I'm going to bring my Sextant.

[Davechipp74]

Cleaning through a family attic I came across this beautiful antique brass working sextant (It was Grandpas) I have since ordered books on how to use a sextant, and been watching a few videos, I have a 12 day solo cruise on a balcony on Jan 20th abroad the NCL Getaway by the end of the cruise I hope to teach myself some basic Celestial Navigation. Any thoughts or comments are greatly appreciated.  

[Aquahound]

Light pollution from the ship and neighbors might be an issue depending on your balcony location.  Otherwise, that sounds kinda cool. 😀

[cruizergal70]

52 minutes ago, DAVECHIPP1974 said:

Cleaning through a family attic I came across this beautiful antique brass working sextant (It was Grandpas) I have since ordered books on how to use a sextant, and been watching a few videos, I have a 12 day solo cruise on a balcony on Jan 20th abroad the NCL Getaway by the end of the cruise I hope to teach myself some basic Celestial Navigation. Any thoughts or comments are greatly appreciated.  

Try going to an upper deck.

 

[navybankerteacher]

The sextant is a beautiful instrument - but all you are likely to be able to do with it is determine the elevation of stars you randomly pick - without having any idea of which stars they are or what their elevation means.

 

Celestial navigation requires identifying the stars you “shoot”, (have you a “Star Finder”?), from an “assumed position”  - which has to be sort of near your actual position, at a precise time (to the second - which means having a reliable chronometer), and access to a Nautical Almanac - so you can do the calculations to generate (hopefully intersecting) lines of position - which you determine by comparing the elevation above the horizon of the known star -at that instant in time- with what you calculate from the Nautical Almanac.  The star shots have to be taken just about dusk (or dawn) when you will be able to definitely identify the stars (at least three) and still have enough light in the sky to be certain of the horizon.

 

A simpler process (somewhat) will be to determine “local apparent noon” and establish your latitude (but obtain no idea of longitude).

 

You would have to be on an upper deck, with an assistant with the chronometer, to log the precise moment when you determined the elevation of each known star above the horizon.

Edited July 12, 2022 by navybankerteacher

[Heidi13]

44 minutes ago, DAVECHIPP1974 said:

Cleaning through a family attic I came across this beautiful antique brass working sextant (It was Grandpas) I have since ordered books on how to use a sextant, and been watching a few videos, I have a 12 day solo cruise on a balcony on Jan 20th abroad the NCL Getaway by the end of the cruise I hope to teach myself some basic Celestial Navigation. Any thoughts or comments are greatly appreciated.  

 

Using the sextant is the easy part, determining a position from the altitude is the part we learned over 3 years, back when we were cadets.

 

Unless planning to use a navigation calculator, you will also need Norrie's tables, Nautical Almanac, an estimated position, a corrected chronometer, plotting sheet, charting tools, ability to determine MerAlt and the azimuth.

 

Our pre-GPS Noon procedure on cruise ships:

  - Calculate time of Mer Alt

  - Calculate estimated position (EP) for Noon

  - Planning to take sights at 08:30, 09:00, 09:30, 10:00 and if required 10:30, we calculated EP's for each of those times. We pre-worked most of the calculations.

 - Using a spotter, just prior to each sight, we brought the sun down to the horizon with the sextant, holding it at the horizon. The spotter provided a countdown and at the precise time, we recorded the altitude and azimuth

 - The resulting position line and intercept were drawn on the plotting sheet

 - Additional sights were taken as planned, calculated and the PL & intercept were drawn on the plotting sheet.

 - We usually aimed to have Mer Alt before ship Noon to get the Latitude. If before Noon, we drew that on the plotting sheet and determined the Noon position from the "Cocked Hat". The daily run and info provided at Noon was then calculated.

 - If Mer Alt was after ship Noon, we had sufficient sights and provided the cocked hat was fairly tight, we got a reasonable Noon position.

 

For star sights, we used 6 stars and pre-calculated the approximate altitude and azimulth. The stars were found by setting the sextant and looking along the azimuth until we found the star. Brightest/dimmest stars were used first or last depending on sunrise/sunset. All results again drawn on a plotting sheet and the position determined from the cocked hat.

 

Good luck

[wcook]

Sounds cool. Hope you let us know how it went. 

[lobsternight]

Nice! I think you should bring it.  Lots of good advice here.  Also when close to land or charted aids one can use it horizontally to plot a fix.  I own 3, a cheap plastic knock off of a Davis, a good Eastern German one, truly a thing of beauty, and an aircraft sextant 24volt that was used through the top of the fuselage. Wishing you success.  Final note, my wife's BFF brother (EX cdn coastguard) used one to navigate from Vancouver to Sydney, but every 3 or 4 days would confirm with GPS.

