31.067 lb. at 70° F
so the wetted surface vs pounds affects speed to what degree? 
How does the effect of hull shape affect speed ?
A longer boat has more wetted surface area so it’s slower, but a heavier boat that displaces more water and rides deeper . . . ?
can’t make a general statement like that.
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All boats do displace water, even if those who have so called planers don’t want to believe it.
The question is not about what it displaces, but where the center of that displacement is,
There is a reason that modern freighters have a bulbous lower bow. It move the center of displacement forward to keep the stern from squatting.
Kayaks are the same. I built a CLC P ax twenty to specs. It had a really hard time getting past 6.5 MPH. The reason is that the cockpit was set at 56 percent from the bow. That caused the stern to squat and made it close to impossible to climb the hill known as a bow wave.
That 56% is great for sea kayaks because it keeps the bow from pearl diving when it meets a wave head on. In fast boat it isn’t.
In between racing boats, because they can be rare things to find, I stripped the deck off of that Pax 20 and moved the cockpit forward a foot. It increased the speed from a fight to do 6.5 MPH to easily reaching 7-7.5 MPH.
The reason is because the stern no longer squatted and the boat no longer had to climb its own bow wave.
Technique is a wonderful thing and I wish more kayakers would work on it, but if your boat can’t go fast, don’t beat yourself to death about it. live with it or payout for a fast boat. They are rare creatures and cost because of it.
I speak from experience because I was a nine time state champion in marathon layaling, down her in Florida, and know I am not world grade as a racer.
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Sorry guys, I know these statements feel right based on experience, but none of this is actually happening. Water is a fluid, it does not take on the characteristics of a solid unless it’s frozen. The fact that water splashes during a belly flop shows that it is a fluid, not a solid - if it was, a belly flop from 100 feet would kill you.
Paddling is not pole-vaulting in water, that’s just not possible. With regard to the videos posted earlier, some of the fluid physics explanations are correct, some are not, likely because the PhD involved has a degree in sports education, not engineering or physics. Having said that, having an incorrect mental model of what is happeing does not necessarily mean all his conclusions are incorrect. Likewise, being able to produce winning Olympic athletes does not mean that the trainer has a true understanding of the fluid mechanics of paddle propulsion.
With reference to the hull lifting or sinking at speed, it depends which direction the net force vector on the paddle is pointing. John Winter’s point that hulls sink with speed is a consequence of the Bernoulli principle - high relative fluid velocity at speed reduces the static pressure under the hull, causing it to sink, slightly. However, the Bernoulli principle is based on a steady-state assumption, which is not quite the case in paddling. However, I expect the effect would be small, and dwarfed by the pitching and heaving (also yawing) motions due to unsteady paddle forces mentioned by others earlier in the thread.
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I just didn’t know . . . I didnt know!!!
I don’t know what you’re asking - a 100 ft fall onto a solid would kill you. Into water, I don’t really know, but I didn’t imply one would survive it, just that the splash shows that water behaves as a fluid, not a solid. Anyway, it’s irrelevant to the paddling discussion.
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No physics expert here, just someone learning. However, on the should the bow rise or dip, this video, which has been around for a while, actually gives a racer and coaches perspective on what he looks for with a good forward stroke, at time stamp 50.47:
(1) Ivan Lawler Racing Kayak (Canoeing) Technique Masterclass - All - YouTube
He looks for the bow to rise as the stroke is made.
Cheers!
I sat back and read those threads about paddles with big blades and small blades, paddles locking in the water and paddles slipping, paddle ain’t supposed to slip, then all paddles slip . . . and stuff like that, until it made me feel dizzy, so I decided how everthing had already been said and nobody needed more confusion. Then I thought about your apology and figure I owed it to you to read it again when I was fulled woke up.
I’m not real book smart, so I wasn’t sure if you never belly-flopped or if’n you was funning me by using fancy words to see if I had ever belly flopped. Well sir, I did and figured out that the higher you jumped, and the flatter you hit the water, the more it hurt and the redder your belly got, and the more your friends laughed. There come a point were it weren’t fun no more.
That’s when I though about what my daddy told me - if a toilet is blocked up, you can’t keep flushing it or it just overflows; you gotta get a stick to bust up what’s blocking it. It probably shows I never read much about water in books, but when I was a young’un, I noticed how easy it was to slice the edge of my hand through water, then if you turned your hand flat it got harder. If you put one of them paddles on your hand to swat wiffle balls back and forth, it got even harder to move your hand against the water.
