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 29-10-2012, 23:43   #31
Registered User

Join Date: Sep 2009
Location: Mackay,QLD, Australia
Boat: planning a approx 45ft cat
Posts: 3,651
Images: 3
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by rebel heart View Post

I understand why people don't lift weights: it's hard. It requires constant engagement and commitment, basically day in and day out. You'll spend months learning the techniques and years learning advanced stuff. The rewards are worth it, but it's a total commitment and most people honestly do the bare minimum to get by.
Learning to do any thing well takes constant engagement and committment.

Navigation, seamanship, diving are the same.

Agreed, most do the bare minimum to get by.
__________________

__________________
downunder is offline   Reply With Quote
Old 29-10-2012, 23:59   #32
Marine Service Provider

Join Date: May 2011
Location: PDX
Boat: Gulfstar 50
Posts: 895
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by goboatingnow View Post
Firstly GPS ( and glonass, and hopefully Galileo , then the Chinese gnss etc) will never be turned off. " we" need it more then the baddies do.

Having said that I'm a student of traditional nav methods , so I have a sextant , and even a lovely Walker trailing log. But a sextant is like a GPS it needs support tools. The fact is any competent sailor can latitude sail and reach ones destination ( or at least land ). A sextant is a tool , like GPS. It has failure modes too. Shackletons great luck was his captain had a few pages of his nautical almanac, not that he had a sextant.


Dave
Firstly the un-encrypted GPS transmissions can and will be shut off in need. The military (encrypted) GPS transmissions will continue. Good luck using them.

Secondly I know of 2 cruisers who have had electrical problems that took our their electronics and did use a their sextant to help on the way home.

Just saying that it can and does happen. What you gonna do?

Regards
__________________

__________________
evm1024 is offline   Reply With Quote
Old 30-10-2012, 00:36   #33
Senior Cruiser
 
osirissail's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: A real life Zombie from FL
Boat: Gulfstar 53 - Osiris
Posts: 5,416
Images: 2
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by evm1024 View Post
Firstly the un-encrypted GPS transmissions can and will be shut off in need. The military (encrypted) GPS transmissions will continue. Good luck using them. . . .
It is not uncommon to only think about a particular thing like GPS in terms of only how we as sailors or truckers or whatever use the thing within our interest area. However, in most cases there are other areas where GPS usage is extremely more critical and as such "nobody" - not government, not the military, etc. will dare to "screw" with GPS. So the likelihood that GPS will be shut of by any responsible "human" action is a non-event. It will not happen.

However, that does not mean that GPS cannot be "shut down" by non-human events such as caused by Mother Nature.

GPS is currently used by so much of the world and world's various occupations that it is quite reasonable to expect that GPS's existence and signal availability far exceeds any national security, etc. considerations.

One interesting area where GPS is being used that we as "navigators" would never expect is the World's Financial Markets. Simply put, "turning off" GPS would crash the world's financial markets and most likely bring financial ruin and disaster. GPS time signals are currently the "nanosecond" scale clocks that are used to date/time stamp all financial transactions in the major world markets. "When" a transaction takes place can mean the difference between profit and ruin.

So the thought/idea that any human/government/etc would turn off GPS is a non-starter. Do a Google search for "GPS and Financial Markets" and you will see a whole "other world" where GPS is critical. For instance:
http://radionavlab.ae.utexas.edu/ima...plications.pdf
GPS 'spoofers' could be used for high-frequency financial trading fraud (Wired UK)
__________________
osirissail is offline   Reply With Quote
Old 30-10-2012, 01:06   #34
Registered User

Join Date: Sep 2012
Location: Australia
Boat: Franz Maas 37
Posts: 237
Re: Poll-Blue water. Is a Sextant Necessary?

Sextants can be used for things other than celestial navigation. Measuring angles to three onshore markers will provide you with a position (here you use your sextant in a horizontal rather than a vertical plane). Just the same as using a hand held compass...but more fun. Also, with all the filters in place there is no better way to observe a solar eclipse. And, they can be used for celestial navigation. Even if you don't learn celestial nav, you should at least be able to take a daily noon site and have good knowledge of DR. It may be redundant, but it may also one day make a difference to your continued existence.
__________________
Auzzee is offline   Reply With Quote
Old 30-10-2012, 01:16   #35
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: Poll-Blue water. Is a Sextant Necessary?

have a sextant aboard, only use it to keep in practice occasionally. Will keep it aboard along with proper charts but is it necessary? no. As ive pointed out before, whats the point of using a sextant when the most accurate timepiece aboard is the bloody gps? To use a sextant you need an accurate chronometer and an up-to-date almanac - total cost- - best part of $1000 or more, hand held gps - $110. If i was starting fresh id buy a handheld, maybe an extra for backup and spend the rest on charts.
__________________
charliehows is offline   Reply With Quote
Old 30-10-2012, 06:43   #36
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 is clear here that most of you never iron your shirts!

Well, to me it happened at least twice that I had to find ways around power outages and equipment failures.

