Sextant?

Hi
I'm looking at different sextants, metal and plastic. Is the plastic easier to use because of weight. Or, is the metal one more stable? Someone with experience please post!!
Mike

 

When plastic sextants where first produced they rapidly became known as "throwaway sextants - you take one sight then ditch it!" by the professional Navigators!

Couple of points to add to that,

for accuracy the proper metal (bloody expensive) full blown sextant has no equal, heavy, a joy to use and bloody acurate with the right use!

If your on the bouncing deck of a small vessel using GPS as your main means of deepsea navigation a plastic sextant whilst not as accurate should be able to give you a reasonable degree of accuracy (if the boat and thus horizon is going up and down like a roller coaster you probably won't be able to get much better accuracy anyway) :idea:

plus of course if in the use of this you either bash, bang or otherwise bend the damn thing (includes dropping it over the side) you wont cry so much when you buy a new one!

The other thing is if your new to sextants (good on you for even wanting to try) :idea: why not start with a cheaper plastic sextant to learn with (obviously the best you can buy, but still cheaper than a metal job) then if .......the above applies.

One last thing, IF you DO get a plastic sextant don't ever tell a big ships (Warship OR Merchant) Navigator or Captain / Master you have one! He'll likely wet himself laughing!

But seriously in the firast place I'd go for the plastic job until I have some esperience -I well remember the first time I used one (in college - THEN I was told the price AFTER I put it down, Good job too! nearly did brown stains somwhere!)

best of luck

After taking a sight by sextant (and all the math - especially in my day - log tables and the like!) it was a wnderful feel of achievment, even better as a junior officer when you got a better fix than either The Chief Officer or the Master!!!)

 

Plastic is fine unless you want to do navigation as a hobby and you have extra money to spend. My first trans-Atlantic was with a Davis and I was only 1/2 mile north of Bishop Rock Light when I was aiming to be 1/2 mile south of the light. I now own a Plath among other models but that’s because I get a lot of enjoyment from using it and I can still use the plastic one and get very good results. By all means start with plastic and as your skill improves you can make an informed decision about upgrading later.
Robert Gainer

By the way, a sextant and taffrail log is still my primary means of navigation and my first offshore passage with a GPS was only last November during a trip to Bermuda from VA. My upcoming trip to Greenland will still be done using traditional means.

 

Robert

Whilst I applaud yor infinite skills I fear Columbus, Nelson, Frobisher Magellan and others of that ilk would find you a crazy person! By all means use the traditional means ( I for one mourn their passing) but please carry a modern method for checking and use in case of danger - a prudent navigator uses everything he has and can get - including and especially his brain!

 

Different people enjoy different hobbies. Some people still fly a biplane and in spite of its archaic design consider that great. Some people will climb a mountain “clean” and forgo the use of aid or protection. Others decide to sail rather then use a motorboat because they do not want an engine to intrude into their world. These people do not tell you what’s good or bad about your hobbies and demand that you do it there way.

I am not telling anyone that they should sail in my style or only use a sextant in preference to more modern methods. As a matter of fact I use the best available technology when it’s appropriate but in pursuing my own interests I may use older methods. I design and build traditional boats using wood and mostly traditional methods.

I sail very simply using my own skills without the help of modern technology for some of the same reasons that the Amish still farm and live without the modern conveniences and distractions. Does this make my “crazy”? You say that you mourn the passing of the older skills, well I teach the older skills and practice them as often as I can. You choose your path and I will not criticize you but let me decide how I will lead my own life.
Robert Gainer
Boat Building Program Director
Hudson Fisheries Trust
Beacon, New York
www.fisheriestrust.org

 

Sextant

My worst nightmare realised. I have to agree wholeheartedly with Walrus.
Congratulations on your enthusiasm Mariner 40. Every - repeat - every would-be sailor (excuse the pun) worth his salt should know how to use a sextant, a compass and chronometer - if only for the joy of the exercise. Too many boaties take to the sea relying on Satnav and its ilk...too many boaties get lost and come to grief because the "computer let me down."

As Walrus - in a rare moment of sobriety - suggest: go for a plastic cheapie to begin with, then when you feel happier buy the "real thing." After all who takes driving lessons in a Ferrarri.

