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From: Craig Jungers <crjungers_at_gmail.com>
subject: [Paddlewise] Mind Experiments on a Cold Winter Day - Einstein was onto something
Date: Sun, 21 Jan 2007 11:07:42 -0800
This weekend I stayed on the farm and did nothing; my wife and I are both
fighting off a nasty cold that has raced through our family and finally
caught up with Grandma and Grandpa. This forced downtime has allowed me time
to catch up on reading some of those paddling articles in the magazines. You
know, the stories you just don't have time for because you're busy packing
to go paddling or skiing, etc.

I usually don't get sick. This is one of the few advantages of getting
older; my immune system has finally figured it out. This time the virus
must've been a new critter because my immune system is busily making me
miserable while it iterates through the calculations required to nip the
next attack of this particular strain of virus in the bud. Meanwhile I'm in
my robe and slippers for two-and-a-half days and catching up on my naps.

There are other advantages to getting older (notice that I'm avoiding the
simpler form, "old"). I no longer lay awake worrying about dying young, for
instance. And the database of cute-young-things has grown to remarkable
proportions. It's just amazing how many attractive over... uh... 35 gals 
including both my wife, Sue, and my favorite paddling partner, Pam  there
are in the world; why I never noticed this when I was 25 remains a mystery
to me.

Um... where was I? Oh, yeah. So this weekend I found myself thinking a lot
about various situations encountered in paddling. Albert Einstein, who was a
theoretical and not an experimental physicist, often said that he conducted
"mind experiments" in which he tried to imagine how the universe would react
to different scenarios. Now, I'm no Einstein, but I can do much the same
thing  but simpler  with paddling.

As an example, this morning I started thinking about the mechanics behind
turning a kayak. We all know that we can edge our boats to make them turn
faster but most of us only learned to edge away from a turn. Motorcyclists
and skiers edge into a turn. Why do kayaks do it the other way around?

The mechanics of edging a kayak to make it turn faster are simple: basically
you convert the hull from an essentially flat surface with little rise from
end to end into a curved surface with rocker. The more you edge the more
rocker you get and the faster the boat will respond to the turning moment
imparted by your paddle blade. Since both sides of the kayak are curved
pretty much identically (you'd know it if they weren't) then theoretically
you can turn just as easily to the left by edging to the left (banking) as
you can by edging to the right.

Why we don't generally turn by edging into rather than away from a turn is
mostly due to two factors: 1) The bracing action of the paddle; and, (2) The
effect of the water the bow is moving through.

In the usual turn we edge away from the direction of the turn and use the
paddle on the lowest side of the kayak to propel the boat through the turn
and onto the new heading. The paddle in the water provides the brace to
stabilize our edge and helps keep us from toppling over. Meanwhile the
bottom of the boat, being raised, protects us from having the water (which
is acting as a current as we turn the bow through it) from moving onto the
side of the boat and having that weight topple us over in the direction of
the turn.

But there are situations in which you might want to do exactly the opposite.

For instance, when you are in one current and want to move into another
current an accepted maneuver is to run along the eddy line (the boundary
between two currents) and then turn the boat sharply through the eddy-line
and into the other current by edging the boat into the turn and using your
paddle in a pry (or ruddering) stroke to keep the turn going until you are
entirely into the new current.

Another situation is when you are on the face of a wave surfing down and
want to turn back up the wave and off the face. You'd edge towards the
direction of the turn (and into the wave-face) while using your paddle to
rudder your stern around. This would probably be really interesting in a
round-bottomed sea kayak and your "edge" might turn out to be more of a
side-slip. Remember that the water particles are move in a circular pattern:
up the back of a wave and down the face of a wave so that you would not just
be fighting gravity as you move across that wave-face.

Skiers talk about "carving" turns as they move down the face of the slope
and so do white-water kayakers. But the face of a wave is more akin to
trying to turn in a moving avalanche than it is to a static snow slope so
it's much more difficult for a kayak to get a "bite" on that surface than it
is for a ski to bite into the snow. This is why kayaks designed for playing
in waves and holes (a white water term) have hard edges and flatter bottoms.

