I'm sorry but its not possible to show the servo under the deck.
One servo directly drives one rudder via a metal link. The other rudder is directly slaved to the first via a horizontal plastic bar that shares the servo movement. So both rudder tillers move the same way, same amount.
But viewed from the rear of the boat, the rudders are splayed out by about 10 degrees.
They don't point the same way. If right is straight, the left rudder will turn the boat counterclockwise to port. I guess to go straight ahead, both rudders try to gently turn the boat in opposite directions.
If now the boat happens to twist a little, without any rudder change, the arrangement would tend to correct the twist.
Eg both rudders slightly splayed out. Boat twists to starboard at front. The right rudder is now straight to the motion and the left rudder more strongly opposes it. So the boat self corrects. But if both rudders were straight it would self correct anyhow.
In reverse, things of course work opposite and the situation is unstable. Which is maybe why in reverse it has always been extremely poor and tends to whiz off to one side