What is Due East?

[Pelagic]

I think the only way to understand their ambiguous question is to work backwards from their approved answer.... Senegal.

Using a GPS Navigator, plot a route from NY to Senegal.
Then compare true bearings via RL and GC to see which one is closest to a 090° True heading. I expect it will be a Great Circle solution.

[boatman61]

Well I have just pulled out a Chart and applied the thought process I originally accredited to some dork in an office with a globe on a traditional stand and a spirit level..
From New York if you work to my theory you end up just South of Cape Blanc, Mauritania..
You have to remember.. these questions are not based on working science.. but designed purposely to trip you up.
Logic is a double edged sword..

[SURV69]

"Due east", has always been a nebulous direction ... and subject to all sorts of conditions and interpretations.

In court cases involving land boundary locations, judges have said Due East is N90deg00min00sec East ... or that Due East is perpendicular to Due North ...

I was involved in a case where Due East of a 5000' long line could include a north jog of over 200 feet.

If sitting judges cannot agree on what Due East means, how is a game-show contestant supposed to know without some specific parameters.

Is it due east from the start ... like on a laser line, or by constant deflection every 100 miles, 5 miles or 10 feet?

[boatman61]

[QUOTE=SURV69;2080617]"

If sitting judges cannot agree on what Due East means, how is a game-show contestant supposed to know without some specific parameters.

QUOTE]

Applied Logic.. its Who Wants to be a Millionaire.. not Cruisers Forum with SatNav/GPS/Sextant..

[Pelagic]

I think it is more about spherical trigonometry.....
The question and answer was based on the real world, not a chart projection or a sailor's compass.
Boatie was close with the globe idea

[valhalla360]

And this is why your math teach made you show your work:


If you defined "due east" as current magnetic heading out of new York and you maintained that as a true heading you would wind up in X. If you assumed that you would constantly adjust the heading to your local "due east", you would wind up in Y. Or for most non-sailors, due east is equal to true east and you wind up in Z.


Final answer.

[belle-isle]

I believe the "fundamental fact of navigation" that the OP is missing and asking about is the fact that we are navigating on a sphere (sort of, it's a bit flattened but that approximation will do), but we chart on plane surfaces.

Therefore navigating can be done along a :
- rhumb line, also called loxodrome, i.e. keeping a constant heading, which is simpler, looks straight on a chart (in Mercator projection of course), but at the expense of a longer distance.
- great circle, also called orthodrome, i.e. along the shortest route, but it looks like a long curve on a chart and the heading keeps changing all along the path.

Now, if the question was asked exactly as posted, it clearly is a tricky question. An additional word or two might have been needed in order to make it more precise, clarifying whether the due east heading was only initially or all along. Clearly, though, if you start heading due east and keep going "straight" (i.e. along a great circle), you will end up in West Africa. If, however, you head east and keep going east all along, thus turning slightly to port all the time, you will end up in Portugal.

This difference between great circle and rhumb line also explains the following fun facts :
- planes flying between Europe and North America sometimes fly over Greenland
- the shortest route for a plane flying from Melbourne to Buenos Aires skirts the coast of Antarctica !
- a flight following the shortest route from New York to Beijing or Bangkok would pass almost directly over the North Pole

The "due" east, though, means for me that you are heading exactly at 90deg, not ESE nor ENE. It does not have a meaning of magnetic or true, and in this context I would guess true is implied as no mention of a compass is made.


Sent from my iPhone using Cruisers Sailing Forum

[SURV69]

valhalla360:

Is that with, or without the la'place(sp) adjustment?

When I taught in College, I never required students to "show their work", but always reminded them that if an answer was incorrect, and they did show their work, I would go through their calculations, in an attempt to ascertain their reasoning.

I would often give credit for the correct portions(of the work), on an otherwise incorrect answer.

I haven't look at this particular question, but is it possible that after taking all possibilities of interpretation in mind that only one answer "could" be correct...

