Drafting can be just as useful in kayaking as it is in bicycling. Times when you might want to draft include:
-- Keep the group integrity when one boat or operator is slower than the other(s)
-- a group is heading out to the fishing grounds
-- extended trip or expedition
Of course on the water you're riding the swell or wake of the boat in front of you. The best place is on the perpendicular swell directly behind the boat, offset slightly from the fin turbulence (if you're pedaling). Here's a good view of the swell generated at fast cruise speed:
The best place to ride is just ahead of one of the humps, as near the lead boat as possible -- just like riding downhill. Here's what it looks like if you're in the wrong spot (you're facing an uphill battle):
This is a much better location:
Here's a slower kayak taking advantage of the opportunity. Notice his position with respect to the swells.
With a little practice, you'll feel it when you get into the groove. You can get a nice rest in this position.
Drafting is not limited to kayaks. Anything moving near your speed will do (stay out of the prop wash):
When the wind picks up it can be harder to see the swell, but it's still there and available.