: Sextant


striblue
11-29-2007, 01:01 PM
My new Davis 25 sextant came today and I am excited about learning how to use it. Obviously I will bring it on board when out with friends since I have no boat...yet ... to learn how it works . I have always wanted to do that. It will go with a new celestron telescope I now have down in Chatham which has a motor driven declination etc.... Despite the GPS technology how many boat owners carry a sextant with them...just curious. I suspect there use is for greater distances off shore, but I was just wondering.

Smcdermott
11-29-2007, 02:33 PM
Definitely a cool thing to know but on small boats I don't see much use in reality.

On my boat I have GPS (boat and handheld backup), paper charts and compass. I also have marine VHF (handheld and fixed) and personal location beacon. I think you would need to be pretty far offshore to use a sextant as taking a rough heading in my boat should get you within sight of land and familiar landmarks.

Sean

josko
11-29-2007, 02:43 PM
Celestial navigation is a great hobby but it's not practical for actually navigating, especially a small boat. Learning sight reduction techniques is hard enough - doing them aboard a small boat is for those tougher than me.

Still, try standing on a beach, doing some rudimentary sightings and going through the math yourself. For a graduate level treat, get a book on early Polynesian navigation methods and try to piece it together for yourself. Remember, they had no knowledge of compass, no north star, and still managed to hit a 1 mile island dead-on after 2000+ miles of sailing.
If you're starting from scratch, Bowditch http://www.irbs.com/bowditch/ is worth reading.

jfbasser
11-29-2007, 02:49 PM
My new Davis 25 sextant came today and I am excited about learning how to use it. Obviously I will bring it on board when out with friends since I have no boat...yet ... to learn how it works . I have always wanted to do that. It will go with a new celestron telescope I now have down in Chatham which has a motor driven declination etc.... Despite the GPS technology how many boat owners carry a sextant with them...just curious. I suspect there use is for greater distances off shore, but I was just wondering.

Modern cruise ships have the best electronics in the world with all types of backups, but still carry a sextant. The use of a sextant gives you a perspective on navigation fundamentals, orienteering, and the solar system that you cannot get any other way....enjoy it!..when my radio navigation work bores me I take out the sextant and some sight reduction tables.Remember that on 2 days of the year you can determine your Latitude directly without the use of a chronometer.

vtloon
11-29-2007, 03:03 PM
John, Celestial Nav is a challenging but fascinating way to get it done. Your sextant will require some other support tools: a precise chronometer and the almanacs (these days that can mean an atomic clock and a celestial nav calculator. Then, charts and a table or flat surface for plotting. Taking sights (even your noon sun sight) from a small boat is usually pretty difficult, but it can be done. A good winter read would be "Mariner's Celestial Navigation", Capt. W.P. Crawford. Let me know if you can't get it locally.

Best backup for GPS: a good set of charts, compass and an RDF for when the fog sets in.

Rip Ryder
11-29-2007, 04:10 PM
John,

You can look into a class on that at Mass Maritime Academy in their weekend classes they have for the general public. Go to their website and look up the schedule or you may also be able to get a class at New England Maritime in Hyannis. Again, check their webpage.

Personally, I have never used one.

Capt Keith

striblue
11-29-2007, 04:59 PM
Thanks Guys for that input. I have also read that a small pocket sextant can also be used when on dry land with the use of the artificial horizon block, providing the sun is out and you can then calculate both longitude and latitude by doing the readings on the local noon meridian passage. I will follow up on all this just to know about it and how to do it. Latitude will require tables, etc....something else to learn whether I use it or not. I know that the GPS does the job, but the history Josko mentions and a book I read on latitude and longitude and the determination of GMT and the difficulties the early voyagers had with determining latitude is interesting to me.

jimS
11-29-2007, 05:14 PM
John, I admire your retro/brain teasing approach to navigating to distant shores. I too am curious about things I don't understand, but if there is math involved, I'm all thumbs.

Now, if your long range plan is to circumnavigate the globe for purely fishing purposes, I'll volunteer, and defer to others for the techy type challenges. I'm really a good salad maker.