You know, while I sit here typing, I come to realize that unless a person is limited to a latitude line or maybe a laser-line(from the beginning), that withing a hundred or few hundred or a few thousand trips around the earth ... virtually any city, in any country could eventually be on the pathway from the North Pole to the South Pole.

Seriously ... what a question ...

[Dockhead]

Originally Posted by belle-isle

. . .

The "due" east, though, means for me that you are heading exactly at 90deg, not ESE nor ENE. It does not have a meaning of magnetic or true, and in this context I would guess true is implied as no mention of a compass is made.
. . .

I think that this is objectively true -- "due" East just means exactly E, without saying anything about whether its T or M.

I think the only reasonable interpretation of the question is that you leave NY harbor and maintain a heading of 90T. In that case, you will end up near Lisbon, not in Africa for sure.

The only other possible interpretation, I think, is that you follow a compass heading of 90M, which obviously changes as you go across, but as someone mentioned the variation is always W, so you will end up N of Lisbon, not S.

Following a Great Circle route is different from maintaining a heading, so I think this is out. The question did say "head" somewhere.


So it looks to me like that question was completely screwed up. I can't think of any possible interpretation which would put you in Africa.

[valhalla360]

Originally Posted by SURV69

valhalla360:

Is that with, or without the la'place(sp) adjustment?

When I taught in College, I never required students to "show their work", but always reminded them that if an answer was incorrect, and they did show their work, I would go through their calculations, in an attempt to ascertain their reasoning.

I would often give credit for the correct portions(of the work), on an otherwise incorrect answer.

I haven't look at this particular question, but is it possible that after taking all possibilities of interpretation in mind that only one answer "could" be correct...

You know, while I sit here typing, I come to realize that unless a person is limited to a latitude line or maybe a laser-line(from the beginning), that withing a hundred or few hundred or a few thousand trips around the earth ... virtually any city, in any country could eventually be on the pathway from the North Pole to the South Pole.

Seriously ... what a question ...

So ignoring the semantics, you did require them to show their work.

I pretty much guarantee if you responded the way I said, the game show rules makers would be scratching their head or have to define "due east" for you.

I know back in school several times, I got full credit when I gave the "wrong" answer but explained why the question was flawed. Usually it was a situation like this where they tried to trick you with poorly defined questions.

[valhalla360]

In the modern world of GPS, the assumption of magnetic heading isn't even true anymore. While you need to understand the difference so you can transition back if the GPS fails, for normal operations, you can certainly use True headings off the GPS.

[Dockhead]

Originally Posted by valhalla360

In the modern world of GPS, the assumption of magnetic heading isn't even true anymore. While you need to understand the difference so you can transition back if the GPS fails, for normal operations, you can certainly use True headings off the GPS.

Except that the GPS won't tell you your heading. It's not capable of that.

[valhalla360]

Originally Posted by Dockhead

Except that the GPS won't tell you your heading. It's not capable of that.

OK, if you want to play with semantics but it's my primary means of determining my heading.

[darylat8750]

Originally Posted by Dockhead

Except that the GPS won't tell you your heading. It's not capable of that.

Ah.. one of the new, fancy, expensive gps compass gizmos can. :big grin:

Good question by the OP. Terrible question by the game show.

I've played with boats all my life and retired from a 30+ year career as an airline pilot. The only time I've heard someone say "Go due East" is when they were talking about someplace "right over there" or someplace you could already see or could see shortly. Never in the context of actually navigating where the actual course needed any precision.

[Our Tyme]

As a Quartermaster in the Navy WAY back when(70s), True course would be implied. Therefore the latitude would not change and you would end up in Portugal.

On a side note: Dockhead, They put 2 GPs units (1 forward and 1 aft) on many ships. The difference is calculated to be the actual heading. Not practical on most of our crafts but done none the less.

Just my 2 cents.

Ken