well, i'll probably say too much and nothing at all, but here goes...

Having built and paddled many kayaks, mostly in kind weather, Ive experianced weather cocking to varying extents. Basic greenland form kayaks have the advantage of shorter waterline length improving manuevrability. the obvious dis advantage is that it gets pushed around by wind and waves. There are several ways to stay in control.

1> Keep a maneuverable boat and steer with the paddle and by leaning. try to design the boat to be properly balanced so that the lateral resistance of the boat in the water balances the wind drag of the boat and paddler. I think the ideal balance is difficult if not impossible to find for all wind and sea conditions. most commercial boats are pretty good if they are not intended to have a rudder or skeg.

2> make the boat strongly track straight. This works well too, again balance is important. it is more important in this type of boat because corrections are harder to make. A retractable skeg is a way to make an otherwise maneuvable boat track straight. It also has the advantage of allowing you to adjust the location of the center of latteral resistance and therefore the balance.

3> Give the boat a rudder. This has all the advatages, you can maneuver the boat and the rudder is effectively a pivoting skeg. I would say that double kayaks must have a rudder because they are to difficult to maneuver with paddles alone.