What is the rationale?

[Leighb]

Walking round the marina this morning I saw a strange, to me, rudder setup on a Trusty. Large single prop, with twin rudders set quite close together behind it. I have only seen twin rudders on twin screw boats, so why twin rudders with a single screw? Presumably there must be some significant advantage to make the additional cost worthwhile.

 

[paradave]

Reduced draft for same surface area maybe?

 

[ANDY_W]

Dutch sailing barges have the same arrangement in order to increase the turning moment when operating in tight spaces.
With a single rudder located on the thrust centre line, the rudder blade can only deflect half the prop wash.
With two rudders located in line with the outside diameter of the propeller, each blade will deflect the entire prop wash thus increasing the turning effect.

 

[NoviceRod]

My Nimbus 335 (previous boat) had the same - 2 small rudders, each side of propeller. It made direction more efficient when under way, but no turning traction when in neutral.

 

[Leighb]

Thanks for replies, that is helpful, I just hadn’t seen that configuration before.