The Titanic had three screws, two on reversible reciprocating steam engines on each side, and one in the middle on a non-reversible steam turbine engine. The rudder design was small for a ship of her size, and the centre turbine was positioned directly forward of the rudder. When they spotted the iceberg, the engine room called for the engines to be reversed to avoid the ice. Because the centre screw could not be reversed, it simply stopped, reducing water flow over the rudder, hence drastically reducing the rudders effectiveness. If the centre screw had simply kept running, the rudder probably would have successfully turned the ship out of danger.