Hi Doug, Boats with long direct drive shafts seem to be common in many countries, not only in shallow water, and also on quite big boats. I saw a picture of one once being driven by a car engine mounted on the after deck.
I remember, it must have been about 1954, an attempt by a garden mower company to produce an outboard with a straight over the stern drive. It was called the Atco Boat Impeller.
I watched a demonstration on the hard at the Medway Yacht Club. The motor was duly attached to the transom of a dinghy, usual clamping outboard method. With some difficulty the motor was started, it then jumped off the dinghy falling into the water. Don't worry, said the demonstrator, it will run under water. Glug, glug, glug, motor stops. End of demonstration.
Advertising ceased after a short time. I never saw one in use or heard of anyone buying one.
All the best, Nerys