At 59 years old, Englishman Alec Rose was finally ready to take care of an old dream of his to sail around the world single-handed. The year was 1967 and Francis Chichester had already become the first person to single-hand since Joshua Slocum had accomplished the feat more than 80 years before. The fact that Chichester had already circumnavigated didn’t deter Rose, who was motivated by personal goals rather than by fame. Today it would take a lot to be impressed by a circumnavigation in a small boat, but in the 1960s it was still a bold, if not foolhardy, feat.
Rose was born in 1908 into a farming family in Canterbury. As a child he was so weak that he had to be wheeled to school. He overcame his physical handicaps and, quitting school at 16, he worked at different jobs, finally going to Canada where he worked as a logger, cowhand and road-builder. He returned to England before World War II and served in minesweepers and in the north Atlantic.
After the war his interest in yachting waxed, and he bought a German lifeboat and rigged it out as a wishbone ketch. At the same time he was learning celestial navigation in cornfields with the help of his son who was in the Merchant Marines.
The owner of a successful fruit and flower shop, Rose, in 1963, entered the second annual Observer Single-handed Transatlantic Race. He bought the almost 20-year-old, 36-foot teak cutter Lively Lady and converted it into a ketch. He completed the race and placed fourth.
When Rose departed he took a stuffed rabbit named Algy — a gift from his grandchildren — along with him.
Rose set out to accomplish a two-stop circumnavigation. He wanted to get to Australia and stop there to visit his grandchildren, whom he had never met. By January 1968 Rose was in Australia where he was greeted with a tumultuous reception. From there he sailed across the Bass Strait to New Zealand to another large crowd.
He finally cleared Cape Horn and returned to Portsmouth on July 4, 1968. His circumnavigation had taken him 354 days. His reception at Portsmouth was attended by more than 250,000 well wishers. The following day he was knighted. His lifelong dream had been realized.
Rose wrote a popular book called Lively Lady and stayed involved in the British yachting scene. He died in 1991 at the age of 82.
Let’s join Rose at sea bound for home. On May 20, Rose is west of the Cape Verde Islands at a DR of 16° 21’ N by 31° 20’ W. His height of eye is 10 feet. There is no sextant error and the watch time is correct. Rose wants a latitude sight and as it was cloudy at noon he decides with the sky clearing to shoot Polaris. The sextant altitude of Polaris is 16° 23.6’. He takes his shot at 19 hours 22 min. 30 seconds. We will be using the 2007 Nautical Almanac.
A. Calculate the time of civil twilight.
B. Using the Polaris tables in the nautical almanac calculate the latitude.
EXTENDED ANSWER:
In my haste to complete the problem I made some gross errors that I failed to check before the problem was published. This occurs on occasion and I feel badly when it does, but it happens at sea as well and I’m not embarrassed to admit my mistakes. At sea, navigational errors would be spotted more quickly- usually at the next shot. At home, it’s a little more difficult to spot my errors until, unfortunately, the die has been cast. Disregard any answers published in the magazine and together we will solve the problem correctly.
We are looking to solve a Polaris sight, which will give us without too much trouble latitude. Polaris is less than 1° from the celestial North Pole. In order to get it right where we want it to be we have to mathematically massage some numbers. Fortunately the formula for doing this is provided in the appropriately named Polaris Tables at the rear of the Nautical Almanac. The directions are relatively simple to follow. If you follow along with this problem you will see how it is done.
For any evening star sight we need to know at what time it gets dark. In this case we need to find the time of civil twilight or the time when the center of the sun is 6° below the horizon. At this time it is dark enough to see the stars but still light enough to still have a horizon. Unfortunately, Polaris is not a bright star so it is not that easy to shoot. A trick in locating Polaris at sea is to do the following: Set the sextant at the DR latitude. As the sky is getting dark sweep the sextant in a northly direction. The lenses on an Astra sextant are good enough to magnify the light from the star so that it is easier to pick up than just by using the naked eye.
We go to the May 20 page in the NA and in the middle right table under sunset you will see the times for twilight. We are looking for the time of Civil Twilight and we see that the time listed at 10° latitude is 18:37. The time at 20° latitude is 18:55. We are in the middle. By using proportions (there is a 1.8 minute of time change for each degree of latitude) I calculate that the time of civil twilight for 16° latitude is 18:48. The tables are written for the times of twilight at the central meridian of each time zone i.e.: 0°, 15°, 30°, etc. As we are at a DR of 31° 20’ we have to calculate how long it takes the sun to travel 1° 20’. To find this out we go to the Arc/Time conversion table at the rear of the NA and see that it takes the sun 4 minutes 20 seconds. So we have the time of Civil Twilight for our meridian at:
18:48
+04:20
18:52:20 time of Civil Twilight
Next we have to find the LHA of Aires: We go to the daily star page of the NA for May 20. At 18 hours we see (under the Aires column) the at the GHA of Aires is 147° 01.7’. Next we add the 52 minutes 20 seconds of time and get 13° 07.1’
Adding them together we get the GHA Aires for 18:52:20 as 160° 08.8’
GHA 18Hrs 147° 01.7’
+52min 20 sec 13° 07.1’
GHA Aires 160° 08.8’
-Ass Long 31° 08.8’
LHA Aires 129°
The reason I created an assumed longitude is that in order to enter the tables we are using we require a whole number of LHA. I derive the assumed longitude from the DR longitude.
Now we have to reduce the Hs to Ho. In the case of Polaris we stop the reduction process when we reach Ha. Then we enter that into the formula for finding latitude.
Hs 16° 23.6’
-dip 3.1’
-3rd corr 3.3’
Ha 16° 17.2’
Remember here to use the inside star and planet table at the front of the NA for the 3rd correction. Also remember that a star is a point of light and has neither an upper nor a lower limb. It is just a speck of light splitting the horizon! Now we are ready to solve for the latitude.
In the NA on pages274-276 are the tables specific for the solution of latitude from Polaris. The instructions are easy to follow: Latitude = Ha –1°+ao+a1+a2.
The table is entered by LHA Aires so we have the following:
Ha 16° 17.2’
– 1°
+ao 0° 59.1
+a1 .4’
+a2 .9’
Lat 16° 17.6’
