: When a kayak is in motion it gains stability, anyone that's paddled a
: skinny kayak knows this, they are much more stable once moving than
: they are sitting at rest. Trying to figure out why this is, is the
: question.

Bill~

I am far from a designer, nor do I know a great deal about fluid dynamics, but I will try and give my take. My first thought when reading your question was Newton's first law of motion: "every object in a uniform state of motion tends to remain in that state of motion unless an external force is applied to it."

Now, certainly their are a great deal amount of forces acting on a kayak in motion, however when paddling forward, the overall momentum of the paddler and kayak is in the forward direction. This i am sure has a great deal to do with why the kayak "feels" more stable. Think about a bicycle (or motorcycle, but bicycles have less mass), at rest they are very unstable, to the point that balancing one at rest is considered a trick by many. However, once moving in the forward direction a bicycle becomes EXTREMELY stable.

Eventually, if a bicycle reaches a high enough speed, it begins to become unstable again (the small forces which were previously of no effect now become a problem). I would think that a kayak would show a similar problem if we would be able to power it to a much higher speed. Its stability would be lost and again the smallest of waves could disrupt the boat and paddler staying upright.

I am not sure if the various surface modeling programs show stability at speed. I know the attempts to model the stability of bicycles in motion have been a number of fun post-graduate studies, and a kayak would have to be more difficult... Just my two pence. I've attached a link to a cool video showing stability of a bicycle in motion (being knocked and righting itself)~

~Johnathan