judging current; rules of thumb?
 

Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of judging
the current, when you are under way, and there are no fixed objects within
sight?

Shaun

judging current; rules of thumb?
 

"Shaun Van Poecke" wrote in message
...
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of judging
the current, when you are under way, and there are no fixed objects within
sight?

Shaun


Yes, there are.

--
jlrogers±³©

judging current; rules of thumb?
 

"Shaun Van Poecke" wrote
Is there any reasonably accurate (say, within a knot or so) way of judging the current, when you are under way, and
there are no fixed objects within sight?


Yes, there is. All you have to do is look on the charts for those little arrow thingies...
Or you can look in the tide and tide current books.

Cheers,
Ellen

judging current; rules of thumb?
 

Shaun Van Poecke wrote:
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of judging
the current, when you are under way, and there are no fixed objects within
sight?

Shaun



No, there aren't.

--
jeff

judging current; rules of thumb?
 

"Jeff" wrote in message
. ..
Shaun Van Poecke wrote:
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of
judging the current, when you are under way, and there are no fixed
objects within sight?

Shaun

No, there aren't.

--
jeff


Yes, there is.

--
jlrogers±³©

judging current; rules of thumb?
 

"jlrogers±³©" wrote in message
t...
"Shaun Van Poecke" wrote in message
...
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of
judging the current, when you are under way, and there are no fixed
objects within sight?

Shaun


Yes, there are.

--
jlrogers±³©



I can't think of any way to do it without some kind of instrument.

If there's nothing in sight, you have no point of reference.

Tell us please....


--
"j" ganz @@
www.sailnow.com

judging current; rules of thumb?
 

jlrogers±³© wrote:
"Jeff" wrote in message
. ..
Shaun Van Poecke wrote:
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of
judging the current, when you are under way, and there are no fixed
objects within sight?

Shaun
No, there aren't.

--
jeff


Yes, there is.

OK, please explain. Maybe this will bring Jax out of the woodwork to
tell us that Einstein proved that dead reckoning is impossible.

judging current; rules of thumb?
 

"Jeff" wrote
OK, please explain. Maybe this will bring Jax out of the woodwork to tell us that Einstein proved that dead reckoning
is impossible.


I can explain it too. I've been thinking about a way off and on since you said there's no
way. Remember way back when we were talking about me getting in irons because of wind
going the same speed as the current? You said unless there's land there's no way to tell.
Well there is and I'm going to tell how.
1-- tie a long string on an empty wine bottle.
2-- throw the wine bottle off the boat when your sailing.
3-- get a stop watch time on how long it takes for the string to go tight and pull the bottle along.
4-- pull the bottle back aboard.
5-- turn around and go the opposite direction
6-- repeat the first three steps.
Since the bottle goes with the current it lets you measure the current. The wind is independent.
The bottle lets you connect to the current. It lets you see it. Your boat measures the wind speed. It's
not as fast as the wind but it's moved by it the same each way. Reaching that is. You have to reach
both ways.

Cheers,
Ellen

judging current; rules of thumb?
 

Jeff wrote:
jlrogers±³© wrote:
"Jeff" wrote in message
. ..
Shaun Van Poecke wrote:
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of
judging the current, when you are under way, and there are no fixed
objects within sight?

Shaun
No, there aren't.

--
jeff


Yes, there is.

OK, please explain. Maybe this will bring Jax out of the woodwork to
tell us that Einstein proved that dead reckoning is impossible.


Use a venturi/pitot boat knotometer and rotate it 360 degrees noting the
speed accurately for increments of angle.

If it reads 0 knots for all angles your GPS speed is the current speed.

If it reads 5 knots forward, 0 knots aft and the GPS speed is 4 knots
the current is 1 knot from aft.

The same procedure is done for sideways currents but one must use
trigonometry, a feat easily accomplished on my Mensa circular mind meld
slide rule. I can do all the calculations in my head while wearing just
a set of Speedo briefs.

I've devised a set of Lorentz contraction gauges to measure all absolute
motion precisely in 3 dimensions. Aliens are after me to keep this gift
to mankind from falling in human hands so I must travel in disguise.

Jax

judging current; rules of thumb?
 

Nope. Don't work. Not Nohow.

Ellen MacArthur wrote:
"Jeff" wrote
OK, please explain. Maybe this will bring Jax out of the woodwork to tell us that Einstein proved that dead reckoning
is impossible.

