Canoe Sprints

Indeed i did, never said my spelling/grammar is perfect either

As I've stated above, the oscillations of the weight changes the radius of gyration. Whether the weight is at its extreme amplitude or on the vessels central axis, changes the radius of gyration of the vessel at each of the different locations in its swing. How much of course depends upon the weight. But DC wanted an assumption of a large one.

The damping coeff's are directly related to the radius of gyration. Ergo it is being influenced. I'm a naval architect not a scientist or mathematician. As such I look at what is being influenced by the external source, whatever it may be. Beyond that i care very little, as i prefer to deal with trends not absolutes.

I'll leave the absolutes to others, if indeed they can find sources for such thought expts. None that I know of for this, other than it is not straight forward at all. "Simple" seakeeping is not so straightforward either, when considering all the aspects that should be considered such a 3D flow coupled and un-coupled behaviour and so on. In this area too, I have little interest other than, the trend produced by X or Y. The "bits" in-between....that's for someone with endless time on their hands (forsaking all other work) and significantly greater maths ability than me...I haven't done maths like that which is required, for such analysis, for over 25years; i can barely add 2+2!

 

OK, fine. That still doesn't seem to address the question though. I understand what you are saying about the shifting of the weight changing the radius of gyration, and therefore changing the pitching charateristics. No problem there.

However, what was asked was whether the pitching would tend to be greater or lesser if the craft was moving forward with an average velocity that was both non-zero and constant, compared to the pitching of the same craft undergoing the same weight shifts but with an average forward velocity of zero.

I can re-phrase this several ways if the wording is still not clear.

PS: Note that I'm saying "average forward velocity" because I am well aware that in the case of a light craft like a sprint canoe the velocity will vary as the weight moves, and therefore must be averaged over a reasonable period of time.

PPS: Taking a wild guess based on what I know of roll damping for moving vs non-moving hulls, I'd say it's likely that the pitching of the moving canoe might tend to be less than that of the stationary canoe. That is a guess though, so I'm quite prepared to be wrong.

PPPS: Mind you, I'm not sure that anyone is really going to give a bugger given that a sprint canoe which is not moving forward isn't going to win many races.

 

No need I have understood from the outset, but DC ends up being obtusely pedantic for some reason, and thus to avoid flip-flopping I wanted to make sure what was being asked. Previous discussions resulted in “I didn’t say that”, when it has been shown to be otherwise, hence the pedantic reply to ensure what was being asked by DC, to avoid further flip-flopping.

In answer to your question, I have answered as best I can; you need to look at which coefficients are influenced by such “changes”. How they are changed and are these in turn influenced by changes in others, in each of the conditions, transient or otherwise. Since once you have established all the coeff’s that exist and then look at coupled and un-coupled behaviour and so on, you begin to realise that the “simple” question is anything but simple. It is not intuitive either.

The basic equations of motion are terribly complex, and as far as I know very few guidance’s are available for such “models”.

For example, last year I was reviewing some lectures for a local university. One “simple” seakeeping example, even simpler than this, was present by the Professor. He lost me (with the maths) after his second line. His first answer took him 90mins of just maths and took up the whole white board (4x2m board) 3 times (he had to scrub out each time to allow more room). That was for just one variable using Green’s function. One, not the many that are required!

Thus either the person asking the question doesn’t understand how complex this is, or is just asking for no other reason than to keep asking as the answers do not satisfy him.

That’s about all anyone can do at this stage. Unless someone wishes to spend a considerable amount of time writing the coefficients and equations of motion of all 6 degrees of freedom for both cases. I won’t be holding my breath.

Unless Leo is out of his PJs and has picked up his dole cheque, he may feel more motivated

 

My only response to the above is to suggest a review of the posts in this thread and other threads where similar claims have been made.

 

If you look at the 2nd graph I showed for rowing in an earlier post,
you will see that dynamic forces and moments increase the pitch angle
at some speeds, and reduce it at others.
Pitch angle in radians is (bow position - stern position)/Lhull.

The pink and light blue curves are independent of speed: the induced pitch
is due only to the forward and backward motion of the rower.

My calculations for kayaks suggest a similar trend, but not quite
as evident because the speed variation during the stroke is smaller.

