Bensens gyro boat was a glider, actually more of a kit was it needed the towline to be stable a correctly designed gyro boat needs to follow all of the rules of a stable wheel equipped gyro but due to the extra weight they can’t carry as much for a given horsepower and rotor size, they are not as smooth in rough air either, the large hull and horizontal stabilizer gets kicked around more.
The designer has improved his craft by using a fairly narrow hull with outriggers. One could reduce weight and drag further by using a closed single float of a width of, lets say, 25 inches with a classic float design using a step to facilitate breaking free from the water. Drag of that float would be completely unimportant due to the slow tow speed. The glider would be a bit heavier than a land based one but there are probably more lakes suitable for training than there are large enough runways open to glider towing, what do you think?
The gyroboats in the film are built with Bensen rigs.
The concept has a couple serious problems, both related to the aerodynamics of the boat.
First, the fuselage is clearly unstable in yaw and pitch. There's more hull area ahead of the CG than behind it. As result the craft will very abruptly yaw stern-first if the towline either breaks or is deliberately released in flight. It may also "pitchpole" (do a forward somersault) under the same conditions, for the same reason. In today's gyro parlance, the latter form of instability is called drag-over (contrasted with pushover).
Second, even with the towline still attached and pulling, the craft will do an uncommanded, abrupt dive if it first climbs high enough that the bow dips low and the relative wind enters the open hull from above. This famously happened to Igor Bensen once when he was flying a gyroboat in front of a crowd. Fortunately, the gyroboat leveled out in response to the towline pull once it neared the water. This aerodynamic effect is powerful enough to overcome the control power of the rotor. A friend of mine had the same experience, but in a powered gyro with floats. He didn't level out of his dive, despite back stick. Instead, he plowed nose-down into Long Island Sound. He got rather badly hurt.
It's possible to make even a Porta-Potty (outdoor toilet) stable with enough tail surface power. The necessary tail area and leverage are hard to achieve within the small triangular space available at the back end of a gyro, though.
Due to the weight of the rotor, head and engine all gyro boats need out riggers, in my first one I put them on a beam across the middle of the boat but later machines had them on the tip of the horizontal stabilizer, the last one that I built was 16 feet and the stabilizer was 12 feet wide so it made sense to put them back there.