Hi William,
looked at from a position aft of the vsl in question, the right prop will always turn clockwise and the left one will do so counter-clockwise. As Leif already said, the lower semi-circle of the rotation has denser water providing a better grip, thus pushing the stern of vsl in the opposite direction of the rotation. In order to counteract this prop-torque, one can align the shafts, engine beds etc at an angle outboards from paralell to the vsl's C/L (usually 1 to 1.5 degrees is enough, makes for a nice neutral helm, when underway on one prop only).
Look at the G/A plans of the German twin screw boats. Voila, their shafting is arranged as above.
As said before, props always rotate outwards from the C/L, i.e. right handed pitch on the stbd prop and lefthanded pitch on the port prop. Do not interchange the props, otherwise you would be going astern, when you tell the engine room 'full ahead'.
It was found early last century, when prop rotation on both props is TOWARDS the C/L of the vsl, top speed is abt 15% LESS than the other way. Reason is not completely understood, but it is thought water flow from blades is interfered with by the turbulance from the other prop.
As you can see from my comments, science of prop pitching etc is mixed with healthy dose of applied art. Rgds, RB