Solo canoes are like Labrador Retrievers. They'll do anything you want if you just communicate your desires. Towards that end, Sideslips are best initiated. A little 6" Draw or Pushaway to start the hull moving laterally to On or Offside greatly increases the sideslips effectiveness or carry.
The data on blade angles is available in ship design literature. Straight panel rudders stall at ~ 38dg angles to forward travel, foiled rudders around 42dg, just one of many reasons we need paddles foiled or faired across the blade. A good reference source is Paffett, Ships and Water, pg 52.
The Center of Gravity/Rotational Center thing is conflicted by hull shape and speed. A useful crutch is the John WInters older concept of Loci of Forces on the Hull which accepts the moveable pivot point observations of Henry Hooyer in Behavior and Handling of Ships, Clyde Winter, the Peripatetic Pivot Point, [Google him], and most simply explained by John McPhee in Uncommon Carriers, pg 56.
John Winters himself suggests the pivot point does not move.
Winter claims the PPP moves a set distance, 2/3, forward, or aft, once under way. That seems true for the large carriers with efficiency-limited forward speed. Our little canoes accelerate to near hull speed and we can alter shape in the water more completely with extreme heel and pitch so we can move that loci, or Apparent Pivot Point, well forward and allow the momentum of the CG to whip the stern around with velocities that would concern a Cruise Liner pilot. Rawson and Tupper offer more nuance in Basic Ship Theory, chapter 13.
More later; I need to lay cork in the guest bath floor so Kim's toes are toasty during her Hockey Games visit early 2015. She's a tough nut and will hopefully be fine.
Some of my examples might be more extreme than what's within practical situations, but they follow the general trend I was thinking of. In particular, the fact that the kind of sideways push provided by the correction phase of a J-stroke, when executed near the center of the boat will primarily act on the stern when you are moving at a good clip, but will only move the whole boat sideways when going very slowly or sitting still. To me, that indicates that the location of the pivot point moves more forward of center with increasing speed, which in fact is what a number of other people have said here over the years. I also find that for a sideways movement (or sideways component added to forward motion leading to diagonal movement with no change in heading), straight pries or draws must be applied adjacent to the center of the boat when stationary but forward of center when moving, and progressively farther forward as speed increases. Still, I'll sit back and listen to how things progress here.
I find that the second part of your statement does not reflect my experience. I do find the prying sideslip has a placement forward; not the drawing sideslip. In fact, with a weight shift and placement well aft in a drawing sideslip, I can make the boat practically stop and move 90 degrees laterally. It should be noted, too, that blade angle in combination with fore and aft placement can be compensating factors. I am not necessarily in position to try and explain the physics as to why that happens. Experimentation over numerous quiet morning paddles have convinced me that there are certainly a number of factors in play.
That may explain things There’s may be things going on here that don’t act the same for every kind of lateral force. All the more reason to pay attention to such things again, once the ice is gone.
Prying Side Slips The mechanics of the prying side slip are similar to the drawing side slip except that the leading (forward) edge of the blade is turned inward (toward the hull) slightly instead of away from it. My experience is that the placement is also further back. Like the drawing side slip, finding the precise placement takes a bit of tinkering, but with practice, you can hit it right on, almost every time.
Below are a couple of video clips, taken in the NJ pine barrens, last spring.
Interesting, Marc I find my prying sideslip placement is usually further forward than a drawing sideslip. I wonder why the difference in that yours is further back?
knowing where vs. feeling where… As can be observed in this thread, different paddlers perceive the Pivot Point, Point of Rotation, et. al., as being in different places. My personal preference in learning sideslips was to develop a feel for where the Pivot Point was a any given moment and go to that sweet spot based on feeling the different pressures on the paddle, with my hands and on the canoe, with my knees. I generally move the blade an inch or two, once placed to fine tune the Sideslip once it begins but that is almost unnoticeable. I practiced Sideslips enough so that the placement is somewhat instinctive.
One thing I like to do is lift the bilge of the hull a bit on the side on the direction of travel, i.e., heel to side opposite the direction of the Sideslip. I find it helps.
Jeese Kim… I think Robin stated quite clearly the situation at hand between you two. I don’t know either of you, but he seemed to say that you violated his site’s rules multiple times with warnings each occasion. Even though I don’t participate on that forum(because I’m a wannabe tripper)I thought you were a huge contributor as I’m sure Robin did. But he made the decsison that his site( that as you had, I also contributed to monitarily wise) Freestyle or any interpitation of it wasn’t what he wanted to pursue even though many participants did. Different strokes for different folks… You could have stepped up after the travesty that led Robin to come to the conclusion that he’d like to continue the site and have some control with little (or none) experience of hosting a website and what it entails. By the way, And this means nothing, I’ve camped with many of builders(boat) on occassion… both Dave’s been to both of their shops, Mark… Midwest Symposium, … Mike Mcrea(who won’t even post here anymore) and many others with so much advise to offer… Hope your recovery is swift…
I suspect that it has to do with body position in the boat, which affects the trim. It’s also possible that you or I or both tend to inadvertently initiate a slight on or offside turn, which we automatically correct for by our placement. I guess this calls for a bit of experimentation, when the water is in a liquid state.
