Sextant Use

[barnakiel]

Originally Posted by SvenG

Thanks for all the great responses.

I'm heartened by how many still know how to use and occasionally do use a sextant. In the age of the GPS it might seem like an anachronism but one good lightning strike is all that lies between a usable GPS and none.

Now I have to become one of those who know how to use one



-Sven

Well. We can also read the course from the GPS and yet most boats hold on to the 'primitive' magnetic compass!

I think any serious offshore skipper will try to know / have as many ways of getting their position fixed as possible, and sextant is one such method.

Good luck with your training. I am sure you will love it!

b.

[S/V Alchemy]

Originally Posted by Maren

Well, I've never had a TV on board so there wasn't all that much else to do.

Strangely, this is part of my logic for when we go offshore. Because for reasons of safety, amp draw and culture, I want to keep "movie night" as a privilege, not a habit, there really won't be a vast amount of screen time happening aboard. Sextant use/practice is, like splicing or other ropework, a diverting and semi-complex task that we can do as a family, and which keeps us in the proper groove of watch-keeping.

Beats Sudoku, anyway.

[barnakiel]

It is also like being able to scull.

Except I am meeting more and more 'sailors' who cannot, actually, row.

b.

[Benz]

When I was really trying to NOT use the gps on multiday passages, which meant I was taking at least four rounds of shots per day, it got to where I could count on about a mile of accuracy. Whenever I checked against the GPS, which I didn't do often as I wanted to go all celestial. Managed two major passages with all celestial, caved in on others and consulted the machine, usually in the midst of a squall when I suspected reefs nearby, all to find that I could have trusted my sights. Point being, practice makes perfect, and by practice I mean taking heaps and heaps of shots at every opportunity. Tedious sometimes, but it's like playing the piano: you bang away discordantly for years before you can play Mozart. But when you can, it's wonderful.

[sneuman]

Originally Posted by SvenG

We just got a sextant to back up the GPS as we get ready to head out in about 6-8 months.

I'm sure the Astra III B is more accurate than our sightings will be on a 39' sloop, but that's better than the other way around.

While I got a sextant crash course from a sailing professor in the 70s and I have a few of the current sextant books, I'd appreciate some first hand experiences.

First of all, what do you use for a time piece ? A radio signal and stop watch or something else ?

Second, what is your honest assessment of how good your fixes are, lat and long (and what size boat are you on) ? I'm looking for numbers to shoot for with practice, not a competition.

Thanks,




-Sven

Timepiece = $10 quartz from K-mart.
10-12nm from actual position isn't bad for accuracy, I understand (only having recently taken up the sport of celestial myself). As they say "you're looking for a landmass, not a harbor entrance."

A couple of tips I found useful: I removed the wristband and velcro'd the watch to the main arm on the quadrant (making sure to place it so that it doesn't disrupt the swing). I also rubber-band a sheet of paper around the handle. That way, your timepiece and sight record are both on the sextant itself -- no need to go fumbling and forget the time. It's a big help when your working solo.

One more. If you're in cell-phone range, you can get the WWV timetick by dialing: 303-499-7111

[Benz]

I forgot to mention, last post but one: boat was a 27 Irwin, pretty bouncy sometimes, but still with practice accuracy can be pretty good. Usually I was looking for a harbor entrance.

[SkiprJohn]

Aloha Sven,
My favorite instructional aid is Celestial Navigation by H. O. 249 by John E. Milligan. I read it often and it makes sense. It has a really simple explanation of how to do sun sights.
kind regards,

[SvenG]

Originally Posted by SkiprJohn

My favorite instructional aid is Celestial Navigation by H. O. 249 by John E. Milligan.

