Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 05-02-2016, 09:33   #31
IRG
Registered User
 
IRG's Avatar

Join Date: Jun 2011
Location: San Francisco, CA
Boat: Molenmaker, Custom ketch, 97'
Posts: 37
Re: A sextant for the 21st century?

Wallah? Is that a navigational term?


Quote:
Originally Posted by Reefmagnet View Post
Most tablets and mobile phones these days can measure angles to 0.1 of a degree. Add one to a suitable holder for taking sights and Wallah!


But back to the OP, it's not rocket science to read a vernier scale. I reckon if you're going to keep a sextant as a backup, everything else related to calculating position should be kept manual as well right down to printed out sight tables. Otherwise, what's the point?
__________________

__________________
IRG is offline   Reply With Quote
Old 05-02-2016, 10:00   #32
Senior Cruiser
 
John_Trusty's Avatar

Cruisers Forum Supporter

Join Date: Oct 2014
Location: Michigan, USA
Boat: Catalina 36 (1999)
Posts: 120
Re: A sextant for the 21st century?

Quote:
Originally Posted by IRG View Post
Wallah? Is that a navigational term?
Can't be a celestial navigation term unless it has an obscure set of initials -- W(l)?

I'm picking this celestial stuff up self-study - I'm in OP's second category of interested in the maths, but don't imagine I'll ever actually need it. I appreciate the comments about never needing it (GPS, terrorism, etc), but then again I'll bet none of you would expect to ever actually need to use a bucket to steer your boat after your rudder left, and yet ...

Anyhow, the US Navy (and others) did develop fantastic programs to aid in celestial navigation -- From American Practical Navigator (Bowditch) chapter 20 https://en.wikisource.org/wiki/The_A...ical_Navigator :
U.S. Naval navigators have access to a program called STELLA (System To Estimate Latitude and Longitude Astronomically; do not confuse with a commercial astronomy program with the same name). STELLA was developed by the Astronomical Applications Department of the U.S. Naval Observatory based on a Navy requirement. The algorithms used in STELLA provide an accuracy of one arc-second on the Earth’s surface, a distance of about 30 meters. While this accuracy is far better than can be obtained using a sextant, it does support possible naval needs for automated navigation systems based on celestial objects. These algorithms take into account the oblateness of the Earth, movement of the vessel during sight-taking, and other factors not fully addressed by traditional methods.

STELLA can perform almanac functions, position updating/ DR estimations, celestial body rise/set/transit calculations, compass error calculations, sight planning, and sight reduction.
__________________

__________________
John_Trusty is offline   Reply With Quote
Old 05-02-2016, 10:15   #33
Registered User

Join Date: Jun 2015
Location: Indiana
Posts: 124
Re: A sextant for the 21st century?

Quote:
Originally Posted by hellosailor View Post
maggied-
If you didn't mind the reliance on GPS, you could use the Google Sky Map feature, an app for Androids that lets you point your phone at the sky and then identifies everything you see. A little added programming and you should be able to get the phone to tell you where you are, working backwards from optical recognition on the sky view, without the GPS.
I'm not sure I understand. You have GPS in the phone to tell you where you are so Google Sky map can identify the celestial bodies in the sky to tell you where you are?? Google Sky map has to know where you are to tell you what's in the sky around you.
__________________
Hoosiersailor is offline   Reply With Quote
Old 05-02-2016, 12:27   #34
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 2,678
Re: A sextant for the 21st century?

Quote:
Originally Posted by IRG View Post
Wallah? Is that a navigational term?
It's what magician's say when they pull a rabbit out of a hat :-)

Sent from my SGP521 using Cruisers Sailing Forum mobile app
__________________
Reefmagnet is offline   Reply With Quote
Old 05-02-2016, 12:45   #35
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 15,948
Re: A sextant for the 21st century?

Actually, I think I have seen at least one sextant with digital read-out.

I do not want one because I find and average alloy sextant joy to use and nearly un-breakable.