[ldubs]

My first thought was that it would be cool if ship's officers would be interested in comparing your findings to their GPS.  

 

Other than that, the discussion of technical aspects of using a sexton is like a foreign language to me.  Lol.  

 

 

[MBP&O2/O]

4 hours ago, Heidi13 said:

Planning to take sights at 08:30, 09:00, 09:30, 10:00 and if required 10:30, we calculated EP's for each of those times. We pre-worked most of the calculations.

Wow ... 9am morning sights and then noon sights was all we did. Stars at 'star time' on the 4 to 8 .. although I often used to take stars at 2am if the conditions were favorable .. more for multiple practice than anything. 

All things considered I think the idea is impractical.

 

Apart from everything else mentioned it will probably be full of errors and they can be a pain to remove.

Edited July 12, 2022 by MBP&O2/O

[John Bull]

Have you no faith in the ship's navigator? 😉 🤣

 

JB 🙂

[whogo]

11 hours ago, Heidi13 said:

Using the sextant is the easy part, determining a position from the altitude is the part we learned over 3 years, back when we were cadets.

Thanks for the details, Heidi13.

 

Holland America cadets(?) were training with a sextant a number of cruises ago, gave a brief explanation, yours is more complete. "Mer Alt" sent me Wikipedia: https://en.wikipedia.org/wiki/Meridian_altitude

 

I saw that a skilled navigator could achieve accuracy of about 1/4 of a nautical mile. There must be horror stories of bad calculations.

 

 

[Mum2Mercury]

What a cool thing to do onboard! 

[chengkp75]

11 hours ago, Heidi13 said:

Unless planning to use a navigation calculator, you will also need Norrie's tables

When I mention sight tables like HO214, HO229, or HO249 to cadets these days, they look at me like I have two heads.  I learned celestial using HO214 and a slide rule, but these days, you can take a calculator into the license exam for sight reductions.

 

Interesting bit of history, each entry in the volumes of sight tables (tens of thousands) was hand calculated by out of work mathematicians, hired by the US's WPA during the depression. 

[chengkp75]

14 minutes ago, whogo said:

I saw that a skilled navigator could achieve accuracy of about 1/4 of a nautical mile. There must be horror stories of bad calculations.

I was a cadet on a freighter that carried 12 passengers (all seniors), and the Captain was trying to impress one of the women (husband was onboard, but that didn't seem to matter).  So, one evening, the Second Mate (navigator), the Deck Cadet, and the Chief Mate (studying for his Captain's license) were all taking star shots.  The Captain came to the bridge, with the woman, and decided he would shoot stars as well.  Quite the huddle around the chart table, and the two Mates and the Cadet plotted positions within a half mile of each other.  The Captain's plot was 6 miles out, but he grandly announced that his was the correct position, we were off course, and ordered a course change.  Needless to say, at the next day's noon sights, we were really off course, and the Mates had to correct the course, but fudge the chart to mislead the Captain.

 

That was my first ship, and I have lots of stories about the goings on there, but that's for a different forum.

[Heidi13]

8 hours ago, MBP&O2/O said:

Wow ... 9am morning sights and then noon sights was all we did. Stars at 'star time' on the 4 to 8 .. although I often used to take stars at 2am if the conditions were favorable .. more for multiple practice than anything. 

All things considered I think the idea is impractical.

 

Apart from everything else mentioned it will probably be full of errors and they can be a pain to remove.

 

On the cruise ships we needed to know our Noon position before Noon, so the Captain could provide the position and distance/speed travelled. Therefore, our AM sights really were a running fix.

 

Even on a really good day, we were only with 1 to 2 miles of the SatNav's position.

[Heidi13]

56 minutes ago, whogo said:

Thanks for the details, Heidi13.

 

Holland America cadets(?) were training with a sextant a number of cruises ago, gave a brief explanation, yours is more complete. "Mer Alt" sent me Wikipedia: https://en.wikipedia.org/wiki/Meridian_altitude

 

I saw that a skilled navigator could achieve accuracy of about 1/4 of a nautical mile. There must be horror stories of bad calculations.

 

 

 

Getting accuracy of 1/4 miles takes some luck, as well as skill.

 

As MBP&O2/O explained on cargo ships they normally took a morning sight once the sun had a reasonable altitude to reduce errors and then crossed it with the Latitude from Meridian Altitude. This only had 2 position lines, so where they crossed was the position.

 

With the multiple position lines of the cruise ship method, the position lines never crossed at exactly the same spot, giving what is known as a "Cocked Hat". The cocked hat would invariably be greater than 1/4 mile spread, so the Navigator picked a spot for the position somewhere within the cocked hat.

 

On a good day we got within 1 mile and thought we did well. The conditions also greatly impacted the accuracy.

