Celestial Navigation

[nigel1]

Originally Posted by sailr69

what is a purely paper approach? that one is new to me. I print a paper form for reductions but still need to do the math to fill it in. btw, I don't do celestial anymore, not for 20-25 years. maybe some things have changed

The sight reduction tables are based on the Marc St Hilaire method, and only requires the ability to look up a set of tables, add and subtract, and maybe a tiny bit of interpolation.
Pre GPS when watchkeeping I could work up a sight using Nories tables in about 5 minutes, but as Dave said, it's easy to make a simple error using logs, haversines etc.

[goboatingnow]

Originally Posted by sailr69

what is a purely paper approach? that one is new to me. I print a paper form for reductions but still need to do the math to fill it in. btw, I don't do celestial anymore, not for 20-25 years. maybe some things have changed

If you use the St. Hilary method and the associated tables , you can work up an intercept using just simple addition and subtraction , a paper workbook is useful to ensure the steps are followed in a correct order.

Yes of course you can easily do the spherical maths on a special calculator , but what's the point of a backup method that needs electronics , you have GPS for that.


Dave

[Sailormantx]

Look for a copy of Blewitt's Celestial navigation for Yachtsmen. That's about as basic as you can get. Learn to do it on a blank sheet of paper from memory, not with pre printed worksheets. It's all in Bowditch too, but that's way more information than you need unless you really get into it.

[Adelie]

Originally Posted by Teknav

With the GPS being as cheap as it is and as easy to use, why on earth learn to use a sextant? Does it make any sense to use a slide rule/an abacus when pocket calculators are easier to use and cost next to nothing? It's time to move forward, folks!

Mauritz
I solve complex engineering problems using very fast computers.

If the calculator is broken or its batteries are dead, the result is of life safety importance and needs to be obtained on a deadline or at a location that precludes going out to purchase a new battery or calculator why then, yes it does make sense to use the slide rule if you know how to use it. On the other hand if you don't know how to use it then you are boned.

Contrariwise, if the result is not of life safety importance or the situation would not preclude repair or replacement then the analogy to being offshore on a sailboat with one or several disfunctional GPS's does not hold up.

Do you feel that there is zero possibility of multiple GPS failures on a boat?
Otherwise you believe that there is a very low possibility of multiple failures and are instead questioning the OP's risk tolerance.

I inspect the product of people that use very fast computers to solve complex engineering questions and about every 3 or 4 years find a mistake that could kill someone or several someones.

[Adelie]

Originally Posted by openseas

Hi all,
I just finished day one of a two-day course about celestial navigation, including how to use the sextant and get a fix.
The people who were taking the course, all have some knowledge about the sextant including some who already use it.
For me, seeing the instrument for the first time, the course had a steep learning curve.
Do you suggest any books or DVD's that would simplify the instrument and take someone like me from scratch.

Thanks a million,

I don't have a suggestion for learning, but I do have suggestions for what to carry underway.

There are actual day to day uses for a sextant, specifically you can use it to determine range to some visible objects.

If you know the height of an object you can shoot it's top and waterline or its top and the horizon (if its bottom is over the horizon) and read the range off of charts.

If you can see an object's waterline and the horizon beyond and know your own height of eye, again you can read the range off of a chart.

All the charts are in Bowditch, perhaps in an older edition, I don't have the current.

You can also use it to determine circle of position on a chart by measuring the horizontal angle between two features on the chart.

For use as a back up to GPS offshore see this post, http://www.cruisersforum.com/forums/...ml#post1000999, I did in another thread.

[steamgoat]

So,according to 'TEKNAV' I should not bother with my 1970 Trans Am [the same age as my sextant] and just use a Honda Civic !!

[Teknav]

I am not the one to advise you on what to use for navigation. It is ironic that some folks use the speed of the computer to search information on an obsolete navigational tool; the sextant. It's like riding a donkey to work, but talking on a cell phone while underway.

If you want to live in the past, that's your prerogative. When I'm sailing, I want to enjoy the trip and not worry about calculating my positions using a sextant. As far as power failure, it would be prudent to carry battery powered pocket GPS'. All it takes is pressing a button, wait until a few satellites' signals pop in view...and voila, you have your longitude and latitude; try doing that with a sextant!

Unless you are an engineer/mathematician/architect/scientist or physicist, you'll have no appreciation of the usage of fast computers. It's no different than riding a donkey to work, and talking on a cell phone in the meantime. It takes all kind of folks...

