Navigation

[Maxparsons]

If I wanted to sail from Lands End to New York what compass bearing would I need to follow, assuming that the boat is unaffected by wind and tides? If I got that bearing wrong by one degree how far south of New York would I be when I hit US soil? All a bit cryptic, I know but I want to use the answer for a teaching excercise. Your help would be appreciated.

 

[FWB]

Use this Great Circle Distance Calc . Put in lat/long of the 2 points. then do it the other way round add 180 to the last one and you will get the start and finish headings.

 

[FWB]

So using approx lat/longs of 50N 005W and 40N 073W I get 285 out of Lands End and 234 into New York.
Your heading will be constantly changing along the route.

 

[narooma]

If you follow a course for 60nm but are one deg. off then you will be 1 nm out at the end

 

[FWB]

Your question about getting the bearing wrong isnt really valid because you are following a great circle and your heading will change all the time.
Using a compass to achieve this would be difficult, also bear in mind Magnetic Variation .Put your cursor over the map.

You could sail a Rhumb Line, assuming you could constantly correct for Variation.
This Rhumb Line Calculator Gives a track of 258deg and distance of 2936nm.
The Great circle distance is 2844nm.
So using Freewinds 1in 60 rule above, if you steered 1 deg out then you would be 49nm adrift at the other end. In reality you would use great circle routes.
Another useful tool here .In fact it's prob better than the original one I posted.

 

[Refueler]

Interesting that he asks a simple question ... one goes of on Great Circles - another assumes it's magnetic compass.

What if he has a Gyro and he can steer virtually True Course ? (allowing for compass error which with Gyro is usually near constant and if set-up correctly small).

 

[FWB]

Well Nigel I think I covered that. He will be about 50nm out for his one deg error. He did ask what compass bearing he would follow.
Just trying to show the practicalities of the question.

 

[Refueler]

Just commenting that replies build more into it than he asked !! /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif

 

[SAWDOC]

DylaN
THANKS FOR SOME GREAT REPLIES AND USEFUL LINKS.

 

[Danny]

Stuck indoors because of the snow so trying to exercise the grey matter a bit... So say we follow Dylan's heading of 258 but forget to stop at New York! Would we all agree that we would spiral south until we arrived at the magnetic south pole? So having arrived there we realise our mistake and decide to backtrack until we get to NY. Ah - that's easy - just steer the reciprocal course 102.

Oh-oh! a problem - can't do that, can we?

 

[Cruiser2B]

[ QUOTE ]
Stuck indoors because of the snow so trying to exercise the grey matter a bit... So say we follow Dylan's heading of 258 but forget to stop at New York! Would we all agree that we would spiral south until we arrived at the magnetic south pole? So having arrived there we realise our mistake and decide to backtrack until we get to NY. Ah - that's easy - just steer the reciprocal course 102.

Oh-oh! a problem - can't do that, can we?

[/ QUOTE ]

The reciprocal of 258° is 078°

 

[Danny]

That's the first mistake but what about the second?

 

[Cruiser2B]

[ QUOTE ]
That's the first mistake but what about the second?

[/ QUOTE ]

You mean no matter what direction you head from the South pole, the direction will be North.

 

[Danny]

Yep - that's it. Now what's the third mistake.

 

[Cruiser2B]

There are a lot of "areas of negative depth" 'tween here and there.

 

[Danny]

True - but I was assuming an amphibious vehicle for the sake of the exercise.
The third mistake is in the premise that we'd arrive at the South Pole. I think that this is untrue. My reasoning: However close one gets to the South Pole it must always lie directly south of you (by definition). Therefore, unless you eventually change your course to due south, you can never actually reach the south pole! You just get closer and closer and closer... /forums/images/graemlins/confused.gif

Sorry about this waste of a perfectly good thread. Just got bored with being stuck indoors because of all the white stuff. Inexcusable really. Promise I won't do it again.