I think a better toy would be a sextant-smatphone combo - you sight the sun, press the button, the toy calculates your horizon and altitude from the smartphone's g sensors. COOOL, NO????

There are air bubble level Apps on Play. All you need to do is to take your sight along the long side of your smartphone ...

b.
__________________
barnakiel is offline   Reply With Quote
Old 05-02-2016, 13:52   #36
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2011
Location: West Sussex, United Kingdom
Boat: Tradewind 33, 33 foot, Parker 27 , 27 foot
Posts: 66
Re: A sextant for the 21st century?

All that's needed is for a large solar flare to occur pointed directly at earth, will knock out all our GPS satellites for several months not to mention major damage to power lines taking out thousands of cities power supply. You don't need WWIII. Lack of land based power will also most likely mean there will not be any land based radio signals to lock onto, that is the reason the US Navy is reintroducing basic Celestial Nav training for their deck officers.
__________________
Martkimwat is offline   Reply With Quote
Old 05-02-2016, 13:56   #37
Registered User
 
Snowpetrel's Avatar

Join Date: Jul 2012
Location: Hobart
Boat: Alloy Peterson 40
Posts: 2,626
Re: A sextant for the 21st century?

Quote:
Originally Posted by SaltyMonkey View Post
How about a Kamel?

Who needs a piece of &@#(&$@ sextant when you can have a string with 57 knots?

The History of the Sextant

ha, got within thirty miles of my position once with a bit of string and a plastic ruler. These thing work, not maybe as well as boatmans DR but good for those longer 5000 mile passages.

Maybe a digital micrometer in a backstaff or something as a cheapo version




Quote:
Originally Posted by woodguy View Post
I've wondered the same thing especially considering the density of pixels in cameras these days, measuring angles should be quite precise,
I tried to take a few pics of the Sun. Far too bright need some sort of good filter, a pair of sunnies held over the lens doesn't cut it!

The Bris sextant is a great bit of kit, very clever and lightweight.
Attached Thumbnails
Click image for larger version

Name:	1454709252195.jpg
Views:	100
Size:	20.0 KB
ID:	118396  
__________________
My Ramblings
Snowpetrel is offline   Reply With Quote
Old 05-02-2016, 13:59   #38
Registered User
 
vtomanov's Avatar

Join Date: Jan 2016
Location: UK , London
Boat: Jeanneau Sun Liberty 34
Posts: 143
Re: A sextant for the 21st century?

there should be a app for ios or android
__________________
vtomanov is offline   Reply With Quote
Old 05-02-2016, 14:33   #39
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 2,678
Re: A sextant for the 21st century?

Quote:
Originally Posted by Snowpetrel View Post
ha, got within thirty miles of my position once with a bit of string and a plastic ruler. These thing work, not maybe as well as boatmans DR but good for those longer 5000 mile passages.

Maybe a digital micrometer in a backstaff or something as a cheapo version






I tried to take a few pics of the Sun. Far too bright need some sort of good filter, a pair of sunnies held over the lens doesn't cut it!

The Bris sextant is a great bit of kit, very clever and lightweight.


__________________
Reefmagnet is offline   Reply With Quote
Old 05-02-2016, 14:36   #40
Registered User
 
Snowpetrel's Avatar

Join Date: Jul 2012
Location: Hobart
Boat: Alloy Peterson 40
Posts: 2,626
Re: A sextant for the 21st century?

Ha , yes got to dig out my welding helmet next :thumbup:
__________________
My Ramblings
Snowpetrel is offline   Reply With Quote
Old 05-02-2016, 15:10   #41
Registered User
 
Adelie's Avatar

Join Date: Feb 2010
Location: El Ciudad del Mission San Diego de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 2,655
A sextant for the 21st century?

