Cruisers Forum
 


Join CruisersForum Today

View Poll Results: Blue Water- is a Sextant Necessary?
Absolutely essential 24 18.90%
Desirable, but not essential 52 40.94%
Good fun, but little practical use these days 39 30.71%
Don't waste your money and time on this 11 8.66%
Sextants make excellent dingy anchors. 3 2.36%
Multiple Choice Poll. Voters: 127. You may not vote on this poll

Reply
 
Thread Tools Rate Thread Display Modes
Old 31-10-2012, 07:16   #61
Registered User

Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 3,537
Quote:
Originally Posted by noelex 77
.....quite unlikely possibilities, in non critical systems, (such as the US government shutting down the GPS system).
Anyone know if it's possible to just turn off the bit of the system we use without affecting all the other services which rely on GPS, airlines, financial systems and health services use the time signal I think as well. Probably many more.
If the whole lot goes down then a lot of stuff will be going badly wrong..
__________________

__________________
conachair is offline   Reply With Quote
Old 31-10-2012, 07:27   #62
Registered User
 
S/V Alchemy's Avatar

Join Date: May 2008
Location: Toronto
Boat: Custom 41' Steel Pilothouse Cutter
Posts: 4,575
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by conachair View Post
Over 50 posts but still no one has even tried to get any reliable data on what level of risk loosing GPS is for ocean cruising. "Heard of a couple of boats" doesn't cut it.

Such is the land of forums..
Not to don the tinfoil sou'wester here, but "reliable data" is unlikely to exist outside of academic journals generally inaccessible to the broader public.

I have seen on my own boat momentary "speeds" of 50-60 Kts. by the GPS, which was basically correcting itself despite having a solid 4 or 5 satellite "lock".

For some undetermined period, my GPS didn't know where it was...until it did. On the ocean, or coastally at night or in fog, I have very little empirical means (short of perhaps following a depth contour) of determining GPS accuracy or function. I wouldn't likely notice a mile off discrepancy, even though I log the LAT/LON hourly on watch.

Given the tendency to sail to the mark or the waypoint, or to allow the magic of GPS to navigate in tight places (on the usually sound assumption that it is working accurately), I prefer to exercise prudence and take GPS as a strong, but not error-free, suggestions as to where my boat and crew are.

The system is aging and can be thrown off. I navigate accordingly, and that can include a sextant. Including a sextant and not accepting GPS as the final arbiter of my actual position is just a part of prudent seamanship, in my view. Yours may vary.
__________________

__________________
Can't sleep? Read www.alchemy2009.blogspot.com for fast relief. Can't read? Avoid www.volumesofsalt.blogspot.com, because it's just personal reviews of sea books.
S/V Alchemy is offline   Reply With Quote
Old 31-10-2012, 07:45   #63
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by S/V Alchemy View Post

The system is aging and can be thrown off.
I think the evidence is that the GPS is getting better not worse. New and better satellites are being launched. The last one just in October.


Welcome to GPS.gov
__________________
noelex 77 is offline   Reply With Quote
Old 31-10-2012, 09:51   #64
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 4,595
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by conachair View Post
Over 50 posts but still no one has even tried to get any reliable data on what level of risk loosing GPS is for ocean cruising. "Heard of a couple of boats" doesn't cut it.

Such is the land of forums..
The problem is that is no good way to get the data.

The only convenient way to get the data would be to look at groups of boats of boats traveling together for long periods.

You might think long distance races, but they for the most part aren't long enough, and they really aren't representative of how boats are a outfitted.

Rally's being longer would be better, but the pool of participants would not be a good representation of the average boat out cruising, self-selection prevents that.

The only other way to get the data would be to interview a lot of boats out actually cruising.
__________________
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 offline   Reply With Quote
Old 31-10-2012, 13:17   #65
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: Poll-Blue water. Is a Sextant Necessary?

