Astro - navigation

>And I bet like us you used the GPS read out time as the 'standard' to input!

No we had two ship's clocks one was set to GMT the other to local time. I also agrree about Mary Blewitt's astro book it has the easiest explanations you will find.
 
816swim said:
Oh ! You all sound experts at this astro stuff.

So please be gentle with an old grandad who still has ambitions !

I would love to learn how to use a sextant - but my maths is some where near nil.

I did manage to cope with those sections of the RYA Yachmaster written (alright, I was one of 5 who had to go back for remedial coaching to get through those bits).

There used to be some chap who did courses in the winter on a ferry down to, I think, Santander, where you stood on the top deck and took sightings.

Suggestions please for the likes of me.
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What maths?
As long as you can add/subtract & look things up from tables (remember ready reckoners & log tables?), thats about as difficult as it gets. Yes, you can make it more complicated, but why?
 
816swim said:
Oh ! You all sound experts at this astro stuff.

So please be gentle with an old grandad who still has ambitions !

I would love to learn how to use a sextant - but my maths is some where near nil.

I did manage to cope with those sections of the RYA Yachmaster written (alright, I was one of 5 who had to go back for remedial coaching to get through those bits).

There used to be some chap who did courses in the winter on a ferry down to, I think, Santander, where you stood on the top deck and took sightings.

Suggestions please for the likes of me.
Click to expand...

There is an excellent instructor based on the IOW. Stokey Woodall.

A friend did the theory course with him last year and found it to be first class.

http://www.ybw.com/forums/showthread.php?61820-Stokey-Woodall
 
Once I've got around to doing YM Offshore I want to do the Ocean course, even bought a sextant to practice with, it's a Freiberger with Zeiss lenses (I'm a photographer so appreciate a good lens!) and it's a thing of beauty, lovely engineering.
 
capnsensible said:
Disregard Ebco, for yer first one try Davies. Brill for sun, moon and Venus and mebbe Sirius. Good enough for nearly all sights.

If you want to get adept with the stars and not spend biggo, try Celestaire. My favourite. When the tables say you can get 6 stars and real world says get three, that one is top for dollar.
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Now much as I am hesitant to disagree with someone with considerably more experience than myself in the ocean sailing department...I know it's accepted wisdom that "budget" plastic sextants are no cop for stars but I've managed perfectly adequately with my Davies Mk. 15, (and not just with Sirius :-) and I'm definitely in the "determined novice" category.

I wonder whether the lore arises because people who're serious about doing star sights may be inclined to invest the money in a "decent" sextant so plastic ones tend to be more used by beginners.

Of course I've never used a "good" sextant in anger so have nothing to compare my Davies to.
 
816swim said:
I would love to learn how to use a sextant - but my maths is some where near nil.
Click to expand...

Can you do add-ups and take-aways? If so you can do astro. When I first started I had to use the Haversine formula using 5-figure log trig tables which was evil. Once I progressed to the Air Navigation tables it became relatively straightforward an with an app on a tablet or phone it is child's play.

Next question - who here has used astro in anger, i.e. when GPS was not available?
 
Please forgive the heresy but I don't rate the Mary Blewit book. I'm a big fan of Sir Tom but I don't think his Ocean text book is his finest work. I've not seen the Tim Bartlett book so can't comment. For me the best book is Adlard Coles Ocean Yachtmaster. My brain seems to work in pretty much the same fashion as the author.

I did the RYA shorebased course 1-to-1 with a retired Master Mariner. We did it over 5 days and I was numb by the end of the course.

For anyone contemplating self study, I would suggest sticking with the sun in the northern hemisphere, longitudes from Europe to the Caribbean. It really isn't difficult and is incredibly rewarding. I've not found a proforma / template that suits my way of thinking so I simply work through the sight reduction process on blank, lined paper.

When you can confidently plot a position line, a meridian passage and transfer one PL to another to obtain a fix, then it's time to think about antipodean longitudes, southern hemisphere, moon, planets, Polaris and other tiny buggars that can only be seen with high quality optics found in a decent sextant.
 
snowleopard said:
Next question - who here has used astro in anger, i.e. when GPS was not available?
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Years ago (pre gps) I was taking a friend's boat from Greece to the S of France (for the canals N). Leaving the Liparia islands (N of Sciliy) we headed for the gap between Sardinia and Corsica. It was an awkward crossing, contrary winds, and with a crew who could not steer a compass course. Eventually our DR/EP had a huge margin of error. A bit of astro narrowed that down, then it was just a matter of getting the latitude right (noon sight) and sailing west.
 
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Minchsailor said:
Years ago (pre gps) I was taking a friend's boat from Greece to the S of France (for the canals N). Leaving the Liparia islands (N of Sciliy) we headed for the gap between Sardinia and Corsica. It was an awkward crossing, contrary winds, and with a crew who could not steer a compass course. Eventually our DR/EP had a huge margin of error. A bit of astro narrowed that down, then it was just a matter of getting the latitude right (noon sight) and sailing west.
Click to expand...

What, exactly did you do, regarding "a bit of astro narrowed that down"?
 
alant said:
What maths?
As long as you can add/subtract & look things up from tables (remember ready reckoners & log tables?), thats about as difficult as it gets. Yes, you can make it more complicated, but why?
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Agreed: I don't in all honesty understand it, or know much maths, but have happily navigated successfully with sextant, Casio watch, and an almanac and NP401 tables. It's all an adding and subtracting sequence.
 
jwilson said:
Agreed: I don't in all honesty understand it, or know much maths, but have happily navigated successfully with sextant, Casio watch, and an almanac and NP401 tables. It's all an adding and subtracting sequence.
Click to expand...

A pre-made proforma with personalised instructions ( as in do this, write result here, look up this in almanac/tables write here, then add this write result here etc) really makes it easy. Hardest bit is finding the pencil sharpener.
 
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Robin said:
All position lines give information even if not the whole deal. Even if not telling where you are it helps decide where you are not?
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Accept that, but he is making a passage between Sardinia & Corsica, presumably Bonifacio Straits.
Having done it myself some years ago, using electronics, interested how exactly he did it.
 
>Go modern, Tom Cunliffe is very good, Tim Bartlett better by a smidge.

I looked at Cunliffe's astro book and he overcomplicates things compared to Blewitt's book. I haven't read Bartlett's book.
 
alant said:
Accept that, but he is making a passage between Sardinia & Corsica, presumably Bonifacio Straits.
Having done it myself some years ago, using electronics, interested how exactly he did it.
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Huh? We used to cross the Straits at Bonifacio to do our shopping. It is not exact far. No navigation needed, just eyeball.
 
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