Hulls and keels experience lift, for sure. The first time I realized just how all that worked was while training in my kayak. I raced whitewater slalom kayaking in high school. My coach was trying to make the Olympic Kayak team. He'd missed it the previous Olympics by one place. They didn't include Kayaking in the next Olympics . Anyhow, I had an Equipe Elite slalom boat and was out on the reservoir flatwater training when I noticed it got much harder to paddle when I was close to shore. In deep water, I'd move along well, but in shallow water the boat would bog down and actually sink lower in the water. The wake would be bigger and the stern rode below the water level in a hole created by the wake.Lift also is affected by hull and keel design.
Analogous to ground effect?In deep water, I'd move along well, but in shallow water the boat would bog down and actually sink lower in the water.
Yeah, that's about right. Anywhere from 1'-3' vs 5' or more. My guess, even 6' would have a measurable effect on my small kayak. For larger boats, you could probably measure the effects in 8 or more feet of water.are you talking 2' deep vs. 6' deep in your kayak? what was your deep vs, shallow?
There is a mixture of ideas being debated here re: hypothesis testing.The hypothesis would be that there is no difference between the predicted and observed data and the null hypothesis is there is a significant difference between the observed and predicted data. If there is a significant difference between the observed and modeled data, then we accept the null hypothesis and reject the hypothesis, loosely translate the model doesn't work and back to the drawing board we go.
@Kings Gambit thanks for the clarification. My background is indeed in statistics, however, it has been decades since I actually had to apply them in a experiment. Now I just read and interpret studies.There is a mixture of ideas being debated here re: hypothesis testing.
The idea of a null hypothesis is borrowed from world of statistics. For example, if I sample two separated populations of fish, 25 specimens each, and determine the mean number of dorsal fin rays in each sample, the two means will not be identical even if the populations are genetically of the same make up. But is the difference between the means a significant one, or is it one where the difference makes no difference b/c it is caused by inherent sampling variation?
The statistical null hypothesis Ho would be: there is no [significant] difference in the means of the two samples. If the null hypothesis is rejected, then one concludes that the difference is significant. Rejection of the null hypothesis depends on the probability of seeing by chance alone a difference in the means as large or larger than the one observed. If the probability is greater than 1 chance in 20, i.e., 0.05, the null hypothesis is not rejected. If the probability is less than 1 in 20, the null hypothesis is rejected and the difference is considered "significant."
Less quantitative approaches to hypothesis testing but of similar nature are widely applied under the Popperian idea of falsifyability. A true hypothesis must be falsifyable. There must be some prediction emerging from the hypothesis that allows it to be tested, and subsequently falsified if it is incorrect, which normally comes via experimentation. Sometimes these hypotheses are formulated as null hypotheses. If the prediction is not seen, the "null" hypothesis is not rejected; if it is seen the "null" hypothesis is rejected. To lessen the confusion of testing with the above semantics, the "null" is formulated as the one where the prediction fails; an "alternative hypothesis" is formulated as the one where the prediction succeeds, or is observed.
It is nearly incompressible. In practical terms, no. That's why pressure vessels, like SCUBA tanks, are tested with water instead of gas (hydrostatic testing), because the liquid can't store enough energy to hurt anyone it the tank fails.does water compress?
No, you are right. I mis-wrote.i always heard and observed that waves break at twice the depth of their height, but i may be wrong.
It is my understanding that the build-up of water at the head of the moving hull needs to go somewhere. It can't stay piled up so it flows toward the hole left behind the moving hull. Gravity and the energy imparted to the water by the moving hull transfer to rearward motion. The water under the boat is also getting displaced by the movement but it can't go down because water doesn't compress well so it flows outwards and up (stern wave). Bernoulli's work shows that the fluid volume entering a pathway in a given amount of time is equal to the volume exciting the pathway in the same amount of time. This would also be true at any point along that path. Since the cross sectional area at midship is more restrictive to that pathway, both by width of the hull and by the depression of the trough, the water, in order to equal the volume entering and leaving the pathway has to move faster towards the stern of the hull, just to catch up.waves do not create current to my knowledge. i have never observed this flow from the bow wave back to the trough.
Waves start to break near shore when the depth of the bottom shoals to 1/2 the wave length. What actually happens, I believe, is that the height of the wave rises relative to the wavelength (or wavelength shortens relative to wave height) when it starts to "feel" the bottom at 1/2 L, eventually to the point where the ratio of H/L becomes > 1/7, where it breaks. This can happen at sea as well, H/L > 1/7, for large (high) waves of comparatively short wavelength, etc.i always heard and observed that waves break at twice the depth of their height, but i may be wrong.
In the words of Einstein, "a consensus of 100 scientists can be undone by a single fact." More importantly, in the words of Michael Crichton in a lecture to the faculty at Cal Tech: "There is no such thing as consensus science. If it's consensus it isn't science; if it's science, it isn't consensus." Science is "settled" only provisionally, awaiting discovery of some new fact that ushers in new insight. We must always distinguish the difference between what the press and others sometimes call "consensus science" or "scientific consensus" and what it really is, a consensus of individual scientists (and sometimes others) who may not have the facts or experiments necessary to "make" the science. Also, discovery and establishment of the truth about nature is driven forward by skepticism of the "accepted" explanations, not by agreeing with them to some government (or other) agency with a social agenda.I wouldn't call it settled science, I would call it a consensus of measurement results. Being able to repeat a measurement doesn't say anything about the underlying mechanism, does it? The pressure difference might be coincidental to, and not causal of the lift. We may never know.