If one data point is any use my GPS has been on virtually continuously for the last 5 1/2 years.
There has been 2 occasions i have lost or had a poor fix.
One due to a malfunction of the primary GPS. Switching to secondary GPS gave an immediate fix.
The second due to a lightning strike. Switching to the GPS, which was an old handheld stored in a faraday cage took maybe 10 mins to get a fix. ( the old single GPS units took a long time to download the almanac and get a first fix). It is still working, but has been joined by a more modern HH GPS that will get a cold fix much quicker.

Some boats do report an occasional loss of GPS fix, but every case I have seen so far is due to poor instalation, a faulty GPS, or incorrect settings.
There must be genuine cases of GPS jamming, but they are rare. GPS coverage is continuous.

To put these outages in perspective celestial navigation will give you a fix on average maybe once a day.

With care and skill you can navigate sucessfully with celestial navigation and DR, but the very best most skilfull celestial navigation is vastly inferior to GPS navigation.

Celestial navigation is easy to learn. The mystyque should be dispelled.
Someone with reasonable intelligence and some mathematical skills can be taught in a Day or couple of days.

Learning navigate a yacht safely with only a modestly reliable fix once a day requires a much higher level of skills.
I worry that many sailors that have mastered the skills to fix their position with celestial navigation and determine a DR position have not learnt the skills to sucessfully complete a voyage this way.

GPS navigation is very different to celestial / DR navigagation. Try It and see. My guess is that if you do you use it seriously many will order an extra HH GPS a metal box and some AA batteries even if you have a back up sextant and know how to use it to fix your position.
__________________
noelex 77 is offline   Reply With Quote
Old 31-10-2012, 14:12   #66
Don't ask if you can't handle it
 
sailorboy1's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: On the boat somewhere
Boat: Hunter 410
Posts: 12,310
Re: Poll-Blue water. Is a Sextant Necessary?

I've lost my fix twice. Once was a bad wire on my unit. Once was in an anchorage that just "fixed" itself the next morning when I left and it came back on at the same spot where I lost it the night before.

I don't plan to ever buy a sextant, but that ony makes me part of the 8%. Could be part of a larger group, but I just don't think a sextant would make a good dinghy anchor and a good dinghy anchor will cost less!
__________________
jobless, houseless, clueless, living on a boat and cruising around somewhere
sailorboy1 is offline   Reply With Quote
Old 31-10-2012, 18:05   #67
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: Poll-Blue water. Is a Sextant Necessary?

It's amazing how many people think MacGyver was a documental.

b.
__________________
barnakiel is offline   Reply With Quote
Old 31-10-2012, 19:13   #68
CF Adviser
 
Bash's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: sausalito
Boat: 14 meter sloop
Posts: 7,260
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by Sailmonkey View Post
Really?! is it a dinghy anymore when it has it's own navigational system
Not necessarily. It might just be a camera. Or a phone. Or a watch.

Pretty soon our toasters will all have integral navigation systems.
__________________
cruising is entirely about showing up--in boat shoes.
Bash is offline   Reply With Quote
Old 01-11-2012, 01:27   #69
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
Quote:
Originally Posted by Don Lucas
people talk talk about the GPS system going down like if that were to happen there wasn't bigger issues, like the end of the world, going on

this IF and that IF

one of those living/sailing in fear things where the fear doesn't cross over into other safety issues

sailing has been going on much longer than GPS and sextants have been around
Yeah. There's a good argument to being lost for a few months at that point...
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 01-11-2012, 03:40   #70
Registered User

Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 3,537
Quote:
Originally Posted by Adelie

The problem is that is no good way to get the data.

The only convenient way to get the data would be to look at groups of boats of boats traveling together for long periods.

You might think long distance races, but they for the most part aren't long enough, and they really aren't representative of how boats are a outfitted.

Rally's being longer would be better, but the pool of participants would not be a good representation of the average boat out cruising, self-selection prevents that.

