Solution to: “A brush with hurricane Marilyn”

March/April 2006

This problem provides a nice review in the procedure of sun sights. This is not a complicated sight-but one that is essential master. Many amateur cruisers, in the time before GPS, would often navigate thousands of miles just using sun sights. To the problem then:

The DR of Ocean Star is 33°50’N by 64°10’W. The Height of Eye is 10 feet. The Index Error is 2′ ON the Arc. We are shooting a Lower Limb sight of the sun on September 20. We are using the 2006 Nautical Almanac. The Hs of the sun is 28°59.4′, The shot time is 12 hrs 30 min 15 sec, GMT.

Let’s reduce the Hs to Ho

Hs 28°59.4′

-Dip 3.1′

-IC 2.0′

Ha 28°54.3′

+3rd cor 14.3′

Ho 29°08.6′

Next we will use both the Nautical Almanac and the Sight Reduction Tables to find the Intercept by the use of the Computed Altitude found in the Sight Reduction Tables:

GHA @ 12 hrs 1°38.2′

+ inc and corr 7°33.8′

GHA for time 9°12′.0

+360° 369°12.0′

-Ass Long 64°12.0′

LHA 305°

While we are in the NA we should also pull out the Declination of the sun at the time of the sight. At 12 hrs GMT the Declination is N 1°02.3′. The d correction is 1.0′ and by inspecting the Declination tables one can see that it is Decreasing. The value of 1.0′ is equal to 0.5′ thus:

Dec. N 1°02.3′

-.5′ N 1°01.8′

For the sake of using Table 5 in the Sight Reduction Tables we will round off the Minutes of Declination and make them 2′

We are now ready to Enter in HO249 Vol 2. We have Assumed Longitude. We have Assumed Latitude of 34°, and we have Declination, and we have the LHA!

We go to Page 204 in the Sight Reduction Tables under LHA 305° 1° Declination:

Hc 29°02′ d +37 Z 110°

Table 5 tells us that 2′ of Declination is equal to 1′ correction that is to be added to the Hc. So we get a final Hc of 29°03′. We compare that to the Ho of 29°07.8 and get the following Intercept:

Ho 29°07.8′

-Hc 29°03′

Intercept 4.8 nm Towards the sun in a direction of 110° True.

You should go to the effort of plotting the numbers so that you can stay in practice with the layout of the plotting sheet. I thank you.  

By Ocean Navigator