Einstein was really onto something with his mind-experiments. There are all
sorts of scenarios you can run through in your head. How to safely move your
heavily-loaded kayak up a beach after landing; a better system of arranging
the load in your boat; a new and safer deck-line arrangement; night
paddling.... the list goes on. While those of us in the frozen north have to
wait to put most of these ideas into practice the southerners can go right
out and try them.

That's ok... I hear the cross-country skiing is pretty slow down there.


Craig Jungers
Royal City, WA
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From: PeterO <rebyl_kayak_at_iprimus.com.au>
subject: RE: [Paddlewise] Mind Experiments on a Cold Winter Day - Einstein was onto something
Date: Tue, 23 Jan 2007 06:40:05 +1100
Craig wrote:
>Motorcyclists and skiers edge into a turn.
>Why do kayaks do it the other way around?

G'Day Craig,

Those were some interesting reflections. Your motor bike reference was very
pertinent. I'm learning to ride a motor bike to try and minimise my
greenhouse gas and was astonished at how many actions on a bike are quite
opposite to what I've been doing in a sea kayak.

Wrists
In a kayak while doing a sweep roll my wrists start off bent slightly
forward to set up the paddle blade
On a motor bike the accelerator wrist is bent slightly back to reduce the
risk of accidentally turning the accelerator full on

Posture
In a kayak: leaning forward with back and shoulders straight
On a motor bike: shoulders slumped forward for better control of direction

Turning
In a sea kayak (not a river kayak): look at the paddle blade in the water as
I turn my torso and take the blade around in a sweep.
On a motor bike: look in the direction I intend to turn

Expect there will be more comparisons while trying not to get confused
learning to ride this motor bike. Did find it was a really bad idea to try
and roll the bike or for that matter surf it:~)

All the best, PeterO
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From: Darryl <Darryl.Johnson_at_sympatico.ca>
subject: RE: [Paddlewise] Mind Experiments on a Cold Winter Day - Einstein was onto something
Date: Mon, 22 Jan 2007 22:45:28 -0500
<snip>
> 
> Expect there will be more comparisons while trying not to get confused
> learning to ride this motor bike. Did find it was a really bad idea to try
> and roll the bike or for that matter surf it:~)
> 
> All the best, PeterO

It's been my experience that salt water and motor-cycles do not mix. 
You could try to find some surf on fresh water: up here in Canada, 
the Great Lakes can put together some impressive waves, as I'm sure 
you know. But you'd have to get a left-hand drive motorcycle for 
driving on our roads. <LOL!!>

-- 
  Darryl
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From: Dave Kruger <kdruger_at_pacifier.com>
subject: Re: [Paddlewise] How a Kayak Turns (was: Mind Experiments ...)
Date: Mon, 22 Jan 2007 13:10:24 -0800
Craig Jungers wrote:

> The mechanics of edging a kayak to make it turn faster are simple: basically
> you convert the hull from an essentially flat surface with little rise from
> end to end into a curved surface with rocker. The more you edge the more
> rocker you get and the faster the boat will respond to the turning moment
> imparted by your paddle blade. 

That's part of it; the other turn-inducing feature is that the hull is now 
asymmetric:  the "down" edge is curved in the direction of the turn; the 
"up" edge is curved in the direction opposite the turn (really, it is a 
portion of the hull you have rolled upward a bit) but has much _less_ 
curvature.  This difference, side-to-side, generates a turning force, also, 
which aids the paddle.  You can see how much this amounts to by starting a 
turn, edged, and then coasting, with no more paddling.  The boat should 
keep on turning, albeit not as tightly as when you were sweeping to help out.

> But there are situations in which you might want to do exactly the opposite.

> Another situation is when you are on the face of a wave surfing down and
> want to turn back up the wave and off the face. You'd edge towards the
> direction of the turn (and into the wave-face) while using your paddle to
> rudder your stern around. This would probably be really interesting in a
> round-bottomed sea kayak and your "edge" might turn out to be more of a
> side-slip. Remember that the water particles are move in a circular pattern:
> up the back of a wave and down the face of a wave so that you would not just
> be fighting gravity as you move across that wave-face.

