Alone across the Atlantic

Nav Problem: Alone across the Atlantic
May/June 2007

In the late 1970s Gerry Spiess, a Minnesota native, had the idea of building a small sailboat and sailing across the Atlantic. This is not a new idea and many before him had voyaged across the Atlantic in small boats. Some had even rowed the distance. What separated Spiess from the rest of these adventurers was that he wanted to do the passage in a 10-foot homemade boat; and grab the record for a trans-Atlantic passage in the smallest boat. His pursuit of this dream and its successful completion resulted in his book Alone Against The Atlantic.

Spiess already had a history of building small boats and sailing them long distances. He had previously built a boat and sailed down the Mississippi, and spent time cruising the coast of Central America. The result of that trip was the desire to build a 10-foot boat to sail across the Atlantic.

Spiess, with no training as a boat designer, built the boat he dubbed Yankee Girl of plywood in his garage and tested the boat on a local lake.

He calculated that it would take him 60 days to make the passage and planned to use his canned provisions – half a ton – as ballast. By the time he was ready to start he had spent a whopping $2,924.

As far as his navigational skills, he packed two plastic Davis sextants and the necessary Nautical Almanac, sight reduction tables and a watch. “Even though they’d only cost about $20 apiece, the sextants deserved special care; along with my compass, they’d be the only navigational tools I’d have.” In terms of what he knew of celestial navigation prior to his trip, Spiess was largely a beginner: Despite what he may have lacked in knowledge, Spiess was able to successfully navigate across the Atlantic and to arrive safely in England. Later on he completed another passage from California to Australia in Yankee Girl. To me the most amazing thing about his story is the fact that his wife, Sally, put up with all his activities, loving and supporting him along the way.

Let’s join our intrepid skipper on a rocking 10-foot boat in the middle of the Atlantic for a sun sight. From such an unstable platform, it would have been almost virtually impossible to get a star sight – even for an experienced navigator. The height of eye is 6 feet. There is no index error. The day in question is June 6, 1979. We will be using the 2007 Nautical Almanac.

Spiess takes a lower limb sight of the sun at 19:53:25 GMT. His DR position is 37° 5′ N by 72° 25′ W. The Hs of the sun is 47° 32.3′. We want to find the Ho and then do a sight reduction and plot the sight.

For those without HO 249 Vol. 2, the necessary information is as follows: Hc 47° 43′; d +31; Z 098°. Table 5 for the minutes of declination tells us that the correction to the declination is +21′.

A. What is the Ho?

B. What is the GHA and declination of the sun taken from the Nautical Almanac?

C. What is the intercept?

D. What is the estimated position of Yankee Girl after plotting?


A: The Ho is 47° 45′

B: The GHA is 118° 41.5′ and the declination is N 22° 40.6′

C: The intercept is 19 nm AWAY

D: The EP of Yankee Girl is 37° 6′ N by 72° 18′ W

Extended Answer for Alone Across the Atlantic

David Berson

This is an interesting problem that requires an understanding of the basic problem solving methods of celestial navigation. We have to calculate the Ho then find the GHA and declination. Once we have this information we need to enter the data into the sight reduction tables and then plot the numbers graphically so we can see where we are. This process needs to be reinforced so we don’t become rusty. With this basic methodology we can safely navigate just using the sun anywhere.

The first step is the reduction of Hs to Ho. We do this as follows:

Hs 47°32.3′

-Dip 2.4′

Ha + 15.1′

Ho 47°45.0′

The next thing we need to do is to find the Greenwich Hour Angle of the sun and its declination at the time of the sight: We go to the daily sun pages in the Nautical Almanac to do this.

GHA 19 hours 105°20.2′

Inc and corr + 13°21.3′

GHA 118°41.5′

Ass Long- 72°41.5′

LHA 46°

Remember to use an assumed longitude based on the DR longitude in order to fiud LHA. The formula is LHA= GHA- Assumed West long

While we are at 19 hours in the Nautical Almanac we look to see the declination of the sun at the time of the sight. At 19 hours the declination is N 22°40.4′ with a +d correction of 0.2′ This means that the sun is moving at 0.2′ per hour. We go to the increments and corrections page in the rear of the book and under 53 minutes of time we see that the sun has moved 0.2′ in that time. We add that to the declination and get a declination of N 22°40.6′ at the time of our sight at 19 hours 53 minutes and 25 seconds. I will round off the tenths of minutes so that the declination will read N22°41′

WE now have enough information to enter into HO249 Vol 2. I go to page 225 and under the 22° declination column at LHA 46 degrees I extract the following:

Hc 47°43′ d +31 Z 98°

For minutes of declination (41) I go to Table 5 at the rear of the book and I am told that the sun’s declination has increased 21′. I add this to the Hc and get the following:

Hc 47°43′

+ 21′

Hc 48° 04′

We also note that the azimuth or Z is 98°. We know that is not possible since we took a shot in the late afternoon and the sun should be bearing in a westerly direction. In order to get the correct bearing we need to convert Z to Zn. The rules at the top of every page in HO249 state that if the LHA is Less than 180° we subtract Z from 360°. Thus our azimuth to the sun is actually 262° which makes a great deal more sense.

To find our intercept we subtract the Ho from the Hc and get the following:

Hc 48°04′

-Ho 47°45′

Int 19 nm Away

Remember the formula: Ho Mo Toward.

The plotting I have to leave up to you. Suffice it to say that you should practice laying out plotting sheets. We get a good LOP that is almost a line of Longitude. Had we waited until the sun was lower we could have gotten that. Anyway Good luck and keep up the good work!

By Ocean Navigator