Thanks, I'll check out the other forum.
There is some science behind the CL thrust idea. It was driven by one of the properties the yellow boat above had, torque effects on steering. At full chat I had a banked turn in one direction, regular airboat style, and flat turns like a hydro in the other. As I'm using spare engines, an Irvine 20 Black Head and a Thunder Tiger GP 25, they will not cancel each other out fully, but I'm leaving provision for interchangeable mounts should I want to tidy that up with matched engines later.