Ad hoc celestial teacher on Royal ClipperDec 4, 2009
She is 437 feet long but takes only 220 passengers and the ship and its appointments are more like a yacht than a cruise ship. You can climb the ratlines to what they call the crows nest but would traditionally be called the top at the level of the main course yard and you get a great view from there. You can also go out on the bowsprit or lay in the net under it and watch and hear the sea rushing by under you. We met many people and most of them had made this voyage many times (some, many, many times) and we are planning to do it again, hopefully next year.
We were under only sail about half the time and we got up to eleven knots solely with sail power. But when the wind was light, usually at night, they would proceed under power to keep to their schedule. I looked over the stern and could see when the prop was driving the ship and the ship had a different feel when under sail alone, a wonderfully different feel.
The ship published a schedule for each day. On the second day they had sextant use and the noon sight on the schedule. I went to the bridge at the scheduled time and found passengers looking through about ten Davis sextants looking at the sun. Not surprisingly they were getting many different readings and I looked through several of the sextants and they all had significant index errors, one of three degrees! I was disappointed that no one was explaining what the readings were used for. That afternoon the schedule said advanced navigation so I went to the bridge for that. One of the ship's officers was explaining very basic stuff to about a dozen passengers and I looked around and found H.O. 249 on the bookshelf. Someone asked about variation and the second officer pulled out a blue book and said that the changes in variation were listed in that book. From where I was standing the blue book looked like the nautical Almanac and I had never noticed variation information in that book. I innocently asked the officer if, when doing celestial, he used H.O. 249 or if he used a calculator or programed computer. He asked me what H.O. 249 was. I figured that maybe he knew it by some other name since he came from the Ukraine so I got volume 2 off the bookshelf and showed it to him. He flipped through several of the pages and had that deer in the headlights look and it appeared he had never seen the tables before! Even if he was not familiar with this particular set of tables I would expect any navigator to recognize a sight reduction table even if it was not the exact same set of tables that he was used to using. He then said no, everything is in the blue book. So much for the level of celnav being practiced today.
I had brought my Tamaya along and planned to take noon sights to gather data for our discussions and to take as many sights as I could to gather data on the accuracy obtainable with celnav (I will write about these things later) so the next day I was on the bridge at noon and took a noon sight. Another of the ship's officers saw me and asked me if I would teach him celnav and I agreed and ended up with about eight other students the next day to take the noon sun. I let them each take a sight as the sun was approaching noon and after it started descending we worked out the latitude the traditional way and it agreed within one NM with the GPS, not bad for first time sextant users. I told them that this was a special case with very simple arithmetic for the solution.
That evening I hit upon a way to introduce the general solution by the St. Hilaire method. I made up a plotting sheet and drew a line showing the latitude line we had determined at 24 degrees 49 minutes North. I then explained that another way we could have done it was to work the standard noon formula from the other end and compute what we would have measured if we had been at 25 degrees North. Then comparing the observed altitude and the computed altitude and knowing the azimuth of the sun was straight south we plotted the LOP and showed that we got the same latitude as before. I then got H.O. 249 and showed that we got the same result using it with an LHA of zero. I then showed them that H.O. 249 would do the computation for the general case. I have never seen it taught this way and I had never thought of it before and I recommend this method to you when you teach celnav.
The next day we had the group shoot the afternoon sun and then we stepped through the entire solution. I had to make up forms for them to use and they were not perfect so there were many math errors due to the unfamiliarity of dealing with degrees and minutes and keeping them in the correct columns, good forms would have made this easier. We then plotted each of their LOPs on a plotting sheet and compared them with the GPS values.
Near the end of the voyage I was talking to the captain and he told me that he does the calculation on a normal calculator and he challenged me to a competition. Later that day I showed up on the bridge with my calculator in my pocket and said I was ready for the competition. He made up a set of values but when he got out his calculator he said it was kaput the battery was dead. I worked the problem, so I guess I won. This gave me a great segue to the flat Bygrave. I got it out of my cabin and gave it to the captain as a gift, with some forms, and told him the batteries will not go bad on this one.