Originally Posted by GordMay
If there's no way on, the rudder
has no effect.
Twin screw boats should generally be close-maneuvered with gear
shif & threottle only, no rudder
This page disagrees with Gord
I have not read the link above yet but I would expect the rudder position to affect the turn. With a double screw installation
the pivot point will be somewhere near amidships, so at or near the stern the rudders will see transverse water
flow even if there is no longitudnal flow due to forward or aft movement of the boat. Changing the aspect of the rudders to this flow can only be beneficial.
I would expect the rudders turned with the turn to increase the rate of the turn.
I would expect the rudder turned against the turn to have the same rate of turn as amidships but to decrease the radius of the turn.
It's been 2 decades since I got to play with a twin screw boat and I don't have access currently or I would have to go out and try this.
EDIT: Never mind about the rudder against shortening the radius, Challenge: Captain's License Questions
post #19 reminded me about the crabbing effects.