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Old 25-03-2016, 11:24   #61
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Re: What is Due East?

For many years the compass was the ONLY instrument that would, on it's own accord give a relatively accurate direction, and even at that it was not so precise that a small error in accuracy could leave you probably hundreds of miles from your destination.

A latitude stick was probably worse, but at least the error in precision( or accuracy ... or both) wouldn't compound, sextants are great, but on ship? Then you have the labourous computations.

In general the compass was what everyone had, but the declination will constantly change ... you "east" in New York, will not be your "east" in London.

Without parameters set up with the question, there are too many variables ... and if it was as simple as following a latitude, the question should've indicated that if one were to follow the latitude at New York, where would be the first landfall after crossing the Atlantic Ocean ... or whatever.




BTW ... about 2 GPS on a ship ... even two "same model"(because of proprietary software), consumer-grade GPS will give a relatively accurate True or Grid bearing, by comparing the given coordinates ... even at about 20 feet or so, since each GPS will, lose and gain the same GPS sats at the same time ... it's called differential.

But a single GPS in the length of a 30' boat ... or even less, might jump with the loss or gain of sats ... substantially. The shorter the boat(or travel), the more off the bearing could be ... even to the point of the GPS, for a moment, saying you're going backwards or at a 90 degree deflection
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Old 25-03-2016, 11:53   #62
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Re: What is Due East?

Serv69,

I agree with the GPS notes you posted. Imagine a 500 foot ship with the 2 GPS antennas say 400 feet apart. The heading would be accurate enough to swing ship without a gyro compass to make a good precise deviation table. The heading would be within a degree or two if the ship was not rolling, but that is a whole different discussion.

Ken
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Old 25-03-2016, 12:00   #63
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Re: What is Due East?

My guess is that the staff for the show pulled the atlas off the shelf - so I did. Following the latitude east from New York with my finger, I landed a little north of Lisbon. At Forespar, we believe in a bit more precision.
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Old 25-03-2016, 12:07   #64
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Re: What is Due East?

Re: The OP. Seems it was predicated on mag. due East. Windage or drift move you a good distance N or S, the compass is still going to show you east of those points to which you are moved. Look at a globe for true true East. Following a compass who knows? South Africa next stop?
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Old 25-03-2016, 12:11   #65
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Re: What is Due East?

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Originally Posted by Our Tyme View Post
Looked it up. Will not disclose but I was close

Ken
You weren't very close if you are still talking St. Lawrence R.

Was Brian there? I don't remember-could be.

There is a gap in the US-Canada boundary approx 30-40 Nm long that is still disputed. The area between the two country's boundary claims has been dubbed the 'grey/gray zone". Both countries "use" this zone.

Sorry for butting into thread-I thought discussion of easterly navigation was over. I will exit for now-just having some Trivial Pursuit / game show fun.
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Old 25-03-2016, 12:15   #66
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pirate Re: What is Due East?

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Originally Posted by leftbrainstuff View Post
The frame of reference is geometric. The tilt and magnetic deviation are important when using instrumentation not for route planning.

Senegal sounds like bs. Due east implies non magnetic and same latitude.

The problem is the question is one of those silly academic questions which has missing information. Therefore you need to make assumptions.

I would state the following assumptions before answering:

1) assume east means true
2) frame of reference is a mercator projection
3) constant latitude

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Flat earth/chart mentality.. and the implications and assumptions are in your head.. not theirs.. they'll have tried and checked they're right.. using their rules.
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Old 25-03-2016, 13:05   #67
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Re: What is Due East?

The question was "If you head due east from New York City where will you hit land?".

Since "due east" was the only hint, I would probably have answered Lisbon. That means going due east (90T) all the way, not starting due east and then continuing with rudder straight all the way in whatever direction that takes you (assuming no winds and no streams). They should have said at least "then continue straight forward" (or "shortest route, starting due east") to justify the Dakar (or some other North Africa) answer.

Dakar seems to be a wrong answer also in the sense that it seems that the boat would land somewhere in Western Sahara, not in Dakar Senegal. That's two countries off. That spot at Western Sahara is closer to Dakar than Lisbon, but you can almost say it's halfway between those two.

Great circles are the shortest routes. I drew the two great circle lines in the attached map (thanks to acscdg.com). The Lisbon great circle line heads first a little bit too much north. And the Dakar great circle line heads too much south.
earth starting point

Great circle lines are not really straight lines since a straight line would take you up to space. Great circle lines curve down below your boat. They are thus the shortest routes and do not turn to the left or to the right, but they turn down.

Google Earth seems to give the direction of the ruler line from the start point. If you draw a line from Western Sahara to New York the direction seems to bee about 303 (i.e. not 90+180 but more than that).
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Old 25-03-2016, 13:32   #68
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Re: What is Due East?

I think it is worth keeping in mind that the magnetic course would not be a straight line at all but only a wave form line as we would have change the (true, over the bottom) course every time declination changes.

It would be an interesting exercise to actually draw such a line even with a limited degree of accuracy!

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Old 25-03-2016, 14:11   #69
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Re: What is Due East?

Initial Great Circle Course from NYC to Senegal's northern border is 099*T, 112*M

An intial course of 090*T will land you in Mauritania.

An initial course of 090*M will see you making landfall even further north.

Whoever decided Senegal was the answer is a dickhead.

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Old 25-03-2016, 14:28   #70
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Re: What is Due East?

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Originally Posted by El Pinguino View Post
Initial Great Circle Course from NYC to Senegal's northern border is 099*T, 112*M

An intial course of 090*T will land you in Mauritania.

An initial course of 090*M will see you making landfall even further north.

Whoever decided Senegal was the answer is a dickhead.

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Ditto on the dickhead. It may have been in jest? A bit of wry humor?
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Old 25-03-2016, 14:53   #71
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Re: What is Due East?

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Where is the still disputed boundary between US & Canada-the "grey zone" ?
I had to look it up as well. It is obvious that at least one of the disputed parts is clearly US territory.

I think we need to go bomb the Canadians into submission and resolve this little issue or maybe take Trudeau hostage next time he visits Washington.
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Old 25-03-2016, 14:55   #72
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Re: What is Due East?

Hey Deblin Close is relative

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Old 25-03-2016, 16:43   #73
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Re: What is Due East?

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I had to look it up as well. It is obvious that at least one of the disputed parts is clearly US territory.

I think we need to go bomb the Canadians into submission and resolve this little issue or maybe take Trudeau hostage next time he visits Washington.
Clearly,you say?

You can come & get Justin if you want. Then you will have a pair

Attack Canada ! We throw a mean snowball.....
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Old 25-03-2016, 16:46   #74
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Re: What is Due East?

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Hey Deblin Close is relative

Ken
Meh-what's a 1000 mi.?
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Old 25-03-2016, 16:49   #75
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Re: What is Due East?

Hint.

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