Penguin is, I presume, penning a post on this topic. Since he is a pilot/captain, and you are the navigator, the obvious name for the boat would be...

Penguin
11-29-2007, 06:25 PM
So...Dead reconning of sorts...
Destination Otis ANGB and your navigator is Major Roger Peltier...:eek:
You're somewhere over the Atlantic heading west...
28,000' & 350mph...
Landfall...
You see glaciers and icebergs...turn left!
You see palm trees and sandy beaches/bicinis...turn right!
Follow the coast until you see Otis!:roll:
John...JUST KIDDING!:razz:

Good on you!
The sextant shot is an almost lost art...GPS is like the meteor that doomed the T-Rex!
My navigator had one in my C-130 and it was a pisser to use...'always a sigh of relief when we would hit MidWay or Johnson Island but it works if done properly.
You'll need the special tables and logs and a suspected location to get you in the ballpark and going...Soundz like a fun project on your back deck in July!:D

Ooops!
What's that?!:confused:
A car just drove past the house...'better go check it out!:Eyecrazy:

striblue
11-29-2007, 06:52 PM
Thanks Pete... I can simply start taking readings at certain locations, even on the beach and then compare to what I come up with by checking my Handheld GPS to see how acurate I can be, But I know I will need tables.... and have a good watch (Rolex Submariner).... so this will be a good start.

Paxton
11-29-2007, 08:35 PM
John.....you just made it official.....fishing season is over and winter is near :)
Seriously......I give you credit in your pursuit of this interest.....lost arts are always a valued find.
I just may dedicate my winter to trying to figure out how Stonehenge was built and why....God knows I will be more successful doing that than I was fishing the fall migration :)
Ron

gordonh
11-30-2007, 12:08 PM
Davis offers a "lifeboat sextant" that is considerably less sophisticated than the one John bought, but it's only $39. I bought one of these to learn a little, and for me that's probably good enough. I think you can get to within a few miles with the cheapie and probably within a mile or so with John's, but I haven't gotten into it far enough yet. You certainly can develop a lot of respect for traditional navigators quickly by fooling around with a sextant!

The cheap unit isn't bad for figuring out whether the tree you are about to cut down will miss the house or not, might be worth $39 for that alone.

RayStachelek
11-30-2007, 01:17 PM
josko Celestial navigation is a great hobby but it's not practical for actually navigating, especially a small boat. Learning sight reduction techniques is hard enough - doing them aboard a small boat is for those tougher than me.


Josko said it well. Want something simple and hit it dead nuts even in a fog.

What do birds use and they have tiny brains at that ?

striblue
11-30-2007, 01:41 PM
Ray, what are you talking about? Birds? I did not follow what you are saying:confused:

FishHawk
12-01-2007, 07:11 AM
Electronics are great until the batteries go dead. I always have a compass in my pack just in case. Ray the birds have micro sextants built into their brains.
FishHawk

striblue
12-01-2007, 10:13 AM
Bill, I know the Birds have that instinct..I guess the use of the sextant is how we would do as the birds do. I just ddn't understand how we would do as the birds do.... without it.

Penguin
12-01-2007, 01:14 PM
John...
You shoulda' $pent a little more for the new and improved personal just-behind-the-ear...
ON-STAR IMPLANT !!! :razz: :hihi:

flydoc
12-01-2007, 03:16 PM
Pete- he called the company to inquire about getting one...unfortunately John didn't meet the memory requirements for their chip:lildevl:
Flydoc

striblue
12-01-2007, 04:22 PM
Jim, your just saying that because I forgot the reason I went to the place to get the implant in the first place. Thanks for reminding me. Now I will have to get rid of the sextant.:hihi:

flydoc
12-01-2007, 06:07 PM
John- just remember you'll have to pay a bit extra to get the augmented memory implant- and that they recommended you watch the Keanu Reeves movie "Johnny Mnemonic" for details on the procedure:whoa:
Flydoc