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Question: Perfect Paddle Part Four :: Total Votes:16
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I prefer a large area "power" blade 4  [25.00%]
I like a smaller area "touring" blade 12  [75.00%]
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Topic: Perfect Paddle Part 4, Grips n' blades: hold onto yer hat!< Next Oldest | Next Newest >
stant01 Offline
Cuda




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Posted: Mar. 05 2006,03:17

Probably the simplest way to look at the paddle size issue is to look at the work involved.  Work is defined as force times distance moved in the direction of the force.  A paddler inserts the blade in the water, then pulls back, and since for every action there is an equal and opposite reaction, the paddler (and thus the boat) is pulled forward.  The total work done is the paddle force times the total stroke distance.  The work done by the paddler on the lower blade goes two places:  the boat moves forward (desired outcome), and the paddle moves backward through the water some small amount (slip).  The work output is the paddle force times the net distance the boat moves forward during the stroke. The wasted work is the paddle force times the slip distance (think distance, not speed).

At the same time, work is lost as the upper blade is being pushed forward through the air.  The optimum blade size is the one which minimizes the total lost energy:  that lost in slip and that lost in pushing the upper blade through the air.  As blade size increases, slip decreases, but energy loss through the upper blade in the air increases.  Given those two opposing trends it follows that for any given wind and kayak resistance, there is an optimum blade size which minimizes total lost energy (work).  That minimum is pretty broad:  that is, small variations in blade size make a very small difference in the total efficiency (which is the net work done divided by the total work done).  And theoretically, the optimum changes with wind, hull resistance, etc.  That is, the optimum blade to paddle Jimbo's newest rocket Yak is much smaller than the optimum to paddle a log raft.  For real yaks, years (centuries?) of experience by paddlers have resulted in blade sizes which are pretty close to this optimum.  

BTW, all that said, I paddle a Mid Swift, feathered.
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Capn Jimbo Offline
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Posted: Mar. 05 2006,06:01

Stan, don't know if you reviewed this thread from the beginning, but please at least review the first few posts.  

This is a series of "Perfect Paddle" posts based on an article by Matt Broze in Sea Kayaker.  Matt is a highly respected kayaker and designer who once spent many, many hours altering and testing paddles.

This one, Part IV, has to with blade size.  Your view assumes that slip decreases with blade size, and that the real limiting factor would be wind resistance of the upper blade in paddling.  An interesting theory, but not borne out by Broze in his extensive testing.

His surprising findings were that relative large differences in blade area (up to 20% larger)  made LITTLE difference in performance.  Broze theorized that beyond some minimum blade area that did not slip, extra area would have no significant effect.  Also that (since resistance is proportional to the square of speed) the smaller blade's speed - by moving faster through the water - compensated for the smaller area.

He found that the slight increase in paddle speed necessary to make up for the loss of blade area was trivial.

The first few posts detail this.

Your theory would likely lead to a much larger blade than Broze found efficient in his lengthy experimentation.  As for me,  I have found that paddling/kayaking is both art and science - not easily understood and that defies simple analysis.  

Broze is no dummy, he understands the issues.  Sadly I couldn't  reproduce his entire article, but I highly recommend to anyone to buy a back issue ("In Search of the Perfect Paddle", Matt Broze, Sea Kayaker).  This details his lengthy (years) of analysis and experimentation.  It's a fascinating and convincing piece of work.

:capn:


Edited by Capn Jimbo on Mar. 05 2006,09:24

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stant01 Offline
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Posted: Mar. 05 2006,13:01

Jimbo,

Actually, I read all the posts in this thread (and in paddle threads 1-4), and I don't disagree with Broze at all.  I was trying to explain his conclusions in terms of basic physics, rather than focus on the subjective items he discusses.  Clearly, there is enough complexity in paddling (in fact, in any human/machine interaction) that simple physics may not give the correct answer, but in this case it gives THE SAME answer as Broze reaches.  I was trying to get the discussion to focus on work (force and distance) and away from the fuzzy ideas of paddle speed through the water, etc.  My conclusion, restated, is that for any paddle craft there is an optimum blade size which minimizes the total energy loss, from blade slip, wind load on the top blade, and swing effort.  My personal conclusion is that for actual paddle craft, that minimum loss occurs with a fairly small blade, and anything larger is wasted.

