I own a 1982 Sabre
28 MkII with a Westerbeke
13 and offset shaft (to port) with a RH turning folding (Flex-O-Fold) prop.
This combination produces the most bizarre, yet predictable behavior when backing under power.
If I am motoring forward and throw the transmission
into reverse while there is still way on the boat, the stern will walk to port.
If, however, the boat is at a dead standstill and I engage reverse, the stern walks to starboard.
This makes backing and filling impossible in the normal way. To get the stern to swing to port in reverse the boat must first be traveling forward. From a dead stop the boat will back to starboard, erasing any gain to port. It's weird, but at least it's consistent.