Fulcrum ray controls sideslip placement So . . . is the paddle placement of a prying sideslip further forward, further aft, or in the same place as a drawing sideslip?
Patrick Moore’s pedagogical concept of the “fulcrum ray” provides the answer.
The fulcrum ray is an imaginary ray projecting straight out from the center of your paddle’s power face blade. To make it more concrete, imagine a kid’s suction cup arrow sticking out from the center of the paddle blade’s power face.
Now you have to figure out where the “pivot point” of the canoe is. This is very inexact terminology and there are various arguments as to exactly where the pivot point is when the canoe is under way. However, we can all agree that the pivot point is somewhere in front of a solo paddler who is SEATED in a standard centralized solo seat.
Physics says a sideslip will be perfectly lateral – that is, it will include no left or right yaw or turning component – when the paddle’s fulcrum ray points directly through the canoe’s pivot point, which we’ve agreed is in front of the paddler.
Now consider that a prying sideslip uses a closed power face blade while a drawing sideslip uses an open power face blade. This means that the fulcrum ray is pointing slightly aft during a prying sideslip and slightly forward during a drawing sideslip.
Inevitable Physics Conclusion: In order for their fulcrum rays to intersect the pivot point, which is in front of the paddler, the prying sideslip must be placed farther forward than the drawing sideslip.
If Marc finds his sideslip placements to be the opposite of this, the only explanation I can think of is that one of his sideslips is not perfectly lateral. He is inducing yaw with one of his sideslips, by having his blade in the “wrong” place, but is more than compensating for that yaw with preliminary initiation turns or carves.
Good Info I hadn’t thought of the ramped surface of a stationary paddle blade acting in that fashion as both boat and paddle moved together, but on thinking about it, it makes good sense (as a thought exercise, or even a real one for those who like to tinker, this could be set up with ropes to apply the lateral force. If one can envision how that would work, the result is unambiguous). Your explanation really “clicked” for me. Thanks.
What would happen if… the blade was placed exactly parallel to the center-line of the canoe and the fulcrum ray (that term was stolen from an old Flash Gordon serial) was exactly perpendicular to the pivot point? Would the hull then simultaneously do an offside and onside Sideslip?
Seriously, the paddle must be placed at the necessary spot laterally (along the length of the hull) and at the proper angle for a Sideslip to work but who knows if it has to be pointed, like a laser, at the Pivot Point. Maybe it must be pointed a bit fore or aft of the PP in each case. Until we can say with certainty where the PP is at any given moment, the fulcrum ray remains just a theory.
... the laws of physics. In fact, it would be a way of accurately locating the pivot point if you wanted to know exactly where it is under any particular set of conditions (though modifying it to use ropes to apply the force, since their alignment can more easily be measured, would be the better way to do it in a lab situation). Complications would arise since (according to many people) the location of the pivot point is not the same at all speeds. But if at a given speed the boat moves laterally without changing its angle of heading, the direction of applied force (this would be illustrated with a vector, if you explained it diametrically) intersects the pivot point as it exists under those conditions. If the force were to be applied along a line such that an extension of the line missed the pivot point, some amount of yawing away from the original angle of heading would occur.
A key point which this method of explanation illustrates, is that changing the angle of the paddle to create a greater or lesser lateral force, by definition, changes how far forward or backward the paddle must be placed in order for that lateral force to remain neutral. And we all know that in real life, changing the angle of the blade changes where the paddle must be located.
I don't want to sidetrack this with a big explanation that is extremely difficult to accomplish without illustrations, but if you ever covered statics in school, think back on what you already know about vector analysis, and try to explain this situation in a way that does not jive with what Glen describes. Note that the vector mentioned above is actually the sum of two. One is the force which keeps the blade from falling behind the boat's position as the boat coasts (this force also slows the forward motion of the boat), and the other is the force which prevents the blade from moving outward or inward as a result of blade angle (we tend to perceive this second one as THE driving force that moves the boat laterally (and this was even tripping up my logic in my first post on this subject), but actually it's the sum of the two forces which moves the boat laterally).
Edit: I see that Glenn has been back to reply to your comment too. The last sentence above is what he describes in his second paragraph (resultant force = the sum of forces, and in this particular case, there are two forces which combine to form the resultant force).
By the way, your introductory scenario makes no point, because no force is generated by a paddle placed alongside the boat when oriented as you described. There is no vector (the fulcrum ray in Glenn's post) to define if there is no force present.
Easy answers to your questions The fulcrum ray pedagogy does nothing more than illustrate elementary principles of mechanical physics. It has nothing to do with Flash Gordon movies.
