A few seconds isn't enough

Not bad for 36 minutes. Well, not really. Make that 108 minutes because I liked it so much I watched it 3 times.

My only complaint is that he didn't tell us what we get. Results. Capt should have explained to the new folks that after all these adjustments. After all these fine tuning points/ After all the methods and swinging. After all the calculations - what the heck do we get? Besides frustrated and put the sextant back in the box. We get a LOP "Line of position" from the sun. If you "shoot" three stars - you would have three separate times and three separate LOP's Where those lines intersect is our calculated position on the sea. People don't have to understand how TO DO all that in the beginning - however - at least explain what they are working towards. Overall, good job Captain for explaining the basic sextant.

We have another video here titled "Celestial Navigation at Sea" that explains what you do with this information... T

Thc

Carry on 😅

A great question. As a Hydrographic surveyor and navigators yeoman, it was my job to maintain and teach others how to use and maintain sextants. Navigation sextants tend to have less degrees on the arc because it is difficult to get an accurate fix from a celestial body that is high in the sky. Sextants with more degrees on the arc are/were used by Hydrographic Surveyors and coastal navigators for taking horizontal sextant angles between three known points on land. Sextants with more degrees on the arc were known as Sounding or Survey Sextants. To keep the weight down they were stripped of shades and lighting. A team of five surveyors would work together to plot a vessels position and record the fix on an echo sounder trace. The routine went something like this; Standby to fix, ready on the left, ready on the right, fix. At this point, the echo sounder operator would press the fix button to mark exact time, fix number and depth on the echo trace. The left sextant operator would call out the horizontal angle between the first and middle mark, the right sextant operator would call out the angle between the middle and right mark ashore. The officer in charge (OIC) would plot the position using a three arm protractor and annotate the time beside the fix number. The OIC may at this point give the helmsman a new course to steer to maintain the planned track. Then this would be repeated minutes apart until an area was saturated with depth and position data. It wasn't so long ago this method of making charts was still in use, as late as the 1970's. As a vessel moved closer towards the coast the angles between the known objects ashore increased. Having more degrees on the arc made it possible to get closer to the shoreline if the known marks ashore where not able to be setup inland.

When planning your star sights you will calculate using Almanacs and/or tables to get a bearing/azimuth and altitude of the star/s your want to use. This makes it easier and quicker to find the star you plan to use. If you have planned a good spread between stars, a bearing to the horizon is enough to help you find your star if you have the predicted altitude already set on the sextant.

+benoitdeg01 As pointed out in the video, you can also adjust the horizon mirror side error by sighting on a star. Either method works, but the result is verified by rocking the sextant while looking at the horizon and in this case there should be no splitting of the horizon if the setting is correct... Being a few meters above the water surface as you point out, is corrected for by the Dip correction, but that's a whole other discussion as explained in the video... MDS

Great video

Freiberger

Yes, the sextant altitude in this case would be zero, but the benefit of the zero altitude shot with the naked eye is that it can be done without a sextant, and there may be times when you want to do that

Hi Andy, in celestial navigation they use the term Index Error because there are additional parallax and horizontal parallax errors that must be factored in when taking sights of the various celestial bodies (sun, moon, planets & stars), when calculating a line of position. It would be very confusing, otherwise.

Sextants seem to be loved by both sides of the FE vs Globe debate. Just a really cool tool.

You must be American.

Yes, I’m American, a retired aviator who spent his career at 38-41,000 feet, who’s circumnavigated the planet many times. . . Psst: it’s round!

@@joemeyer6876 I don't think that flat earth is a thing anywhere but America. I have had the personal pleasure of meeting one. Until that point in time I thought it was all just trolling.

The split horizon mirror covers the right half of your field of view... The horizon image (blue ray) comes past the left side of the horizon mirror in your field of view... T

It is a good idea to do the checks prior to taking a set of sights. Often there will be no need to adjust much, so it will not take long to check. Having a well adjusted sextant will help you obtain accurate position lines.

A bit late, I know, but here goes: (1) no need, the two mirrors seem to balance out a lot of the ship's movements, and (2) you need to swing the sextant from side to side like a pendulum to make the image of the sun (or moon, star, planet) move in a curve and the lowermost point is the one you make the measurement with.