I can explain it too. I've been thinking about a way off and on since you said there's no
way. Remember way back when we were talking about me getting in irons because of wind
going the same speed as the current? You said unless there's land there's no way to tell.
Well there is and I'm going to tell how.
1-- tie a long string on an empty wine bottle.
2-- throw the wine bottle off the boat when your sailing.
3-- get a stop watch time on how long it takes for the string to go tight and pull the bottle along.
4-- pull the bottle back aboard.
5-- turn around and go the opposite direction
6-- repeat the first three steps.
Since the bottle goes with the current it lets you measure the current.

but the boat is also going with the current. The boat speed is
"through the water," not "over the bottom."

The wind is independent.

The wind that the boater would call "true wind" is actually the vector
sum of the wind and current (adjusting signs as appropriate).

The bottle lets you connect to the current.

nope. You're connected to the current while you're in the boat.

It lets you see it.

nope.

Your boat measures the wind speed.

Nope. The wind it feels actually has a component added by the current.

It's
not as fast as the wind but it's moved by it the same each way. Reaching that is. You have to reach
both ways.

And how do you tell the boat speed over the bottom, as opposed to
through the water?

judging current; rules of thumb?
 

"Jeff" wrote in message
. ..
Nope. Don't work. Not Nohow.

Ellen MacArthur wrote:
"Jeff" wrote
OK, please explain. Maybe this will bring Jax out of the woodwork to
tell us that Einstein proved that dead reckoning is impossible.

I can explain it too. I've been thinking about a way off and on
since you said there's no
way. Remember way back when we were talking about me getting in irons
because of wind
going the same speed as the current? You said unless there's land there's
no way to tell.
Well there is and I'm going to tell how.
1-- tie a long string on an empty wine bottle.
2-- throw the wine bottle off the boat when your sailing.
3-- get a stop watch time on how long it takes for the string to go
tight and pull the bottle along.
4-- pull the bottle back aboard.
5-- turn around and go the opposite direction
6-- repeat the first three steps.
Since the bottle goes with the current it lets you measure the
current.


You're right Jeff... but Neal is an idiot, so what do you expect.

--
"j" ganz @@
www.sailnow.com

judging current; rules of thumb?
 

"JaxAsby" wrote in message
...
Jeff wrote:
jlrogers±³© wrote:
"Jeff" wrote in message
. ..
Shaun Van Poecke wrote:
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of
judging the current, when you are under way, and there are no fixed
objects within sight?

Shaun
No, there aren't.

--
jeff


Yes, there is.

OK, please explain. Maybe this will bring Jax out of the woodwork to
tell us that Einstein proved that dead reckoning is impossible.


Use a venturi/pitot boat knotometer and rotate it 360 degrees noting the
speed accurately for increments of angle.

If it reads 0 knots for all angles your GPS speed is the current speed.

If it reads 5 knots forward, 0 knots aft and the GPS speed is 4 knots the
current is 1 knot from aft.

The same procedure is done for sideways currents but one must use
trigonometry, a feat easily accomplished on my Mensa circular mind meld
slide rule. I can do all the calculations in my head while wearing just a
set of Speedo briefs.

I've devised a set of Lorentz contraction gauges to measure all absolute
motion precisely in 3 dimensions. Aliens are after me to keep this gift to
mankind from falling in human hands so I must travel in disguise.

Jax


Stupid sockpuppet can't even read:

"Here's one for those of you out there without onboard
instruments/knotmeter/gps"

--
"j" ganz @@
www.sailnow.com

judging current; rules of thumb?
 

"Jeff" wrote
Nope. Don't work. Not Nohow.

but the boat is also going with the current. The boat speed is "through the water," not "over the bottom."

It will work. Where you go wrong is saying the boat is going with the current.
It is if it's dead in the water. When it's sailing it's also going with the wind.
You never want to give the wind any credit. So the current goes two or three
knots. And the wind makes the boat go double that. You can use the boat motion
caused by the wind to measure the current. You just have to go back and forth.
You don't need instruments to measure the wind. You can use Beaufort. The
wind becomes your reference point. It's better if you go back and forth at least
every forty-five degrees to really tell what's going on with the current.

The wind that the boater would call "true wind" is actually the vector sum of the wind and current (adjusting signs as
appropriate).

And if there's no boat around? There's still apparent wind if you have
a bottle drifting with the current.

nope. You're connected to the current while you're in the boat.

Only if your just drifting along. Once your sailing the wind makes your boat
move independently of the current. The current still affects it but it affects it
different in different directions.

Your boat measures the wind speed.

You just contradicted yourself.

And how do you tell the boat speed over the bottom, as opposed to through the water?

The bottom's got nothing to do with this. He just wanted to know if you could know the
current with no outside landmarks and the bottom is an outside landmark.

Cheers,
Ellen

judging current; rules of thumb?
 

