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Old 21-11-2010, 06:49   #16
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Challenge?

Hopefully anyone crossing an ocean would not consider it a "challenge" if their GPS failed.

My first step would be to go with Mark's plan and run a tight DR plot. Then use any and all of the other ideas as appropriate for the location and potential hazards. Yes I still have a sextant and paper charts.
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Old 21-11-2010, 09:30   #17
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I think it's the other way around.
Exactly. You can determine the longitude from the UTC of sunrise or sunset. To determine the latitude, measure the elevation of the sun above the horizon at local noon (accurate time not required).
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Old 21-11-2010, 10:42   #18
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Old 21-11-2010, 11:35   #19
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Might want to think about carrying a copy of Bodwitch II

it will have everything needed in it for any navigation question

http://www.irbs.com/bowditch/pdf/chapt18.pdf
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Old 21-11-2010, 15:34   #20
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I think it's the other way around.
DOH, typo! Yes Lat (N to S) you use sextant and Long (E to W) you use other.
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Old 30-11-2010, 22:47   #21
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Here is the challenge:

While on a long passage i.e. crossing the Pacific/Atlantic/etc... all your GPS equipment fails (including backups) halfway thru the passage. With what you currently have on your boat what would you do to plot your course? Do you carry a sextant? Paper Charts? SSB? Also if your GPS is tied to a chart plotter then you also lose that feature as well.
Yes, for cross-ocean passages I carry a sextant, the 229 tables, a wrist watch set to GMT (don't actually need a watch for noon sites), and paper charts for each port I could possibly divert to.

GPS is great - don't get me wrong - but it's complex, outside of your control, and there are numerous single point of failures built into using it to navigate your boat. If GPS goes down, it's handy to have a backup that's simple, has a reduced set of failure points (don't drop the sextant overboard), and is easy to work assuming you have time to do the arithmetic.
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Old 01-12-2010, 21:44   #22
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don't actually need a watch for noon sites
If you want longitude, which is often useful, you do. You don't need GMT for any object's LMT if all you seek is latitude.
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Old 01-12-2010, 21:54   #23
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If you want longitude, which is often useful, you do. You don't need GMT for any object's LMT if all you seek is latitude.
That would be true; however, if you don't have a watch, at least you know what latitude you're on and then can travel north-ish or south-ish before striking out due east or west reasonably confident in which particular continent you might run into.
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Old 08-12-2010, 17:32   #24
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My friend had is boat capsize then right itself on the way to Bermuda. He and his wife had just ridden out the worst of a storm, had gone below for a warm drink when the boat was hit by a large wave. It rolled 360. Water shot in through the vents like 4 inch hose and all his electronics went out. He used basic charts and time distant speed to reach Bermuda...no problem. The mast and rig stayed intact; ripped the storm jib but had more. It can happen and does. His message to me was...."Keep basic navigation skills up".

Of Note: He is an ex-Search and Rescue Helicopter Pilot and a great sailor.
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Old 08-12-2010, 20:42   #25
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A sobbering tale. Another good idea might be to keep a charged hand held unit in a waterproof container or grab bag. Then if the above happened, you'd have something to fall back on.

I personaly have a car GPS unit that would be suitable for this, although (obviously) it won't show maps in the ocean, it will still give an acurate Lat Long fix that you can then use with a chart.
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Old 10-12-2010, 10:43   #26
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Today I suspect most have back up GPS somewhere. We had chartplotter, radio, and Navtex all giving location, plus 2 x handheld units. But no sextant or tables.

Means what's key for us is always noting each hours location / direction / speed in a scribbled log so we can fall back on DR in the event the sats all fall down.

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Old 10-12-2010, 11:07   #27
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If you have sunrise & sunset charts you don't need a watch either.
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Old 10-12-2010, 11:26   #28
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sextants are but a flash in the pan in the history of crossing oceans.
Gotta disagree with you. The sextant as a tool might be new, but its predecessors and the concept of celestial and constellation navigation have been around since Ptolemy theorized the quadrant around ~130AD, and it was in use by mariners for about two thousand years.

Vikings used sunboards and bearing circles which accomplished roughly the same tasks. So yes, the sextant as a tool is relatively new but it represents nothing more than the steady refining, simplification, and enhanced accuracy of navigational methods that are literally as old as the human race.

Plenty of folks on the water have no clue how to use the stars and bodies above them to get from A-B and for good reason: it's hard to learn, takes practice, and it's easier to turn on the GPS and twenty seconds later have the number in front of you.

But the idea that celestial navigation is "new" or "dead" is hogwash. The Department of Defense at any point in time with absolutely no warning can suspend GPS signals: it's a standard question for anyone getting their Master's license, and it's why Masters with the "Oceans" endorsement have to know celestial navigation to this day.
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Old 02-02-2011, 17:11   #29
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Originally Posted by Chattcatdaddy View Post
Here is the challenge:

While on a long passage i.e. crossing the Pacific/Atlantic/etc... all your GPS equipment fails (including backups) halfway thru the passage. With what you currently have on your boat what would you do to plot your course? Do you carry a sextant? Paper Charts? SSB? Also if your GPS is tied to a chart plotter then you also lose that feature as well.
I am going to be really boring and predictable, but I always have my sextant and paper charts up to date, I personally get tremendous pleasure and satisfaction from using the old ways and only use my GPS (Oh yes I always carry an old hand held Garmin 45, steam powered version) as an occasional check to see how close I can get.

But that is MY choice, and I do NOT decry or judge other sailors who use other methods and skills, including GPS, plotters etc, that is their choice. Most of my early years I never even had an engine, I learned to sail in a Royal naval 32 sailing cutter, no engine or boom, and loved the simplicity.

It got me a super job offer from a brewery owner in the Channel Islands, I won a bet that I could get his yacht on his mooring without using the engine, all in a days work. The bet was a tot to a bottle of good scotch, the job offer was a bonus.

There is room for every one in sailing

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Old 02-02-2011, 17:15   #30
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