35.5’ (assumed longitude)
LHA 317°
Hs 51° 39.0’
-dip 3.1’
Ha + 15.2
Ho 51° 51.1’ for the first sight
GHA for the second sight is 23° 21.5’. To that we add 360° thus
383° 21.5’
-65° 21.5’ (assumed longitude)
LHA 318°
Hs 52° 22.0’
-dip 3.1’
Ha 52° 18.9’
3rd cor +15.2’
Ho 52° 34.1’
Next we go to the sight reduction tables HO 249 Vol. II
Latitude Same as Declination. I’m using assumed latitude of 33° N since it is closer to the DR latitude of 32° 47’ N
For the first sight Hc 51° 02’ d +24 Z 094°
Go to Table 5 for the declination correction. The declination at the time of the sight was N 23° 26.3’’ and there is no d correction. Table 5 shows that 10’ are added to the Hc thus
Hc 51° 02’
+10’
Hc 51° 12’
Ho 51° 51’
Subtract Hc from Ho and get and Intercept of 39 nm toward (Ho is greater than Hc)
The second sight is basically the same except now the LHA is 318°, thus
Hc 51° 52’ d+24 Z 094°
Once again add 10 for the declination correction (26’) and we have a final Hc of 52° 02.0’
If we subtract Hc from Ho we have:
Ho 52° 34.1’
-Hc 52° 02.0’
Intercept is 32.1nm toward
The sun lines, when plotted are close together and if you take the time you will see that the Estimated Position is 32° 47’ N by 65° 45’ W. Not bad for someone who hadn’t used a sextant in 25 years!
