sextant??

[Tamboo]

So, sextants cost HOW MUCH!!

Anyone tried out this simple KISS sextant yet for a bit of fun?  ;)

http://www.tecepe.com.br/nav/CDSextantProject.htm

[TJim]

There is a Davis plastic sextant on ebay right now.  It'll get you close enough if you ain't laying a minefield... probably go for $25 to $35... Tjim

[Bill NH]

The Davis plastic sextants are passable as long as you don't leave them in the sun and let them warp...  For most people using them as a navigational backup or for learning, the error in a plastic sextant will be less than the human error from lack of practice and experience anyways...

People often don't realize that celestial navigation is an art as well as a science.  Learning to use an almanac and doing the math to reduce the sights is easy -  the calculations are either right or wrong, and very straightforward once you learn how to do them.  It's the actual physical observation that's the tricky part, and that just takes lots of practice.  Learning to deal with the motion of your ship, the sun poking in and out of the clouds, finding the max altitude at local noon, getting a round of evening stars between when the stars show up and the horizon disappears into dark...  this is where the art comes in.  An old mentor once told me that celestial navigation is exponential - the same increase in accuracy that you see after 10 sights will take you 100 sights to do again, and to make your fixes even more accurate by that same amount will take you 1000 sights.

If celestial nav is something you plan to put the time into learning though, a decent metal sextant is a worthwhile investment.  You don't need a new, several thousand dollar model - a few hundred dollars can get a good quality used sextant if you look around.  You'll appreciate the solid feel as opposed to the flimsy light plastic (steadier when observing) and increased accuracy of the observation itself (better optics, finer tolerances, less wear over time and better dimensional stability).  Once you've used a good sextant it's hard to go back!  (like so many things, isn't it?)    ;)

[Captain Smollett]

The Davis plastic sextants are passable as long as you don't leave them in the sun and let them warp...  For most people using them as a navigational backup or for learning, the error in a plastic sextant will be less than the human error from lack of practice and experience anyways...

Agreed.  I have a Davis plastic sextant and it has been a great learning tool.  I've gotten numerous dry land sites within 2 miles of a known position.  At sea I need more practice.   ;)

getting a round of evening stars between when the stars show up and the horizon disappears into dark...

I've read, and have found with my own (admittedly limited) experience that taking star sites is actually far easier in the morning.  Your eyes are night-adapted and you are picking up a bright spot on a dark background (both the star and the horizon), rather than picking up a more-or-less bright spot on a light-but-getting-darker background with light adapted vision. 

If celestial nav is something you plan to put the time into learning though, a decent metal sextant is a worthwhile investment.

I did not want to poo-poo this CD sextant idea outright, but I am wondering what the accuracy will be - short arc, vernier  with 20' increments, plastic body and mirror mounts...  In short, if the instrument is inaccurate, one just learning might well get discourged.  I've run into that with my plastic Davis.  It is not a bad instrument if you know it's limits and take care to account for them (the biggie is to measure IE for each shot).  But, if you forge ahead without the extra care and get poor readings, you can well assume taking good sights is impossible.

[Tamboo]

If celestial nav is something you plan to put the time into learning though, a decent metal sextant is a worthwhile investment.

I did not want to poo-poo this CD sextant idea outright, but I am wondering what the accuracy will be - short arc, vernier  with 20' increments, plastic body and mirror mounts...  In short, if the instrument is inaccurate, one just learning might well get discourged. 

Hey guys, this sextant (and the octant) were just a couple of things I stumbled across and knowing there are quite a few Sailfar'ers into their celestial navigation, as per the original post I just wondered had "Anyone tried out this simple KISS sextant yet for a bit of fun?"[/color].

Yes, the accuracy is always going to be very much a case of 'thereabouts' rather than 'there', but it would be interesting to know the results if anyone tries it.

Although I'm a bit rusty around the gills, in times past I was a professional navigator so the art of celestial navigation pre gps/sat nav is not alien to me and if you are going to seriously undertake this art then a decent metal sextant is the way to go.

[RadioRay]

Google the "Bris mini sextant".  It was developed by Sven Yrvind of VERY small boat fame.  It is a simple to build, fixed angle(s) sextant which is so simple, once you see it, you'll want to build a few just for fun.  I bought a pack o 74 microscope slides from Edmund Scientific  for under five dollars and can probably make several dozens of dozens of these mini sextants for that price.  I find that it works very reliably and is a fun idea for just playing with celnav and/or in your ditch kit. Even without taking a day to calibrate it, assuming that you have an almanac (or can approximate the offset from GMT noon passage)you could easily determine LAN from averaging a few before and after noon sights - to get your LAN and longitude - no calibrated device needed. That's cool.