Aren't the water particles moving _up_ on the _face_ of the wave and down 
on the backside?  If they were moving down on the face of the wave, 
wouldn't the water level on the face be falling instead of rising?

> Skiers talk about "carving" turns as they move down the face of the slope
> and so do white-water kayakers.

And edging on skis with heavy sidecut is an entirely different game than 
edging a kayak (WW or other wise) because sidecut generates a curved edge 
that interacts with the surface to generate turning forces _toward_ that 
side, not away from it.  [I feel particularly unqualified to discuss the 
mechanics of sidecut on snow, inasmuch as I never learned to do parallel 
turns!  Strictly a skidded turn guy, perhaps a consequence of my surfer 
heritage and upbringing!]

-- 
Dave Kruger
Astoria, OR
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From: James Farrelly <JFarrelly5_at_comcast.net>
subject: Re: [Paddlewise] How a Kayak Turns (was: Mind Experiments ...)
Date: Mon, 22 Jan 2007 16:41:28 -0500
People talk about skidded turns and carving. Beautifully executed  
piloting of elegant craft. And then there is me...

I seem to make skid marks and cow licks.  Not pretty but it makes me  
feel young. Especially when I dont die in an endo. Not dying is good.  
At least for awhile.

Jim et al
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From: Derek <glamourpets_at_yahoo.com>
subject: Re: [Paddlewise] How a Kayak Turns (was: Mind Experiments ...)
Date: Mon, 22 Jan 2007 14:57:42 -0800 (PST)
> That's part of it; the other turn-inducing feature
> is that the hull is now 
> asymmetric:  the "down" edge is curved in the
> direction of the turn; the 
> "up" edge is curved in the direction opposite the
> turn (really, it is a 
> portion of the hull you have rolled upward a bit)
> but has much _less_ 
> curvature.  This difference, side-to-side, generates


Shall we add another layer to the discussion by adding
"reverse hard chine" to the discussion?

Example:
http://www.borealdesign.com/_en/kayak.php?id=5

Derek



 
____________________________________________________________________________________
TV dinner still cooling? 
Check out "Tonight's Picks" on Yahoo! TV.
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From: Craig Jungers <crjungers_at_gmail.com>
subject: Re: [Paddlewise] How a Kayak Turns (was: Mind Experiments ...)
Date: Mon, 22 Jan 2007 17:43:21 -0800
On 1/22/07, Dave Kruger <kdruger_at_pacifier.com> wrote:

> Aren't the water particles moving _up_ on the _face_ of the wave and down
> on the backside?  If they were moving down on the face of the wave,
> wouldn't the water level on the face be falling instead of rising?

Here is a quick quote from http://www.mos.org/oceans/motion/wind.html:

'As a wave arrives it lifts water particles. These travel forward,
then down and back so that each particle completes a circle. "

Of course, there could be some confusion as to what constitutes the
"face" of a wave and what is the "back". For me, the face is the
frontside of a moving wave and the water particles are moving down
that face. Even though the water rises, the particles in the water on
the face of that wave are falling.

Counter-intuitive, I know.

An excellent animation of various wave motions can be found at:

http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html

The animation of water waves (3rd animation down) clearly shows how
the particles of water behave in a wave.

> And edging on skis with heavy sidecut is an entirely different game than
> edging a kayak (WW or other wise) because sidecut generates a curved edge
> that interacts with the surface to generate turning forces _toward_ that
> side, not away from it.  [I feel particularly unqualified to discuss the
> mechanics of sidecut on snow, inasmuch as I never learned to do parallel
> turns!  Strictly a skidded turn guy, perhaps a consequence of my surfer
> heritage and upbringing!]

My downhill skiing days left with the ligaments in my left knee
somewhat before the onset of "heavy sidecut". I believe that Head
pioneered sidecut with their metal skiis back in the late 60s so that
turns could be "carved" back then but it took a lot more effort (or
technique). The "carving" is caused by shifting weight forward to flex
the tips up and turning the ski (if viewed side-on) into a slight
u-shape. We can't change the shape of a kayak hull by moving weight
back and forth in the cockpit but we can come close to carving if the
hullshape has an relatively sharp edge. Or perhaps we just confuse it
with a "bite". My poor Nimbus is almost certainly doomed to forever
sideslip down the faces of any waves I want to carve turns on. But you
can come very close with a playboat and even closer with a surfboard;
however whether these include more "skidding" than "carving" is
probably a point of debate.