Sorry Ellen, its basic physics. Galileo figured it out about 400
years ago. He called it the Principle of Relativity. (Einstein used
the word "relativity" as a homage to Galileo.)

Here's a portion of his writings n the subject:
http://physics.syr.edu/courses/modul...E/galileo.html


Ellen MacArthur wrote:
"Jeff" wrote
Nope. Don't work. Not Nohow.

but the boat is also going with the current. The boat speed is "through the water," not "over the bottom."

It will work. Where you go wrong is saying the boat is going with the current.

Your boat isn't affected by the current? That's quite remarkable!

It is if it's dead in the water. When it's sailing it's also going with the wind.
You never want to give the wind any credit.

The boat moves according to the wind it feels. Its not the same as
the wind it would feel if there were no current.

So the current goes two or three
knots. And the wind makes the boat go double that.

That's speed over the bottom, which you can't determine.

You can use the boat motion
caused by the wind to measure the current.

No, you'll measure the speed through the water as the same in both
directions.

You just have to go back and forth.

Won't help - you'll measure "zero" current

You don't need instruments to measure the wind. You can use Beaufort. The
wind becomes your reference point. It's better if you go back and forth at least
every forty-five degrees to really tell what's going on with the current.

You might be able to guess that there's a strong current against a
strong wind if the steepness of the chop doesn't match the wind, but
this is only a guess and certainly not accurate to a knot. Otherwise,
what you're saying is just gibberish.



The wind that the boater would call "true wind" is actually the vector sum of the wind and current (adjusting signs as
appropriate).

And if there's no boat around? There's still apparent wind if you have
a bottle drifting with the current.

Sure, but there's no way to determine the components.


nope. You're connected to the current while you're in the boat.

Only if your just drifting along. Once your sailing the wind makes your boat
move independently of the current. The current still affects it but it affects it
different in different directions.

How is that? Do you have some sort of "magic" current? Up here, the
current affects you the same no matter what direction you're pointing.


Your boat measures the wind speed.

You just contradicted yourself.

Never.


And how do you tell the boat speed over the bottom, as opposed to through the water?

The bottom's got nothing to do with this. He just wanted to know if you could know the
current with no outside landmarks and the bottom is an outside landmark.


If you know the current, and the speed through the water, then you
know the speed over ground. If you can't determine the speed over
ground, then you can't determine the current.

judging current; rules of thumb?
 

Shaun Van Poecke wrote:
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of judging
the current, when you are under way, and there are no fixed objects within
sight?

Shaun



The ocean current at the surface is mostly wind driven. The surface
current diminishes rapidly with depth. Researchers have used with
limited success a long thin float dropped into the water. About one
meter sticks above the surface and about 3-6 meters below. The angle
that the stick tilts indicates the surface current speed relative to the
deeper layer current and the direction of tilt shows the current
direction. A bamboo pole on a weighted clorox bottle works ok. If the
float is anchored it is a better indicator.

Popeye

judging current; rules of thumb?
 

jlrogers±³© wrote:
"Jeff" wrote in message
. ..
Shaun Van Poecke wrote:
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of
judging the current, when you are under way, and there are no fixed
objects within sight?

Shaun
No, there aren't.

--
jeff


Yes, there is.

No, there aren't.

judging current; rules of thumb?
 

"Shaun Van Poecke" wrote in message
...
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of judging
the current, when you are under way, and there are no fixed objects within
sight?

Shaun



Yes, Shaun, there is. For your edification, I refer you to, "We, the
Navigators The Ancient Art of Landfinding in the Pacific," by David Lewis.
Specifically chapters 5, "Keeping course by Sun, Swills, and Wind," chapter
6, "Dead Reckoning," which directly addresses your question, and chapter 7,
"Orientation Concepts in Dead Reckoning."

http://books.google.com/books?vid=IS...H54BfXwOv1l5Zs


--
jlrogers±³©

judging current; rules of thumb?
 

"jlrogers±³©" wrote in message
et...
Yes, Shaun, there is. For your edification, I refer you to, "We, the
Navigators The Ancient Art of Landfinding in the Pacific," by David Lewis.
Specifically chapters 5, "Keeping course by Sun, Swills, and Wind,"
chapter

Would they be the '6 o'clock swills' they had in Australia before they
changed the drinking hours? It was a helluva job keeping any proper course
after those... :-)

judging current; rules of thumb?
 

"Edgar" wrote in message
...

