paddlesports quick physics

My series of five articles on canoe and kayak techniques have been steadily and increasingly visited by anonymous readers. There have been more than a couple thousand visits to them on my blog, and some of the articles have even been taken to other sites (rather than just providing a link to them). Despite this apparent interest, virtually no comments have been left on my blog by readers, though people have referred to them, and presented links and commentary to them on other sites.

The latest was on this site, on the subject of weathercocking. Previous pulses of interest have been on the subjects of kayak self-rescue, trajectory control in pushy water, the principle of the moving pivot point and how it affects solo and tandem boat control and human relations while tandem paddling, flotation and ballast, buoyancy and gravity.

I’m surprised and pleased that so many people interested in paddlesports have found their way to my little out-of-the-way blog. I am a bit disappointed that virtually none of them have made a comment, whether critical or in praise, of these articles meant to share and increase awareness and proficiency in our mutual joy and environment. But I didn’t study and write them in order to hear from people, so no need to drop me a note unless you’d like to. I am gratified that paddlers are reading and finding my articles helpful, or at least interesting.

I have just today substantially revised “The Peripatetic Pivot Point” to make it simpler and more accessible, while retaining accuracy. In case the hyperlink doesn’t work here, just go to my blog at

The table of contents has hyperlinks built in, connecting each title to the article itself.

Good stuff

Your Blog
Good stuff including the paddlesports stuff. Thanks for exposing yourself.

related to john winter? NM

Very refreshing thanks
Excellent and refreshing. Well done.

by the way what happened to the one on Kayak Capsize Recovery and Survival. It appears empty?


My favourite
At the bottom of post:

Possibly related posts: (automatically generated)

* Emergency Contraception for Victims of Rape


emergency contraception
That article is one in a series I wrote for our local newspaper on that particular subject. The other articles are found in the category, “womens rights” in my blog. A little-known fascinating political pattern emerged from that story, and also applied to other seemingly unrelated issues that came before the Wisconsin legislature. That series I called “How the Wisconsin legislature voted on …”, and was undoubtedly the reason my column was canceled after six years by the publisher. Thank you very much for your interest.

kayak capsize
The link in the table of contents was bad. The article was there, available by clicking on the category in the side bar called, “Recreation - paddlesports”. I have just corrected the link in the table of contents. I’m sorry for the inconvenience. Thank you for informing me of the problem.

Not that I am aware. At least he is not a member of what we call my immediate family. But if he’s a river rat or salty, he’s family.

good stuff, but …
Thanks for commenting, Falcon.

It’s probably been noticed by some readers that the “pivot point” discussion is a bit over-simplified, and it also doesn’t answer the penetrating, perennial question, “Why?”

The peripatetic pivot point on displacement vessels (like our canoes and kayaks) is a well-established phenomenon, extremely useful for any vessel operator to be aware of. But why does the pivot point move where it moves?

I did not offer an explanation based in physics. And I confess I don’t have one I can offer with certainty. Some of the earlier discussion on the subject of weathercocking might have been right on course, but I can’t say for sure. (In particular, the suggestions involving pressure differential and bow wave versus stern hollow are intriguing.)

Whether or not we get a definitive answer, complete with physical laws and pertinent equations, grasping the concept of how the pivot point in your boat moves depending on the relative velocity of the boat and the immediately surrounding water, will help people in gaining greater boat control and having more fun. The moving pivot point is kind of a rule of thumb. It doesn’t have to be real precise, and we don’t even have to know why it works for it to work just fine for us.

turning is only the beginning
Thank you for your interest and for the compliment, salty.

The pivot point discussion is a prelude to some stuff I wrote up in “Momentum and Energy - Use it or Lose it”. I’ve frankly been desperate for any specific feedback to my brief discussion there about “flanking turns” as applied to paddlesports on pushy rivers.

I think you river lovers are just the ones to enlighten me.

Clyde, you are not alone.
If your blog does not get comments it’s because it’s good.

If you convey knowledge in your articles there are probably two scenarios why others don’t leave a comment:

a) the reader is greatly impressed and feels inadequate to leave a comment because his/her knowledge is way lower then yours

b) the reader is jealous of your achievement and rather not compliment you on your work

Very good blogs generally have a lot of followers (mostly hidden) and don’t get a lot of comments.

After all a decent blog attracts a different type of reader (read: not the Twitter type:-).

Seeing your articles quoted on other sites confirms that your stuff is good.

