I would like to share my experiences taking and reducing sights while on two cruises.I’m going to assume you already know how to take and reduce sights.
My kit for doing celestial navigation consists of my sextant, a precisely set quartz watch, my cellphone with a GPS app, a bound copy of the Nautical Almanac (download versions are available), and my laptop computer.My laptop computer contains an Excel spreadsheet that does the sight reduction calculations via the Law of Cosines method; the spreadsheet is fast and doesn’t make arithmetic errors. If you prefer a table method for reducing sights, H.O. 229 is available as *.pdf files for download. I also bring a plotting pad and plotting instruments, but in practice I hardly ever do any plotting.
My sextant case takes up a lot of room in my suitcase.
You will need to get the Universal Coordinated Time (UTC) and your sight height above the water.Unfortunately, the folks at the Guest Services desk generally have no idea what these are or how to get them.UTC can be gotten off the Internet (https://www.time.gov), and some pre-cruise research will give you the height above the water (a.k.a. air draft)or overall length for your ship.Given one of these, you can scale off your sight height above water from the ship profile drawing that came with your cruise ship orientation package.Beware of the “elevation” feature on cell phone GPS apps – the GPS app I use has sometimes claimed the Lido deck to be below sea level.
Should you not have Internet at sea, you can set an inexpensive quartz watch to UTC before you go on your cruise.Of course, you should check your watch’s accuracy before you go on the cruise.Beware of “UTC” cellphone apps- they either will not work out of land cellphone range or the time they give is based on the internal clock in your cellphone and cellphone clocks can have significant error.
Now, on to taking sights:
I try to take my sights from an open deck high in the ship, but I have gotten surprisingly good results taking sights through window glass.I get my sight heights by scaling off the ship profile drawing.Don’t sweat the sight height – if you take your sights from high in the ship the resulting dip correction will be insensitive to small changes in sight elevation.
I get my actual position from my cellphone GPS app.Bear in mind the ship will travel several nautical miles during your sight taking session – you will have to take that travel into account when you reduce your sights.
My Excel spreadsheet takes my inputs and does the sight reduction calculations; the final result being the intercept and the azimuth based on my entered actual position.The smaller the intercept, the more accurate your sights are.
When you do take your sights, be prepared to attract a small crowd of onlookers.I delight in showing them my sextant and explaining how celestial navigation works.
navigational sextant
in Princess Cruises
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I would like to share my experiences taking and reducing sights while on two cruises. I’m going to assume you already know how to take and reduce sights.
My kit for doing celestial navigation consists of my sextant, a precisely set quartz watch, my cellphone with a GPS app, a bound copy of the Nautical Almanac (download versions are available), and my laptop computer. My laptop computer contains an Excel spreadsheet that does the sight reduction calculations via the Law of Cosines method; the spreadsheet is fast and doesn’t make arithmetic errors. If you prefer a table method for reducing sights, H.O. 229 is available as *.pdf files for download. I also bring a plotting pad and plotting instruments, but in practice I hardly ever do any plotting.
My sextant case takes up a lot of room in my suitcase.
You will need to get the Universal Coordinated Time (UTC) and your sight height above the water. Unfortunately, the folks at the Guest Services desk generally have no idea what these are or how to get them. UTC can be gotten off the Internet (https://www.time.gov), and some pre-cruise research will give you the height above the water (a.k.a. air draft)or overall length for your ship. Given one of these, you can scale off your sight height above water from the ship profile drawing that came with your cruise ship orientation package. Beware of the “elevation” feature on cell phone GPS apps – the GPS app I use has sometimes claimed the Lido deck to be below sea level.
Should you not have Internet at sea, you can set an inexpensive quartz watch to UTC before you go on your cruise. Of course, you should check your watch’s accuracy before you go on the cruise. Beware of “UTC” cellphone apps- they either will not work out of land cellphone range or the time they give is based on the internal clock in your cellphone and cellphone clocks can have significant error.
Now, on to taking sights:
I try to take my sights from an open deck high in the ship, but I have gotten surprisingly good results taking sights through window glass. I get my sight heights by scaling off the ship profile drawing. Don’t sweat the sight height – if you take your sights from high in the ship the resulting dip correction will be insensitive to small changes in sight elevation.
I get my actual position from my cellphone GPS app. Bear in mind the ship will travel several nautical miles during your sight taking session – you will have to take that travel into account when you reduce your sights.
My Excel spreadsheet takes my inputs and does the sight reduction calculations; the final result being the intercept and the azimuth based on my entered actual position. The smaller the intercept, the more accurate your sights are.
When you do take your sights, be prepared to attract a small crowd of onlookers. I delight in showing them my sextant and explaining how celestial navigation works.
Have fun.