Back in the late '80s Steve Dunlap and I modified a beat-up Ultramax by cutting 4"-5" out of the seam line. The potato chip that resulted didn't have enough volume to float Steve (at 175 lbs) without him constantly paddling forward. (I was only 145 lbs, so somewhat less "stressed".)
The boat had absolutely no directional stability, since the hull was basically a shallow arch in every direction. It was, however, dynamite at Mystery moves. Lean forward for a front-ender, lean back for a back-ender, all done in flat water. Learned how to do Windmilling too.
Neither of us ever had the gonads to paddle it in anything more difficult than Class 2. We eventually raised the cockpit opening with a tower in the center for safety. The original boat had bumps in the rear deck for our heels.
