Every boat has a designed load range and an optimum load range, which is
the engineering view of the world. I have a personal story.

I one time tried to use a friend's sit-on-top kayak. Now I am a big
guy, around 200 pounds, and heavier than he is. I found that if I took
my feet out of the water and put them on the deck, I went over almost
instantly, in calm water. With my feet and lower legs in the water, the
boat sat higher in the water, and was reasonably stable. However much
my legs weighed, maybe 30 pounds (15 kg), it was the difference between
stability and instability. After swimming a few times, and failing to
get far from the dock, I gave him back his kayak.

I think that the extra weight took away the initial stability that the
kayak was intended to have. My guess is that the boat was designed for
smaller people, but usable for medium sized people. My weight was
outside the operating range of that design, making the boat unusable by
me. I would make a guess that overloading a boat is generally much more
detrimental than underloading a boat. A large boat paddled by a small
person probably will be slower and more subject to wind and wave than a
smaller boat paddled by the same person, but probably still safe and usable.

My two cents.

Richard


Wright wrote:

Having noticed that most touring kayak manufacturers recommend shorter
lighter kayaks for lighter weight paddlers (without really specifying why) I
am looking for an explanation of the effect of a person's weight on initial
stability, secondary stability, and performance. Given two identical
touring kayaks and two people of equal abilities, if one weighs 125 lbs and
the other weighs 190 lbs what would be the differences, if any, on stability
and performance?
Chuck