Sextant and finding out where you aren't - Page 5 - SailNet Community
Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.

 13Likes
Reply
 
LinkBack Thread Tools
post #41 of 69 Old 01-06-2016
Senior Member
 
Join Date: Jan 2003
Location: Martinique
Posts: 463
Thanks: 6
Thanked 0 Times in 0 Posts
Rep Power: 17
 
Re: Sextant and finding out where you aren't

Quote:
Originally Posted by cb32863 View Post
I have never seen one cheaper in price than this one and it is far north of $100. I have this one myself and it is good for learning.

Davis Master Sextant Mark 15
The 25 is perhaps a bit better, but a perfectly fine instrument for practicing the craft.
sneuman is offline  
Sponsored Links
Advertisement
 
post #42 of 69 Old 01-06-2016
Senior Member
 
jackdale's Avatar
 
Join Date: Dec 2008
Location: Calgary, AB, Canada
Posts: 9,378
Thanks: 36
Thanked 78 Times in 73 Posts
Rep Power: 11
 
Re: Sextant and finding out where you aren't

Quote:
Originally Posted by Uricanejack View Post
There are several unfortunately I don't know which ones to recommend. I do have a good little book
The Marine Sextant from a second hand book store it was printed about 50 years ago.

There is a British sailing journalist Tom Cuncliff. His books have a good rep. You tube have a film of him and a sextant.

On line is a mystery to me.
Cunliffe has a excellent book, although I found a typo on page 42 of my edition. That made for some frustration until I figured out that "page 35" should be "page 38."

He does not waste words, you have to read everyone of them.

__________________
ISPA Yachtmaster Ocean Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline  
post #43 of 69 Old 01-07-2016
Master Mariner
 
capta's Avatar
 
Join Date: Jun 2011
Location: somewhere south of civilization
Posts: 7,043
Thanks: 135
Thanked 370 Times in 358 Posts
Rep Power: 9
 
Re: Sextant and finding out where you aren't

Quote:
Originally Posted by sailorseb View Post
I am extremely interested in learning this ability and honing it once I do. I haven't purchased a functional sextant yet but it I'd most definitely on my wish list!
Kindergarten of celestial navigation: Revisited [Joseph Sellar] is way easy. Mary Blewitt really blew it, IMO.
As for flying with a sextant, I'd never, ever check a real sextant. Even in it's wooden case it would not be safe from damage that could make it useless, if not dangerous. It is a fine instrument but quite fragile. Knock the mirrors out of alignment and you'd better not NEED your sextant. Remember, 4 seconds error in time can be a mile off in navigation, so imagine what an unknown error in the sextant could do.

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

facebook.com/svskippingstone
capta is online now  
post #44 of 69 Old 01-24-2016
Senior Member
 
skygazer's Avatar
 
Join Date: Sep 2011
Location: western Maine
Posts: 586
Thanks: 26
Thanked 16 Times in 14 Posts
Rep Power: 8
 
Re: Sextant and finding out where you aren't

Quote:
Originally Posted by sneuman View Post
The 25 is perhaps a bit better, but a perfectly fine instrument for practicing the craft.
I believe the Mk 25 is simply the Mk15 with a lighted scale and a so called "full horizon mirror", a misnomer in my opinion for a mirror I would prefer to NOT have. The half silvering reduces transmitted light.

The lighted scale is of questionable value. I find I need a red flashlight to look at the time and preserve my night vision, the scale is locked while you look at the time and you can read it after with no hurry. A white light on the scale will reduce your night vision. My NIB metal sextant has a lighted feature but I have not even considered using it. Perhaps if I install a red LED I might try it, but really do not see an advantage. I am however new at this business. Your experience may vary from mine.

Personally, I'm considering getting the Mk3 cheapo. Why? Because given the limitations of plastic (high thermal expansion/contraction rates, general slop) I believe I could get similar accuracy in a more compact, flatter, more robust package suitable for ditch bag or spare, not requiring the largish box of the more complex models. The cheap plastic scopes (15/25)are not that useful, plastic optics add little. Magnification while good in a larger boat is not helpful in a lifeboat, good metal sextants often come with simple sight tubes - no optics. The vernier scale will provide similar accuracy to the vulnerable plastic micrometer scale of the 15.25.

The worst feature of these instruments is the soft easy shifting of the mirror alignments, requiring recalibrating for each sighting. I'm considering something thick like heavy cosmoline to slow the movement. Good practice though to lose your fear of adjusting the mirrors.
skygazer is offline  
post #45 of 69 Old 01-24-2016
Junior Member
 
Join Date: Dec 2015
Location: Cape Canaveral
Posts: 11
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
I'll check into that. I don't want to replace modern gps and navigation. But it would be an awesome skill to learn nine the less
sailorseb is offline  
post #46 of 69 Old 01-24-2016
Senior Member
 
skygazer's Avatar
 
Join Date: Sep 2011
Location: western Maine
Posts: 586
Thanks: 26
Thanked 16 Times in 14 Posts
Rep Power: 8
 
Re: Sextant and finding out where you aren't

I need to correct my evaluation of the Davis Mk3 to mention that there are no pinch tabs to lock and unlock the index arm. I rely on that to hold my reading while I look at the time. The more delicate and bulkier Mk 15 might be more accurate because it does have pinch lock tabs. I have one so I actually know.