"jlrogers±³©" wrote in message
et...
Yes, Shaun, there is. For your edification, I refer you to, "We, the
Navigators The Ancient Art of Landfinding in the Pacific," by David
Lewis.
Specifically chapters 5, "Keeping course by Sun, Swills, and Wind,"
chapter

Would they be the '6 o'clock swills' they had in Australia before they
changed the drinking hours? It was a helluva job keeping any proper course
after those... :-)



Swills, smells, swells. Every data bit plots the navigator home.

--
jlrogers±³©

judging current; rules of thumb?
 

jlrogers±³© wrote:
"Shaun Van Poecke" wrote in message
...
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of judging
the current, when you are under way, and there are no fixed objects within
sight?

Yes, Shaun, there is. For your edification, I refer you to, "We, the
Navigators The Ancient Art of Landfinding in the Pacific," by David Lewis.
Specifically chapters 5, "Keeping course by Sun, Swills, and Wind," chapter
6, "Dead Reckoning," which directly addresses your question, and chapter 7,
"Orientation Concepts in Dead Reckoning."

http://books.google.com/books?vid=IS...H54BfXwOv1l5Zs

Ah! One of my favorites books! Thanks for the mention, I think it
may be time to read it again!

However, I don't think it supports your position. For instance, in
the chapter on Dead Reckoning, it begins the section on Current Set
with "This presents a difficult and intractable problem of which the
Pacific Island navigators were only too well aware ..." It goes on to
describe how they memorized all of the currents, and then took careful
back bearings on departure to determine how the currents were
deviating from the expected norm.

The traditional navigators did make use of a variety of signs, such as
the steepness of waves (as I mentioned in another post) but I doubt
the casual Western observer could reliably use these sign to measure
to within a knot.

judging current; rules of thumb?
 

"Jeff" wrote \
Sorry Ellen, its basic physics. Galileo figured it out about 400 years ago. He called it the Principle of Relativity.
(Einstein used the word "relativity" as a homage to Galileo.)

Here's a portion of his writings n the subject:
http://physics.syr.edu/courses/modul...E/galileo.html

Your just trying to confuse me with the relativity stuff. That's got nothing to
do with sailing. It's all about mass and energy and the speed of light. Physics and
the galaxy.
But, darn you, you had me thinking about it all night and I tried to think of some
way to prove it. But my bottle on a string doesn't work. Your right all it does is tell
the boat speed through the water. I was getting confused because I just kept thinking
about land and the current vs. land and it made sense. But he asked how to tell current
when no land's in sight and no instruments allowed. So I had to totally get rid of land.
I thought about that Star Trek episode where they found a planet that was just a
big ball of water all the way to the center. No land. So, if your sailing there you'd
never know if there was a current because you only have the water and the air.
There's no way to know (you can't use a sextant for a star sight) which is moving,
the water or the air. Your right on the edge between the two. You can't know.
So I was ready to say I lose and you win but I had a dream and in the dream
I saw big waves in the Gulf Stream which were really really big and breaking because
the wind was blowing like a hurricane against the current. Ah ha! That's it.
All you need is a table with wave heights and periods. If the waves are larger and
have different periods than they'd have in still water then there's a current.
So you CAN tell after all. No instruments needed just wave tables.

Cheers,
Ellen

judging current; rules of thumb?
 

"Jeff" wrote in message
...
jlrogers±³© wrote:
"Shaun Van Poecke" wrote in message
...
Here's one for those of you out there without onboard
instruments/knotmeter/gps....

Is there any reasonably accurate (say, within a know or so) way of
judging the current, when you are under way, and there are no fixed
objects within sight?

Yes, Shaun, there is. For your edification, I refer you to, "We, the
Navigators The Ancient Art of Landfinding in the Pacific," by David
Lewis. Specifically chapters 5, "Keeping course by Sun, Swills, and
Wind," chapter 6, "Dead Reckoning," which directly addresses your
question, and chapter 7, "Orientation Concepts in Dead Reckoning."

http://books.google.com/books?vid=IS...H54BfXwOv1l5Zs

Ah! One of my favorites books! Thanks for the mention, I think it may be
time to read it again!

However, I don't think it supports your position. For instance, in the
chapter on Dead Reckoning, it begins the section on Current Set with "This
presents a difficult and intractable problem of which the Pacific Island
navigators were only too well aware ..." It goes on to describe how they
memorized all of the currents, and then took careful back bearings on
departure to determine how the currents were deviating from the expected
norm.

The traditional navigators did make use of a variety of signs, such as the
steepness of waves (as I mentioned in another post) but I doubt the casual
Western observer could reliably use these sign to measure to within a
knot.


True, but with "enough experience" a bow wave will tell one the speed of the
boat through the water. Wind judgment with knowledge of your boat will tell
you what your speed ought to be sans current. The difference is the
current.

