Any force on a boat afloat, whether exerted through paddle stroke, wind or water (or for that matter, through oar, sail, propeller, or jet thrust, or contact with another object) acts to change the vessel’s momentum and turn the boat around its pivot point. (Of course, if that force just happens to be exerted along a single line that, like an arrow, goes right through the pivot point, the force will alter the boat’s momentum, but it will not act to turn the boat. But a force like that is pretty exceptional. Almost any force on your boat acts to turn the boat.)
Now here is the tricky and the important part: The location of the pivot point depends on the relative motion of the hull and the water in contact with it. Only when a boat is becalmed and drifting, dead in the water (that means it is not moving with respect to the adjacent water) is the pivot point in the center (the fore-and-aft center of the waterline of a reasonably trimmed and symmetrical hull). When a non-planing displacement hull (like a canoe, a kayak, a fish tug, a cruise ship, or a supertanker) moves forward relative to the adjacent water, its pivot point moves forward relative to the boat. Figure that when you’re moving forward through the water, your boat’s pivot point is about one-third of the way along the boat’s waterline, abaft the bow. And don’t forget that when you’re moving backwards (relative to the water close to your hull), the pivot point of your boat moves aft to a point about one-third of the waterline length forward of the stern.
The basic seat-of-the-pants experience, and operating assumption you need to have is that the pivot point of your canoe or kayak is near the bow when your vessel is moving forward through the water, and the pivot point is near the stern when you are moving backward through the water. (This pivot point discussion does not apply to a planing hull, like a speedboat when it is “on step”. “Force” has a precise definition, but it basically refers to anything that acts to change your boat’s speed, direction of motion, or rate of turn.)
The pivot point helps us to understand “weathercocking”. Wind pushes on all exposed parts of the canoe or kayak, but when you’re moving forward, most of the sail area is aft of the pivot point, so no matter what direction you wish to go, virtually all displacement boats tend to head into a strong breeze, just like a weather vane. You will need to correct for this tendency. (Exceptions to this occur if the below-waterline trim is radically uneven, and/or the above-waterline wind profile (”sail area”) is drastically unsymmetrical.) If you’re backing through the water, your boat will tend to back into the wind. However, when a canoe or kayak is allowed to drift in windy conditions it quickly falls off to lay more or less broadside to the wind (depending on the geometry of the wetted area and the configuration of the area exposed to wind) as the pivot point returns to the fore-and-aft center of a reasonably symmetrical boat on an even keel that is making no way through the water.
The pivot point helps enable you to punch upstream out of an eddy into a strong current and to stem that current without getting swept away.
Awareness of the pivot point helps you anticipate that turning while you’re moving forward through the water, causes your bow to move one foot to the right, while your stern simultaneously moves two feet to the left. Anything that moves one end of the boat to one side, moves the other end in the opposite direction, and how much the other end moves depends on the direction you are moving through the water. When a paddler moves the bow at the last second to avoid a hazard, the boat itself may not be out of jeopardy.
In a forward paddled tandem canoe or kayak the pivot point coincides approximately with the bow paddler’s backbone. So the bow paddler doesn’t have much leverage, and that’s why the stern paddler usually seems to “overpower” the bow. It has nothing to do with who is stronger. It’s about fluid dynamics.
In river descents or ascents with a competent paddling team, verbal tactical co-ordination can be initiated from either end of the boat, but typically the bow paddler reads the river and initiates the positioning or defensive moves. The stern paddler responds appropriately to the bow’s lead. In open water the bow paddler primarily provides forward propulsion and the stern paddler establishes and holds the desired course without slowing the forward motion unnecessarily, and efficiently paddling ahead. In open water it is better for the person with the more powerful stroke to paddle bow, provided that person doesn’t mind breasting the wind and waves and provided that the stern paddler enjoys paying attention to selecting trajectories, and to holding an efficient course.