Just added it to my Amazon list

Thanks,



-Sven

[barnakiel]

Originally Posted by SkiprJohn

Aloha Sven,
My favorite instructional aid is Celestial Navigation by H. O. 249 by John E. Milligan. I read it often and it makes sense. It has a really simple explanation of how to do sun sights.
kind regards,

This book:

Amazon.com: The Complete On-Board Celestial Navigator, 2007-2011 Edition: Everything But the Sextant (9780071485692): George Bennett: Books

I started using only after our big trip. I love it - it has the almanac, sight reduction tables and examples to learn from and an extended but not too much extended introduction to celestial navigation and sextant. Accuracy is less (than with NO249), simplicity is more - to me the best thing since sliced bread.

Have a look at it in your shop. You might like it too.

b.

[barnakiel]

Originally Posted by sneuman

(...)

That way, your timepiece and sight record are both on the sextant itself -- no need to go fumbling and forget the time.

(..)

Grab a stopwatch and start it at an even minute of your timepiece. Take note of the time.

Go to the deck, take the sight and stop the watch when you have the sight. Add the stopwatch time to the timepiece time. You can deduct 2 secs if you are an accuracy freak.

b.

[barnakiel]

Originally Posted by Benz

(...) it got to where I could count on about a mile of accuracy (...)

You were very lucky to get this close.

And even more lucky not to work under scrutiny of experts ... ;-). Read on.

Years ago when I was a cadet we were tortured by deck officers and by my supervisor (who was a proper merchant navy master) to shoot countless series of sights. We were young, sharp-sighted and ambitious. We were shooting from a high deck of a big ship.

And yet, the best I can remember I ever got to was like within about 2 Nm from our actual position. One of us got as close as 1.5 mile but his achievement was rejected and labeled as ... an error.

barnie

[Mark Johnson]

Sven,
It is great that you have the discipline to maintain the skills! We carry several battery operated spare GPSes instead, in separate areas of the boat. Some are wrapped in an inch of aluminum foil, as a "wishful thinking" hedge against an inducted lightning charge.

Our guess is that damage to ALL of them at once, is as unlikely as the sextant being badly bumped or dropped, but that may be laziness leading to rationalizing on our part...

I would suggest that the sextant as a backup is a great move, IF you get a fix every week or two to maintain the skills. It is not like riding a bicycle. I still know how to do that!

My hat's off to ya... M.

[kefroeschner]

And yet, the best I can remember I ever got to was like within about 2 Nm from our actual position. One of us got as close as 1.5 mile but his achievement was rejected and labeled as ... an error.

So, barnakiel, given that this was 'years ago,' before GPS I assume, how do you know were 2NM off and not them?

Yeah, I know, they had more stripes.

[gjordan]

I would suggest that you NOT learn to do a noon sight. I know that sounds like blasphamy to the start up navigators . I saw too many people that once they learned to do a noon sight , they never went any farther. A noon sight is one of the more difficult sights to get any accuracy on, and if you have a few minutes of cloud cover at the wrong time, you are out of luck for another 24 hours. Once you know how to do a proper LOP, you have the basic for the rest of the joy of celestial nav. Star sights only take a couple of more steps than sun sights, and are not any more difficult (if you have a scope on your sextant) and planets and moon are just a small variation of stars. One of the nice things is to do a sunsight and a moon sight for an actual fix during daylight hours. Yes, the moon is available during the daytime for about 1/3 of the month. I tried star sights with a Davis lifeboat sextant, and could not get any sort of clarity of the horizon. I used an English EBBCO plastic sextant for about 12 thousand miles, and it worked fine with its 3 power scope. As far as time went, I used a Radio Shack Time Cube, and a stop watch. With the wife taking times and recording my readings, I could take a round of 3 stars, 3 shots each during evening twilight. I know that was overkill, but it (Mexico to Marquesas) was my first long passage. A year later, going from the Tuamotus to Hawaii, I took a shot every other day until we got close. I eventually baught a nice 3/4 size Tamaya at about the same time as GPS was becoming affordable, and I have only used it a few times. I need to relearn it all, but I will be up to speed before I go off shore again. I like electronics, but I have no faith in it. ____My 2 cents worth. ______Grant.

[goboatingnow]

I find unless I average several shots. I get about 5-8 nM on noon sights. That's improves to,under 5nm. Rarely get much lower then that

Dave