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Sextant Tutorial

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also see

viewtopic.php?f=14&t=14140&start=0&hilit=sextant

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Jonathan

Posted: Tue Jun 19, 2007 8:45 am Post subject: Sextant Tutorial

 

Whats the best tutorial you have seen on sextant use.....

 

I want something that is purely table based not palm or PDA, by the time I am relying on Sextant about 5 gps's have failed and I have to assume at this point that all power or electronics have been fried.

 

Peter

 

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dana-tenacity

Posted: Tue Jun 19, 2007 9:06 am

 

Mary Blewitt's little paperback, everything you need, clear and concise and easy to follow.

 

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dana-tenacity

Posted: Tue Jun 19, 2007 9:08 am

 

http://www.amazon.com/Celestial-Navigat ... 0070059284

 

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PaulR

Posted: Tue Jun 19, 2007 9:43 am

 

Fully agree with DT. Mary Blewitt very simple & small enough to fit inside sextant case.

 

Practice at sea or get a tray of water and sit outside in the sun and practice. You will measure "double" the angle. Very easy with the winter sun so low.

 

Tip: put some (cooking / vege) oil on the water, especially if little swirls of wind come round the side of the house.

 

Alternatively at the waters edge on a north facing beach is good as you can have a very small height of eye and the horizion is visable.

 

BTW Mary Para nee Blewitt was a major organiser office person in the RORC in the 1970's, Secretary or Committee member, I recall, but that was more than 2 weeks ago!! .

 

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MuzzaB

Posted: Tue Jun 19, 2007 3:39 pm

 

I also agree re Mary Blewitt's book. A good alternative, if you can find it, and with a Southern Hemisphere spin, is Blue Water Navigation by Craig Coutts. No more than you need to know - and well written.

 

Even with 5 GPS units on board, I hope you'll have a go with the sextant just for the hell of it.

 

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Jonathan

Posted: Tue Jun 19, 2007 3:49 pm

 

I took sights on way back from tonga.

Will practice next wek as well here if the weather clears.

 

I think its a try every day thing.

 

we have main chartplotter/gps which interfaces to autohelm

backup gps only

chartplotter/fishfinder in cockpit

handhold gps in grab bag also great in rib for finding dive sites

and I think at least 2 crew will bring there own handholds......

 

and I have two sextants, one a davis plastic and the other a ziess

will seel the sextant I most dislike on trademe once back.

 

boat books has a copy for me on hold getting it later today.

 

thanks for the advice.

 

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dana-tenacity

Posted: Tue Jun 19, 2007 7:06 pm

 

Sell the Davis, Keep the Zeiss, easy choice.

 

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Knot Me

Posted: Wed Jun 20, 2007 7:19 am

 

dana-tenacity wrote:

Sell the Davis, Keep the Zeiss, easy choice.

 

 

No question. Fully concur. Same with Craigs book.

 

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PaulR

Posted: Wed Jun 20, 2007 9:01 am

 

If you already own both, kepp the Ziess for your "real" navigation and the plastic one for guests, crew etc wanting to have a go.

 

Read somewhere (many years ago) that some people also kept their plastic sextant as backup / in the grab bag.

 

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Jonathan

Posted: Wed Jun 20, 2007 9:11 am

 

Blue Water Navigation by Craig Coutts is out of print according to boat books. got Celestrial Nav. have a handheld gps in grab bag, no space for sextant as well

 

just imagine trying to climb into raft with a huge grab suitcase

 

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MuzzaB

Posted: Wed Jun 20, 2007 3:54 pm

 

Out of interest - my "main" sextant is a 1952 Heath Hezzanith. A heavy brass number that is a pleasure to work with on a rolling deck in a breeze. It's amazing to think that she's now 55 years old and only two owners. (her first owner was a deck officer on merchant ships). Her scope is a very simple 3x and unlit (the Zeiss and Tamiyas are more sophisticated in this regard, but you really only notice the difference for star shots). In other respects she is a beautiful sextant to work with. Even though I will probably never need to use her "in anger" again - I would never sell her. They turn up on EBay these days as collectors items.

 

My "grab bag" sextant is an "Ebco Special" - a cheap plastic sextant I bought new years ago. It's mirrors would need replacing or resilvering now, but it was adequate as a back up. (Note that this sextant is an "it". It doesn't merit the feminine gender of my classic brass sextant).

