PaddleWise by thread

From: Jackie Fenton <jackie_at_intelenet.net> subject: (no subject) Date: Thu, 17 May 2001 15:24:39 -0700 (PDT) · This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:33:22 PDT

From: "John Winters" <jwinters_at_onlink.net> 
To: <PaddleWise_at_PaddleWise.net>
References: <200105160657.XAA26639_at_onlink.net> 
Subject: Re: a paddle selection issue 
Date: Thu, 17 May 2001 09:47:54 -0400
Content-Transfer-Encoding: 7bit
Status: RO
Content-Type: text/plain; charset="iso-8859-1"
Content-Length: 14567

At 12:36 PM -0700 5/15/01, Peter A. Chopelas wrote:
>  Nick Schade  wrote:

I apologise if this gets lengthy. I will put N in front of Nick's 
comments and P in front of Peter's

N> > More apparent slippage is inefficient...."Slippage" is an indication
 > > that you are accelerating water and thus wasting energy.

Nick is correct here. Ideally we would eliminate as much slippage as is
consistent with the efficiency of the power whether an engine or a human. We
can't get rid of it all because we need some motion to develop thrust. I use
the term "thrust" because you can develop thrust with drag, lift or a
combination of both.

P> Your first statement is meaningless, how can you say more slippage is
> inefficient?  Did you ever measure it?  How?  You are making unwarranted
> assumptions.   What is slippage anyway?  (not the 'feel' but something
> measurable).  So it depends on how you measure "slippage"...either it is
> all slippage, or none of it is.
>
> The word "slippage" is meaningless unless you define it, and depending how
> you define it could mean almost anything.  It is best to avoid such
> vague words.

Actually naval architects (and I presume aeronautical engineers) have
precise meanings for slippage. The formula used by Taylor is slippage =
speed of the propeller - speed of advance divided by the speed of the
propeller. For paddles he uses Slippage = velocity of the paddle blade - the
velocity of the boat divided by the velocity of the paddle blade. Basically
the same thing. So, "Slippage" is hardly vague.

N> > As long as you move the paddle parallel to the direction of motion
> > desired all the force applied will go directly to propelling the
> > boat.

Nick is right although I doubt if anyone actually accomplishes this
regularly. I suspect Nick mentioned this elsewhere as I recall him
discussing it some time back.

P> This is totally false and again based on uninformed intuitive ideas.  A
> propeller on a boat or aircraft moves exactly perpendicular to the
> direction of travel yet fairly efficiently provides all the forward
> motion.  you can do the same thing with a paddle in a sculling type 
> stroke, providing forward motion without any movement of the paddle in 
> the direction of travel.

I think Peter has missed the point. Nick was talking about the paddle using
primarily drag for thrust. I do  not think he meant that you could not
create lift with a paddle. Peter also failed to recognise that the flow
across the propeller is more important than the direction of travel of
the plane. While the blades rotate in a plane lying across the plane's path
they actually travel through the air at an angle called the angle of attack.
Imagine yourself sitting on a propeller facing forward and observing the
direction of the air. Would it come from directly ahead or would it come
from the side or radially relative to the propeller and you?

P >You could also have a shape on the blade the provides
> very little forward motion even though you are pulling parallel to the
> hull.

True and it supports Nick since if you tried to paddle with your blade
oriented fore and aft you could paddle as hard and fast as you wanted in
have difficulty making much headway. I.e. lots of slip = very little thrust.

P.Paddle wheel boats move
> parallel to the line of travel, but why do you think they are not used
> commercially?  They are very wasteful and inefficient.

Actually paddle wheels have proven to have greater efficiency than most
propellers. Taylor has some graphs on this that show efficiency of
propellers and the losses due to slippage. A tank test study done in New
Zealand shows paddles (old racing style) having efficiencies of 87% which is
quite good compared to even the best propellers. The reason paddle wheels
are not used has to do with their vulnerability to damage and the fact that
side-wheel are alternately in and out of the water in waves and so lose
efficiency in this way. We paddlers get around this by not having our
paddles fixed to the boat. Also, modern, lightweight,  high speed engines
work more efficiently with propellers

N>  It does not matter how the force is created: drag, friction,
> > turbulence, lift, whatever. The only time there is wasted force is
> > when there is a component of motion perpendicular to the direction of
> > propulsion, then all the same things - drag, friction, turbulence,
> > lift, whatever - are bad things. The only useful force is one
> > propelling you in the direction you want to go and it doesn't matter
> > how you create it.

