Navigation poll

[GordMay]

I can’t imagine using celestial navigation on most inland waters, except for practice.

US SAILING's Celestial Navigation Certification Standards only require a 5 mile accuracy, which I can reliably surpass with dead reckoning:
Celestial Navigation Certification Standards

Of course, you could use an altimeter (/w local pressure and temperature info’), or a 3D-fix on your GPS.

Great Lakes water levels are officially measured from the International Great Lakes Datum 1985 (IGLD 1985). This datum is referenced to sea level, as measured at Rimouski, Quebec, near the mouth of the St. Lawrence River.

Goto:

Great Lakes Information Network:
Great Lakes-St. Lawrence Levels and Hydrology

and

Current Great Lakes-St. Lawrence Water Levels:
Current Great Lakes-St. Lawrence Water Levels

[NavPak ECS]

Celestial Navigation is like riding a bicycle; it looks intimidating, but once you know how, it is easy. Most people say that they don't need it because they stay coastal, but when you leave the harbour and the mast breaks, there's no telling where you will end up. Other people will tell you that if they turn to port (or stbd) then they will find that big continent. If you are approaching land and you don't know how far off you are then you are lost.

[Ex-Calif]

"If I had absolutely no GPS/Loran/Radar Etc. aboard I would... "

Interesting poll. One question? Are we underway or at the dock. If I was at the dock I'd wanna know if there is any ice left in the cooler. Gotta know if this is an emergency or not.

[Jenia]

" One question? Are we underway or at the dock. "

What? This is a navigation poll. navigation implies fixing your position and that implies out of sight of land.
jenia

[camaraderie]

The "right" answer for me does not appear.
Buy enough cheap GPS's and batteries so that you never need be concerned about one or more not working properly short of thermonuclear war. Cheaper and easier than using a sextant and a hell of a lot more reliable day and night and in all kinds of weather.
Flame away guys but I stopped hitching a horse to my car bumper some years ago too. (GRIN)

[Ex-Calif]

"What? This is a navigation poll. navigation implies fixing your position and that implies out of sight of land."

I guess I could use an education. How do I get a fix using Ded Reckoning?

PS - I am with Cameraderie. Learning celestial navigation is an interesting mental exercise but practicality is multiple GPSs. If the satellite network goes down you take the current charts, last known postion and aim for a big landfall...

[Lodesman]

Originally Posted by Ex-Calif

"How do I get a fix using Ded Reckoning?

...you take the current charts, last known postion and aim for a big landfall...

I think you just answered your own question.

[Amgine]

The deduced (ded) reckoning will not provide a fix, but rather a good estimated position. If you can accurately determine speed, leeway, drift or set, course, and time this estimated position is quite reliable. But the longer you are from a true fix, the further you are likely to be from your estimate due to the accumulation of small errors.

Amgine

(To get the fix with ded reckoning, find the nearest safe landfall. Or have a sextant or other means of astronomical position fix.)

[Ex-Calif]

"I think you just answered your own question."

I don't think so because when using DR after your last known fix you are lost. The magnitude of how lost depends on the currents, time and speed. You could be 800 meters lost or 800 miles lost.

"The deduced (ded) reckoning will not provide a fix, but rather a good estimated position."

That's exactly my point I guess. A fix is a fix and you can't get one by DR. You can know your last fix and you can estimate (deduce) where you've gone but without at least two landmarks (in sight of land), a star shot or a gps you don't know where you are and the circle described in a previous post just starts to grow.

Sorry to get so literal about this my previous post was meant to be a joke. Probably a bad one at that.

I guess it's important to be accurate in case anyone lurking without navigation skills gets the wrong idea.

Ded Reckoning - Time, drift and speed since a last known fix.

A Fix - A position on a chart confirmed by two (or more) bearings from known landmarks or a position calculated using celestial navigation or a gps lat & lon.

[Lodesman]

Originally Posted by Ex-Calif

"I think you just answered your own question."

I don't think so because when using DR after your last known fix you are lost. ..."The deduced (ded) reckoning will not provide a fix, but rather a good estimated position."

That's exactly my point I guess. A fix is a fix and you can't get one by DR. You can know your last fix and you can estimate (deduce) where you've gone but without at least two landmarks (in sight of land), a star shot or a gps you don't know where you are and the circle described in a previous post just starts to grow.
...I guess it's important to be accurate in case anyone lurking without navigation skills gets the wrong idea.

Ded Reckoning - Time, drift and speed since a last known fix.

A Fix - A position on a chart confirmed by two (or more) bearings from known landmarks or a position calculated using celestial navigation or a gps lat & lon.