I also noticed that there is not a complete set of filters for the horizon sight on the Mk3. This is fine for sighting with a sea horizon, which is never blinding.

But if you are on land using an artificial horizon reflection you need full protection from the sun's reflection as well, so it would not be good for land based practice unless you can rig up some more filters for the horizon mirror. It's nice if you can balance the brightness of the reflection and the sun. The Mk 15 has both sets of filters.

Knowing all this, I just purchased a Davis Mk3 anyway, hoping I'll find that it is either tight, or I can make a way to hold the arm fairly tight. I feel confident I can add more filtering on the horizon mirror.

By the way, for an artificial horizon I use a cheap aluminum (foil) cookie sheet, got two for $1.69. I pour in some used motor oil and it doesn't freeze at zero degrees. I've found that when sighting a low body a longish pool aimed in the general direction is best. I set the pan on a very cheap plastic tray type folding table. I use a cover from a plastic tub to set over it and keep out dirt and snow, couple small split firewood pieces holds the cover down. My "observatory"

If I find I really like the Davis Mk3 I may put my Mk15 on eBay. If I do I'll try to remember to post a link here so anyone interested gets a heads up. Either model would be good to learn with. In fact, I think I could get rough data with a plumb bob and protractor, if I had a helper to read it or held the string with my left hand.

In the northern hemisphere Polaris alone gives pretty good latitude. Think of the Vikings and others in the old days, there is lots to this stuff and it's fun to learn. Without chronometers they used to find their latitude and cruise down it till they reached their landfall. Dangerous at night though.
skygazer is offline  
post #47 of 69 Old 01-24-2016
美國佬
 
willyd's Avatar
 
Join Date: Feb 2008
Location: Maryland
Posts: 619
Thanks: 36
Thanked 16 Times in 15 Posts
Rep Power: 12
 
Re: Sextant and finding out where you aren't

Quote:
Originally Posted by titustiger27 View Post
Question: are their good Sextants under $100?
Harbor Freight has 'em for less than $100 : Brass Sextant
Couldn't be worse than any of the other tools they sell... For $20 you could buy five, takes sights with all of them, and use the average. That's what Columbus did.
titustiger27 likes this.

1964 Whitby 25
Severna Park, Maryland
willyd is offline  
post #48 of 69 Old 01-24-2016
arrgh!
 
titustiger27's Avatar
 
Join Date: Jan 2013
Posts: 1,816
Thanks: 119
Thanked 69 Times in 68 Posts
Rep Power: 7
 
Dock
Re: Sextant and finding out where you aren't

I would be a little nervous trusting a $20 Sextant... and can you learn on something you don't trust...


And I just noticed in the description: Brighten any room or office with this decorative brass sextant


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Vector X Y
titustiger27 is offline  
post #49 of 69 Old 01-24-2016
美國佬
 
willyd's Avatar
 
Join Date: Feb 2008
Location: Maryland
Posts: 619
Thanks: 36
Thanked 16 Times in 15 Posts
Rep Power: 12
 
Re: Sextant and finding out where you aren't

Quote:
Originally Posted by titustiger27 View Post
I would be a little nervous trusting a $20 Sextant... and can you learn on something you don't trust...


And I just noticed in the description: Brighten any room or office with this decorative brass sextant
This guy says he crossed the ocean with an EBCO plastic one: Solo across the Atlantic in a Folkboat ? Yachting World

I think I'm going to get the Harbor Freight one just to see how it differs from my Davis sextant, which, by the way, being gray plastic, is not something I would use to decorate my home or office.

1964 Whitby 25
Severna Park, Maryland

Last edited by willyd; 01-24-2016 at 06:17 PM.
willyd is offline  
post #50 of 69 Old 01-24-2016
arrgh!
 
titustiger27's Avatar
 
Join Date: Jan 2013
Posts: 1,816
Thanks: 119
Thanked 69 Times in 68 Posts
Rep Power: 7
 
Dock
Re: Sextant and finding out where you aren't

Quote:
Originally Posted by willyd View Post
This guy says he crossed the ocean with an EBCO plastic one: Solo across the Atlantic in a Folkboat ? Yachting World

I think I'm going to get the Harbor Freight one just to see how it differs from my Davis sextant, which, by the way, being gray plastic, is not something I would use to decorate my home or office.
I look forward to your review

I just wonder about an item that has 'decorative' in the description.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Vector X Y
titustiger27 is offline  
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Why aren't these cruisers sailing? Frogwatch Cruising & Liveaboard Forum 11 05-26-2015 10:00 AM
Why aren't you using your boat? nemier General Discussion (sailing related) 13 10-25-2010 12:30 PM
What is a wing sail and why aren't they many of them? jbarros General Discussion (sailing related) 12 11-25-2009 11:36 AM
Yeah... the forecasters aren't always right :) labatt General Discussion (sailing related) 11 11-09-2008 08:14 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome