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Old 22-01-2010, 08:10   #181
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Originally Posted by alan2 View Post
Interestingly or troublingly, it seems that more and more vessels clear port without a sextant, and or the charts, tables that would be used with same, to determine one's position. As I understand, possibly incorrectly, this applies to naval vessels as well as commercial ships.
Gee, you know even more people are putting to sea without an astrolabe, and I've even heard in the pacific that people are now attempting to go from island to island without a polynesian navigator on board. Surely these things are needed as backup when someone drops the sextant overboard. The polynesian navigators were able to navigate without any instruments so they are clearly the ultimate backup. Of course if he dies you're screwed. Perhaps everyone on board should be required to be a fully skilled polynesian navigator, that way if anyone is left alive they'll still be able to find their way. Does anyone know where we can learn polynesian navigation techniques?
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Old 22-01-2010, 10:50   #182
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Man, I have to get an Astrolabe? I do plan on going to the South Pacific and get a polynesian navigator. I wonder what she will charge?
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Old 25-02-2010, 20:07   #183
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cyca flinders island report

This has some relevance to the discussion, from the cyca report into the Flinders Island disaster. See http://www.cyca.com.au/sysfile/downl...iry_Report.pdf


216. The chart plotters are a great navigation aid but need to be used with caution. They have created a situation where people can put to sea with little understanding of navigation and the associated seamanship.
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Old 25-02-2010, 21:11   #184
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I'd estimate 5-mile accuracy to be typical for the average user. A meticulous person who practices daily might see 2 NM accuracy or slightly better. This is more than suitable to get you to within sight of land, then a sextant can be used for visual fixing (with typical visual-fix accuracy).

A sextant is quite sufficient on a small slow sailing vessel if one know's how to use one, and like you say keeps up the practice, but it takes time to become proficient in the use of one, and as the old saying goes "if you dont use it you loose it"....
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Old 25-02-2010, 22:42   #185
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Sextant v.s. GPS for Navigation
Under the hand of a competent user, there is absolutely nothing wrong with using a sextant for navigation. There is also nothing wrong with a GPS. Both can fail (drop the sextant, loose power to the GPS). My opinion is that most offshore equipped boats will have backup GPS (I have 3 total - two fixed & 1 handheld), I doubt many will have back up sextant.

No - I don't carry a sextant, but agree that it is a backup (provided you know how to do the calculations longhand - if everything electrical on board has gone - so has your calculator)

Paper Chart vs Chartplotter for Navigation
Again, both in the hands of a competant user are fine for navigation. Both can fail, but again I would guess there are more chances of having backup electronic charts on board than paper ones (I have 2 sets of electronic charts on 2 laptops, with backup discs and one on the handheld - I rarely have backup paper charts)

Yes - I do carry paper chart for most (ideally this would be all) of the places I sail

The Real Issue
The problem does not lie in the tools, it is in how the tools are used. As we approach a shoreline we must transfer from Navigation to Pilotage. A competent sextant user will do this earlier due to the known (lack of) accuracy of the sextant (I suspect there is actually a transition period where he goes to GPS navigation). A competent GPS user will make the transition later because of the perceived accuracy of the GPS.

I would hazard a guess that a great number of those who rely on GPS/Chartplotter navigation, never actually make the transition from Navigation to Pilotage because of the perceived accuracy of GPS. I propose that his is the real issue - not the tools, but the user.
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Old 26-02-2010, 01:24   #186
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sextant accuracy

After 58 years at sea and most of them before the electronic age took over theuse of GPS is as all nav is an art not a science. The person that can get a 2nm fix with a sextant on a yacht of say 40ft is a dreamer. More like 8-10nm. The use of GPS in the areas that are used alot by commercial traffic is better because this is where they make new charts for. In the more remote areas they dont bother. I have used dead reconing ,tides and time for most of my nav and got near enough to where I was going. I like my GPS but I dont rely on it we more or less agree to differ some times.
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Old 26-02-2010, 20:50   #187
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IslandHopper :

If memory serves, I read somewhere, re the use of the sextant, the first 1000 shots will show progressive improvement, the next 1000 are better still, as are the thousand following. Practice might not make perfect, likely nothing does, but is helps.
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Old 26-02-2010, 21:16   #188
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Gee, you know even more people are putting to sea without an astrolabe, and I've even heard in the pacific that people are now attempting to go from island to island without a polynesian navigator on board. Surely these things are needed as backup when someone drops the sextant overboard. The polynesian navigators were able to navigate without any instruments so they are clearly the ultimate backup. Of course if he dies you're screwed. Perhaps everyone on board should be required to be a fully skilled polynesian navigator, that way if anyone is left alive they'll still be able to find their way. Does anyone know where we can learn polynesian navigation techniques?
---------------------------

I don't know about the polynesian navigator you mentioned a couple of times, or their techniques, but the gentleman who wrote the following seems to know what he is talking about.
Keeping both GPS and sextant onboard is advisable
Capt. Kelly Sweeney
I was sailing as the chief mate on an oceanographic ship working in the Adriatic Sea between Italy and Croatia. It was the evening 4-8 watch, a clear night with little ship traffic as we were following a grid of tracklines laid out by the scientists. I walked over to the starboard GPS receiver to get my 1900 position, and was surprised to find that there was no readout. A check of the port receiver showed there was no readout there, either. Neither the captain nor I could figure out what was wrong, and then half an hour later the display on both receivers came back on. This continued to happen each time we entered roughly the same area while crisscrossing our grid throughout the night. The following morning the chief Italian scientist overheard the captain and me talking about the GPS problem and said, “I think that your signal was jammed by a local military base here on the Italian coast, a holdover from the war in Bosnia.”

At first I was skeptical that our GPS signal could have been jammed. Then the captain reminded me of an incident a few years earlier when the master of Point Sur, a famous research vessel based in Moss Landing, Calif., noted that the GPS readout on his ship didn’t work while the vessel was in the harbor and up to a mile offshore. Other vessels in the harbor reported the same thing and it continued for weeks on end. After involving everyone from the U.S. Navy to local yacht owners, the culprit was found to be the television antenna on a small pleasure boat which was creating strong interference, jamming the GPS signal on every vessel in the port.

GPS, or NAVSTAR GPS as it’s officially called, utilizes weak radiowave signals currently generated by about 30 satellites 12,000 miles above the earth. As a result, it can be jammed or rendered unusable relatively easily — naturally or intentionally. A strong solar storm could completely knock out the system, according to a recent National Academy of Sciences report. Other militaries can jam GPS signals intentionally. Early on during Operation Iraqi Freedom, U.S. troops captured six GPS jamming units reportedly developed in Russia. Our government can also pull GPS from public use without notice due to national security concerns, a decision then President Bush announced in 2004. GPS is not a new technology. It’s been 20 years since the first GPS satellite was launched into space, and many of the original satellites will soon be at the end of their useful life. Some GPS satellites have already begun to fail, the latest falling out of service just weeks ago. A report issued by the U.S. Government Accountability Office in April 2009 pointed out that although the aging GPS system is due for upgrades, the Air Force is facing delays, huge cost overruns and technical snafus, and is falling behind schedule on modernizing the system. The report noted that the Department of Defense admits that over the next few years the satellites will go out of service faster than they can be replaced.

A shutdown of the GPS system could have disastrous consequences. The Federal Aviation Administration (FAA) is currently using a GPS-based system to guide some commercial airplanes, and is implementing a complete changeover at airports nationwide. Imagine if GPS failed shortly before a fully loaded airplane touched down going 185 miles per hour in zero visibility.

Losing GPS capability would have calamitous effects on shipping. The Automatic Identification System (AIS) relies on GPS and is used to direct/monitor vessel traffic in major ports. Without GPS input AIS would essentially be rendered useless, putting our ports at increased risk for collisions, oil spills and breaches of security as vessel traffic authorities would be unable to identify and track thousands of vessels in harbor areas around the country. Offshore, the numerous drillships worldwide which use GPS input while in active dynamic positioning mode could fall off station, possibly ripping out pipe and causing oil spills as a result. For all close quarter situations, an effective backup to GPS is obviously needed — and available.

Enhanced Long Range Navigation (eLORAN), is the next generation of LORAN, a radio navigation network that has been in use for decades. It has a reported accuracy near that of conventional GPS positioning in coastwise and harbor applications, and uses the infrastructure that is already in place. Its effectiveness is a result of solid-state transmitters, advanced software applications and uninterruptible power sources, along with a new generation of shipboard receivers. Because the signal is much more powerful than GPS, eLORAN is not nearly as susceptible to jamming. In February 2008, the U.S. Department of Homeland Security announced that eLORAN would be implemented as a national backup for a GPS failure — but funding squabbles threaten to scuttle this implementation. Even when fully installed, however, eLORAN’s effective coverage would only be several hundred miles offshore.

The International Maritime Organization mandates the use of GPS or some type of electronic navigation system onboard oceangoing ships, but makes no such requirement for celestial navigation equipment — a time-tested means of determining the ship’s position at sea. I was the mate on a 323-foot ship running from Seattle to Alaska several years ago that didn’t have a ship’s sextant onboard. I remember thinking then how odd it is that the Standards of Training, Certification & Watchkeeping code requires deck officers to show proficiency in celestial navigation — but SOLAS (International Convention for the Safety of Life At Sea) doesn’t require ships to carry a sextant! I would like to see SOLAS Chapter V, Regulation 19, amended to require every oceangoing vessel to have a sextant, along with the appropriate books and tables to make the necessary calculations, as a backup to GPS in case of a failure while the ship is far out to sea.

I believe that the development of new technology is vital to the modern merchant marine, but we should not forget that even the best technology can fail. The money to upgrade our GPS system and fully implement eLORAN needs to be allocated, in my opinion, to help keep our American ports and coastal areas safe. Adding a requirement that oceangoing ships carry a sextant and celestial navigation equipment would then give mariners the navigational backup capability we should have — wherever we need it.

Till next time I wish you all smooth sailin’. •

Kelly Sweeney holds the licenses of master (oceans, any gross tons) and master of towing vessels (oceans), and regularly sails on a wide variety of commercial vessels. He lives on an island near Seattle. You can contact him at captsweeney@professionalmariner.com.
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Old 26-02-2010, 21:27   #189
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bewitched wrote:

The Real Issue
"The problem does not lie in the tools, it is in how the tools are used." To my uneducated ear, that sounds about right.

If everything electrical fails, I suppose that one could use log tables to solve Law of Cosines sight reduction equations, god forbid. Personally speaking, I wouldn't go out without spare batteries for my old HP 11C. Matter of fact, I'd try to find a second.
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Old 26-02-2010, 21:31   #190
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My wife won't let me leave sight of land- does this mean all I need is good pilotage skills? Really, I tend to use DR even after I loose sight of land, so does that make me not a good navigator because I refuse to navigate with a GPS or a sextant? Or a wise one that prefers to island hop?
I agree that the real issue is the user, and that we are dancing around the real issue...That a BLUEWATER sailor need to know how to navigate and not just read a video screen. Buck up and learn a sextant as well as the limitations of GPS, and become good at pilotage in all situations. Its not user friendly out there boys and girls...
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Old 26-02-2010, 22:00   #191
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IslandHopper :

If memory serves, I read somewhere, re the use of the sextant, the first 1000 shots will show progressive improvement, the next 1000 are better still, as are the thousand following. Practice might not make perfect, likely nothing does, but is helps.
Sounds about right, i seriously doubt though i have met anyone in the last 10 years that has even picked one up more than 1000 times let alone used one. In fact at work, (I am a Master on AHSV's) other than myself keeping my hand in, in the last fifteen years i have never seen one being used seriously. Honestly though i think if i was caught using one for serious navigation, and not in an emergency, the client would probably insist my employer remove me from the vessel citing safety concerns...
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Old 26-02-2010, 22:25   #192
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My wife won't let me leave sight of land- does this mean all I need is good pilotage skills? Really, I tend to use DR even after I loose sight of land, so does that make me not a good navigator because I refuse to navigate with a GPS or a sextant? Or a wise one that prefers to island hop?
I agree that the real issue is the user, and that we are dancing around the real issue...That a BLUEWATER sailor need to know how to navigate and not just read a video screen. Buck up and learn a sextant as well as the limitations of GPS, and become good at pilotage in all situations. Its not user friendly out there boys and girls...
Not at all, as long as you know your limits and abilities and are prepared to stick to them, the problems arise with those that think they know what they are doing and don't. When these people venture out with family/friends on board who belive in them, to me that is unacceptable....

By the way, hang onto the wife, sounds like you have a smart one there...
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Old 27-02-2010, 09:19   #193
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Of course even without GPS one advantage "we" have over many of our forebears (whether wielding a sextant or not ) is that our charts show exactly where the Continents are - even if still a bit fuzzy on some of the finer details. Yer might not know exactly where you are with no GPS (or Sextant) but not too hard to work out when you could start bumping into a continent.......even if yer window of uncertainty is a week

I kinda like the approach of Shane Acton ("Shrimpy" - 18' Foot plywood Caprice) back in the 70's to crossing the Atlantic from UK to the Carribean. "Sailed a few days south into the Bay of Biscay and then turned right"

Admittedly he did actually make landfall in South America ......but in my book it's the principle of the approach (even allowing for some literary licence).

I vaguely recall he had a sextant
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Old 28-02-2010, 16:10   #194
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Of course even without GPS one advantage "we" have over many of our forebears is that our charts show exactly where the Continents are.
Tell that to the Nuclear Sub who just ran into a mountain that wasn't on the charts...I personally believe that the underwater topology may change with a major earthquake. That be what it may, I am always finding hazards which are not on the charts, and some of them are right in the way...
Oh, and thanks for the complement to my wife. She says that either I keep her or I can be poor paying for her lifestyle without me. My choice.
"hey did someone spill grape juice on the chart or is that a restricted zone?"
Newt- who still prefers the pop up and look around school of navigation...
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Old 28-02-2010, 17:46   #195
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That be what it may, I am always finding hazards which are not on the charts, and some of them are right in the way...
I think that was covered by: "even if still a bit fuzzy on some of the finer details"
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