Can You Really FIND Your COORDINATES With a SEXTANT? | Sailing Wisdom 

Thank you so much for all your wisdom. I learn so much and clarify so much from your generosity of sharing.

Glad to hear it!

We will be doing more videos that will go deeper into the small factors that are involved.

Yes I'm totally lost with all the values. What is local apparent noon, or noon sight? Or maybe rather when is it? I mean, is it just you wait until you believe the sun is at the highest point? Sounds rather unprecise already? Then in the latitude calculation, what are the values involved with the calculation. 67 was threading, where do the other two come from?

You are very welcome!

I love GPS but keep up my paper skills in the event that I find myself without gps one day!

Hi Craig , I’m a newcomer to the sextant, I understood the first part but the second part where he had the figures . He had 89degrees 60 , then subtracted 67, 44 but he didn’t explain what the figures were ?

@@sailingthalassa it was the declination from the almanac for the given day/hour

@@theHDRflightdeck thank you , that’s what I was missing .

longitude calculation need to factor in equation of time

Bingo

Thank you very much

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That’s why I learned it as well!

We’re going to be making other videos that will go into deeper detail on all the finer points.

This is an excellent backup to electronics which can be destroyed by lightning

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You are very welcome!

Thank you

Where did he get the 89 degrees and 60 minutes from. Why did he take 40 minutes from 90 degrees.

89° 60' is just 90° with one of the degrees broken out into minutes to make the next calculation step easier. There are 60 minutes in 1 degree, not 100.@@robertkello7334

Thank you! Glad it was able to finally tell you how to figure it out :)

Yay!

I do not know but there is a method where you use the moon to do all your time keeping calculations. I do not comprehend it but those who can are called Lunarians. Basically, from the moon they get everything without a book or time. Like I said, it’s beyond me but maybe that guy was one of them.

Thank you!

Oh the algorithm

I should explain the math more in depth. For this video, it was just “how to do it” without any of the why you do it.

A few tricks to it (I’m pale so I can’t sit in the sun for hours taking an average to figure out noon so I do a single shot at the right time) 1. When the shadow on the lubbers line is pointing north over the compass, it’s time. 2. I know my position and time from yesterday’s noon sight, and I know my direction and speed, so I use Dead Reckoning to estimate when it will be. If I feel like it’s “noon” but it’s the wrong time based on 1 or 2, then I keep waiting. I also set an alarm for 5 min before the predicted noon that way I don’t miss it. All of these factors come together to getting a single noon sight that is close enough to the actual noon that it works well enough for ocean travel.

When you do your math, if your noon occurs after noon in England, then you will have a positive number and be West of the Prime Meridian. If you are East of it, your time will be before noon and therefore smaller than 12. When you subtract 12 from it, the number will be negative which tells you that your longitude is East.

Thanks!

this is the measurement in degrees he got by taking a site of the sun with the sextant.

Yes, it can only be done once a day, at noon. You can do it the way you mentioned but I found that I was getting sun burnt from the process. To save my pale skin, I would plot ahead with Dead Reckoning and figure out where I think we will be tomorrow at noon and work the math backwards to find the time of Local Noon. I would go sit out in the sun a few minutes before the necessary time and get my sight as the sun would stop climbing. Once the sun stopped climbing, I would wait a few moments and proclaim that time to be my Local Noon. Doing this everyday you begin to get a good feel for when noon is occurring and your longitude gets more accurate, but it puts you in the ballpark of being able to tell if you should see land today or not.

​@@RiggingDoctor this is interesting, the reverse math of any longitude will give you the solar noon for that longitude?

Woohoo!

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The difference between them was used to calculate longitude

@@RiggingDoctor Thank you for the reply...will think about it more

@@RiggingDoctor Oh, ok...will watch again. Thanks for the reply.

90°00’ is the same as 89°60’ If you start with 90, you will have to convert it to 89 60 as soon as you begin subtracting the sextant reading (unless your sextant value is xx°00’).

I’m not familiar with that video. This is the method I have been using with great success. It is a method I devised by simplifying the correct method which is much more tedious and time consuming to complete.

ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-UV1V9-nnaAs.htmlsi=qx6uBbSpVUZ7Dpd9&t=1428@@RiggingDoctor

Hi, if you wish to calculate LHA then 'East is plus' and 'West is minus '. An example. The GHA of the Sun is 33°, your dead reckoned longitude is 10° East. LHA is always calculated westwards from the observer. 10°E + 33°W = an LHA of 43°.

3:57pm UTC means that the sun is directly over you at 15:37 time in England. From the time difference, you can figure out your longitude

Thank you

Yes it is. But there is most likely an index error To find that sight the apparent horizon and line the two images up to a straight line using the micrometer in whatever direction it takes. The reading on the drum afterwards is the index error. It can be zero, positive or negative. Then sight the sun and apply the index error (with it's sign) on that sight as the first step in the following calculations.

