Much has been already said by others, regarding blade width. Pete spoke about how a wide blade would cause the boat to turn, because it would need to be held far out from the boat (I'm paraphrasing here). Let me elaborate.
Ideally, we'd be able to place the paddle through the center line of the boat, with the shaft vertical, and stroke straight back. If we installed the equivalent of a centerboard trunk (anyone who sails will visualize this) this might theoretically be possible, but the truck would cause other issues. The further offset the paddle is from the center or keel line of the canoe, the more the canoe will turn toward the offside, with each forward stroke. This is called yaw.
Other factors which limit yaw have already been discussed by others.
For practical purposes, this means we want the shaft to be held vertical, with the blade at rt. angles to the keel line and as close to the gunwale as possible during the stroke. (Note: The path of the blade is front to back in a straight line, not following the curve of the gunwale.) If the grip hand is held out past the gunwale, it is possible to have the blade partially beneath the hull (closer to the center line). Well designed paddles are shaped so that the upper portion of the blade is relieved so that it will allow the lower portions to "fit under" the hull.
The point of this is that making the blade excessively wide, would force the shaft further away from the side of the hull and thus further from the Keel line resulting in excessive yaw. Any potential gain from the larger blade would be offset by the increased correction necessary as a result of the yaw.
From what was originally stated, I'd suggest (as others have already) that improvements to your technique may do much to improve your performance. A properly sized (length) paddle is also necessary. I'd suggest trying several before investing in one.
I don't know where in Florida you are located but from March 15- 18 will be the Florida Canoe Symposium in Yulee, just N. of Jacksonville. You'll not only have access to top notch instruction there, but also the ability to try out many paddles and canoes. Full information about the symposium is available from the home page at www.freestylecanoeing.com.
Dogpaddle Canoe Works
Custom Canoe Paddles and Woodstrip Canoes
Kayak Motor Kit
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