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Paddler's Weight vs. Stability and Performance?
I do not buy your argument at all. If the issue was center of gravity,
the trunk of my body, where most of the weight was, did not move when I pulled my legs out of the water. Also my legs were on the deck, just a few inches above the waterline, so the change in center of gravity was minimal. However, the effect on stability was extremely dramatic. (I am less than 6 feet tall, so my center of gravity is not unusually high.) In other words, I can't see how a very small change in the center of gravity could effect a dramatic change in boat stability. There has to be another cause. Remember that this was a sit on top type of kayak, kind of like a surfboard with depresions for the butt and feet. Most of the kayak was underwater even before I pulled my legs out of the water. I think that part of what happened was that the extra weight of my legs put even more of the kayak under the water, and that affected the hull design. It started to look more like a submarine than a conventional boat. One that you said that I might agree with is the idea that weight increases the stability of a boat, up to a certain point. (You mentioned the gunwales). It is really a function of the hull design. If you think of the hull design as kind of an ellipse (or other geometric shape), then as long as the waterline is below the center of the ellipse, the boat is likely to be stable. Once the waterline gets above the center of the ellipse, the effective hull width actually starts to decrease, and the boat becomes less stable. When the hull leans to the left, there is less and less boat above the waterline on the left side resisting the left lean, so the boat rolls. When a boat gets loaded past the maximum hull width, at that point the boat does start to look like a submarine. Conventional canoes are less likely to suffer this kind of instability, since the width of the boat at the waterline, for most hull designs, tends to increase as the boat is first loaded, and most people will never load a canoe to the point where it is close to the gunnels, which is where the canoe hull sometimes narrows, if only a little bit. If you think about the playboat kayaks, they have relatively low volume, which means that much of the hull is below the waterline, reducing stability, which is how they can do some of the tricks that they do, endos, etc. Even they have to have some width at the waterline, because the hull width at the cockpit has to be wider than the person, and the cockpit coaming is several inches above the waterline, so at least the part of the hull around the cockpit tends to provide stability. Conventional touring kayaks have most of the volume above the waterline, so they never hit this form of overload instability, which would probably require a lot more weight than a person and camping gear would provide. Think about the center of volume of the hull, it would always be above the waterline. Since the sit-on-top kayaks have relatively little hull above the waterline, they are more prone to his kind of instability caused by overload, I would think. Richard Your issue was not likely one of absolute weight, but center of gravity. The only way one can be too heavy for a kayak is if you literally push it under water. However, the higher your center of gravity, the less stable the boat will be. Also, the heavier you are, the more effect you will have when you shift your weight or lean. People who are tall and heavy will find a given boat to be much less stable than a person who's short and light. I think that the extra weight took away the initial stability that the kayak was intended to have. My guess is that the boat was designed for smaller people, but usable for medium sized people. My weight was outside the operating range of that design, making the boat unusable by me. That's highly unlikely. With most kayaks, the stability increases as you push the boat deeper into the water, up to the point that the gunwales submerge. I would make a guess that overloading a boat is generally much more detrimental than underloading a boat. A large boat paddled by a small person probably will be slower and more subject to wind and wave than a smaller boat paddled by the same person, but probably still safe and usable. Actually, the opposite is true. A heavier person pushes a boat down farther in the water, increasing the length of the waterline. While this adds more surface friction, it also increases the theoretical hull speed of the boat, making it possible to paddle it faster before "hitting the wall", so to speak. I paddle low volume boats and am at the upper end of the recommended weight range for all of them. I also build skin-on-frame boats that are even lower in volume. All of my boats perform well and have the added benefits of a better fit and less windage. |
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