Mauritz
Simplicity and elegance through engineering.

[C4 King Cobra]

My understanding of this discussion is that you want something when all else fails! A sixth grader could be taught the basics of taking and calculating a noon shot. With practice they could plot there position with accuracy. That is all you need to know for a when all else fails system. IMHO

[SV Sea Monkey]

Originally Posted by Teknav

Unless you are an engineer/mathematician/architect/scientist or physicist, you'll have no appreciation of the usage of fast computers. It's no different than riding a donkey to work, and talking on a cell phone in the meantime. It takes all kind of folks... Mauritz Simplicity and elegance through engineering.

Teknav,

I am an engineer/scientist, I walk to work (sometimes talking on a cell phone), I do appreciate the use of fast computers, and I also see the value of learning to use a sextant. I haven't used one in years, but when I did I got a sense of satisfaction from connecting with the traditional roots of ocean navigation. As an engineer/mathematician I also enjoyed practicing and understanding the process of sight reductions. I don't feel compelled to venture out on the sea using celestial navigation as my primary tool for navigation, but I can understand those who do--and also those who want to learn as a backup or just to better appreciate traditional methods. I will certainly brush up my own skills, then teach my son how to navigate with a sextant when we're out cruising. I expect he will gain a better appreciation for GPS from that lesson.

By the way, I also enjoy watching servo-pendulum steering systems operate for hours or days on end (as opposed to electronic autopilots) and appreciate the mechanical elegance of those systems. Likewise I appreciate the beauty and workmanship of well-maintained wooden boats, but I wouldn't want to own one. The list goes on...

[Teknav]

Hiya SV! ++

It should be obvious, by now, that I like flying to my destinations, rather than spending a great deal of time sailing to get there; speed is of essence. I have a limited amount of vacation time; I need to maximize its usefulness!

I used to use a sextant, a stop watch, all kind of tables and a slide rule in the early 70's. A pocket calculator in 1971 that could do 4 simple arithmetic functions cost around $400 USD. As an undergrad, while taking Physical Chemistry, I was spending a considerable amount of time crunching numbers using a rudimentary computer in the Chemistry department. I even used to "punch cards" to write simple programs in FORTRAN IV.

Moving forward...I am not one of those folks who like to dwell on the past. Having endured a slow paced time capsule, I am better off enjoying today's and future technologies. Now, you know why! Take care!

Mauritz
Life's too short!

[highseas]

On a small boat mistakes are easily made using sextant,mostly due to fatigue.Poor visibility also reduces its usefulness.With GPS ,far less likely.If you had to choose one or the other?

[thomm225]

The book Barefoot Navigator by Jack Lagan is quite interesting and knowledge gained from it can be useful if you lose GPS.

The knowledge gained can get you to land. No sextant is involved just knowledge of earth, moon, stars etc............plus wave pattern, clouds over islands and more.

The Barefoot Navigator: Jack Lagan: 9781574092325: Amazon.com: Books

[Bestathook]

If you achieve a thorough understanding of celestial navigation, you will understand almost all of the elements of navigating a boat.

I took a one semester course in celestial navigation 40 years ago but never used celestial per se in cruising. But I have used the various elements of the course to navigate thousands of times, and consider the course time well spent.

Much depends on your boating style. Some see sailing as a race, to be concluded rapidly as possible to achieve a specific goal, or a test of themselves. Others love the sailing process, taking longer than necessary, at times, because they enjoy the process itself. I am sure there other styles as well, and styles involving elements of both.

I don't look forward to the destination. I get great satisfaction from enjoying what I am doing now to the fullest. I'll enjoy the destination when it becomes the present. As Huxley advised, Be here. Be now.

Do what you find makes you happy. I like the slow way too. We are all moving steadily toward a hole in the ground. I am in no great rush to get there.

[Jimbo485]

Originally Posted by C4 King Cobra

My understanding of this discussion is that you want something when all else fails! A sixth grader could be taught the basics of taking and calculating a noon shot. With practice they could plot there position with accuracy. That is all you need to know for a when all else fails system. IMHO

Yes. My son could get long and lat from noon sites when he was 11. Nice skill to have...even if just for basic education.

[thomm225]

Originally Posted by Jimbo485

Yes. My son could get long and lat from noon sites when he was 11. Nice skill to have...even if just for basic education.

Yep, that is an awesome skill to be able to actually get a longitude from a noon siting.