And to think that an iron is more reliable only because it is flying in space is IMHO a proof of technical ignorance.

;-)
b.
__________________
barnakiel is offline   Reply With Quote
Old 30-10-2012, 06:49   #37
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?

And on the lighter vane, there may be some gradation of how absolutely necessary sextant is depending on the passage.

I would think if our electronics kicked the bucket mid-Atlantic, then I would be just somewhat worried.

But if the same were to happen sailing Marquesas to Tuamotu or crossing the Indian, then I would probably give myself a few unpronounceable names for not taking a sextant along.

b.
__________________
barnakiel is offline   Reply With Quote
Old 30-10-2012, 07:51   #38
Registered User
 
svHyLyte's Avatar

Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,434
Images: 25
Re: Poll-Blue water. Is a Sextant Necessary?

I do not feel a Sextant is "Necessary" unless one will be at sea for some while. That said, we carry a very accurate tho' inexpensive (relatively) Astra IIIB obtained from Celestaire quite some while ago, Two copies of HO 229 (15-30º and 30-45º), a current Nautical Almanac (the commercial version is available annully for about $25.00 from various vendors) an accurate quartz watch ($150.00) that remains in the Nav table against the possibility of damage; and, an accurate stop-watch. I have copies of work-sheets that were once produced by Davis in laminated covers that can be reused as necessary although I do use an old Merlin II navagational computer based on a Sharp hand held calculator most of the time. While understanding the detail is nice, one really doesn't need a comprehensive understanding of Celestial theory to utilize the process, which is really pretty easy. Depending upon where one is sailing, morning and evening LOP's can give one a reasonable estimate of one's distance off (shore) and a noon "Lat" can give one a very good position fix. The only problem I seem to be having these daze is deteriorating eyesight, which makes taking a sight problematic.

As for prospective failures of GPS, we did experience the loss of our GPS system mid-way between Tampa Bay and Key West a few years ago which was rather disconcerting (I opened a thread about that at the time). As a matter of course, however, we keep a paper plot and so had no diffficulty carrying on much in the manner we did when sailing off the California coast in the 1970's-80's, before the advent of GPS. If one has never sailed without GPS, one might find being deprived of the system disconcerting. Considering most folks' sailings however, it really isn't too much of an issue, eh?

FWIW...
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
svHyLyte is offline   Reply With Quote
Old 30-10-2012, 08:28   #39
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: 10,619
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by svHyLyte View Post
an accurate quartz watch ($150.00).
The problem with this is that most of the things that would take out a HH GPS with spare batteries would also damage a quartz watch.

You can keep a quartz watch in a faraday cage, but then why not do the same with a HH GPS?.
A mechanical watch / clock is better, but you are likely to lose radios that would give a time signal so it needs to be accurate (which means expensive particuarly if you want accuarcy on a boat) and need to keep track of how much it gains or loses each day.

Very few people seem to take these precautions. While latitude alone is better than nothing I wonder if they are as prepared as they think they are for a scenario like a severe lightning strike that wipes out everything.
__________________
noelex 77 is offline   Reply With Quote
Old 30-10-2012, 08:43   #40
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,334
Re: Poll-Blue water. Is a Sextant Necessary?

The old ship captains made do without an accurate watch, and you can too. You sail to your desired latitude and then go east-west to your destination.

Still need a sextant to do that.
__________________
donradcliffe is offline   Reply With Quote
Old 30-10-2012, 09:23   #41
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: 4,637
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by charliehows View Post
To use a sextant you need an accurate chronometer and an up-to-date almanac - total cost- - best part of $1000 or more,
Wrong, total cost about $200. If this is a backup system, not a primary system you can get by with bottom of the line until you hit the next port and can make repairs.

60 - Davis Mark3 sextant
30 - Long-term almanac by Geoff Kolbe
45 - 3 cheap Casio watches set to GMT time & date.
20 - Small steel cash box
5 - Rite-in-the-Rain note book.
______________________
$160 - total

The almanac is good until 2050 for the sun and stars and it contains a compact sight reduction table. Not the easiest sight reduction system, but small, cheap and convenient to carry. If you want an easier, smaller sight reduction system, download and print out LaPooke's update of the Bygrave method, https://sites.google.com/site/fredie...ave-slide-rule, 2 sheets. Laminate the bottom sheet and print the top on transparency.

The watches are kept in the cash box. Every week check each watch against an external time source, shortwave is best, but GPS time will do if you keep track of how much it has varied from UTC. UTC occasionally has leap seconds which GPS doesn't. Currently you subtract 16sec from GPS to get UTC (GPS, UTC, and TAI Clocks). I would not reset each watch weekly, I would log the error in the Rite-in-the-Rain so I knew what the error rate was. In the event that the watches survive whatever kills all the other electronics I know what the most recent error was for each watch, and can project forward what that error will be so as the error changes. Three watches is so that you can tell if one of the watches goes seriously off the rails, and so you can average all of them if there isn't one that is obviously wrong.