But recognize that Broze's discussion is biased toward racing kayaks:  he wants to minimize energy loss and maximize boat speed in a situation where the boat is a) very low resistance, and b) already up to speed.  (The start of an ocean race takes a few seconds out of a total time that mey he measured in hours.)  Look at a very different situation, a white-water paddler, where the paddler takes relatively few strokes, and relies on each one to put the boat where he needs it to be.  In that case, the paddler applies high effort to each stroke, and wants to minimize slip.  Thus he optimally uses a much bigger blade than the tourist or the ocean racer.  This type of experience is probably what prompts many kayakers to buy huge blades:  the huge blade gives great "grip" even starting from rest.  The decision that a smaller blade works better seems to take time and experience to reach, hence the value of Broze's article.

Somewhere in this discussion I seem to recall a brief mention of the effort that is required to turn the blade in the water; that is, the blade goes in more or less vertically, and is lifted out with a backwards tilt, so turning the blade in the water is wasted effort.  I don't mean twist around the paddle shaft axis; I mean rotation around a transverse axis across the hull waterline.  That energy loss is larger for a long, slender blade than for a short, wide blade of the same area. I've never paddled a wing blade, but suspect from watching them in action that they capture some of this otherwise lost energy.

Another factor not addressed by this simple physics analysis is that a larger blade also increases side forces on the top blade that can upset the paddler in crosswinds, thus pushing the sea kayaker to prefer the smaller blade even if it meant some loss of efficiency.

Stanton
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Kiyu Offline
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Posted: Mar. 05 2006,13:14

Yes your right force.  Once you have reached the speed you wish to paddle at, it takes a lot less force to maintain it, than the force it took to get there, and less to maintain it. If your touring a fair distance on a nice day in fairly calm waters or a slow running river, a 6''x14'' might be the ideal paddle It takes a lot less force to move it through the water than a lager paddle saving a lot of energy. The reason turing paddles are so popular. On the ocean conditions can change rapidly, it can go from, its a beautiful day, to o my gosh am I in trouble. Now you must understand that i am  a fisherman that kayaks, during the winter months the wind seams to blow hard all the time, so i decided to see how good i could do in bad conditions. When i went the wind was blowing 23 mph with around 5 mph gust, using the paddle i normally us I starting paddling into the wind,  well after about half a mile I had decided no one in there right mind should be out in that stuff at my age. After resting a while I switched paddles to the one my son likes to use when fishing past the surf, it has a 7.75'' x 18.5'' blade, started out again and boy was I surprised the paddling went from one heck of allot of work, to just trudging along. Not fun, but something I could put up with for shorter distances.  I now fish a lot more in the winter.  So i agree, as far  reaching a certain speed and the force maintaining it is concerned. But I still won't use a 6.25''x14.8 (20% less) paddle when launching and returning through the serf, nor in high winds with heavy chop.  Would love to give the wing a try but since I don't often  go much more than a mile or two from my launch point, they might be a wast of money.
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stant01 Offline
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Posted: Mar. 05 2006,13:16

p.s.  Note what I said originally:  "That minimum is pretty broad:  that is, small variations in blade size make a very small difference in the total efficiency (which is the net work done divided by the total work done).".  I consider a 20% change in blade area to be pretty small; a big change might be of the order of 50%.  Again, I don't disagree with Broze in any way; I just don't find his conclusions surprising, in light of the basic physics involved.  I apply the same skepticism to my other sport, of cycling, where my racers will agonize over the choice of 170mm cranks vs. 172.5 mm cranks.  The difference is 1.4%, and the efficiency curve is so flat that it DOESN'T MATTER.  I tell my athletes GET OUT THERE AND RIDE.  To yakkers, I say "get out there and paddle"!  Maybe we're all spending too much time at our keyboards and not enough time on the water.  Which reminds me:  the bass are bedding here.  I caught 11 Friday evening, largest about 7 pounds, and lost a much bigger one at boatside.  Why am I typing this? :laugh:

Stanton
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Capn Jimbo Offline
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Posted: Mar. 05 2006,17:42

Stan, thanks for the clarification, I understand you better now.  Decided to check back with Broze's article - turns out his bias is not toward racing but let me quote Matt:

Quote
What is most important to me is moving a fast sea kayak over long distances at near hull speed.  My choice of paddles is intended to minimize wear and tear on my ligaments and joints.  I paddle in a contemporary style using a paddle with feathered blades.