I finely calibrated my sextant to remove all errors in the drum and in the mirrors, so zero is zero. It takes a bit of effort to calibrate the sextant but it then makes all the math so much simpler because there is no error to correct for.

I was hoping someone would chime in on this as it is of interest to me.

Myself a navigation officer who sailed the globe for past 14 years can surely say that the coordinates in the book is wrong 😊

There are a bunch of methods that you can use such as taking a. Inch and averaging them to figure out when noon actually happened. I just get a feeling that noon is coming and keep an eye on the lubbers line on the compass. When the shadow is pointing N I know it’s soon time. I also throw a little dead reckoning in and figure where I was and what speed I’ve been moving to guesstimate what time noon should occur. All of this comes together to a point where I only do one noon sight at noon and I tend to be within a few miles of our actual position. For finding land while out in the ocean, that’s been good enough.

It’s a plastic one by Davis instruments.

I’ll be making an entire video on it and how to determine it while sailing, but the short answer is: it’s the time when the sun is at its highest position in the sky.

It's simply 90 degrees put into a format easy to do subtractions

Indeed!

Yes, but the local time zone is spread across 15 degrees which could be as much as 1000 miles.

I guess when noon will occur based on my last noon sight and which direction and speed I have been moving. This lets me estimate when noon will occur so I can be ready. I also watch the compass as it has lubbers lines that stick up and cast a shadow. When the sun is at its meridian in the south, the lubbers line shadow will point north (plus or minus the local magnetic variance which is known). All of these clues help tell you when to take the noon sight. I only do one because I’m pale and will burn to a crisp if I sit out in the sun measuring it the correct way where you measure and average the sightings to figure out mathematically when noon occurred and then use that correct time. I always start my plotting when we leave so that I know where I started and can then estimate when noon will occur on each day of the passage. Comparing the calculated position with the Dead Reckoning position helps let you know if you need to look earlier or later when you do your next noon sight tomorrow.

At local apparent noon shadows will be at their shortest.

You would get a negative number which would mean your Longitude is East. Negative = East Positive = West

is there any possibility pf txting you directly ?

You are correct!

The sextant will help you determine when the Sun is at its highest altitude. You do need to know that.

Very nice!

It’s not the most accurate, but at 45nm of error, you are probably going to see more traffic and start getting radio signals from shore to clue you in to the fact that you are approaching land. I managed to get within 20nm of my true position and regularly within 6nm of my true position using this less than accurate method. It’s not perfect but it’s really easy and that makes it more likely to be done. Spotting an island from about 100nm is possible if you can spot the land cloud over it. It’s how we would find islands long before they appeared over the horizon. The goal of this is to be able to find land, and then using other aids to navigation, find your way from there.

Yes, absolutely. Thanks for reply

They are printed yearly and have existed for a very long time.

It can be horribly off by keeping it simple, but if you do it carefully enough and also compare it to your dead reckoning, I have managed to keep it down to just a few miles of error at 5°N. If you think you are 300 miles ahead, land will just take about 3 more days to come over the horizon and you will figure out that you were a tad off 🤣 These are quick calculations. If you find that your position is way off, then other more accurate methods can be employed. Otherwise, the noon sight comes in a few miles from the DR and then you have lunch 😎

Not too sure about the +/-4° error though. Going minute by minute instead of second by second for longitude, the error is only 15’ per minute of time. To be off by +/-4° would mean taking the noon sight 16 minutes before or after LAN. That’s a 32 minute window of time which would naturally make a big area for error, but being careful I keep it down to just a few miles. Knowing when the LAN occurs is more important to longitude than working the sextant.

The method would be perfect if the earth's orbit around the sun would be a circle and and the axis of the earth would be perpendicular to the orbit's plane. But the orbit is ellipsoidal and the axis is tilted - this results that the sun is not always appearing at the highest point at noon. This difference is called "the equation of time" and can be +16 /-14 minutes trough the year. If you are lucky, there are 4 days in a year, when the error is 0.

Hmm. Thanks for that information. I guess my errors in calculations canceled out those errors in time because I was usually within a few miles of my gps position. I will look into this further.

Glad to hear so, how would you go about it then?

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Noice 👍

Wiser words were never spoken!

0:47 I show the nautical almanac

That is a topic for another video. There is a lot of math involved in creating a book of tables for our easy reference.

@@RiggingDoctor Does it involve the angle between the center of the earth and the center of the sun and the line from any point on the earth and the center of the sun?

The NA gets its data from the International Earth Rotation Service and the US Geospatial Intelligence Agency.

It’s the time when the sextant recorded the greatest angle between the sun and the horizon.

@@RiggingDoctor Hm, that was maybe a bit unprecise by my side. So how do you measure the greatest angle? Do you shoot the sun multiple times around a dead reckoning time?

Make sure you start before local noon, and only dial bigger angles. That is, when the sun starts going down, stop shooting and note the time.

That’s exactly the reason to not try and be super accurate in the math, the boat was rocking so your measurements are not going to be perfect. Close enough is good enough

@@RiggingDoctor Navy 'Signalman' is a rate you'll be interested in.

