Along these same lines, I've come across some rower types who also seem to be pretty good with mathematics. They've derived some formulas for how total weight affects speed for a given power output. Their basic formula for rowing shells is (%change in speed) = 1/6 (%change in weight). The weight is the total system weight of paddler + boat, but it correlates pretty well with a chart I saw posted some time ago by some scandanavian kayakers(I think).
As an example, for a 250lb boat+paddler who loses 10 lbs, (down to 240 total weight), that's a 4% weight change. If we assume a kayak hull is basically similar in the water to a rowing hull, speed change will be 1/6 of 4% or about 2/3%. At 4mph he/she will see a speed increase of a whopping 0.027 mph. 5 hours of paddling at 4.027 mph will get you 0.13 miles further along - about 700 feet. Sheesh
Sort of makes you wonder what all the fuss is about weight. At least as it concerns paddling speed. Just thought I'd toss that out 