However, the great majority of tandem mixed-sex couples paddle with the male in the stern and the female in the bow. I have a question about this. On rivers, is this because these couples acknowledge the woman’s superior river reading skills and capability for decisive action? On open water is this due to their concurrence that the woman has the stronger stroke and because she has selflessly volunteered to take the brunt of the blast of wind and wave that is the special privilege of the bow station? Is it because of a macho tradition with no useful or rational basis? (Do “real men paddle stern”?) Or is it because the guy refuses to be on the “short end of the stick” when it comes to the leveraged power of the pivot point? Tell me what you think?
The best way to learn and enjoy paddlesport is to begin in a solo boat. Develop an understanding of the subtle and complex interaction of the boat, the water, the environment, and yourself. You will almost certainly enjoy it more than you imagine. If, after you’ve achieved this understanding and joy, you wish to challenge the additional complexities of communication and coordination with another person in the same boat as you, do so with someone who has also achieved an enjoyment and comprehension of the basics through solo boating. Be proud to paddle with a partner who you acknowledge is as good as you are. And switch positions. Paddle on the other side of the pivot point. You just might like it, and you’ll definitely improve as a team.
Learn a tip or two on how to use the pivot point and turning maneuvers to achieve much better control, trajectories, and paddling performance, in “Energy and Momentum – Use It or Lose It“.
Go HERE to see the table of contents and other articles in this series. I appreciate any comments you care to make. This article and series is published and copyright by Clyde Winter, canoeist, kayaker, and U.S. licensed master and chief engineer of motor vessels to 1600 gross tons on any waters.
I first read about the peripatetic pivot point in “The Behavior and Handling of Ships”, and excellent text by Hooyer, 15 or 20 years ago.
During the summer of 2009, an article and a video came to my attention that more closely examines and seeks to explain the complex, ever-changing forces that affect the lateral movement and the rotation of a displacement vessel. Although this article and video are directed towards large ship handling, they can significantly increase your understanding of the hows and whys of the peripatetic pivot point, and provide important insights into canoe and kayak control.
http://www.cpslc.com/understanding_the_pivot_point.pdf
http://ohlinthermotech.com/pivotpoint/
Last time I paddled a canoe it was with Regina M, and she took the stern. All the other canoes were left far in our wake.
Comment by Howard — March 23, 2007 @ 10:29 am |
Clyde,
I for one, like your post. You state that the pivot point moves forward as hull speed increases. Do you offer any explanation why this occurs? I have always been quite curious about this phenomena.
Good stuff!
Kris
Comment by Kris D — June 23, 2009 @ 10:25 am |
I am not certain, but I suspect the explanation for the peripatetic pivot point lies in differential “pressure” on the hull created by the bow wave. It is my distinct impression that the movement of the pivot point is not directly proportional to speed. In fact, the rule of thumb I use is that when moving forward through the water, the pivot point is a third of the way back from the bow, when moving aft through the water, the pivot point is about a third of the distance along the waterline forward of the stern, and when dead in the water, the pivot point is centered.
Have you seen bow thrusters in use on ships? I have been informed that the effect of a thruster cannot be explained by “thrust” of the engine. Apparently, the power of a bow thruster is also caused by differential water “pressure”. The thruster actually pumps water from one side of the vessel to the other, resulting in a slightly higher water level on one side. The water pressure is greater on every equivalent submerged portion of the bow, and the resulting cumulative force moves the bow sideways, quite handily. When the vessel is dead in the water, the thruster is most effective. As the vessel moves forward (or aft) with increasing speed, the pumping effect of the thruster is negated and soon overwhelmed by the relative movement of the vessel forward through the water. A thruster has virtually no effect on a ship underway at more than just a very few knots.
I think the pressure differential caused by the bow (or stern) wave (depending on direction of movement) may be the explanation for the peripatetic pivot point. But fluid dynamics is complex, and I hesitate to say that with certainty without some study.
Thanks for your comment, Kris. There have been about 2500 visits to my series of paddlesports articles over a couple years, and just yesterday, there were actually 200 reader visits to them on my blog. Don’t miss the “Momentum and Energy – Use it or Lose it” article, if you liked this one about the pivot point. Thinking about, and learning the flanking turn will make your day on the next pushy river.