 

By God Bergalia if this is sobriety I'm back on the beer! Can't handle the Bergalia being nice to me!

Robert I'm not knocking your lifestyle (you may not think so) you obviously are good at it, unfortunately when a learned person such as yourself states "I do such and such in the old style and it's fantastic" many others without your competance look at this and decide if HE can do it so can I. They then proceed to go ahead and kill themselves (their problem admittingly) this causes some problems to the poor devils that try to rescue them and their families both of who suffer!

Perhaps a better way would be to state "I do such and such in the old way, but I AM AN EXPERT in my field and will use other more modern technical things as back up should I need to!

Remember the Amish do what they do for all their lives which makes them experts in their field (no pun intended), whilst they shun modern ways they do it entirely from birth (though they may leave if they so wish), this is diferent from the guy who does it at weekends only - no matter the action! So please feel free to live your life as you deem fit, just don't ruin anybody elses in the process - a mere statement can accomplish this without you realising it!

 

Hello Guys
I have purchased a used Plath on ebay for the price of a new plastic sextant. My desire to have knowledge of use of a sextant is for backup to GPS system. I do not want to go to sea and the battery die and depend on someone else to bail my *** out!! I want to use both GPS and sextant together to improve my accuracy of in using a sextant. Then and If the GPS goes away, I won't be saying "WHAT NOW" "WHERE AM I"!! If I have learned the proper use of the sextant, I can keep right on. Thanks for the input guys!! Maybe some of you might refference a good instructional book on use. Better yet, maybe some of you old seadogs might want to venture out one day with me to places unvisited!!!
Mike

 

Mariner 40,

Way to go! I learned on a Plath myself. Except I bought it new in Annapolis.

And don't let those wild stories about bouncing boats discourage you, I did my sailing on a 25 foot Contessa . . . and managed to find land every time using only my trusty sextant, a digital watch, and a nautical almanac. Which brings me to the point of this post.

The math for getting a position using stars is tedious, to say the least. Good to know, but tedious. For a start, I would concentrate on the venerable noon sight. This will give you your position in both latitude and longitude quite accurately (within a mile, usually), but is limited to, well, a noon position. It also involves nothing more than a nautical almanac, a chronometer (and a good modern digital watch works pretty well for that) and a sextant. The whole thing takes about 30 minutes. No fancy tables are involved, and the math is a couple of subtractions and a lookup in the almanac. With a small sailboat you aren't going anywhere all that fast anyway.

The other point I would like to make is that even if your chronometer fails you can find your port with your sextant and almanac alone, just like Columbus did. The almanac will tell you how high the sun will get on any given day, and thus the latitude you would be if it was directly overhead. Using the same math as for the noon sight you can therefore determine your latitude directly, even if you don't have a clue about the time. So, like Columbus you sail to the latitude of the port you are trying to find and simply sail East or West as appropriate until you run into it.

That sextant is a wonderful backup to the GPS. Electronics fail, but sextants are quite reliable . . . unless you drop it overboard! I kept a light line tied to mine at all times when I was on deck with it.

Fair winds!

Bill

 

Hello
I have a backup GPS, compass, watch, and leadline. I hope I will never need them but, it's worth the extra for comfort.
Mike

 

Billy you seem to know a lot about Columbus, you wearn't his Yeoman were you by any chance? (actually sextants were not invented in his day) and I bet you found the nearest land every time eh! Straight down!!!

Mike for books on the subject best have a chat with the ancient mariner your side of the pond, one Robert Gainer - he after all will know the in book on your side of the pond (actually as Bill will tell you there's not a lot of difference between methods [unless you use air tables!] but it's best to be talking the same language as the rest of the people in your area! That is if the salty old bugger hasn't gone of in a huff 'cos I popooed his use of gunpowder!

 

Plastic melt and break.......... sometime the marking is....... well for cheap asian version. We always get the reject.

Stick to the metal expensive item........ dont buy one in Indonesia unless u r the one selling it.

 

Walrus,

Lately I've been feeling old enough to have been Columbus's yoeman, but, alas, I never met the man.