That’s the reason some paddlers can present the edge of a paddle and get a catch that’s virtually splashless, yet in the same seamless stroke, the fatter surface of the paddle piles all the little drops of water against each other drops and makes the boat move. The faster you move the paddle, the harder it is to move those lazy water drops out of the way. Somebody said that’s on account of them being heavy and they look for low places to rest. This is a little off topic, but even though water might be heavy, a book said the moon pushes and pulls water to make it pile up. Where I launch, it goes up and down about a foot and a half twiced a day. I only mention it because I was told that water don’t actual move much with waves; one drop just pushes another drop, like when a pool ball bumps another ball that moves, but the one that did the bump just stops. However, if you push enough water drops, the other drops try to move like cattle on those cowboy movies. I seen them do it.
Something else about water. It don’t matter how heavy something is, it won’t sink if you spread out enough water. Archimedes explained it - professors call it displacement? I think a gallon jug of water weighs about 8.3 lbs. If you fill a pool to the top and put a 26 lb boat in the pool, the water that overflows will weigh exactly 26 lbs. If you try another boat that’s exactly the same size and shape but weight 57 lbs, the water that overflows will weigh 57 lbs. That’s what boaters call displacement. Even though the boats are shaped the same, the heavier boat sinks deeper. That means it has to push 31 lbs more water out of the way. The pointier the boat, the less distance the water has to get pushed out of the way. That seems to count for something, because racing boats are lighter than most boats, thinner, and the long ones seem faster.
If you put more weight in front of the boat, seems like the boat won’t try to climb the wave that builds up. Instead of climbing a little wave hill and falling back, it just pushes the water aside. That way, if you’re a strong paddler, you can go faster by pushing the water out of the way instead of climbing up the little wave hill. Sounds right that more weight up front holds the front down. I read where some people did the opposite and moved the seat back, so I tried it and just the opposite happened. Instead of going faster and going straighter. The boat seemed to have a mind of its own. It didn’t go as fast and the nose slapped the waves and the boat skittered sideways. The faster I paddled, the worse it got, but maybe I was doing something wrong. I posted pictures, but nobody paid attention to it, because the only thing I had was a GPS and everybody doesn’t trust them.
Back to the immediate topic, the more water you try to push against, that’s called surface area, the harder it is for the water to get out of the way. The news shows how waves knock beach house over. Probably a good idea to build a beach house in the shape of a boat. Wonder why nobody figured that out yet. Everybody keeps building square houses; maybe because books have pictures of square houses and no pictures of pointed houses.
I understand that water is fluid, but I figure its also lazy, seeing how it always tries to find a low spot to rest. You can slice a paddle through it with ease, but if you smack the paddle flat, it don’t go so far. I imagine a lot of kids jump off 100 ft cliffs and their friends laugh at the how red the person looks and the funny faces they make, but I wouldn’t try to jump off something as high as the Golden Gate Bridge. I think it’s about 200 feet, and most people who try that end up ded! D-E-D, ded! Don’t do it, no matter what books say.
Not sure what to make of it, but that’s what I noticed when looking at water. Now that I think about it, I figure you were testing me and that other feller.
That wasn’t a statement, it was a question.
Is it winter?
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I can’t say that I know.
Nor do I know the airspeed velocity of a sparrow . . . either the African or the European variety, laden or unladen. So heaven to Betty, sink me!
Ha! Of course I was testing you! There is no specific record of a an African Swallow. A South African Swallow does exist; however, not much has been published on it.
An average Eurpoean Swallow is 12.2 cm (4.803 inches) with a mass of 20 grams (0.705 oz). It’s suggested that it would have to flap it’s wing 43 times a second to maintain sufficient airspeed velocity while carrying a coconut.
Extensive research by C. J Pennycuick, and the Avian Demography Unit of the Univ of Capetown compiled data on wingbeat frequency based on the wing length of the average European Sparrow. An actual bird of 20 grams weight was tested and found to average 12 wing flaps per second with an amplitude (from crest to crest of the wave) totaling 20 cm (7.784 inches). A single stroke covered an estimated distance of .75 meters, so 12 flaps would cover 9 meters per second, or 32.348 km (20.1 mph).
For a European Swallow to carry a coconut is questionable. The smallest coconut on record weighed 3.8 grams (0.134 oz), which is far beyond the ability of a typical sparrow. Just curious if anyone knew the answer.
You forget that I paddle a 145 Tsunami that’s 24.5 inches wide and weighs 56 lbs with 230 lbs of ballast. I’m not familiar with the concept of glide. I think most other boats will glide if given the opportunity.
still has glide just not as much as a thin kayak.
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Depends on who is paddling it.
It is the kast day of July