Double rudder systems are used mainly in blue water sailing since this is the arena in which their excellent steering qualities are particularly telling. They are also particularly well suited to the centre-cockpit designs increasingly favoured by yacht manufacturers such as Hallberg Rassy, Oyster, Westerly, Moody, Najad, Malo, Camper & Nicholson and Amel. The auxiliary rudder is something of a handicap when manoeuvring in harbour, which reduces the appeal of this type of gear for weekend and holiday sailors.
For a small crew on a long trip, however, the steering performance of a windvane steering system can never be too good. Inadequate steering, regardless of the cause (poor choice of system, transmission problems in a servo-pendulum system), always manifests itself in difficult wind and sea conditions when manual steering is at its most unpleasant. Double rudder systems represent the very best in windvane steering force and performance. They combine the advantages of auxiliary rudders and servo-pendulum gears (with none of the attendant transmission problems): the connection between the pendulum rudder and its dedicated auxiliary rudder is direct, and the auxiliary rudder, relieved by the main rudder of any basic steering functions, effects course corrections with maximum leverage thanks to its position at the very aft end of the boat.
A theory surfaces from time to time which suggests that a pendulum rudder should provide better steering through a boat's main rudder because the main rudder has a far greater area than any auxiliary rudder. This reflects a misunderstanding of the interactions between the elements involved in steering. The main rudder is designed to cope with all potential steering tasks. The rudder angles required for course corrections though are always small. The relatively short line travel and ever-present transmission losses (weather helm, stretch, slack, play, wheel steering and its transmission to the main rudder quadrant, friction in the main rudder bearings) anyway restrict the amount by which the pendulum rudder can turn the main rudder.
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