Comment by clydewinter — June 23, 2009 @ 10:55 am |
When paddling my sea kayak in heavy wind the bow blows downwind or leecocks and I have a very difficult time trying to get the bow to turn back up wind. If I follow your theory correctly if I slow down my pivot point should move more to the centre of my kayak and make it easier to turn the bow. I don’t find slowing down helps.
This problem occurs when my boat is unladden. Any suggestions to get better control without adding weight?
Comment by Steve H. — June 30, 2009 @ 11:33 am |
Your problem is serious. I wouldn’t paddle a boat whose heading I am unable to control.
First, you don’t want to turn the bow, you want to turn the boat. And you are more able to turn the boat (all other things being equal) the farther the pivot point is away from where you apply force. Going slower definitely will not help that. You’re probably hardly moving through the water anyway when trying to head into a “heavy wind”.
Second, it is far more important that you have control of your vessel than that your vessel be unladen. Getting where you’re going is the most essential component of getting there fast. Especially in stiff breezes, the less sail area of your vessel, the better; and the longer the waterline, and the deeper and more even the keel, the better. Check my article on flotation for a few tips on ballast.
Third, compare and contrast your kayak with others, and connect with other paddlers. Compare by actual paddling. Connect by listening carefully. Maybe your kayak cannot be rigged to do what you expect. Either change your expectations, or learn what you need to learn, or find a kayak that will do what you need and are able to do.
Sliding seats are employed in some canoes, in order to shift mass, the center of gravity, and the sail area profile. In a solo paddle boat, where paddling forward in wind has the effect of turning the stern into the wind (rather than the more normal effect of the bow heading into the wind) consider the following factors:
(1) the further forward the peripatetic pivot point is when paddling forward, the greater the tendency to head into the wind. (The location of the pivot point depends on the geometry of the wetted surface area and the velocity through the water.)
(2) the greater the distance between the pivot point and the application of a force, the greater is the leverage of that force in effecting a change in heading. (In other words, the farther aft you are of the pivot point while paddling forward, the more control you will have of your heading.)
(3) While paddling forward through the water, sail area forward of your pivot point tends to make your bow fall off of the wind. Sail area aft of your pivot point tends to make you head into the wind. Since the solo paddler presents substantial sail area in a kayak, the further aft you are seated, the more your body’s sail area tends to encourage weather cocking (heading into the wind). However, moving your weight aft shifts the center of gravity aft, which lightens the bow and sinks the stern, which may more than counteract the beneficial effect of simply moving your body’s sail area aft.
In summary, moving your position aft while carrying ballast forward may provide you the heading control you need while paddling forward in a stiff breeze which (in your particular case, in your particular boat) would otherwise result in your bow being blown downwind. Another thing to experiment with is adding sail area at the stern of your kayak. Something like a skeg or rudder in the raised position might make the needed difference. And while the rudder or skeg in the water helps you track in a light to moderate breeze, it may not help in strong, especially gusty winds. You are certainly aware that your rate of turning is slower while using a rudder than with it up. The symptoms you described may be partly (and ironically) due to a down rudder or skeg.
This preceding comment and my reply here was about a paddlesport boat that lee-cocks excessively in certain wind conditions. A similar type analysis ( with somewhat opposite recommendations) would apply to a paddlesport boat that weathercocks excessively.
A well designed sea kayak is a series of compromises. One compromise of any paddlesports boat (other than a flat out sprint racing competition boat) is that it should perform best while carrying a load besides the paddler(s). Obviously, that is true of an expedition boat. So don’t think you’re always getting the best performance out of your boat by paddling it as light as possible. Should it perform best in the worst conditions you will encounter? Probably not, because marketing understandably urges that other criteria take precedence. It’s up to you to choose the boat you need, and make it work in the conditions you place yourself. Build on a sound base of knowledge.
