I sent the folowing message more than 3 hours ago but it doesn't show
on Google News so I try once more. Sorry if it is a double.:

Should have been "unless you cross the equator exactly after the first
21 hours" instead of 7 - I thought you went North first. My teacher
apparently forgot to tell me to read the question thoroughly before
answering.

Maybe I should comment a bit further on the "geometrical component".
It could be defined as a trigonometrically function of your
start-latitude and your speed over the ground.
Hint: A "parallel", the circle that consists of al points at a given
latitude (for instance 56 degrees North), is larger (has a larger
circumference) than any parallel closer to the poles and smaller than
any parallel closer to equator, but they are all crossed by the same
number of longitudinal.

Peter S/Y Anicula

"Peter S/Y Anicula" skrev i en
meddelelse ...
"Thom Stewart" wrote:
......wouldld include leeway, tide, deviation and variation,
windage,
helmsmans error, etc.

That's pretty close, but you are missing one thing:
Unless you crossed the equator exactly after the first 7 hours which
is statistically very unlikely there vould also be a geometrical
component due to the fact that you are sailing on a globe
and not on a pancake.

Velocity over the ground (?) ("beholden fart" in my native
language)
in a unit of nautical miles
per 56 hours, would be the closest I can think of, but it doeen't
make
much sense.


Peter S/Y Anicula

Donal--I'll give the points to you.

The point of this question was as follows.

If you travel a path where all other factors
are constant, and you do not return to your
starting point, something external force is
acting on your boat. That force is called
current, although it could be wind or
anything else--a barnacle on one side of
your bottom. Anything that you can't
explain is attributed to current.

I apologize if the question was too
vague.



Donal wrote

"Bart Senior" wrote

You sail directly East for 14 hours,
then South for 14 hours,
and then West for 14 hours,
and then North again for 14 hours.

Now if you draw a vector between your starting
position and your final position. What would you
call that vector?

A Tidal vector.

Donal

Peter;

I have to give you the same advice I gave to the Jax. Re-read the
question. There aren't any distances given. The distance is a creation
of your own mind. Only time and directions were stated. The start and
the finish, in the problem, were different. The question, IN THE
PROBLEM. was what the line drawn (vector) between these two locations
(start & finish) was called. An Analytical Geometry Solution to a
navigational readings.

There are no distances asked for. There are no directions asked for.

The question; Name the line indicating the difference!!

Is that such a great PROBLEM? Can all the great minds, that have elected
to discuss this problem, admit they are looking for something other than
what was asked for! Don't be misled by Jax's ramblings ( He's caught in
the Gulf Stream again )

Ole Thom

If you sail due east, north, west and south over the ground with the
same speed over the ground and there were no current, no leeway or
other "disturbing factors", you would still not end up at your
starting point (unless....). In fact on the northern hemisphere you
would end up in a position due west of your starting point.

(Assuming we are on the northern hemisphere): When you go back west on
a more northern latitude you will get further west than your starting
point, due to the fact that the meridians are closer together closer
to the pole. The north and south-going legs will even out each other,
but not so for the east and west going leg. If you don't believe me
try to plot it on your chart (and remember to use the right (but not
the same) latitude to measure the length of the nautical mile for your
east-going leg and for your west-going leg.

For this reason if would not give much meaning to call the difference
in start and end position current, set or a tidal vector.

Peter S/Y Anicula



"Bart Senior" skrev i en meddelelse
t...
Donal--I'll give the points to you.

The point of this question was as follows.

If you travel a path where all other factors
are constant, and you do not return to your
starting point, something external force is
acting on your boat. That force is called
current, although it could be wind or
anything else--a barnacle on one side of
your bottom. Anything that you can't
explain is attributed to current.

I apologize if the question was too
vague.



Donal wrote

"Bart Senior" wrote

You sail directly East for 14 hours,
then South for 14 hours,
and then West for 14 hours,
and then North again for 14 hours.

Now if you draw a vector between your starting
position and your final position. What would you
call that vector?

A Tidal vector.

Donal

Yes Peter,

You're correct in what you've said but again you've deviated from the
origin problem. It doesn't matter THIS TIME!

Pete, this is and old trick question. used in teaching GREAT CIRCLE
NAVIGATION.
(Sorry Bart) Another explaination "Is a fat man wearing his belt under
his gut because the distance around his stomach is to large.

If the four legs were sailed in a vacuum, without tides and currents but
on a globe the start and finish would still be different. Since most DR
Navigation call the difference (Off Set) between start and finish Drift,
That was the term I used.
The etc was used to let Bart have his fun.

