Propshop made me a pair of counter rotating 3 blade cleaver props for my 4 foot aerokits Fireboat. After some discussion, they suggested having the props turning outwards viewed from the rear. It made sense, however on turning, particularly at speed, the hull wanted to roll quite severely.
I went back to same direction cheap two blade "x" props, and the problem went, although the hull now suffered from torque roll going in a straight line. I swopped over the counter rotating 3 blade props to turn inwards, flipping over the brushless esc's so they ran in the opposite direction, a very easy thing to do as you just swop over two of any of the 3 motor wires.
Problem now solved, no torque roll due to counter rotating props, and it handled great in the turns.
Morale here is try both ways, see what works for your boat, but make sure you use thread loc on the props, as one will be turning in a direction to come lose, I know this by experience, as one of my £25 each brass beauties is at the bottom of a lake
and a twin screw boat with one prop is a hard job to get back to shore!