Broze by reputation is more into touring, albeit faster touring.  Valid point too bout energy loss near the end of the stroke.  Accordingly a number of leading paddlers favor a far forward, vertical catch with most force applied early - with a relatively early, quick and clean exit before the hand passes your hip.  

I've transitioned to a wing which I love and to which I've adjusted.  Where typical paddles work more on drag/resistance the wing is designed to create and use "lift" to minimize slippage.  And it works.  The stroke is NOT straight back, but at a 30+ degree angle OUT (creating the lift).

It is interesting to note that some very good paddlers have found that even typical Euro blades can create some lift with an alteration in stroke.  

Last, the Greenland paddle also uses lift and depends on the very motion we try to avoid with typical paddles - namely a zig-zag motion through the water.  This motion is more down-up than the front-back motion of a typical paddle.  This avoids flutter and creates lift.  Their wood construction and buoyancy is said to be important to their effectiveness.  

I can't vouch for the Greenland paddle but kayak regularly with a gentleman who has built a number of fine Greenland kayaks (both stitch and glue and skin-on-frame) and paddles.  I have always marveled at his easy and relaxed motion that is also very fast.

Nice.

:capn:


Edited by Capn Jimbo on Mar. 05 2006,17:49

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stant01 Offline
Cuda




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Posted: Mar. 05 2006,20:25

Good points, Jimbo.  Along the lines of your last post, I have a question that may have an obvious answer, but it has not occurred to me yet:  why don't kayak paddles use a bent shaft to make the blade more vertical at the power max of the stroke, just like bent shaft canoe paddles?  Bent shaft canoe paddles go back at least to when my wife and I raced in the 1970's, but the only bent kayak paddles I see are "crank" paddles where there is a kink to straighten the wrist, but the blade is still in line with the shaft.  Bent canoe paddles tried angles from 5 degrees to as much as 30 degrees between the shaft and the blade, finally settling on something like 18 degrees.  The paddle makers must have thought of it, so there must be some reason for not doing it.  Any ideas?  ???

Stanton
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Capn Jimbo Offline
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Posted: Mar. 06 2006,04:44

This should almost be a new thread, but your question is a very good one.  You are right - if the blade is angled toward the bow it would allow power to be applied longer, ie it would stay vertical longer.

And paddle makers do this.

Racers discovered this some time ago - ergo the wing paddle was developed.  Wings not only are angled foward, they also exhibit varying degrees of twist - with the same objective in mind.  More power, longer.  A few wings are angled but without twist.  

I will tell you that the difference between a wing and an ordinary blade is like night and day (once you unlearn your old stroke and use a proper wing stroke).  Unlike a normal stroke which is hopefully front-to-back in a straight line, the wing stroke starts close to the kayak and angles out.  

This means the "wing" is also moving sideways (out) as it moves back.  The "wing" is actually shaped like an airplane wing a bit, and the water moving sideways over it.  In a plane this creates lift upwards; on a wing paddle the lift is forward!  This means the paddle tends not to slip anywhere near as much as typical paddle. Accordingly the wing feels and is much more stable, tends to stay where you plant it, no wobble, much less turbulence.  

One final note:  because most blades are not so slanted most leading teachers advise that power should be applied early - the first half of the stroke (when the paddle is vertical) is really the power phase of the stroke.  Many advise that the last half of the stroke is more the coasting and exiting phase.

Unfortunately most paddlers apply power too late, or at the least too long.  This accomplishes little other than to slow you down and tire you out.

:capn:

(For those who care - Washout: An intentional twist in an airplane wing, causing the wing tips to have a lower angle of attack than the wing root. In other words, the trailing edge is higher than the leading edge at the wing tips. Washout helps prevent tip stalls.  I have read that twist in wing paddles helps maintain the correct angle of attack in paddling, maintain lift.)


Edited by Capn Jimbo on Mar. 06 2006,05:42

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