hey K.,

Just to turn the question sideways as to be more applicable to your circumstances. Have you ever paddled for 3hrs. or 5 miles? This might be more significant if you are doing something new and those on land are expecting you at some particular time. That said , 3.5 mph seems to be the realistic top range. My experience in doing aerobic activities is that if I am pushing the aerobic limits then I have to have the specific muscle conditioning for that activity,ie. if I have never walked for more than 10miles then the first time I walk 15 my feet are going to be the limiting factor. If the longest brisk paddle I have done is 3 miles then a 5 mile brisk paddle might be harder on my wrists and butt. So theoretical speeds and horsepower outputs are useful for folks that are at the limits of human efforts (racers and the like).