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Storm tactics innovator

Oct 31, 2008

A few days before the summer solstice of 1928, 25-year-old William A. Robinson, left his job as an engineer at a textile factory on the lower east side of New York and joined his yacht Svaap for the 1928 Bermuda Race. Svaap was a three-year-old John Alden design 27-foot gaff-ketch Robinson bought for $1,000.

Svaap means "dream" in Sanskrit and Robinson had a dream to sail around the world in what was then the smallest yacht to circumnavigate. After completing the Bermuda Race he set off. Two years later he returned to New York to a hero's welcome. He wrote a best seller, 10,000 Leagues Over the Sea, lectured, wrote magazine articles and became famous.

Robinson started a shipyard in Ipswich, Mass., where he began building Baltimore clippers and trawlers. During World War II he built boats for the Navy. With the help of W. Starling Burgess and L. Francis Herreshoff, he also built and designed his ideal yacht, the 50-ton, 70-foot brigantine Varua.

After the war he took his wife and sailed to Tahiti where he settled. In 1955 he took his new wife, his child and a couple of Tahitians and went looking to test his boat by sailing into the roaring '50s. It was there, about 1,500 miles west of Cape Horn, that he met what he called the ultimate storm. With estimated sustained winds of more than 100 mph and seas greater than 50 feet, Varua struggled to stay afloat. He wrote: "I had tried the conventional methods of riding it out by holding Varua into the wind under riding sails, but had abandoned that when the seas became too steep and high."

Finally, and against the accepted wisdom of the time, Robinson ran off before the wind streaming hawsers astern. "Although under bare poles Varua picked up speed and began running 6 or 7 knots...we at once put out our rope drags and slowed her to the point where she had just enough forward motion for good steering. It took 75 fathoms of 2-inch diameter manila line which we dragged in a big bight, plus four 75-foot mooring lines of the same size."

The fear was that Varua would pitch pole going down the steep waves, but Robinson discovered that by slowing the boat down, he could maintain steerage and keep the bowsprit from digging into the waves and the boat from going over.

After this adventure, which he chronicled in another book, he returned to Tahiti. By the time of his passing, Robinson had written six books.

Let's join Robinson on Varua on October 26 (use the 2008 Nautical Almanac). He is at 53° 25' S by 110° 25' W. He is trying to get a lower limb sun sight before the clouds move in. His height of eye is 15 feet and there is no index error on the sextant. The chronometer is four minutes, 20 seconds fast. The time of his sight is 16hrs, 53min, 30sec GMT. The Hs is 41°, 10.5'.

We want to find the Ho, and then the intercept. We then want to plot the position and compare the sun line to the Dead Reckoning position. We also want the estimated position.

A. What is the Ho?
B. What is the Intercept?
C. What is the estimated position?

ANSWER:
A: Ho is 41° 21.9'
B: Intercept is 9.1 NM away in direction 046°
C: EP is S 53° 18' by W 110° 17'



Extended Solution


Robinson is aboard Varua in the midst of what he calls "the ultimate storm." It is October 26, and the DR of Varua is 53° 25' S by 110° 25' W. When the clouds break Robinson attempts to get a lower limb shot of the sun. The height of eye is 15 feet and there is no index error on the sextant. The chronometer is 4 minutes 20 seconds fast. The time of the sight is 16 hrs 53 min 30 sec GMT. The Hs is 41° 10.5'

What is the Ho?
Ans. Finding the Ho from the Hs should be easy work. Basically we factor in some corrections including height of eye, semi-diameter, parallax, refraction, and reduce the sextant shot, Hs to the observed altitude also called the Ho.

Hs 41° 10.5'
dip -3.8'
Ha 41° 06.7'
Alt. Corr + 15.2'
Ho 41° 21.9'

Next thing we need to find is the intercept. This means we have to calculate the LHA and find the declination for the time of the sight so we can enter the sight reduction tables HO 249.

The time of the sight was 16hrs 53min 30 sec. The chronometer is 4 min 20 sec fast, so we have to subtract that from the time of the sight:

16:53:30
-4:20
16:49:10 Time of Sight

Finding GHA from daily sun pages Nautical Almanac Oct.26

GHA 16 hrs 64° 01.5'
49min10sec +12° 17.5'
GHA 76° 19.0'
360° +436° 19.0'
Ass long -110° 19.0'
LHA 326°

We also need to find declination at the time of the sight:
At 16 hrs dec S 12° 43.2' (d) 0.9+
Dec S 12° 43.2'
+ 0.7'
Dec S 12° 43.9'

We are now ready to go to Vol.3 of HO 249. Assumed latitude is S 53°. Dec is S 12° and LHA is 326°. These are the three required entering arguments required to calculate the intercept.

HO249 declination same as latitude:

Hc 40° 51' d +54' Z 134°
          +40'
Hc 41° 31'

We need to convert Z to Zn for southern latitudes as per the instructions on the page: LHA greater than 180° Zn=180°-Z so 180° minus 134°= Zn 46°

We next find the intercept by subtracting Ho 41° 21.9' from Hc 41° 31' and get an intercept of 9.1 nm away because in this case the Hc is greater than the Ho thus the intercept is away from the celestial body bearing at 046°

For the Estimated Position you have to plot the numbers. I know most of you don't want to be bothered but to me this is the great joy of celestial navigation - turning numbers into something that actually represents our position in relation to the celestial body. Great Stuff. Anyway, after plotting I came up with an EP of 53° 18' S by 110° 17' W.

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