With counter rotating twins the preferred setup is to have the right
handed prop (clockwise viewed from aft) on the starboard side (that's
the right hand side of the boat Harry) & the left handed prop
(anticlockwise viewed from aft) on the port side (that's the left hand
side of the boat Harry)

This means that counter rotating twins should have the props turning
out away from each other at the top. So prop walk can be harvested to
advantage when maneuvering (it behaves like a wheel, at the bottom of
the prop the water is denser than the top, imagine Harry upside down).

Say trying to spin the boat to starboard with twins the starboard,
right handed prop (now turning anticlockwise from aft in reverse gear)
will try to walk the stern across towards port, the port left handed
prop (also turning anticlockwise from aft still in forward gear) will
also be trying to walk the stern to port, so even if the boat stays
almost stationary, it will assist the bow to swing to starboard. K





The above is basicly correct... but not the full story.
The navy tend to put props on the other way around because props turning
inwards towards each other at the top is more efficient
This is done on the basis that navy ships have tugs etc to assist manouvers
in port.. so they trade the manouverability for better efficiency at speed.
When all is said and done, you will have to fit the props to suit the
engines/gearboxes as fitted to the boat unless you wanna swap them round?