I always say, "A tailwind can make anyone a great paddler." Realistically, I can not imagine any beginners maintaining 4 knots for even an hour. To do so for 8 hours is extremely unlikely. Most beginners would be hard-pressed to maintain 3 knots for even one hour and could not paddle continously for 8 hours at all. I suspect that some other forces must be at work. (currents? wind? accuracy of course measurement?)