The fulcrum ray is simply a visualization of the resultant vector force line, which represents ALL of the forces that the paddle exerts on the canoe via the paddle’s interaction with the water. There are no paddle forces acting on the canoe other than the mathematical resultant vector force represented by the line of the fulcrum ray.
If the paddle is sliced through the water parallel to the direction of travel there will be no paddle force acting laterally on the canoe, and hence there will be no fulcrum ray. (Stated differently, the resultant lateral paddle force will be zero.) In such a case, the canoe will not sideslip or turn in any direction and will simply keep going in the direction of travel. In other words, there will only be a fulcrum ray when the paddle is held such that there is water force acting on the power face. For this to happen, the paddle blade has to be at some angle other than zero to the direction of travel.
For purposes of this analysis the pivot point is more accurately called the center of lateral resistance (CLR), which is the center of pressure of all the hydrodynamic forces acting on the hull.
If the fulcrum ray (the mathematical resultant of all paddle forces) is aimed forward of the CLR, the bow will yaw toward the paddle. If the fulcrum ray is aimed aft of the CLR, the stern will yaw toward the paddle. This is how a paddle boat is turned. These are physics truisms no matter where the CLR is in boat.
When the all the resultant paddle forces (the fulcrum ray) are aimed directly at the CLR, then, and only then, will the boat slip perfectly sideways without any yaw.
Therefore, no matter where the CLR is located in the boat, the prying sideslip must be placed forward of a drawing sideslip in order to execute a perfect sideslip–i.e., one without any yaw. Again, this is because of the closed vs. open angles of the prying and drawing sideslip.
Huh? Alright, you guys have lost me. This is turning into a math thread. My failing calculus is a major reason I wound up finishing college on the GI Bill.
I never have learned the language of mathematics, and being dyslexic didn’t help any.
I canoe in order to enjoy the rivers and nature. So I’ll skip over the mathematical explanations, stick to the discussions in plain English, get down the rivers the best I can, and just enjoy the rivers.
However, I am still hoping I can make the Wisconsin Canoe Symposium this June … as long as it does not include any math tests.
Hey Vic I was never that great at math either, and fortunately this is something that can be analyzed with simple trigonometry (I never took calculus at all). Even more fortunately, once you get the principle, analyzing such a situation to the degree needed to know the overall result is as easy as drawing stuff on paper (or seeing the drawings in your mind), but yeah, you need to know the working principles for such simplification to work.
I’m very interested in that canoe symposium too, but am not yet sure if I can or will be there.
Imagine a dot in the middle of the canoe a little ahead of center. This is the pivot point (= CLR).
Hold your paddle vertical in the water on the right side of the boat at a slight open angle (pointing, say, at one o'clock). Imagine a ray (or line) projecting straight out from the power face of the paddle.
If you aim the ray ahead of the pivot point dot, the canoe will turn right. If you aim the ray behind the dot, the canoe will turn left. If you aim the ray directly at the dot, the canoe won't turn left or right but will draw sideways toward the paddle. You may have to move the paddle forward or aft to get the proper aiming angle. Getting the paddle in the proper fore-aft place is the "sweet spot" Pag is referring to.
Goosing the sideslip Assume you are doing a perfect drawing sideslip–i.e., one that induces only lateral motion and no bow yaw. The boat starts to slow. You want to maintain the perfect sideslip until the boat stops going forward. To “goose” the boat to do so as it slows, do you move the paddle position further forward, further aft, or just keep it in the same position?
Same question for the prying sideslip.
I’m not clear on the practical, empirical answers to these questions (though I have some theories based on the peripatetic pivot point hypothesis, which I’ll hold in abeyance until practical responses are given).
and Glenn raced to the rescue with far more information than most of us can digest. That's not necessarily bad. For those that can follow the math and descriptions, it's all good.
Being a bit dyslectic and of weak memory I misspoke. After reviewing some video and notes I've discovered that my original statement (my placement for the prying sideslip is further back) was bass ackward. My prying sideslip placement is in fact a bit forward of that which I use for the drawing sideslip which jives with Glenn's/Pat's theory.
That being said, there are other factors to consider that may play a significant role and they would be nearly impossible to accurately account for. The theories are based on a perfectly neutral trimmed boat. In practice, there is no such thing. If the paddler slips or leans a bit forward or aft (we all do at various times) the boat pitch changes and therefore the pivot point. The bow wave that forms when moving at any speed, creates additional resistant at that end of the boat. There are eddies that form along the hull, particularly near the stern (when traveling forward). What effect do they have? If the boat is heeled slightly, what new factors come in to play? I don't claim to have answers to these questions. My reason for raising them is to point out that while knowledge of the physics and theories, can be helpful, it doesn't answer all of the real world questions. Eventually one has to practice and develop a "feel" for what works.
Often, we host "chalkboard talks" at the symposiums. Though we don't often get too deep into the numbers, some of the presenters are known for sticking suction cup arrows on paddles, and climbing aboard mock canoes to illustrate the basics. Occasionally snoring is heard from the audience.