 

By "speed" do you mean forward speed of the boat or how fast the rower is moving relative to the boat?

What do each of the four curves represent in the figure you refered to?

 

Forward speed. The speed of the rower is the same for both situations.

The pink and red curves are the height of the bow, the light blue and dark
blue curves are the height of the stern. When the bow and stern are
at the same height, the pitch angle is equal to zero.

As I wrote in that post:
The pink and light blue curves are for the case where the rower
moves forwards and backwards in the shell, but no squat forces are
used in the calculations. It can be seen that the bow is up at the
start of the stroke (when the rower is farthest sternwards) and down
at the middle of the stroke when the rower is farthest bow-wards.
Similarly, the stern is down at the start, and up at the middle of
the stroke. The red and blue curves include dynamic forces and moments
in the calculations.

 

AdHoc: I have been doing a bit on this topic recently...
The fact is that:
(1) Estimating pitch at zero speed is of no interest
to me.
(2) My computer model predicts the speed and acceleration
of kayak hulls quite well.
Figure 1 shows my predictions compared to experimental
results. Tweaking the model further by including those
horrendous equations you mentioned doesn't seem
worthwhile given the experimental scatter. That data
is for an Olympic Gold medallist: the scatter for
amateurs would be far greater.

NoEyeDeer:
Figure 2 shows the yaw, pitch and roll for the same paddler.
They should give you an idea of the range of angles that you
should be considering in your thought experiments.

I do have data for different speeds, but the dole bludger
lifestyle is playing merry hell with my research. I have
to contend with Mongolians and Romans attacking my empire
at the moment!
I'll try to post some data showing the pitch angles during
the stroke at different speeds. That might give an indication
of the importance of forward speed on pitching, but I'm not
confident. The situation is complicated by the fact that the
paddler exerts larger blade forces at high stroke rates and
the highish speeds at the start of the race.

 

Good discussion. I race canoes/kayaks myself and design them too (open class hulls of various sizes...largest being 31ft war canoe).

The initial stability of racing hulls can turn off many prospect paddlers. One only need watch a novice paddler hop in/on a racing hull only to be in the drink within a couple of seconds. Paddling technique and other variables come into play to make a hull stable. A good stroke executed properly braces racing hulls very well.

I can say Leo or anyone else would need to write a good volume of information that captures a lot of other variables aside from hydrodynamic info. Aerodynamics also plays a role on windy days. Aside from this, the following can vary quite a bit:

-paddler weight/height
-paddle dimensions (shaft length, blade size/style)
-stroke technique (high vs. low angle & in between)
-crew position
-ambient & water temps

Take temperature for example. It's a known fact that the colder the water & air temps, the less reliable a paddler can rely on his/her core muscles to balance the hull during the glide portion of a stroke. In short, a highly skilled racer may be able to paddle a particular hull very well in the summer, yet capsize several times if they attempt to paddle it in early spring or autumn.

Rather than trying to understand the minute subtleties of these racing hulls on paper or computer...you're better off just showing up at some training sessions and doing some empirical analysis on existing hulls. Better yet, hop on a canoe or kayak ergometer and learn to paddle them using proper strokes. At a good training center you'll find older hulls lying around. Compare them to newer hulls. You'll find some amazing differences though subtle to most eyes, make a big difference while under way.

With boat specs being equal, taller paddlers with long arms tend to do better in the Olympics. This is because their height offers additional leverage, and their longer stroke lengths mean longer glides. However, shorter paddlers have trained to overcome them with faster stroke rates. The Olympics are marvelous to watch. Hats off to all the paddlers.

 

Thanks, JosephT. But you have made many incorrect assumptions about my model and methods.

I am lucky in that I have a lot of good data for rowers and paddlers.
That includes their anthropometry, physiology, on-water measurements of
blade forces, hull speed and acceleration, video of on-water trials and races,
hull roll pitch and yaw (and their accelerations and velocities) and, very
importantly, how those quantities vary as a rower/paddler trains up from a
break back to peak fitness.

I agree that aerodynamics is also important and I have accounted for this in
my models. (For rowing, aero drag is more than wave drag). I have some
wind tunnel data and more tests are planned now that there is a wind tunnel
here.