The only other way to get the data would be to interview a lot of boats out actually cruising.
I think to be honest, even talking to every ocean crossing boat out there today completely loosing a GPS fix offshore might turn out to be so rare that it would be difficult to draw any firm conclusions.
Part of the point of the previous post was that people tend to make their mind up about what the world is like without actually making the effort of trying to find out what actually goes on.
But despite that I do have a sextant. Lovely object in its' own right, and fun to learn. though with even just an ais reciever needing a gps signal its getting more difficult to enjoy the feeling of sailing offshore completely disconnected from the modern world.
__________________
conachair is offline   Reply With Quote
Old 01-11-2012, 04:35   #71
Don't ask if you can't handle it
 
sailorboy1's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: On the boat somewhere
Boat: Hunter 410
Posts: 12,310
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by conachair View Post
though with even just an ais reciever needing a gps signal its getting more difficult to enjoy the feeling of sailing offshore completely disconnected from the modern world.

Why, can't you just turn it all off if being disconnected from the world is your goal?
__________________
jobless, houseless, clueless, living on a boat and cruising around somewhere
sailorboy1 is offline   Reply With Quote
Old 01-11-2012, 06:22   #72
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: Poll-Blue water. Is a Sextant Necessary?

GPS will never fail! And if it does, then we have another unit held in a Friday cage.

GPS is a unique system, on so many levels:
- it has been built with parts hand made in China (no planned obsolescence),
- all technicians and engineers are still married (to the same partners),
- it denies gravity (see, it is in the orbit),
- it is protected from solar fluxes (eight layers of International bottomkote),
- etc., etc.,

So, do not listen to naysayers. Go big, go now. Yes, you can!

b.
__________________
barnakiel is offline   Reply With Quote
Old 01-11-2012, 06:27   #73
Registered User
 
Tom Stormcrowe's Avatar

Join Date: Jul 2012
Location: Indiana
Boat: 1984 Johnson Boatworks Inland Scow, 20' and a 1975 sailMFG Bandit 19 Pocket Cruiser
Posts: 204
they also said the Titanic didn't need enough lifeboats for all the passengers...... just sayin' if necessary you could rig up an astrolabe something like that but when you can buy a sextant so cheaply that's at least good enough to get you a shore landing with 1 of the little Davis mark 3 is that it seems to me that stupid not to carry 1.
__________________
"Dum vivimus, vivamus! -- 'While we live, let us live!"-Heinlein (Among others)
My Refit and Travel Blog
Tom Stormcrowe is offline   Reply With Quote
Old 01-11-2012, 07:29   #74
Don't ask if you can't handle it
 
sailorboy1's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: On the boat somewhere
Boat: Hunter 410
Posts: 12,310
Re: Poll-Blue water. Is a Sextant Necessary?

I wonder in which direction the sun rises and sets in? Does it change? If I were to lose my GPS and were to just follow the sun what would happen? If I keep spending money for things on the boat "because it might happen" would I ever go anywhere? If I'm that worried is it smart of me to get on a boat to start with?

Just so many unanswered questions, just what is one to do?

By the by the poll at the moment says that 81.25% of responders don't feel a sextant is needed. What fools!
__________________
jobless, houseless, clueless, living on a boat and cruising around somewhere
sailorboy1 is offline   Reply With Quote
Old 01-11-2012, 07:43   #75
Moderator
 
carstenb's Avatar

Cruisers Forum Supporter

Join Date: May 2012
Location: Copenhagen
Boat: Jeanneau Sun Fast 40.3
Posts: 4,936
Images: 1
Re: Poll-Blue water. Is a Sextant Necessary?

Don,

The sun always rises in the west and sets in the east, unless of course you are in the southern hemisphere, where it is the direct opposite (except wednesdays and during full moons - then it's like the northern hemisphere).

O course you should note and be aware that if you travel far enough north (or south) there will be times when the sun doesn't rise for several months at a time - what will you do then? I would suggest that you make a chalk mark (or similar) at the bow of your boat sometime when you know you are sailing due north.

That way, if all your GPS's and compasses do a tube job and quit on you - you'll always know which way is north!

I mean - how hard can it be?

jus' sayin'

__________________

__________________
I spent most of my money on Booze, Broads and Boats. The rest I wasted - Elmore Leonard
carstenb is offline   Reply With Quote
Reply

Tags
sextant, water

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 20:51.


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.