This again is for measuring fixed angles, so you wait until the object you are viewing presents a reflection on the horizon, then HACK! take the time from your watch and work backward through the tables.


Not bad for a few pieces of glass and adhesive.


>RadioRay ..._ ._
s/c Milenka
near Irvington, Virginia - USA

[Tim]

Very Cool, and Welcome to Sail-Far!

Tim

[RadioRay]

Thank You Tim,

Nice to be here!  I've been a long time reader, and should be posting more. It is enjoyable and a good learning experience to be reading about 'my kind of boats' and especially about those who sail them.

---

An update on the Bris mini-sextant project here.  Per Sven Yrvind's notes, I ordered 'beam splitter glass' from Edmund Scientific.  Making these mini sextants using the beam splitter is a significant improvement in the quality of the reflections seen in the instrument.  My 5x6" piece of this precision beam splitter glass cost roughly $14USD and I can likely make 10-12 sextants from the amount provided. The only significant difference between Mr. Yrvind's original design and mine, is that I've fully enclosed the sides of my unit with epoxy and fiberglass board (printed circuit board material) so that the inner glass surfaces are fully sealed against seawater, dust etc.

I would highly recommend anyone who already enjoys a working knowledge of the basics of celnav and has a horizon to look at, build some of these, either using the very inexpensive microscope slides, or the much nicer beam splitter glass. I could easily see this included in David Burch's "Emergency Navigation" - rev. 2 that just came out. If a sailor is at all handy (and most sailors ARE...) it would be easy to produce very accurate noon sites and more with odd bits of window glass formed into a Bris mini-sextant. This also works for the moon as well.


RadioRay ..._ ._
s/v Milenka
nr. Weems, Virginia - USA

[OptiMystic]

You got me interested enough to look.

Here: http://www.yrvind.com/various.html

you can find the info. At the bottom of the page are two small page pictures which take you to full size ones (scans of an article, I think) with fairly complete instructions. Biggest limitation seems to be that it is for the sun and only the sun, but for the size and cost, that isn't so bad.

[Shipscarver]

Gee, do you think it was called,

the "Bris mini sextant"

because they clipped the Arc too short?

[chris2998]

so where can I buy a sextant is there anything online that sell one. I want to say cheap but that is impossible to find a cheap one to learn on i bet.
so anyone know of websites I can check out?

[CapnK]

Chris -

The Davis Mark 3 is what you are looking for. Cheap, functional - some people have actually used them as primaries during their circumnavigations...

Here's one at Defender.com :

http://www.defender.com/product.jsp?path=-1|17|6626&id=83267

[chris2998]

Thanks i was wondering should I buy an L-cheapo now and then buy a better later or what. I could swing maybe 250 for a metal one but seems like the cheapest I seen was like 572 for a metal one I think it was called a Astra.

Thanks
Chris

[AdriftAtSea]

Unfortunately, a new metal sextant is going to be expensive.  The plastic Davis ones are great, provided you don't leave them out in the sun and have them warp. :) Good as an emergency sextant too.

[Oldrig]

Chris,

You've probably already checked out the Celestaire web site:

www.celestaire.com

This company offers a wide variety of new sextants, some of them top-of-the-line.

You might also look on eBay. I've seen some good-looking (haven't bought any), older, used sextants. But on eBay you'll also find a lot of Indian-made "reproduction" instruments that probably look great as cocktail-table ornaments, but won't work under maritime conditions.

You might also check with various instrument companies, such as Robert E. White Instruments,
[url]www.robertwhite.com[/url)]
--but they'll be very expensive. You might want to find an older sextant and get it reconditioned by somebody like White. I assume that most major seaports have such companies. White was in Boston for many years (the mailing address for the internet company is in the southwest suburbs), but I'm sure places like Baltimore, Annapolis, and other places have similar companies.

My own sextant, which I've owned for more than 40 years (and never used at sea, I regret to say) was built in London by Heath and Company in 1904. I mentioned this instrument once to Ridge White, the current owner of Robt. White, and he suggested I not bother to use it at sea--but, darn it, sailors used vernier-gauge sextants for centuries.

The key to using a sextant is practice, practice, practice. Trying to bring a star to the horizon in a small boat must be one of the trickiest aspects of celestial navigation. In fact, I can't imagine trying to do so on my 25-footer.