Actually I would amend this to include any drag forces acting at an angle to
the direction of travel. Even for a paddle operating in pure lift you would
want to reduce the drag on the paddle as much as possible.

P
(SNIP)>how you move the paddle is
> not even important since it will vary with the type of paddle you are
> using.

Actually the type of paddle would make it very important how you move the
paddle. I think Peter contradicts himself as later on he tells you how
important it is to use the "proper" stroke.

P> Take the extremes:  An ice cream scoop type paddle would probably be best
> pulling strait back, linearly accelerating the fluid.  But the other
> extreme, a paddle that looked like an airplane propeller, would be best
> used by sweeping it through the water in an arc, and WAY more efficient
> than the ice-cream scoop paddle--hence the native style paddle.

I am not sure what Peter means by "WAY" more efficient. The Wing paddle
which uses a more efficient stroke than that used by most recreational
paddlers is only about 7% more efficient than the conventional stroke and
old style paddle. (I wish I could remember the names of all the researchers
on that project. I will look for it if there is interest).

Peter earlier commented on precision in terms so I have to take issue with
his use of "native style paddle" . What  characteristics define a "native
style paddle" and when would a "Euro" style paddle become a native style and
vice versa? This kind of term really is meaningless since the range of
shapes and sizes of traditional paddles covers such a wide range. Some of
them rather poor as paddles. Precision in this kind of discussion would
improve if people would describe paddles by their aspect ratio (span squared
divided by area), chord depth, area, and plan form. I don't know of any
proof that the native style paddle is more efficient. I think it only fair
that he would have to provide the same proof that he requires of Nick.

One of the things that no one (that I know of) has addressed are the energy
losses due to the starting vortex at the surface (interface between fluids
of differing densities). I also have not seen any objective testing of the
so called "traditional" stroke as to its overall efficiency. This has been
done with the sprint stroke and conventional stroke. Without objective
testing I don't know how one can say anything concrete about the traditional
style.

P> Do not forget that there are a lot of other demands we put on a paddle
> besides forward motion.  And the propeller blade vs. the ice-cream scoop
> will have to be used very differently to meet these different demands, 
> some better than others, and some requiring more skill and practice.  But
> overall it is my observation that the native paddles and techniques are
> superior.  JUST GO TRY IT!  (but learn to use it properly first!).

Karl Popper has shown that a scientific theory must be presented in such a
way as to provide a test for the theory's falsity. If you cannot test for
falsity then the theory is not a scientific theory. For example, what test
can you recommend to prove the existence of a god? If a person were to
follow Peter's advice and test the suggested paddle and technique and
determine it was not more efficient would that prove him wrong? Test
paddling only creates, destroys, denies, or supports opinions.  Of course, a
person's opinions are important - to him - but we should not confuse them
with facts.

P> Perhaps the ice-cream scoop is more easily learned, and proper technique is
> more obvious to the beginning paddler or in rental fleets.  But that is no
> reason for all who hope to become experienced and skilled paddlers to use
> it. obvious It would be like never graduating from a tricycle or training
> wheels to a two wheeler.  You never experience the full advantage and 
> benefit of the sport with such a severe handicap because you are forced 
> to use inefficient techniques and poorly designed equipment.

The logical failing here is that Peter equates experienced and skilled
paddlers with a particular type of stroke. I don't know who set him up as
the guru of paddling but I doubt if he has worldwide standing on this. I
have no idea what he means by "severe handicap". How much is severe? What
handicap is he talking about? If person A can paddle faster and farther than
B using a different stroke what would that prove?  That "A's" is better? If
you tested hundreds of paddlers would the average suggest one of the
immutable laws of the universe? If only one out of  a hundred did better
using "B's" style would that mean "A's" style was worse or vice versa?

N>It will require fewer strokes to maintain the same speed.