Quote:
Originally Posted by Lepke View Post
A ursae minor:
You nailed it. I often wondered why we couldn't have a digital sextant, stabilized, and artificial horizion.
I am a navy trained navigator and do shots to keep the skill and as backup. I spent years on boats and ships and except for the ones I owned, almost all suffered a power/engine failure at some time.
Also with the international politics of today, the various GPS systems could be shut down or made inaccurate w/o notice.
A sextant turned horizontally makes a very accurate piloting device. With a 3-armed protractor, I get very close to GPS positions.
I crossed the Pacific before GPS was available, mostly overcast. Navigated w/depth soundings and the rare shot. Also Loran when in range. Set and drift was often 1 knot. Dead reckoning, unknown currents over a couple thousand miles would be much more than 50 miles.

Digital sextants would suffer from two problems:
A. Cost
B. If it's a lightning strike that does in you electronics, it will do in you sextant too.


Sent from my iPhone using Cruisers Sailing Forum
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is online now   Reply With Quote
Old 05-02-2016, 15:15   #42
Registered User
 
Adelie's Avatar

Join Date: Feb 2010
Location: El Ciudad del Mission San Diego de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 2,655
Re: A sextant for the 21st century?

Quote:
Originally Posted by Snowpetrel View Post
Often wondered if a digital camera could be calibrated to read angles accurately.

If so take a few snaps of the Sun and horizon with a smart phone, and let some app do the calcs for you.

Yes they can. There's a whole long discussion of various aspects of this on the NavList forum I'm also part of. The bit trick is prevail rating the camera so you know how many pixels per minute of arc. In use the photo is exported to Paint or any thing that will give you x,y coordinates in the photo.


Sent from my iPhone using Cruisers Sailing Forum
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is online now   Reply With Quote
Old 05-02-2016, 15:23   #43
Registered User

Join Date: Dec 2014
Posts: 452
Re: A sextant for the 21st century?

Quote:
Originally Posted by hamburking View Post
I think I'm in the minority, but I think a digital blue tooth sextant is a great idea. It combines the power of computing with the raw data of the stars...a great application of hardware and software.

I have to wonder how reliable the GPS satellite system would be in case of a terror attack or war. Although there are many satellites, they work in concert. Any error would cause havoc with so many devices. I wonder if this is a possibility and what sort of reliability the system really has? Attack on the system could be via "hacker" into the system, or a more conventional physical attack on the satellites themselves.

Take a picture of the sky (stars) and get your position....that would be awesome.
No, you are not alone. I think the OP has some good ideas.
__________________
captlloyd is offline   Reply With Quote
Old 05-02-2016, 15:23   #44
Registered User
 
Adelie's Avatar

Join Date: Feb 2010
Location: El Ciudad del Mission San Diego de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 2,655
Re: A sextant for the 21st century?

Quote:
Originally Posted by Snowpetrel View Post
. . . I tried to take a few pics of the Sun. Far too bright need some sort of good filter, a pair of sunnies held over the lens doesn't cut it!

Welding shade from a welding supply shop, shade 11 or 12.


Sent from my iPhone using Cruisers Sailing Forum
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is online now   Reply With Quote
Old 05-02-2016, 16:58   #45
Registered User

Join Date: Sep 2015
Location: Fremantle
Boat: S&S34, 10.3m
Posts: 149
Re: A sextant for the 21st century?

Quote:
Originally Posted by Snowpetrel View Post
Often wondered if a digital camera could be calibrated to read angles accurately.

If so take a few snaps of the Sun and horizon with a smart phone, and let some app do the calcs for you.
Snowpetrel, that is clever. I want one.
__________________

__________________
Olddave is offline   Reply With Quote
Reply

Tags
sextant

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not 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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
21st century clipper vs multihull hydrofoil sailboat for freight tbodine88 Off Topic Forum 1 05-08-2013 15:25
Southwest Boat Show Houston March 21st Lanlocked General Sailing Forum 6 13-03-2013 13:27
Hong Kong to Taiwan Race - May 21st Gone2long Pacific & South China Sea 0 06-05-2011 01:45
18th Century Wooden Ship Found Under World Trade Center Site Bill_R Off Topic Forum 0 15-07-2010 11:39


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 13:06.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.