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Thrust vectoring
Gould 0738 wrote in message ... See my other post. If conditions are such that water is ingested from one direction, and exits in another, there is a change in lateral momentum. That's a lateral force, usually behind the C of G. That's a yaw. That's turning a boat. I think you're making the assumption (without stating it) that, engine in reverse, water will always be ingested from dead astern; ie, the rudder is small and of such a distance from the prop that it has no effect on the direction of ingestion. JimB JimB: Are you attempting to make the case that a rudder controls the direction of a power driven vessel primarily by changing the side of the prop on which water is "ingested"? No. I'm starting from the point that the rudder changes the lateral momentum of water traveling past the stern, and this creates a lateral force. It's obvious that, engine ahead, the water comes from straight ahead and can then be deflected laterally by the rudder to create a lateral force. With the engine in astern, I was saying that *if* the water entering the prop is constrained to come from one side (big rudder etc) then it's momentum is changed from having a lateral component to having no lateral component, therefore a similar force is developed. However, you've made me reflect on that. Yes, there will be a force on the rudder, since it is deflecting the water (and you can feel this on the tiller). And I've witnessed (and had explained to me) the effect on trawlers and tugs. But I can't square this with the idea that, in astern with no motion, the water ultimately has started with zero momentum (if we're standing still) and is accelerated to have solely a fore and aft element. That implies no net lateral force. So something is missing here! Perhaps there's a subtle change in prop walk in these types of boats caused by the rudder angle in astern Thanks for making me think . . . JimB |
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