: Weight is not the first concern. With a small car, I cannot carry anything
: longer than 10 to 12 feet. Water sources are not any where near, so
: driving 50 to 100 KMs with a long boat on top, at slow speeds would be a
: killing!

Hmmm, the crossbars on my roof rack are about 3 feet apart. I put 16 and 18 foot kayaks on them, and drive at hwy speeds, on a regular basis. I use a bow line, too. I don't think that the size of the car underneath the roof rack makes much of a difference. So what if it overhangs more than you'd like? Just tie a red flag to the stern and go.

Alternatively, Tom Yost made a rack extension for his car, to support a longer boat. As has Reg Lake. I can't find any pics, but they work.

In any case, be sure to tie down the bow! Some people tie down the stern, too, which can't hurt. Try not to bend your boat in half.

So, you can go with a longer boat, and likely you'll be happier in the end.

Heeling is a term that sailors use to describe when their boat leans over to the side. Is that what you were referring to? Realistically, any kayak you build, or ever paddle, will lean over - though some are tippier than others, of course. Most sit-on-tops are designed to be fairly stable . . . .