Horv, I know it doesn't make a difference in Units in this problem but
it did to Jax's conception.

Ole Thom

Sorry Thom, but I still don't get it.

Lets say I wanted to visit my girlfriend, and she lives on an island
just west of my island. There is a lot of reefs in the area so to stay
clear I calculate a trip-plan that will bring me to her by sailing 14
hours east, 14 hours north, 14 hours west and 14 hours south. Since
there is no tide and no wind and the water is totally flat, I have to
use my twin engines (asymmetrical). Every thing goes as planed and
after 56 hours I arrive at my destination.

Would you still call the Vector from my start-point to my destination
for drift, current or any such thing?

Peter S/Y Anicula

P.S. Please, don't ask me how the reefs survive if there is no wind no
current and no waves.



"Thom Stewart" skrev i en meddelelse
...
Yes Peter,

You're correct in what you've said but again you've deviated from
the
origin problem. It doesn't matter THIS TIME!

Pete, this is and old trick question. used in teaching GREAT CIRCLE
NAVIGATION.
(Sorry Bart) Another explaination "Is a fat man wearing his belt
under
his gut because the distance around his stomach is to large.

If the four legs were sailed in a vacuum, without tides and currents
but
on a globe the start and finish would still be different. Since most
DR
Navigation call the difference (Off Set) between start and finish
Drift,
That was the term I used.
The etc was used to let Bart have his fun.

Horv, I know it doesn't make a difference in Units in this problem
but
it did to Jax's conception.

Ole Thom

I forgot to mention, that the speed was absolutely constant during all
4 legs of the trip.

Peter S/Y Anicula


"Peter S/Y Anicula" skrev i en
meddelelse ...
Sorry Thom, but I still don't get it.

Lets say I wanted to visit my girlfriend, and she lives on an island
just west of my island. There is a lot of reefs in the area so to
stay
clear I calculate a trip-plan that will bring me to her by sailing
14
hours east, 14 hours north, 14 hours west and 14 hours south. Since
there is no tide and no wind and the water is totally flat, I have
to
use my twin engines (asymmetrical). Every thing goes as planed and
after 56 hours I arrive at my destination.

Would you still call the Vector from my start-point to my
destination
for drift, current or any such thing?

Peter S/Y Anicula

P.S. Please, don't ask me how the reefs survive if there is no wind
no
current and no waves.



"Thom Stewart" skrev i en meddelelse
...
Yes Peter,

You're correct in what you've said but again you've deviated from
the
origin problem. It doesn't matter THIS TIME!

Pete, this is and old trick question. used in teaching GREAT
CIRCLE
NAVIGATION.
(Sorry Bart) Another explaination "Is a fat man wearing his belt
under
his gut because the distance around his stomach is to large.

If the four legs were sailed in a vacuum, without tides and
currents
but
on a globe the start and finish would still be different. Since
most
DR
Navigation call the difference (Off Set) between start and finish
Drift,
That was the term I used.
The etc was used to let Bart have his fun.

Horv, I know it doesn't make a difference in Units in this problem
but
it did to Jax's conception.

Ole Thom

Peter?

When was the last time you laid out a trip; point to point in Hours?
That is the hook!

A DR route point to point is laid out in Distance. (Miles not time) Each
leg to your Swertheart would be four legs, point to point in miles, with
calculated Drift/mile vectored in. Compass Dev & Var considered to set
up your course heading. When you had that all done, then and only then
would you estimate the lapsed time.
The old saying Pete, "Sailors schedule only departure times, after that
they only have control of direction."

Hope this clears up the problem.

Ole Thom

Would you arrive at your destiantion if you left on a Friday?

Peter S/Y Anicula wrote

Lets say I wanted to visit my girlfriend, and she lives on an island
just west of my island. There is a lot of reefs in the area so to stay
clear I calculate a trip-plan that will bring me to her by sailing 14
hours east, 14 hours north, 14 hours west and 14 hours south. Since
there is no tide and no wind and the water is totally flat, I have to
use my twin engines (asymmetrical). Every thing goes as planed and
after 56 hours I arrive at my destination.

"Peter S/Y Anicula" wrote in message
...

If you sail due east, north, west and south over the ground with the
same speed over the ground and there were no current, no leeway or
other "disturbing factors", you would still not end up at your
starting point (unless....). In fact on the northern hemisphere you
would end up in a position due west of your starting point.

Well!!! Excuuuse me!

Look, I don't often get points, so I feel that I must defend them.

In most places, the effect of tide would be much greater for a 14 hour
"square" than the curvature of the Earth.



Regards


Donal
--