Well Amgine got it ("To get the fix with ded reckoning, find the nearest safe landfall"). Now to be very technical, a lot of fixing methods require a DR - visual and radar fixing can't be done unless you have a reasonable idea what your fixing points are; celestial with the intercept (or Marcq St Hilaire) method requires a starting point (assumed position); and even GPS - if your GPS didn't run its own DR, it would be forever in start-up mode and fixes would take minutes, rather than fractions of a second.
So we don't confuse anyone lurking without navigation skills, I'll correct your definitions: Dead reckoning - time, speed and course since last known position;
Estimated position - an improvement on the DR, as set is calculated so as to provide course and speed made good; and
Fix - is a position derived by measurement from reference points; when it is plotted on a chart, it is ancient history - in the time it takes for you to plot your lat and lon, lines of bearing, ranges etc, you have travelled away from that position and are on your DR. You are not "lost" when you are dead reckoning. If you are conscientious about maintaining it, you will find it surprisingly accurate. In the days before GPS (not that long ago) ships managed to find their ways across the oceans, thanks to DR.

Kevin

[Ex-Calif]

"So we don't confuse anyone lurking without navigation skills, I'll correct your definitions: Dead reckoning - time, speed and course since last known position;"

Actually Ded reckoning can be reduced to distance covered and direction. Distance covered is usually plotted as Speed * Time.

Course: Is the intended path over water or land. This is the line you plot on the chart.

Track is the actual path taken. Sometimes called course over ground or course made good.

It is relevant that both speed and track are influenced by current and wind. Speed over the earth will be different than speed through the water due to the influence of current and wind.

I don't disagree with anything you are saying actually and I use the word "lost" in a very figurative sense. The only time you know where you are with precision is when you have a good fix.

BTW - This is an interesting discusison thanks for your patience. But to remain in context I was only replying to this statement -

"What? This is a navigation poll. navigation implies fixing your position and that implies out of sight of land."

Navigation does not alway imply fixing your postion and in the context of the poll by asking to choose between Ded Reckoning, GPS and Celestial Navigation is specifically "excluding" position fixing in one of its answers. in particular we agree that you cannot get a position fix using DR when out of sight of land. The best you get is an estimation of your position calculated as best as possible using distance travelled and direction which is heavily influenced by the factors considered in the DR calculation.

[hellosailor]

"I don't think so because when using DR after your last known fix you are lost. "
Nah. Lost means LOST as in, I was docked yesterday at the club and when I woke up today, the boat was surrounded by fog and sea with no power to anything. That's LOST.

When all you have got is your last DR position estimate and a vague idea of how long ago that was, you are still not LOST. Rather, the circle of uncertainty is just a bit larger than you might prefer.

Whether you've got DR, or fixes, or a GPS showing you where you MIGHT be located...all that counts is the circle of uncertainty, and the size of that circle.

Need to get through an inlet in the fog? Then the circle has to be pretty tight. Just need to "go west" in midocean? OK, then the circle can be rather large--and still not be a problem.

As Daniel Boone supposedly said, "I have often been surrounded by lostness, but I have never been lost." And he never had GPS!

[Dreaming Yachtsman]

I voted to "comfortably switch to DR but not mess with the celestial stuff."

To all you qualified navigators and wannabe navigators, a word of caution based on a year of cruising the West Coast of Mexico and the Sea of Cortez: Do NOT put all your eggs in one basket (i.e. trust any ONE position source to the exclusion of all others).

Several times we sailed toward a port using our GPS/chart plotter only to find that the plotter showed us to be up to 2.5 miles east of where we actually were in relation to land. Several times it showed us on land when we were actually in the middle of a bay. This is not because of any shortcomings with GPS but rather because many charts of Mexico are based on surveys from the 1800's when navigation was not nearly as precise as it is now. Of course land masses on today's chart plotters reflect what the paper charts show.

One tool not listed in the poll that I find very useful when entering a port for the first time is radar. Often it is easier to fix your position by laying out range arcs than bearing lines, especially when navigation marks are difficult to identify (only a few mountains have distinguishing enough features to be reliably identified from sea).

I must confess that GPS has allowed me to become quite cavalier about navigation. Most of the time when not entering port I rely almost exclusively on the chart plotter. I have a hand held battery powered GPS and paper charts on board should a disaster strike the chart plotter. If the entire GPS constellation goes down, we will probably have bigger things to worry about than where our boat is.

[Lodesman]

That's a very good point about the radar, John. Have successfully used a radar station plotter (a chart-sized sheet of acetate with a manoeuvring circle on it) to plot fixes nearly 100 miles off-shore. Helps if there are distinct peaks, and you can't forget to convert radar miles to naut. miles. Not overly accurate mind you, but give or take a mile that far from land is pretty darn good.

Kevin

[Ex-Calif]

Excellent discussion. The point about the charts vs. gps positoin is excellent. Of Course if you obtain a fix with any method other than land based features you will have the same problem assuming the same chart.

As the little kid in the store yelled at the security guard, "Of course I'm not lost. I'm right here. Mommy is lost!"

I'm not lost I'm in the boat. Tahiti is lost...