@@karhukivi Thanks for the reply!🙂👍🏻

Good input Robert. There are many "fake but shiny NAV items that looks good but are not accurate. Also, knowing that GPS units for the ocean are different that those for land navigation. Knowing the Marine radios are different than CB radios...you brought up a great point.

Yes, he forgot to mention it. The rule to help remember is, if the error is 'on the arc' take it off (subtract it). If the error is 'off the arc' add it on. They are opposites, which helps you remember. He did explain the difference of errors 'on' and 'off' the arc...... just forgot to mention the rule. So, the procedure is to note your index error (On or off the arc), take a sextant reading and then apply index error rule above. You must also apply the 'height of eye' (called dip), which is always subtracted from the sextant reading. There are height of eye tables in the Nautical Almanac. Once you have applied these two adjustments, you then must apply an altitude correction for the celestial body and time of year (altitude correction tables are also in the almanac). You now have the Observed Altitude (Ho). I hope that helps.

It's a more advanced version of a nautical navigation device called a backstaff. Which served a similar function but was much cruder and bulkier.

Freiberger Yacht Sextant

We convert all times to GMT for the calculations. It also helps to use the 24-hours clock method

You need a nautical almanac.

The bubble sextant has been used in airplanes which don't usually rock and roll like a boat at sea. I've tried a bubble sextant on a boat and found that it was not nearly as effective as using the earth's horizon, so stick with the basics

***** Thanks, you make a valid point. The problem is that the horison is only visable in the day and stars at night, then there's cloud and weather conditions. G.P.S. could possibly fail, so I am interested in Sextant, but there seems so many limitations. I'm told there was once "DECA" that used radio beams. Sadly, that seems to have died the death. What would you recomend for a novice?

SonofBlackDefiance View our KZfaq video titled "Celestial Navigation at Sea" and take our online Celestial Navigation course this winter where we cover the questions you ask very thoroughly. Also, send us an email at office@mdschool.com for additional guidance

+SonofBlackDefiance "I'm told there was once "DECA" that used radio beams." Yes, and also LORAN. GPS has pretty much replaced the other forms of radio navigation. It's fast, relatively simple, and very accurate. The advantage of celestial is that no one can hack the system, and power failure isn't an issue; the sun and stars aren't going anywhere, and if they do navigation will be the least of your worries. ;-)

Abham Amin Is that critical ? Why does the instructor does it the other way around ?

All a sextant does is measure an angle. Measuring an angle on a flat earth or a globe is easy with a sextant. Celestial navigation only works on a sphere and would not work on a flat earth.

Ill make a 2nd post because i believe my first one wont pop up on your feed because i used a certain word. Look up your original comment to see it. Celestial navigation requires the earth to be a sphere to work. Celestial navigation works, therefore the earth is a sphere.

Sextons have measured angles over the ocean, the horizon is measured at 0 degrees, 0 minutes and that is a flat plane. The ocean is the bottom of the triangle and is required to be flat for the trig to work, otherwise it would be impossible for ships and planes to navigate over the ocean. NASA is a very well funded incorporated government bureaucracy. How did NASA sent Apollo to the moon and there if there was greenhouse roof in the way to stop the Apollo moon mission, if space is a vacuum, how do we have pressurized air without a greenhouse roof to contain and pressurize it? ~ When "science" is unquestionable and c∈ns0r∈d on social media then it's dogmatic "science" becomes a religion based on lies. The real science is being hidden from us, so they can scam us into non-existence.

@@martentrudeau6948 "the horizon is measured at 0 degrees, 0 minutes and that is a flat plane. The ocean is the bottom of the triangle and is required to be flat for the trig to work..." WRONG-O!!! There Marty. The rest of your comments really speaks volumes about why you should just be ignored. Sucks to be you.

In the early 15th century a Portuguese navigator, Pedro Reinel, is also credited with the first nautical chart that depicted latitudes in 1504. They used the Astrolabe an astronomical instrument to determine the position of celestial bodies. The Portuguese mapped the continents in the 1500s all with flat maps. The earth was mapped flat!

No, the micrometer does not reset when you change the whole degrees with the trigger release. It stays where you last left it no matter what you do with the whole degrees... T

Great video do start with zero on the micrometer and index arm? Thanks Joe