The Sextant in Practice: Sun-Run-Sun explained

[@pradipkrsaha976]

Its an excellent video. Really liked in how detail u hav explained even for a layman. Thanks

[@reginasailing]

Thank you! Very kind!

[@RP-zm9kh]

Very interesting. I enjoy learning the techniques involved. Excellent explanations. Thank you

[@andypdq]

A good few years ago I learned how to do this, more out of interest than anything. If you have a clear sky around local noon, why can't you just determine the exact time of local noon by taking timed measurements of equal altitude before and after Noon and divide the time difference by two, then use the exact time of local noon to determine longitude? This seems to me to be a simple way to do it, yet it doesn't seem to be used. Perhaps I'm missing something?

[@reginasailing]

Thank you for asking! This is a very common question and also taught by some sailors. And yes, it works surprisingly well if..... The reason this is not taught by the RYA is that it only works when sailing east to west (or vice versa) but not north to south (or vice versa). Because by the time you have moved (the faster the bigger the fault) you will have gone closer or further away from the sun. Say you are sailing 4 hours from 2 hours before noon to 2 hours after noon, this could well be 4 x 8 knots = 32 nm or 32 minutes on the sextant, i.e. half a degree. But you could argue you only use the method when sailing on westerly course with a constant distance to the sun (same latitude) but then you have one big issue: Will the sky be clear exactly that second we are talking about? You may not touch the wheel! Just sit and wait until the sun has the exact same hight and hope that you a) did not oversleep the time and b) no clouds. If you miss it, you need to wait for another 24 hours for a fix. And that day might be cloudy all day, so then it goes on.... It's so fast to just to a sight reduction and get a fix any time of the day when you can see the sun. And it works on all headings. That's why it's not taught by RYA, but yes, you are right, it does work if you get it all right. Hope this helps!

[@andypdq]

@@reginasailing Thanks for your prompt reply,it's all obvious after having it explained, I knew I must be missing something! Being self taught, you pick up things that would not be taught on a course, I'm particularly interested in Sumner lines, the first line of position method, used before the St Hilaire method became universal. Calculate a position North of your assumed latitude, by solving the nav triangle using your sextant observation, calculate one south, a straight line between the two gives you your LOP. 1830s I believe. Regards.

[@andypdq]

See : www.siranah.de/html/sail040t.htm

[@BytasRaktai]

Can we download the A4 size forms you have been using for the exercise anywhere?

[@reginasailing]

Glad you liked the Reginasailing templates! Please check on the website Reginasailing.com for more information how to obtain them or send me an email. Address on the website.

[@sempertalis1230]

All the correction and finetuning until you realize that you have sailed miles away from where you where when you take the numbers 😂😂😂 Jokes beside, thanks for the in detail walk through the process. As an engineer i can only recomment not to get too picky with corrections if you anyhow do not need the pecission anyways. In the mid of the Atlantic a position of +/- 10-20 miles is good enough 😊

[@karhukivi]

the second position line can be transposed by the distance log, so the fix is for a certain time and plotted as such. That takes care of the distance sailed between the two fixes. If you omit all the corrections the position would be far worse than 10-20 miles. So if you have to do some of them, why not do all of them properly?

[@wollekemper8317]

@@karhukivi Because the actual value of a sextant is as an emergency backup. You may use it as a hobby or to kill some time, so do it like it is 1763 .Have fun. But as a backup in case some really bad has happened to my electronics, I am in a different situation. I need to plot a fast curse to the next Island, cost line or anything where I can fix my boat . Finding Hawaii does not need a +/- 1 mile precision . If I use the sextant I am in distress having to work all kinds of problems in parallel . So KISS is the motto of the situation. To be honest , I have a sextant and also the needed paperwork on the shelf. Sometimes I pull it out and do all the calculations (including all corrections) just for fun. But if I really need a sextant to get me someplace save, I will need a quick but rough curse plotting. What do you say if you make calculation errors because you are in distress? There are worlds between having some afternoon fun with tea and biscuits to nibble on while you plot your course and having to plot a course while doing first aid on a crew mate and getting the bilge pumped by hand at the same time. In summary it is all fun and games until something serious happens and you need to do everything as fast as you can. I was there , I know what I am taking about.

[@wollekemper8317]

@@karhukivi BTW, I did not say to ignore all corrections, I said "do not get too picky with corrections" Just use some common sense when to decide how much precision is needed . I still double down on that +/- 10/20 miles on ocean crossings are good enough :-) Peace

[@karhukivi]

@@wollekemper8317 Yes, I agree with you in general terms. It is worth reading Sir Francis Chicester's account of sailing towards the Bass Straits without an adequate fix for several days of cloudy weather and realising he might arrive at night into a narrowing area with currents and wind pushing him. In his panic he made a big error in calculating his last position and later realised the mistake, which is reproduced in the book. My point is simply that if one is going to make a fix it might as well be as good as possible, rather than a quick and inaccurate position.

[@karhukivi]

@@wollekemper8317 It is worth reading Sir Francis Chicester's book Gypsy Moth on heading towards the Bass Straits pushed by wind and current without an accurate fix for several days of cloudy weather. He made an error on his last position which he later realised and it is reproduced in the book. The effort required to do the best fix possible is the same as doing a bad one, so I would always opt to do the best one I can even if it is not warranted, as much for personal satisfaction as to have at least one reliable position... just inn case...!