I just love these winter discussions. :)


Craig Jungers
Royal City, WA
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From: Dave Kruger <kdruger_at_pacifier.com>
subject: Re: [Paddlewise] Water Motion Within a Wave (was: How a Kayak Turns)
Date: Mon, 22 Jan 2007 18:38:36 -0800
Well, this topic has generated more uncertainty than I had expected.  Bob 
Myers and I have a discussion going on, back channel, in which each of us 
is hedging on which of the diagrams we each submitted might be "correct." 
I'll confess I'm at sea, so to speak.

However, I'm pretty certain of this:  Craig, watch that animation in your 
second link closely and you will see that the _motion_ of the blue dots 
does not correspond to what the _language_ in the first link says, if "As a 
wave arrives" is taken to mean "beginning with the trough," and "forward" 
is taken to mean "in the same direction as the wave is traveling."

In fact, the animation in the second link shows the water moving _back_, UP 
the face (like you said originally), until the crest arrives;  then the 
water moves _forward_ and down. (I took out the ":" so the link will come 
up without editing)

Craig wrote:

> Here is a quick quote from http://www.mos.org/oceans/motion/wind.html
> 
> 'As a wave arrives it lifts water particles. These travel forward,
> then down and back so that each particle completes a circle. "
> 
> Of course, there could be some confusion as to what constitutes the
> "face" of a wave and what is the "back". For me, the face is the
> frontside of a moving wave and the water particles are moving down
> that face. Even though the water rises, the particles in the water on
> the face of that wave are falling.

> Counter-intuitive, I know.

And, at odds with the animation in the second site [below], I believe.

> An excellent animation of various wave motions can be found at:
> http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
> The animation of water waves (3rd animation down) clearly shows how
> the particles of water behave in a wave. 

-- 
Dave Kruger
Astoria, OR
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From: Craig Jungers <crjungers_at_gmail.com>
subject: Re: [Paddlewise] Water Motion Within a Wave (was: How a Kayak Turns)
Date: Mon, 22 Jan 2007 20:40:46 -0800
Ya... you're right. The animation doesn't fit the description. So, isn't
*that* interesting.

Craig Jungers
Royal City, WA


On 1/22/07, Dave Kruger <kdruger_at_pacifier.com> wrote:
>
> Well, this topic has generated more uncertainty than I had expected.  Bob
> Myers and I have a discussion going on, back channel, in which each of us
> is hedging on which of the diagrams we each submitted might be "correct."
> I'll confess I'm at sea, so to speak.
>
> However, I'm pretty certain of this:  Craig, watch that animation in your
> second link closely and you will see that the _motion_ of the blue dots
> does not correspond to what the _language_ in the first link says, if "As
> a
> wave arrives" is taken to mean "beginning with the trough," and "forward"
> is taken to mean "in the same direction as the wave is traveling."
>
> In fact, the animation in the second link shows the water moving _back_,
> UP
> the face (like you said originally), until the crest arrives;  then the
> water moves _forward_ and down. (I took out the ":" so the link will come
> up without editing)
>
> Craig wrote:
>
> > Here is a quick quote from http://www.mos.org/oceans/motion/wind.html
> >
> > 'As a wave arrives it lifts water particles. These travel forward,
> > then down and back so that each particle completes a circle. "
> >
> > Of course, there could be some confusion as to what constitutes the
> > "face" of a wave and what is the "back". For me, the face is the
> > frontside of a moving wave and the water particles are moving down
> > that face. Even though the water rises, the particles in the water on
> > the face of that wave are falling.
>
> > Counter-intuitive, I know.
>
> And, at odds with the animation in the second site [below], I believe.
>
> > An excellent animation of various wave motions can be found at:
> > http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
> > The animation of water waves (3rd animation down) clearly shows how
> > the particles of water behave in a wave.
>
> --
> Dave Kruger
> Astoria, OR
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From: Craig Jungers <crjungers_at_gmail.com>
subject: Re: [Paddlewise] Water Motion Within a Wave (was: How a Kayak Turns)
Date: Thu, 25 Jan 2007 23:55:29 -0800
I've given some thought to the "particles in motion within a wave" issue and
have come to the conclusion that Dave is (mostly) right. In addition, the
two url's I gave do agree with each other but you have to think about it
carefully.