Let's assume the watches get fried in a lightning strike despite all the protection you have given them. Then you need a mechanical watch ($35) and the current Nautical almanac ($33) which brings the total up to about $228 plus tax and shipping. If you want to be diligent you can wind the watch daily and record the error like the other watches and you will have current time even after lightning strikes.

Assuming the watch has wound down and isn't keeping time, wind it, set it to what time you think it is and shoot a round of stars plus the moon and reduce the sights. If the moon line agrees with the other lines (you need at least 2 star sights) then the time you guessed is correct. If not adjust your time for the moon and all the stars and rework the sights. When the moon line hits the pinwheel for the stars you have found how much in error your watch is. If you have previously established what the error rate for the watch is then you can do sun and star sights most of the time and only do moon sights weekly or so to check the actual error. This method of Lunars is discussed in "Self-contained celestial navigation with H.O. 208" by John S Letcher. Yes I know that reworking all the sights is tedious and time-consuming, but if you have no other way of knowing where you are then it's probably worth the effort.

Yes, I understand that this is a limited accuracy solution, the goal is not to let you continue your cruise through reef strewn waters like the Tuamotu archipelago, but to help you make a landfall with limited outlying submerged dangers at someplace you can make repairs. It's the difference between knowing where you are within 10-15nm and and guessing where you are within 200nm or so.
__________________
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 30-10-2012, 10:10   #42
Registered User
 
Capt Phil's Avatar

Join Date: Jun 2010
Location: Stateline NV
Boat: Prior boats: Transpac 49; DeFever 54
Posts: 2,749
Re: Poll-Blue water. Is a Sextant Necessary?

Learned to do sight reductions to attain my Mates Ticket in Canada back in the early 60's. I was terrible at it and barely passed that portion of the exams. But bought a Plath a year or two later, reduction tables and a decent chronometer. Periodically, over the years, I kept practicing as I worked and cruised around the world and as the mystic vanished, it became more of a conversation activity. When GPS came out and became generally available, it was fun to check out the accuracy of my calculations against a GPS. Tables now available on-line.
I'm sure it will become an anachronistic talent as the years pass but still fun to play around with. If you still have an old Davis or Plath, hang on to it because it will be great for your grandchildrens' show and tell. Phil
__________________
Capt Phil is offline   Reply With Quote
Old 30-10-2012, 10:49   #43
Registered User

Join Date: Jan 2011
Location: St. Petersburg, Florida
Boat: Sabre 42
Posts: 206
Images: 1
Re: Poll-Blue water. Is a Sextant Necessary?

I received a sextant as a gift from my father once he discovered that I was getting into sailing. I'm still working at getting proficient, but understand that it's a skill that I will likely never NEED. Just like learning to tie really cool knots when a bowline will do, it's something that I'm choosing to do because I like to learn, and the idea of figuring out where you are with such simple tools and a little math is just plain cool.

When on passage about 125 miles offshore, I was awakened in the deal of night by a freaked out crew member on watch shouting "THE GPS JUST DIED! WHAT DO I DO?" (Our heading had been the same for two days). I calmly suggested that the same heading might be ok for a couple of hours until I fixed the chartplotter. (by the way, we had three other GPS sources on board).

I used to be a flight instructor and saw firsthand the dangers of gadgetry fixation. One of the traps new pilots (and to a lesser degree sailors) get into is staring at the gizmo screen when they should be looking out the damn window.
__________________
Gary H is offline   Reply With Quote
Old 30-10-2012, 11:17   #44
Registered User
 
Capt Phil's Avatar

Join Date: Jun 2010
Location: Stateline NV
Boat: Prior boats: Transpac 49; DeFever 54
Posts: 2,749
Re: Poll-Blue water. Is a Sextant Necessary?

Gary H... +1! great comment... Phil
__________________
Capt Phil is offline   Reply With Quote
Old 30-10-2012, 11:24   #45
Senior Cruiser
 
Vasco's Avatar

Cruisers Forum Supporter

Join Date: Apr 2004
Location: Toronto
Boat: CS36Merlin, "La Belle Aurore" Ben393 "Breathless"
Posts: 7,140
Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by Gary H View Post

I used to be a flight instructor and saw firsthand the dangers of gadgetry fixation. One of the traps new pilots (and to a lesser degree sailors) get into is staring at the gizmo screen when they should be looking out the damn window.
I got hit while at anchor by a 46 ft Irwin. Came right at me, doing six or seven knots and never wavered. Found out later the helmsman was looking at a laptop in the cockpit, following some line on the screen rather than looking out for other boats in the anchorage. This was around eight in the morning, broad daylight. Two "qualified" guys with six-packs but no brains or common sense. Looking ahead is not an esoteric nautical practice, you have to look ahead whatever you're driving!
__________________

__________________
Rick I
Toronto in summer, Bahamas in winter.
http://groups.yahoo.com/group/beneteau393/
Vasco 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 21:37.


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.