Comment by clydewinter — June 30, 2009 @ 11:35 am |
I’m sure you are familiar with the technique of “carving circles” or “paddling the inside circle” as it is sometimes called. For those who are not, this describes a phenomenon in which a boat can be paddled in a circle to the paddler’s onside without using correction strokes. By increasing the radius of the circle, the boat can be paddled in a nearly straight line using short forward power strokes without cross-forwards, J stokes, stern prys, bow draws, or C strokes.
As one paddles an inside circle, one can feel and actually hear a small wave build up on the boat’s offside bow. An adjacent paddler can see it. The resistance on the offside bow resists the normal tendency of the boat to turn toward the paddler’s offside.
This seems to work best in rockered hulls, only works after gaining some forward momentum, and often seems to me to be facilitated by weighting the bow with some forward lean.
Your article explains how forward momentum and weighting the bow would both move the pivot point forward. It also seems logical that increasing rocker serves to increase the amount the pivot point shifts. It seems intuitive that the shifting of the pivot point is fundamental to this technique but I’m still not sure I grasp the mechanics of how it works.
Comment by pblanc — July 1, 2009 @ 6:10 am |
There is a “sweet spot” one finds in employing the hit-and-switch technique of forward paddling that is related to pblanc’s carving circles comment. I find that sweet spot when I can paddle (single-blade, straight ahead) using only forward power strokes, several strokes on one side, switching to several strokes on the other, etc. with the heading never significantly altering. It depends on achieving a good forward speed, a fast, steady stroke cadence, and proper anticipation of the swing and timing of the switch. If I did it more often I’d probably be better qualified to describe it. The key is to switch paddling to the side towards which the boat heading is just barely beginning to veer, and paddling several forward power strokes (3 to 5?) to counter the yaw that would otherwise develop, switching again just as the heading begins to veer in the opposite direction.
This “sweet spot” in “hit-and-switch” power paddling, or the “carving circles” described by pblanc, is achieved by your power stroke just countering the incipient yaw before it has developed and gone out of control. The balance of forces is perhaps easier for me to experience than to scientifically and rigorously describe. Knowing it is there encourages you, too, to find it.
A solo single-blade paddler can paddle strong, hard, straight and fast this way, for long satisfying stretches. Tandem paddlers can also hit-and-switch in coordination, and paddle long distances efficiently. Whenever my boat’s heading changes significantly and has to be corrected with rudder or other steering strokes, the energy I have expended in building the boat’s forward momentum is lost. The very quickest way to stop a boat (without hitting something hard) is to allow or cause it to rapidly change heading. If you want to get a good hard workout, without going very far, or seeing very much country, just zig-zag through the water between here and there, rather than hold a steady heading.
Now, I am going to leave you to your suppositions and the mechanics of how a canoe or kayak turns, because my priority is the health care crisis that our country is in. We can no longer leave the administration of America’s health care system to corporations which have virtually all of us playing Russian roulette with illness and injury; which have driven health care costs so high, with so little return, that we are now paying twice per capita for “health care” what is paid by the three dozen other industrialized countries of the world which have better overall measured health care outcomes than does the United States of America. There is no excuse for that. It’s not the doctors and nurses, or the people at fault. It’s the administration of the system by insurance corporations that is at fault.
We don’t need health insurance, we need health care.
It costs less to administer comprehensive health care as though it is a basic human right than to ration and distribute it according to who individually “deserves” what standard of care for what particular condition.
Insurance corporations have failed to efficiently and effectively administer America’ health care system in terms of the needs of people and families, and they cannot rationally be expected to do otherwise.
Businesses that employ American workers are at a competitive disadvantage with businesses that employ workers in other industrialized countries that have lower health care costs while providing comprehensive health care for everyone, regardless of employment.
We need government that is of, by, and for the people – not government that is by and for the corporations and the lobbyists – in order to get the health care America needs.
Support HR 676 and S 703 now – as if your life and your future depends on it.
Comment by clydewinter — July 1, 2009 @ 10:34 am |