 

Just wanted to share. I go all mushy and weepy eyed when I talk about my sextants

 

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Jonathan

Posted: Wed Jun 20, 2007 4:11 pm

 

there is a really nice Tamiyas for sale on trademe at the moment, but it is not reaching reserve in last few auction he wanted $1150 for it. auction before he wanted $1500

 

 

http://www.trademe.co.nz/Antiques-colle ... 06.htm?p=5

 

 

looks a good sextant.

 

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PaulR

Posted: Wed Jun 20, 2007 4:37 pm

 

MuzzaB wrote:

... sextant is a 1952 Heath Hezzanith. A heavy brass number that is a pleasure to work with on a rolling deck in a breeze... now 55 years old and only two owners. (her first owner was a deck officer on merchant ships)... In other respects she is a beautiful sextant to work with. Even though I will probably never need to use her "in anger" again - I would never sell her.

 

My "grab bag" sextant is an "Ebco Special" - a cheap plastic sextant I bought new years ago. It's mirrors would need replacing or resilvering now, but it was adequate as a back up. (Note that this sextant is an "it". It doesn't merit the feminine gender of my classic brass sextant).

 

Just wanted to share. I go all mushy and weepy eyed when I talk about my sextants

 

 

My sextant is a C. Plath LIGHTWEIGHT alloy also of same age and heritage ex deck officer and also only 2 owners same as Muzza.

 

The advantage of the lightweight version is that it is 1.5kgs "lighter" than the brass versions, so its easier to handle and get up/down from near mast etc. when in use especially for stars and in the rough. Just try using your sextant with an extra 1.5kgs weight for say 15 mins and then remove the weight and note the difference, Climbing up & down off saw horses is a useful land based test comparision!!

 

Also has zero manufacturing errors, zero index & zero side errors, with built in light and x8 telescope. the plastic sextant case is designed to be mounted on board and has a really good lock in clamp for quick stowage.

 

Even used a lot in coastal races for Vertical angles e,g, Syd-Hobart, Fasnets etc.

 

A treasured gem!!

 

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Knot Me

Posted: Wed Jun 20, 2007 5:58 pm

 

I've got a Alpha 40. Made for the chinese navy, full sized and in alloy. The lighter weight is magnificent. A telescope the size you can see the next galaxy with, lights, no errors and all the required bits yet while being very simple. A serious pleasure to use.

 

Last trip pulled it out and ran parallel nav to the gps. Missed Nth Cape by only 10mls, I'm happy yet slightly surprised I remembered enough to use it

 

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dana-tenacity

Posted: Wed Jun 20, 2007 6:07 pm

 

Zeiss Yachtmaster I got for my 21st birthday a mere 30 years ago from transpac marine.

 

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pwederell

Posted: Wed Jun 20, 2007 6:12 pm

 

I struggle with the necessity of having a sextant or GPS in the grab bag. You're at the mercy of the sea in a Cat 1 liferaft and can't go anywhere you want & I'm sure your recuers will be able to tell you where you are when they pick you up. EPIRB is cheaper and easier to use.

BTW I have a Davis plastic model, learnt to use it in below freezing conditions and was happy with it's accuracy. Even calibrated it next to an electronic sextant gizmo on a Herc aircraft and it was spot on.

 

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David Lackey

Posted: Wed Jun 20, 2007 10:10 pm

 

If you are buying second hand avoid vernier scales - found on many pre 1960's sextants. Hard work. Degrees/minutes is what you want.

 

Tamiya excellent - the Lexus of sextants. If you can pick up a Tamiya Astro Nav calculator with the post 2000 tables in it you will have a great deal of fun. You need to know your way around the tables first, then put them away and , hopefully, never open them again. There is, of course, computer software which does the same thing but the beauty of the calculator is that you can put in a ziplock bag and keep it dry and have it instantly available.

 

I have a cast iron stomache until I start reducing sights. The Calculator allows you to bang off a whole batch of sights, and reduce half a dozen of them in no time at all, before the puke factor intervenes.

 

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MuzzaB

Posted: Thu Jun 21, 2007 2:39 am

 

Quote:

I have a cast iron stomache until I start reducing sights.

 

 

I know that feeling. I used to wedge myself into the nav station with a bucket!

 

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