-- Last Updated: Jun-25-13 8:18 PM EST --
I regularly row a modern version of an Adirondack guide-boat that's 15 feet long. It's certainly more efficient than most canoes, but not so hugely different that my conclusions are wrong, and actually, the fact that most canoes are a bit less efficient supports my idea that a canoe is a bad choice for a sliding-seat rig, rather than contradict it.
With the guide-boat, I can achieve hull speed (which is essentially the maximum speed that the boat is capable of reaching in the absence of an astronomical amount of power, like an engine) for short spurts, and stay within 0.5 mph of hull speed for an extended time. I do that without a sliding seat. In fact, I can do it using the very poor technique of rowing with arm power alone, not even rocking my upper body back and forth. It is EASY to get the boat up to that speed with a fixed seat and standard-length oars. But when you hit hull speed, you can multiply your power output about ten-times and the boat simply does not respond. It will not go faster, no matter what (unless one or two tenths of an MPH is worth paying attention to, and for racing it would, but not at any other time).
Because of that, I figure that all you can really gain by installing a sliding seat as well as outriggers to allow use of substantially longer oars (using a sliding seat with standard-length oars would be crazy) is the ability to cruise at hull speed, or about 0.5 mph faster than what can easily by done with a fixed-seat rig. In other words, you'll have the ability to waste a huge amount of energy via your full-body exertion to accomplish very little. Maybe if you are really strong, you can go 1 mph faster and exceed hull speed by half a mile per hour or so, or maybe since canoes are inherently less efficient, your practical top speed with a fixed seat would be less, meaning your overall gain would be slightly better than what you could get with a guide-boat. Also, with two people rowing instead of just one, you might do a bit better than what I am describing. But if you are going to put forth that kind of effort, you might as well be rewarded by getting enough extra speed to at least make it seem worth it. The only way you will get extra speed in proportion to your full-body effort is to use a long, skinny, competition-style (or at least a semi-competition-style) rowing shell. I've seen some boats made by Alden (I think) that are even passable for use in semi-rough water, and thus won't be so dependent on water conditions as normal rowing shells are (I believe they are self-bailing, with the forward surge of the boat due to each stroke causing water to simply slip out the back end).
Forget the canoe. Go for the real deal. That is, if you must have the sliding-seat setup.
Oh yeah, don't forget that canoes have thwarts that will invariably be in the way of a sliding-seat rig (usually they interfere with fixed-seat rowing too), and a canoe with thwarts removed is pretty "floppy". Also, consider the amount of room you need for TWO sliding-seat rigs, including the necessary space between them so the rear-most rower can lean back without hitting the feet of the other guy, and for the forward-most rower to lean back without getting pinned where the boat's width tapers in, and you are probably using up most of the available space in the wider portion of the average tandem canoe (thus you'd need to remove two or three thwarts - usually a bad idea).
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