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Thrust vectoring
It seems to be a consensus among experienced twin screw
captains that leaving the rudders amidship is good practice for most maneuvers. There are exceptions of course but having the rudders amidship leads to more predictable response in my experience. Much depends on the size of the rudders. Twin screw boats tend to have much smaller rudders than single screw for a variety of reasons. Some of these reasons have to do with rudder support when the rudder is not directly aft of the keel, others involve the reduction of drag to achieve greater speed, and still others calculate the combined area of both rudders. In the final analysis, on most twin screw vessels the rudder has a very marginal ability to change the direction of the boat through the water compared to the application of unequal thrust from the engines. I'll be out on a speedy twin screw boat later this morning to collect some data and get some photos. I fully expect that at crusing speed or better and with equal thrust from the engines the turning circle of this 42 footer will be close to 1/8 mile in diameter. And that won't be particularly unusual. Obviously not much rudder in play. When close quarter maneuevering we consider the wind and current and compensate for any significant forces. Seems to make sense that one should respond with the most efficient and significant force available....whether that's unequal thrust, a big rudder, or an oar. |
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