And that should be the best compliment.

I track the readers of my blog ( and I have figured out that I have a lot of followers but little feedback however I know that people refer to my posts

(I am not implying that my material is good, only that it gets referred to often).

It’s the tall poppy syndrome: we all love an underdog but as soon as he/she improves we are jealous.

its allright
but I can’tremember when the last time was that I crashed through a rapids and tried to remember the equation to determine my pivot point.

It’s good informative stuff, but really - is it all that applicable, or needed?

yes for those interested
it is good to get us hard head to think outside the box of our bodacious paddling adventures to other ways of doing things.

alone is not lonely
I learned about some things I had never before wondered at or worried about on your gnarlydog blog. Nice to learn from someone giddy with joy.

I took a four month plus solo sea kayak voyage once, and a professional social worker and student of human nature (one who professionally packs heat) asked me with interest whether I ever felt lonely. On that voyage, I answered honestly, (surrounded as I was with life at all times), I often felt alone (paradoxically), but never lonely.

I am amazed at that bicycle video. Thanks for sharing.

crash and burn
I crashed a lot of rapids, too, and never did an equation occur to me, either - (except for the classic “i=shitferbranes”).

The basic pivot point phenomenon is awful easy to recall and apply while paddling. You don’t need to bring along the laptop or tax the memory.

If you think a seat-of-the-pants operating knowledge of basic principles of physics might possibly be applicable or helpful, at times, at sea or on the river, check out “Momentum and Energy - Use it or Lose it”. Comprehending the principle of the flanking turn will make it a lot easier for you to get into, out of, and through, much hairier water than you otherwise would.

Pivot point
I read the articles as well, they have facts but not causes so I’m not sure what to say about them. You mention that the pivot point of a boat in motion is around 20% back from the bow - Benford in Naval Arch for Non-Naval Archs says the same thing; neither presents a mechanism why it is so. I suppose it could be analogous to the location of the CP at the quarter chord point on an airfoil - but there’s a theory and proof behind that.

John Winters in the Shape of the Canoe disagrees, and implies that the forward pivot point is more psychological than physical. But truth is truth (at least in low-speed physics) so there IS a real instantaneous center of rotation on a turning boat, although I assume it is not fixed. For now, I lean towards John Winters because he provides a bibliography that backs up his extensive work. I guess that leads to a logical question for your online posts - what are your technical sources?

In the earlier thread following “weathercocking”, another contributor cited two sources. One was my article, which caused me to backtrack here. I haven’t time to look up my sources. They are all from my study of ship handling for my line of work.

It is true that my discussion of the peripatetic pivot point does not address the question, “Why?” It is a rule of thumb (as I confessed and indicated in a previous response to another contributor). The rule is on-third of the distance, not 20 percent, by the way.

I suspect that the hydrodynamic principle underlying the pivot point is (as suggested by yet another contributor) differential pressure resulting from the bow wave. I discussed that a little with another contributor, with a related example. But I have not studied the physical principle, so cannot say for certain.

Experience certainly confirms the operation of the pivot point in any displacement vessel, and it is most definitely not psychological. I do not wish to quarrel with what John Winters may have said because I only have it second hand or out of context.

Right, it’s Benford that says 20% is the max distance to the center, you said 33%. If it is caused by the bow wave, then I guess it should move around depending on the yaw angle, speed and vessel shape. I hopefully will be able to do some testing of this issue someday, should be a good student project.

The rule of thumb position of the pivot point when traveling at or around hull speed is one third of the distance along the keel at the waterline, measured back from the bow where it intersects the water. That would put the pivot point 5 feet from the entry of a vessel with a 15 foot waterline. (That would be near or at the tailbone of the bow paddler in a tandem boat.)

That point is also 2 and a half feet forward from the center of the vessel. 20 percent of 15 feet is 3 feet. You might want to be sure that you aren’t comparing percentages of apples with fractions of oranges. But that’s just a detail, and can perhaps be cleared by careful reading.

The phenomenon of the pivot point in displacement vessels is so well know and widely accepted (at least by professional mariners) that I suggest a search of the pertinent literature and some conversations with such persons, before looking for the forest between the trees, and before embarking on scientific research in what might not be such uncharted waters.

Again, I believe that one or two sources on the subject were cited in a comment by another correspondent in the recent thread on weather cocking. I apologize that I still have not found the time to cite other specific references for you, and I probably won’t because of other things that need doing.