Sighting with a sextant - wow!

[Yardarm]

Till last week I'd never even held a sextant in my hand, but the 3rd officer on the Tall Ship Stavros Niarchos (here she is moored in La Gomera, Canary Islands)

was a top guy, and spent some time with me and another crew member who wanted to learn. It took a few goes to get it right, but (excuse the non-technical terminology) splitting the sun and then bringing it down to the horizon was amazing. I felt like a proper salty sea-dog.

 

[iangrant]

I've got that far and I'm on a promise from tome that he will show me what to do with it afterwards. the numbers that is.

I think there are 56 stars used, or is it 60 something plus the moving things, now where is that gps?



Ian

 

[dulcibella]

Nice work - now try reducing the sights if you want to experience all the joys of celestial nav! Good courses for Yachtmaster Ocean shore-based ticket are to be found at evening classes. By next Spring you'll love the "star spanner" and be independent of GPS when Dubya decides to switch it off so that he can bomb the hell out of someone else.

 

[Talbot]

Did my final exam for Ocean Yachtmaster last night. I have to say that although I did get what I wanted from the course, I was very disappointed by the support material. Less than half the exam is concerned with astro, the rest is passage planning and weather, but where is the supporting publications for this - quick answer is that they dont really exist.

Tom Cunliffe's Celestial Navigation is fine as far as it goes, although Wilkes book has more information.
Chris Tibbs' Weather handbook is a good basic primer for yachtmaster, but does not cover long passage making requirements, use of gribb files, weatherfaxes etc.
There is a good section in Eric Hiscock's Voyaging Under Sail about planning the voyage that is definitely worth a read.

According to the tutor, the lack of documentary support is not confined to the student, there is very little available for the tutor as well.


What is even more worrying is that the course has been severely dumbed down in the last 6 years. Astro exam was restricted to a sun-run-sun - very little on star sights and no teaching on how to identify the stars.

Having said all that, I am going to be a tad embarassed if I dont pass /forums/images/graemlins/blush.gif

 

[snowleopard]

the ocean syllabus is supposed to bolt on the extra bits that are missed out by the offshore but are necessary for ocean crossing. i would say that world weather and passage planning are more important than astro for today's voyager. the astro tends to get more emphasis because it's totally new to coastal sailors where the other topics are just extensions of old stuff.

being a bit long in the tooth i pre-date gps and had to use astro in anger for a good few years. in all that time i never used anything but the sun. i can see the theoretical benefits of stars, not least the ability to get an instantaneous fix, but if the gps goes down, the sun will get you where you want to go.

compass check by amplitude is also of limited use. how many steering compasses have azimuth rings these days?

One thing i learned from experience that wasn't taught on the courses was the many uses of a single sun position line.

 

[MarkJohnson12345]

I have bought a 2nd hand sextant.

Reeds shows the sun declination to 1 degree. Is that accurate enough?

The sextant came with student tables accurate to a minute or so.

Regards

Mark J

 

[Talbot]

[ QUOTE ]
the ocean syllabus is supposed to bolt on the extra bits that are missed out by the offshore but are necessary for ocean crossing. i would say that world weather and passage planning are more important than astro for today's voyager.

[/ QUOTE ]
I am equally long in the tooth, and have navigated by sextant before (Rio to Madeira is one short trip that comes to mind) I did the course as much to stir the old grey cells as anything, having done the yachtmaster shore based last year. Thus I have recent experiance to be able to judge the missing bits.

Yes you can do the whole thing purely by use of the sun, but adding in morning and evening stars provides a nice task to fill the tedium of the dark hours.

 

[Guest]

Sun sights ok are position line... stars are a FIX

There is a large difference between suns sight and star sights. The main difference being that with the sun you must wait a significant period before another sight .... then do a running fix to obtain a position. Should you not wait enough - the position lines do not have sufficient angle to give a good position. On the other hand a star fix is a fix in the true sense - as it consists of a number of sights conducted of different azinuths. Common practice being to split the sights into 3 stars taken in rotation twice. Meaning approx. spread of 120 deg between lines. There is a short run to correct for each line to a specific time - but this is minimal in stars case.

Accuracy of star fix is generally accepted as greater than that of a calculated sun running fix.