I don't know where you got the idea that I (and the several people I work with) don't do that.

 

I suspect you have misunderstood the sort of answer he was looking for. I think he was probably just wondering if anyone had done empirical comparisons, rather than expecting a complete solution to be calculated mathematically from first principles.

The latter is obviously not going to be an easy thing to do, if it's even possible at all. You don't need to know the actual equations involved to realise that. A bit of reflection should make it obvious to most people.

Anyway, point is that the best answer may have been something along the lines of "Nobody has done any actual testing of this, and calculating accurately it is totally intractable, so you're on your own." Short and sweet. Saves a lot of typing.

 

I disagree, but only a bit.

I know that a couple of rowing shell manufacturers test hulls in short narrow
tanks. They get a crew to move forwards and backwards (or use bags of
sand) and measure the amount of movement at the bow and stern.

They can, of course, also test the hull in open-water where those forces and
moments are in effect. Thus they would have a pretty good idea of the
difference that forward speed makes. But it's of no interest to me, so I have
never bothered collecting the data.

Anyway, that's enough from me.

 

Hello Leo, VERY glad to hear you're working closely with the paddlers...much practical knowledge to be gained. I read some of your posted analysis and did not see mention of it. Thanks for filling me in and keep up the good work! I know it can be frustrating (for some anyway) examining minute differences with these highly refined hulls. Howerver, we are still learning. I'm particularly excited to see the evolution of the surfski. It appears to be on course to be an Olympic sport!in due time. I would like to see them being used for 2 events:

-Ocean surfski racing
-River canoe/kayak marathons

Both sports are expanding and often times surfskis are the dominant hulls in use. It's possible to use a K1 hull in a river marathon, but surfskis fare better overall because they can handle crazy currents & eddies, not to mention occasional choppy & white cap conditions if a storm comes in. Such real-life scenarios would cause a K1 to fail. Many of the newer surfskis also have well designed hatches to accomodate the need for hydration systems. The Olympic hulls are just so narrow in their event application (flatwater sprints...that's pretty much it). On top of this the athletes paddle 200, 500 or 1000 meters only...then it's all over and time to go home. I could not imagine flying to another country to paddle such a short distance.

I've seen some of these sprint racers try to cross over into ultramarathon canoe/kayak racing and most just don't have the patience for it. There's a much more pronounced mental and physical aspect to longer races in real-world conditions. If a paddle doesn't have both the pysical & mental make-up they drop out of the race. I would like to see a 125km Olympic marathon in the cards some time. This would separate the men from the boys, as well as 250 & 500km events.

Until then, the Olympics in paddling events will leave a lot to be desired in the real world of paddle sports.

There's my pitch for Olympic paddle sports. It needs an overhaul on the event management side of the house.

 

1. I agree with Carl Scragg and Bruce Nelson that theoretical
and computer methds can be more reliable at discerning small
differences in performance between hulls than experiments.
(Scragg and Nelson were very talented hydrodynamicists/naval
archies.)

In their work on designing a rowing shell, they did a lot of tank
testing and found that the results were too muddied by
experimental error to be useful. The trends were much easier
to discern using (essentially) thin-ship theory.

Think of what would be required to discern, on-water, a 1/2%
difference in wave resistance, or roll stability, or surge etc.

You would need to repeat the experiment many times over several
days. I don't believe that you could eliminate paddler biases,
environmental effects (e.g. wind, temperature etc) or paddler
weariness or improved fitness with less than 20 or 30 trials.

Ideally, it would be best to do a double blind series, but that
would be difficult to arrange.

2. Olympic events > 150km would be as exciting as marathon
synchronised swimming.
I agree that they would be a better test of stamina and
technique, but the Olympics is not necessarily the best
venue for that.
If you want to make paddling more exciting, take a leaf from the
BMX events, and make it a "demolition derby".

 

Leo, are you using a quasi-steady state assumption when modeling the wave drag of a kayak, shell, etc being paddled or rowed? By quasi-steady state I mean assuming the wave drag at any instant of time is the same as the wave drag would be if the boat was moving with constant speed at the speed of that instant in time.