--
jlrogers±³©

judging current; rules of thumb?
 

Ellen MacArthur wrote:
"Jeff" wrote \
Sorry Ellen, its basic physics. Galileo figured it out about 400 years ago. He called it the Principle of Relativity.
(Einstein used the word "relativity" as a homage to Galileo.)

Here's a portion of his writings n the subject:
http://physics.syr.edu/courses/modul...E/galileo.html

Your just trying to confuse me with the relativity stuff. That's got nothing to
do with sailing. It's all about mass and energy and the speed of light. Physics and
the galaxy.

No, not at all. That's Einstein Theories of Special and General
Relativity. Galileo's Principle of Relativity is much more mundane.
Read that link again - its an interesting scientific observation made
almost 400 years ago.

But, darn you, you had me thinking about it all night and I tried to think of some
way to prove it. But my bottle on a string doesn't work. Your right all it does is tell
the boat speed through the water. I was getting confused because I just kept thinking
about land and the current vs. land and it made sense. But he asked how to tell current
when no land's in sight and no instruments allowed. So I had to totally get rid of land.
I thought about that Star Trek episode where they found a planet that was just a
big ball of water all the way to the center. No land. So, if your sailing there you'd
never know if there was a current because you only have the water and the air.
There's no way to know (you can't use a sextant for a star sight) which is moving,
the water or the air. Your right on the edge between the two. You can't know.
So I was ready to say I lose and you win but I had a dream and in the dream
I saw big waves in the Gulf Stream which were really really big and breaking because
the wind was blowing like a hurricane against the current. Ah ha! That's it.
All you need is a table with wave heights and periods. If the waves are larger and
have different periods than they'd have in still water then there's a current.
So you CAN tell after all. No instruments needed just wave tables.

Too late, I already mentioned this possibility twice. However, this
only works in limited situations, and is highly variable. The wind
has to be strong, and against a real current for a significant period
of time before the chop is measurable. "Wave tables" would be of
little use, it would take someone with serious local knowledge to be
able to determine the current to one knot accuracy even in the most
favorable situation.

judging current; rules of thumb?
 

I have a very vague memory of maybe having read that book.... is that the
one where the guy sails to the pacific in a sloop or something and does a
bunch of research on how the navigators there follow 'star paths' by having
them navigate the boat in double blind tests (he locked away all his charts
and compass)? If so it was a pretty good read. Ill have to have a look for
that one again....

If i recall, there was something about finding land by phosphoresence as
well?

Shaun

Yes, Shaun, there is. For your edification, I refer you to, "We, the
Navigators The Ancient Art of Landfinding in the Pacific," by David Lewis.
Specifically chapters 5, "Keeping course by Sun, Swills, and Wind,"
chapter 6, "Dead Reckoning," which directly addresses your question, and
chapter 7, "Orientation Concepts in Dead Reckoning."

http://books.google.com/books?vid=IS...H54BfXwOv1l5Zs

judging current; rules of thumb?
 

Shaun Van Poecke wrote:
I have a very vague memory of maybe having read that book.... is that the
one where the guy sails to the pacific in a sloop or something and does a
bunch of research on how the navigators there follow 'star paths' by having
them navigate the boat in double blind tests (he locked away all his charts
and compass)? If so it was a pretty good read. Ill have to have a look for
that one again....

That's the one


If i recall, there was something about finding land by phosphoresence as
well?

"Telapa"


Shaun

Yes, Shaun, there is. For your edification, I refer you to, "We, the
Navigators The Ancient Art of Landfinding in the Pacific," by David Lewis.
Specifically chapters 5, "Keeping course by Sun, Swills, and Wind,"
chapter 6, "Dead Reckoning," which directly addresses your question, and
chapter 7, "Orientation Concepts in Dead Reckoning."

http://books.google.com/books?vid=IS...H54BfXwOv1l5Zs

judging current; rules of thumb?
 

"Shaun Van Poecke" wrote:

I have a very vague memory of maybe having read that book.... is that the
one where the guy sails to the pacific in a sloop or something and does a
bunch of research on how the navigators there follow 'star paths' by having
them navigate the boat in double blind tests (he locked away all his charts
and compass)? If so it was a pretty good read. Ill have to have a look for
that one again....

Your vague memory may in this respect be refreshed, and also expanded,
if you lread the discussion in Wikipedia about the Polynesian
Voyagaing Society and also the material/links on the PVS's own website
-- re. which, see, e.g.

http://pvs.kcc.hawaii.edu/aboutpvs.html
http://hokulea.soest.hawaii.edu/
http://en.wikipedia.org/wiki/Polynes...yaging_Society