I agree - whenever anything moves in a fluid or whenever that fluid moves past anything there is a turbulent boundary layer. But it can be a darned small boundary layer, smaller than our ability to perceive it.
Even in fairly swiftly flowing deep water, like I’ve occasionally paddled in the Mississippi and other large rivers, I can’t feel anything like differing resistance between paddle strokes or altered resistance to the passage of the boat for long stretches at a time. The water feels of uniform “thickness” to me. Maybe others are more sensitive to this than I, but at such times wind has a much more perceivable effect on the boat and that’s where my attention turns. If I paddle in, say four feet of flowing water over a boulder bottom with a long bladed canoe paddle I can sometimes feel the turbulance a little, but not if I’m paddling over a similar depth and current flowing over sand or gravel. I’m not sure it has much effect on speed over the long haul.
As an aside re: float planes. Another interest I used to sometimes indulge when I was young was building stick & tissue rubber powered model airplanes. I once built a model Supermarine S5. It takes a lot of the decidedly limited power (= lotsa’ winds) of a rubber strip to take off; Much more than it does to climb or maintain flight - and even more for a float plane to break surface tension. Then I learned a trick: A swizzle stick inserted from the top of the float to the step (and, of course trimmed to not be unsightly) introduced air and broke that tension. It helped take-offs but I still never managed to get any very good flight times with a water take-off. Hand launch is the way to go.
But I’m not about to drill holes and insert long swizzle sticks in my canoe. I’d rather paddle harder.
Surface tension is a pretty insignificant component of hull drag.
Intermittent motion due to paddling like rolling, yawing, surging (i.e. varying forward velocity) etc., will definitely affect the structure of the turbulent boundary layer. I’ve never seen any research on that, but overall I think each will give a small but nonzero increase in drag. Hard to say which effect would be largest, would have to think about it a lot more…
That’s very interesting and an excellent idea. Terminology-wise, the air vented to the bottom of the float broke the suction due to the Venturi effect, there’s not really any tension involved.
On the other hand, since the model float was so small, it is true that surface tension enabled to water to effectively block the step in the model float, which is there to allow the air to vent downwards on the full-size float. It’s the same reason why model ships in old movies look fake - the surface tension in the water gives the waves and splash droplets the wrong scale.
I once read an account of the development of float planes written in the 1920s, the evolution of the step design in the float was really interesting - same concept used later in the step design for hydroplanes to get them up on top of the water.
Thanks, carldelo. While working with my nephew, he asked why my boat rolled slightly with each stroke. I never noticed before, and watched for a bit, finally deciding I must be reflexively edging slightly to keep the boat tracking straight. I wondered if it would create drag or break the tension. You seem to think any impact would be minimal. I’d be interested in any further thoughts if you come up with any further info. I did notice that I can track straighter since I resumed paddling following a hiatus of several years.
Rolling is rotation caused naturally by the torque of paddling, as are yawing and pitching. It’s a product of the off-axis forces exerted by the paddle faces and will always happen unless the paddler actively tries to counter it.
I imagine experienced paddlers unconsciously edge a little to reduce rolling, and I believe the J-stroke in single blading is used to reduce yaw. It would be difficult to completely suppress all of those rotations, though.
Two blade rowing rigs are more symmetric, so rolling and yawing are not a problem, but those boats do appear to pitch a little while underway.
I agree. I frankly don’t know if its suction or surface tension (or both) that’s being broken. Y’know, stick and tissue modelers are every bit as obsessive about their passion as we are about paddling. I read of the swizzle stick trick in an article one of them wrote. I added it as an afterthought and it did help. There’s a principle in modeling called Reynold’s Factor, you probably know of it, that good model designers use to modify scale model designs to compensate for the difference in the relative density of the air acting on a real airplane - weighing hundreds or thousands of pounds and flying at much greater speed than a model that is often under 2.5 oz and flying under 10mph. The result is a model that isn’t exactly scale but flies decently and is close enough to pass for scale. Wing loadings don’t scale well either. And the torque range of rubber powered propulsion is WAY different from that of an IC engine. I’m thinking there’s probably something similar to a “Reynold’s Factor” that would come into play with the water acting on a moving model float also, but it would be different because water is so much denser than air and surface tension surely plays a disproportionate role at smaller scales.
This, however, is a pretty fair example of what I was trying to get at earlier… we can’t help but get ideas in our heads about the “cause of the effect” of things we observe. Its human. They may or may not be exactly right, and it may not change a single stroke in how we paddle. Still, they nevertheless can influence our perceptions of things like the “thickness” of water in ways we may not consciously be aware of. Or cause us to think we see/feel things that aren’t quite objectively real. Perception vs reality, as this post is at least partly about.
That’s why racers and long term averages are so helpful. They are readily quantifiable.