First, if you view the wave motion from left to right then the water
particles do move in a clockwise circle; not just up and down.

Now the quote:  "As a wave arrives it lifts water particles. These travel
forward,
then down and back so that each particle completes a circle. "

Now look at the animation here: (The third animation, "water waves" is
pertinent)
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html

The trick here is to focus on the blue particles and, at the same time,
focus on the wave motion. It's apparent that the quote is correct but not
very well written. The animation is clearly right, however. The confusion
(for me ) is that I was imagining the particles staying within the wave.
Instead the particles travel from the trough in front of the advancing wave,
up the face to the crest, then forward within the wave and finally down the
back of the wave to the trough again... where they'll repeat, rinse and
dr... oh, wait.

So the quote which says that the wave lifts the water particles is
correct... they are lifted as the face of the wave travels forward. This
would have to be along the face of the wave as the animation shows. When the
particles are at the crest of the wave they are now within the wave and
following the motion of the wave they move forward. If the wave slows and
steepens at this point then the crest of the wave collapses because the
particles within it carry their own momentum forward and move off the wave
and become unsupported.

But in a swell (or non breaking or cresting wave) the particle would be at
the top of the wave moving forward (in the direction of motion of the wave).
At this point the waves move forward and out from under the particle (in a
non-breaking wave) and the particle descends along the back of the wave (the
trailing edge) and into the trough completing the clockwise circle.

This means, of course, that the animation and the textual description both
describe the same things. And Dave, I submit, is mostly right. Water
particles in the face of the wave are rising, not falling.


Craig Jungers
Royal City, WA



On 1/22/07, Dave Kruger <kdruger_at_pacifier.com> wrote:
>
> Well, this topic has generated more uncertainty than I had expected.  Bob
> Myers and I have a discussion going on, back channel, in which each of us
> is hedging on which of the diagrams we each submitted might be "correct."
> I'll confess I'm at sea, so to speak.
>
> However, I'm pretty certain of this:  Craig, watch that animation in your
> second link closely and you will see that the _motion_ of the blue dots
> does not correspond to what the _language_ in the first link says, if "As
> a
> wave arrives" is taken to mean "beginning with the trough," and "forward"
> is taken to mean "in the same direction as the wave is traveling."
>
> In fact, the animation in the second link shows the water moving _back_,
> UP
> the face (like you said originally), until the crest arrives;  then the
> water moves _forward_ and down. (I took out the ":" so the link will come
> up without editing)
>
> Craig wrote:
>
> > Here is a quick quote from http://www.mos.org/oceans/motion/wind.html
> >
> > 'As a wave arrives it lifts water particles. These travel forward,
> > then down and back so that each particle completes a circle. "
> >
> > Of course, there could be some confusion as to what constitutes the
> > "face" of a wave and what is the "back". For me, the face is the
> > frontside of a moving wave and the water particles are moving down
> > that face. Even though the water rises, the particles in the water on
> > the face of that wave are falling.
>
> > Counter-intuitive, I know.
>
> And, at odds with the animation in the second site [below], I believe.
>
> > An excellent animation of various wave motions can be found at:
> > http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
> > The animation of water waves (3rd animation down) clearly shows how
> > the particles of water behave in a wave.
>
> --
> Dave Kruger
> Astoria, OR
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From: <cholst_at_bitstream.net>
subject: Re: [Paddlewise] Water Motion Within a Wave (was: How a Kayak Turns)
Date: Fri, 26 Jan 2007 12:02:38 -0600 (CST)
Here's another way for you ocean paddlers, whitewater playboaters, and
other surfers to think about it: If the water particles traveled downward
in the face of a wave, you would find it very difficult to brace in that
face. The upward motion gives a much firmer purchase.