I bought my Heath sextant after my celestial navigation class while in college. The university was forcing the instructor to retire, and depleting its inventory of teaching instruments. It seemed like a bargain at the time, but it looks like you can find used vernier sextants (much harder to use than modern micrometer instruments) for a few hundred dollars. I paid $125 for my sextant (in 1967 dollars) and found one online for only slightly more than that (in 2005 dollars, of course).

Anyway, good luck.

--Joe

[chris2998]

yes I have heard of celestaire that was the website I seen the astra sextant on.

Joe do you know of any good books that teach you about useing a sextant? This sextant here http://www.defender.com/product.jsp?path=-1|17|6626&id=83267 says it comes with a book but usually there is a book out there that goes more into detail your know?

Chris

[Oldrig]

Chris,

There are a number of textbooks with worksheets out there, and there is at least one UK-based company that offers highly regarded online courses in celestial navigation.

I just looked up the book that I have, and a rewritten version is still available here for under $11 bucks:

http://www.mdnautical.com/cmcn.htm

This was the course written by my navigation teacher, the late Frances W. Wright, in 1969 and revised in 1982. There are certainly many more courses out there. Celestaire sells a bunch and there is that British website. (I thought I had bookmarked it, but apparently not.)

I think the US Power Squadron gives courses in celestial navigation, too.

The most important thing is to practice. There are navigational computers, roughly the size of pocket calculators, that can do all the math for you, but it still makes sense to learn how to do the math, which isn't all that difficult if you have an almanac and the right forms.

But sextant use is--if I remember correctly--as much an art as a science. I haven't practiced it in years.

I'm sure there are people on this board with REAL experience at celestial navigation, and they can probably give you better leads.

Once again, best of luck in your quest.

--Joe

[mrbill]

There are always sextants available on ebay...I bought my Davis there.

And don't let anyone tell you these plastic sextants are just toys or only good as a backup or just for learning. I routinely get my position to within 1 Nm or less. I wouldn't bother buying an expensive metal sextant.

[chris2998]

Thanks guys I'll have to order this plastic one for sure then

[Bill NH]

Get a plastic sextant to start learning.  However, know that the optics are c**p and they are dimensionally unstable.  MrBill, if you're consistently within 1 nm with a Davis I'm very impressed.  On a moving small boat that's hard with any instrument.

We use the Davis Mk15 and MK 25 as teaching sextants because they get used (and abused) by many students.  They are the better of the plastic sextants.  The MK3 is a practice or backup sextant, period.  Far inferior to even the MK15 and MK25.   

With sextants, as with many things in this world, you get what you pay for.  For yacht use I'd highly recommend the Tamaya Venus model.  It's 7/8 size and correspondingly lighter.  The smaller size stows easily and the weight is good on a moving boat.  I used to own one and wish I still had it - I sold it when I switched to commercial ships from schooner sailing...

The one I kept is a C. Plath (Hamburg,1960s) with both a high power scope for the sun and a lesser magnification star scope.  On a bigger, more stable vessel it can't be beat.  With the sun scope its like setting a basketball on the horizon!  I did use it on a delivery to the Marquesas and Tahiti on a 38 footer (without electronics), but my preference would be for the Tamaya Venus for SailFar size boats.  Another good 7/8 sextant is the Frieberger Yacht Sextant (also German) which is a bit less expensive. 

Both of these come available on eBay periodically.  However, make sure you have the option to have it checked out and return it if it is other than as advertised.  I can highly recommend Robert E. White in Boston for sextant sales and service, ask for Ridge White if you call.  I've both bought sextants and had them maintained by them.  Incredible personal service.  They also stock used sextants that they have gone through and made sure are in proper adjustment.

But back to the original question.  Get any sextant and start practicing.  Celestial navigation is both a science and an art.  The science is in the calculations, but the art is in using the sextant itself.  Calculations are either done correctly or not, and once you learn how to do them you can't get any better at it.  However, the learning curve is in actually using the sextant.  Fortunately you can improve rapidly at first, but it takes progressively more and more shots to continue to improve.  One of my early mentors once told me that the improvement I'd seen in my first 10 sights would take another 100 sights to replicate, and to do the same again would take 1000.  I'm not sure if its that extreme, but the message is that you can get passably good pretty easily, but it will take lots of time and practice to get really good. 

So get something and get out and start learning.  When you're ready for an expensive metal sextant you'll know it, just like a beginner taking guitar lessons who eventually realizes that he wants a better guitar.  Meanwhile, you haven't tied up your cash in an expensive instrument until you need to.