[Heidi13]

56 minutes ago, chengkp75 said:

When I mention sight tables like HO214, HO229, or HO249 to cadets these days, they look at me like I have two heads.  I learned celestial using HO214 and a slide rule, but these days, you can take a calculator into the license exam for sight reductions.

 

Interesting bit of history, each entry in the volumes of sight tables (tens of thousands) was hand calculated by out of work mathematicians, hired by the US's WPA during the depression. 

 

I learned the old-fashioned way with Norrie's Nautical Tables and never did move to sight reductions tables, or navigation calculators.

 

When I did my Masters in Vancouver, I was the only one with significant deep-sea time, who had lots of sights practice. The others were all discussing the pros/cons of various formula, but I could calculate sights faster with Norries, the Almanac and my pro-forma worksheet.

 

Sadly, our son with about 15 yrs at sea, has never had to use a sextant in earnest. 

[navybankerteacher]

49 minutes ago, Heidi13 said:

 

On the cruise ships we needed to know our Noon position before Noon, so the Captain could provide the position and distance/speed travelled. Therefore, our AM sights really were a running fix.

 

Even on a really good day, we were only with 1 to 2 miles of the SatNav's position.

Which emphasizes the necessity of being aware of the exact course and speed of the vessel during the time the shots were being taken, so you could properly advance the earlier lines of position to correctly intercept the latest to provide the fix.  “Target” fix was expected to be within 1/4 mile.

 

Our noon position was actually something like 1145 - advanced  by course and sped for the next 15 minutes. And had to be figured in advance so the twelve o’clock reports could be delivered to the captain early enough so the OOD’s request for “permission to strike  eight bells on time” actually had meaning

Edited July 12, 2022 by navybankerteacher

[MBP&O2/O]

1 hour ago, Heidi13 said:

Even on a really good day, we were only with 1 to 2 miles of the SatNav's position.

Ah ... we didn't have such technical luxuries 1🤔

One 'oddity' was that BP training promoted long by chron and P&O always favoured Marc St. Hilaire ... strange how traditions vary.

I used to confuse one 3/O and do one of each on morning sights. But I always MSH when I did stars.

I still occasionally use the Sextant ... it's great when there an eclipse, but you do get strange looks from the neighbours.  The 7x50 monocular still has its uses....handy for popping in a pocket and ship spotting when walking hound on the beach.

Edited July 12, 2022 by MBP&O2/O

[Heidi13]

4 minutes ago, MBP&O2/O said:

Ah ... we didn't have such technical luxuries 1🤔

One 'oddity' was that BP training promoted long by chron and P&O always favoured Marc St. Hilaire ... strange how traditions vary.

I used to confuse one 3/O and do one of each on morning sights. But I always MSH when I did stars.

 

We covered Long by Chron at South Shields, but on both General Cargo & Pax Division, all the officers used MSH. Never did try out long/chron at sea.

[MBP&O2/O]

South Shields brings back memories.... did both my second mates and mates there ...

 

It's  changed beyond recognition ... or memory .. now.

[rkacruiser]

For the OP, I think your idea to bring your sextant is a cool idea and will be a conversation piece with other guests, maybe even an Officer or two.  Depending on the ship, finding a spot on the upper decks that is really dark enough could be a quite a challenge.  Some of the best ones are off limits to the guests; some are off limits at night.  And, then, when the ship is moving, the wind could be an issue, I would think.  

[chengkp75]

28 minutes ago, rkacruiser said:

And, then, when the ship is moving, the wind could be an issue, I would think.  

And, yet, mariners have coped with wind on the bridge wings (most ships don't have enclosed wings), and the motion of the ship to make sun and star sights for centuries.  And, remember, it can't be that dark out, you need to see the horizon as well as the star.  That's why its called "navigational twilight".

Edited July 12, 2022 by chengkp75

[Toofarfromthesea]

20 hours ago, DAVECHIPP1974 said:

Cleaning through a family attic I came across this beautiful antique brass working sextant (It was Grandpas) I have since ordered books on how to use a sextant, and been watching a few videos, I have a 12 day solo cruise on a balcony on Jan 20th abroad the NCL Getaway by the end of the cruise I hope to teach myself some basic Celestial Navigation. Any thoughts or comments are greatly appreciated.  

 

Sounds both cool and fun.  I bet after a few days one or another of the ships officers will wander by to kibbitz, and maybe give you some tips.

[Heidi13]

5 hours ago, MBP&O2/O said:

South Shields brings back memories.... did both my second mates and mates there ...

 

It's  changed beyond recognition ... or memory .. now.

 

I did 2MFG at South Shields:

 -- Sept to December 1976, stayed in Flag House, which was a college house across the street

 - April to July 1978, stayed in Winterbottom Hall