Chuck Holst
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From: Michael Daly <mikedaly_at_magma.ca>
subject: Re: [Paddlewise] How a Kayak Turns
Date: Tue, 23 Jan 2007 01:00:33 -0500
Craig Jungers wrote:

> I believe that Head
> pioneered sidecut with their metal skiis back in the late 60s so that
> turns could be "carved" back then but it took a lot more effort (or
> technique). 

I've seen old wood skis with side cut, so it goes well back before the '60s.

 > The "carving" is caused by shifting weight forward to flex
> the tips up and turning the ski (if viewed side-on) into a slight
> u-shape.

You can reverse the camber of a ski without shifting weight forward.  In fact, 
with cambered skis, you can do this without any sidecut but sidecut makes it 
easier.  But you are right - once it's reversed in camber, it's gonna carve.

Mike
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From: Bob Myers <qajaqbob_at_gmail.com>
subject: Re: [Paddlewise] How a Kayak Turns (was: Mind Experiments ...)
Date: Mon, 22 Jan 2007 13:46:53 -0800
On 1/22/07, Dave Kruger <kdruger_at_pacifier.com> wrote:
> Craig Jungers wrote:
> Remember that the water particles are move in a circular pattern:
> > up the back of a wave and down the face of a wave so that you would not just
> > be fighting gravity as you move across that wave-face.
>
> Aren't the water particles moving _up_ on the _face_ of the wave and down
> on the backside?  If they were moving down on the face of the wave,
> wouldn't the water level on the face be falling instead of rising?

No...  circular pattern, not just up and down.  At the top of the
wave, they move faster than the wave, forwards, and then down the
face.  Think about what happens when a wave breaks!  The top of the
wave is going too fast and can't complete the circle.
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From: Dave Kruger <kdruger_at_pacifier.com>
subject: Re: [Paddlewise] How a Kayak Turns
Date: Mon, 22 Jan 2007 14:03:17 -0800
Bob Myers wrote:
> On 1/22/07, Dave Kruger wrote:

>> Aren't the water particles moving _up_ on the _face_ of the wave and down
>> on the backside?  If they were moving down on the face of the wave,
>> wouldn't the water level on the face be falling instead of rising?

> No...  circular pattern, not just up and down.  At the top of the
> wave, they move faster than the wave, forwards, and then down the
> face.  Think about what happens when a wave breaks!  The top of the
> wave is going too fast and can't complete the circle.

Bob, I think Craig's reference was to the _face_ of the wave, not the 
breaking crest, which does indeed topple after the broken crest moves ahead 
of the rest of the wave.

In swell, sure, circular motion, shifting to elliptical as the wave reaches 
shallower water.  But the issue is whether there is an upward component or 
a downward component on the face of the wave.  Don't have my Waves and 
Beaches at hand, but ...

Check out this animation and you'll see that the water motion on the face 
of the wave is _upward_ and rearward just as the trough passes, shifting to 
_upward_ and forward as the crest approaches; it runs too fast to see -- 
you'll have to stop it in mid-stroke:  http://tinyurl.com/5vawv

-- 
Dave Kruger
Astoria, OR
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From: Dave Kruger <kdruger_at_pacifier.com>
subject: Re: [Paddlewise] How a Kayak Turns
Date: Mon, 22 Jan 2007 14:16:20 -0800
Bob Myers wrote:
> See, for example, 
> http://hyperphysics.phy-astr.gsu.edu/hbase/waves/watwav2.html

Ooops! You're right!  Ignore that previous posting!

Looking at faces of the waves in the figure labeled "Progression of the 
Wave," I see a downward component and a forward component, with the 
relative magnitudes changing as the face passes.  The water particles 
within the water have a _different_ motion than the _surface_ does.  I 
think I'm getting it, now.  The surface rises _not_ because bulk water is 
moving up, but rather, the disturbance is moving from left to right.

OK.  Apologies to Craig for doubting him, and thanks to Bob for clearing 
this up.  Mea culpa -- always glad to learn about a misconception.

-- 
Dave Kruger
Astoria, OR
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