P> There is your inaccurate assumptions showing themselves again; this is
> false.  I have measured this before on a human dynamometer.  The number of
> strokes it takes to maintain the same speed is not related to how much
> energy out put you are producing.

True. It varies with the type of stroke and paddle. Large blades and slow
strokes generate as much power as small blades and fast strokes (although it
is possible that Nick has been quoted out of context, I missed his comment) .

P> The 10-speed bike analogy makes this
> clear, peddling slow and hard in high gear, or fast and easy in low gear,
> could mean you are expending exactly the same amount of energy.  However,
> with the human "machine" there is an optimum speed for the same output of
> energy to minimize input (this is actually true with most machinery).
>  Generally the low gear (higher speed, less force) IS MORE EFFICIENT with
> the human body.

Depends upon the muscle groups used and the objective. I.e. are you using
fast of slow twitch muscles. Experiments by the Canadian Olympic team showed
that slower stroke rates in rowing shells actually produced more speed. So
this varies with  a lot of factors including the variations in human anatomy
propulsion etc. Canoeists in the COT found that they were faster over short
distances using only their arms but were faster over longer distances with
longer slower strokes using more upper body muscles. One must use analogies
carefully.

(SNIP)

P>
> This may be true, but it is clear from your arguments you still have a lot
> to learn. Why don't you just go out and learn the native paddle technique
> and try it,?  You do not need to know anything about fluid mechanics to
> know which works best, but you are at a clear disadvantage if you put
> forth technical arguments about things you do not understand, and without 
> the knowledge of actually trying it out.  I contend IF you use PROPER
> technique, you will know how much better native paddles are.

This puzzles me a bit since I missed what Nick said. I have tried the so
called native paddle using the "proper" stroke and I think it nice but not
as effective as my shorter paddle using a modified sprint racer's stroke. I
suppose I would contend that if Peter knew how to use the proper stroke he
would know how much better modern paddles are. You know, try it, you'll like
it. :-)

P> If you think of the forces on the paddle surfaces as high and low
> pressure areas (rather than moving fluid, which is actually what causes 
> the high and low pressures, but in very complex ways) to create the forward 
> movement you want, it become easier to understand.  with a propeller shaped 
> blade (i.e. native paddle blade) you make your stroke a downward slicing arc 
> movement, kind of like a quarter turn of a propeller (but also pulling back 
> at the same time with your body), you get a very efficient stoke that is 
> also easy on your body.  You can not do this with a "Euro" paddle.

All very confusing. Why won't this work with a low aspect ratio blade? My
own tank testing (which did nothing more than confirm what C.J. Marchaj
reported) shows that a low aspect ratio blade (1:1) operating at an angle of
attack of approximately 38 degrees produces a higher thrust coefficient than
higher aspect ratio foils. with all due respect for Peter's opinions, test
results seem to contradict him. I would certainly be interested in results
that differed as would Mr. Marchaj who went out on a limb and published a
book.

P> You also learn real quickly that you get little resistance against the
> paddle for rolls or braces unless you have some lateral movement of the
> blade through the water.  And it is much less effort to create, and the
> amount of power you can generate is much larger on the high aspect ratio
> blades than with the "ice-cream" scoop Euro blades.  This is why you must
> learn proper technique to get it to work, and it has to become automatic.

Well, maybe a little time spent learning "proper" technique with a modern
paddle will change his opinion. Who knows, maybe Peter was using a poor
example of "Euro" paddle.

P
> So if you want to scoop ice-cream, or shovel manure (as it appears many on
> this list are in the habit of doing), use your Euro blades, for efficient
> paddling you need a high aspect ratio paddle.  There is no way around it.
>  Do not argue, it is a FACT of any fluid machinery.  You can go look this
> up for your self in any fluid mechanics textbook if you are so enchained
> (check out aspect ratio, propeller design, etc.), but do not put forth
> such statements until you have done so.  Short of that you will either 
> have to take the word of people who do know, or just go out and try it!

I find this paragraph  insulting and one of the things that I don't like
about mailing lists. In view of the rest of his message I consider Peter's
comment "DO NOT ARGUE" laughable.

Keep in mind that a lot more could be said about this. So much impacts on 
what we call "efficiency".

Cheers,

John Winters

***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************