This is my short hand math for finding your position. Dip, refraction, and eye height are ignored because they complicate the calculation a little and don’t improve the calculations much. Remember, you are taking a sight on a pitching deck. Everything is moving so the sight is imperfect. This is why I also don’t calculate seconds either. It’s close enough to work, easy, and far from perfect.

@@RiggingDoctor Thank you for the clarification. I just ordered a cheap 2022 nautical almanac, and I look forward to testing your "easy, no LOP" method, to see if it works for me. Fair winds. ⛵

Haha! Thankfully, the tooth pulling is much more error-free

@@RiggingDoctor That's what CHRIS. CONSTANTINE SAYS

3:57 PM is 15:57 UTC and the time difference from “my local noon” to “actual noon in Greenwich” is 3 hours and 57 minutes. It’s a positive number so we are West. If it was a negative number it would be East. Imagine that my local noon happened at 8:47AM. In 24 hour time, that would be 08:47. Remember, the clock that we read the local noon from is always set to UTC If we subtract 12:00 from that: 08 : 47 -12: 00 ---- -4 : 47 x15 x0.25 ------ -60°+11.75° Since it’s negative, that means that our longitude is 71°15’E

Remember, the clock you are measuring noon off of is set to UTC but it’s not a 24h clock so we need to convert AM and PM to 24 hour time. That’s the +12 since it was PM.

I’m going to be doing a separate video on the noon sight in particular which will go into all that in greater detail.

Where did you get 23 24.7 from, your almanac?

90°00’ is the starting number but when you start the subtraction you will switch it to 89°60’. It saves a step which makes the math go faster.

It’s the 90°00’ that you start with but converted into what you need it to be for the calculation

@@RiggingDoctor But you are not showing the conversion. Where is the place in the equation where you decided to subtract 40 minutes from 90 degrees? I thought one simply would use 90 degrees all the time. You simply put 89 degrees and 40 minutes on the screen without showing why you choose those numbers. Please show me where you got those 40 minutes from.

a degree is 60 minutes. You seem to be assuming a degree is 100 minutes.@@robertkello7334

Exactly. It’s the time of your local noon taken on a clock set to UTC time. If you’re on the east coast of the US and your local noon occurs 4 hours after noon occurs at England, than your longitude would be 4*15=60W and your local noon would occur at 12+4=16:00 Your local noon will occur at some time period around this hour and the minutes of the 16:xx will help fine toon your longitude.

'local noon' is not local 12:00 (well it might be at a particular longitude) 'local noon' is the moment when the sun is locally at its highest point in the sky, this changes with longitude. Your 'local noon' and that of someone a mile down the road are different

89°60’ or 90°00’ are the same thing. When you subtract your reading which will be xx°xx’, you will need to reduce the 90°00’ into 89°60’ to finish the math. It just speeds it up a step.

@@RiggingDoctor yeah but what is it, I got confused cause you pulled it out of know where

You are trying to find your angle relative to the sun. The sextant gives you one reading, and you need to subtract it from 90°. There is a very complicated method to figure out your position which takes me a while to do it all. This is my “cheat sheet” version. It’s quick and easy and gives you almost the exact same value. To make it work, you start by subtracting your sextant reading from 90° (or 89°60’)

@@RiggingDoctor so you always subtract it from one of those?

[54°15’] 3h*15=45° 37min/60=0.6167*15=9.25 (9°) 45°+9°=54° 9.25-9=0.25*60=15’ 54°15’

Thank you l confuised

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Big red bird in the room!

They were survival food .

😎 love that movie!!

🤣 exactly

A little birdie told me the coordinates

Thank you :)

Sorry it wasn't more helpful for you. Sextants are easy to use, but the standard math is unnecessarily complicated. My goal was to demonstrate a simplified calculation that is accurate enough for celestial navigation, but still simple enough to do quickly to obtain your latitude and longitude.

@@RiggingDoctor You were explaining a noon sight. Who was your intended audience? If it was a novice, I can’t imagine that you could launch into this without a lot of background I think a lot of graphics would be helpful. Anyhow,I ’m coming off way more critical than I intended. Many have attempted to simplify celestial navigation (eve a noon sight), few if any have succeeded. In a single lesson. Thanks.

@@RiggingDoctor I taught myself how to solve the PZX triangle by watching YT videos. I enjoy seeing how you do it. Will you be taking a sextant on your next passage?

Fixed the audio!

No…

Lol 😜

Yes, but the reason you do it is if your local noon is BEFORE 12:00 GMT then you will have a negative result and your longitude will be East Use the same method every time and then you make fewer mistakes when it matters (it's also technically correct)

But also simply explained. It’s easy to do and gets your position to within a few miles of your actual position. If it’s easy to do, you will do it; if it’s complicated to do, you will know how to do it but will never want to do it 😉

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There is plenty of room for improvement! This is just a good starting point that can get you to within sight of land.

😎 just living my best life in the simplest way.

She’s in our lives forever!