I lowered the seat slats by 3/4" with spacers and find that it helped stability more than I expected. Pretty much what you folks suggested. The only problem is that I'm now getting a wedgie from the keel since it's now higher than the slats. I rounded the top corners of the keel and will use some 1/8" dense craft foam as a cushion. I'll give this a paddle next week. I was considering shaving a 1/4" off the top of the keel to get some more clearance. I know the stiffness of a beam varies as the square of the depth so it wouldn't take much to weaken the keel. On the other hand, the seat area is close to frame #4 so maybe not so bad. I'm trying to avoid raising the seat and decreasing the stability.
Thanks for any and all comments.
Rich Wagner