And you are definitely right about the sextant not being invented then, in fact, I believe a countryman of yours invented it, one I. Newton. But Mr. Newton's invention was an improvement in the instrument, not the method. Columbus would probably have been quite familiar with the Cross Staff or Back Staff, both of which measure the angle of the sun over the horizon just like a sextant, and darn near as accurately too. Of course you go blind using the Cross Staff, a slight problem.

Bill

 

I started out with instruction from someone that know what he was doing and used the book “Navigation the Easy Way” by Carl Lane and John Montgomery. That book is long out of print and you might try "Common Sense Celestial Navigation" by Schlerith instead. I have read that book and found it very usable. "A popular one is Celestial Navigation for Yachtsmen" by Mary Blewitt. I have not read this one myself but instructors whose opinion I respect very often recommend it. When you read an older book keep in mind that some of the terms are named differently now. Time was measured using GMT and now it is called UT. That means Greenwich Mean Time and Universal Time. For all practical purposes, they are the same thing. If the book is old enough you will see RA instead of HA. This is the change from Right Ascension to Hour Angle. They are not quite the same thing but today’s nautical almanac used GHA, which is Greenwich Hour Angle instead of the term RA, used in astrometry.

Navigation does not have to be complex and the noon sight is about as simple as it gets. You don’t need to know time and all you do is follow the sun as it reaches your local noon and record the greatest altitude. Correct that for dip, refraction, and index error. Subtract that number from 90 degrees and add the sun’s declination that you get from the daily pages in the nautical almanac and you have latitude as accurately as you can read the sextant. The dip is just a correction for the height of your eye above the water and refraction is a correction for the fact that light bends as it goes from one density to another. The air becomes denser as you get closer to the surface of the earth compared to higher up. The index error is how far off the sextant is and you find that by a simple test using the sextant and looking at an object more then 1 mile away. You cannot find your longitude with a noon sight. The sun or any heavenly body during a meridian transit hangs at the same altitude for several moments. This makes it imposable to get the time of the meridian transit unless you are on dry land with very precise equipment. Meridian transit is just the name for the time at which a body crosses your meridian of longitude, otherwise called noon.

Modern inspection tables have removed the need to use trig or log tables unless you are doing this as a hobby. The books Ho. 229 and HO. 249 are the old standbys but HO. 211 is a small booklet that will fit into you sextant case instead of the seven volumes needed by some other methods. The current Nautical Almanac also has a set of sight reduction tables in it that are not hard to use.

Try it and you’ll be surprised at how easy this is and you will get a sense of satisfaction that most other people will never realize. By the way, don’t go offshore and kill yourself. Offshore work after all is reserved for the privileged few who got there experience in mystical ways that are imposable to duplicate today.
Good luck and all the best,
Robert Gainer

 

You guys are getting my interest!

Chop it out - I can't afford a sextant!

Actually a guy just advertised a course on celestial nav using sextant - hoping to get enough students to run a class locally and I was very sorely tempted to go along - but am short on $ and time right now!

Safewalrus... re:

Hey - I believe your likely right, about the invention of the sextant - BUT having said that AND watched the TV show bout the guy who invented the reliable timepiece for vessels (ships chronometer) so that longitude could be reliably determined at sea.. I figured I knew a little bout such things.

A while back I visited one of our matritime museums.., and they have relics from various sunk Dutch east indiamen discovered along our west coast!.

These seemed to have all sunk round Chris Columbus' time - when they would round cape whatever in africa (good hope / horn)?...and sail west on the roaring forties till they sighted good ol Oz and then turn left at alberquerky...and er, well - you get the idea arrive in the nightime and run aground!

Now - this was apparently because they couldn't tell the time.. sounds like my missus when she's getting her war paint on to go out!

BUT - the point of my question is this.

Often one of the relics recovered from such Dutch east indiamen is a round brass instrument graduated with a long needle pivoted in the middle, that is usually referred to as an "astrolabe" and was apparently used in their primitive attempts at navigation??.

So - what was an astrolabe? how'd it work? and how is it different from a sextant?

I'd appreciate the encyclopedia britannica explanation - but would settle for the readers digest version!

Thanks in advance!

Cheers!