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"T-boned to a dock"?
Assumptions: 1. You are describing a boat with a rh prop. 2. "T-boned to a dock" means the stem is jammed against the dock to prevent forward movement.......(until the stern swings far enough that the angle is no longer sufficient to brake the boat). With those assumptions........... Q: Which way does the stern of a boat t-boned to a dock turn when, with the rudder turned to port and the tranny in forward, you give a 2 second burst of the engine? A: I think we all agree the stern will move starboard. (you mean a two second application of forward gear, as the engine remains at least idling, but otherwise......) Correct. Q: same question but rudder turned to starboard? A: the stern will move to port. Correct Q: same question but rudder centered? A: the stern will move to port due to prop walk Incorrect. Here are some excerpts from my old copy of Chapman's. We can probably assume that propellers still behave the way they did 20 years ago. "Another factor also effects a boat's readtion to propeller rotation. While this factgor is sometimes referred to as 'sideways blade pressure' it is more properly an 'unequal blade thrust', exerted by the ascending and descending blades of the propeller. Figure 709, top. Here we are looking at the starboard side of a propeller shaft, inclined, as most shafts are, at a significant angle to the water's surface and the the flow of water past the blades. The actual pitch of the blades as manufactured, of course, is the same, but the water flows diagonally across the plane in which the blades revolve. Figure 709 shows clearly how the effectof this is to increase the pitch of the descending starboard blade, (right hand propeller) as compared with the ascending port blade, when considered relative to the direction of water flow past the propeller. The importance of this factor is reduced as the shaft angle is decreased, and naval architects sometimes take pains to have the engine installed as low as possible to keep the shaft nearly parallel to the water's surface and to the flow of water past the blades. This contributes to greater propeller eficiency, and is a factor worth considering if it is consistent with other design requirements. Once a boat is built, shaft angle is difficult, usually impossible, to modify. The relatively greater blade pitch on the starboard side creates a stronger thrust on this side, causing the bow to turn to port. As far as this single factor is concerned, THE STERN OF A SINGLE-SCREW BOAT WITH A RIGHT-HAND PROPELLER THUS NATURALLY TENDS TO GO TO STARBOARD WHEN THE PROPELLER IS GOING AHEAD, AND TO PORT WHEN IT IS REVERSING." Q: same question, rudder centered, but tranny in reverse (bow of boat tied to dock)? A: the stern will move to port due to prop walk Correct. Q: same question (tranny in reverse) but rudder to port? A: the stern will move to port due to prop walk Correct, particularly when the bow is secured to the dock and the vessel cannot develop sternway. Q: same question (tranny in reverse) but rudder to starboard? A: the stern will move to port due to prop walk Anybody but sherr doubt that? Chapman's, for one. According to an indpendent and recognized authority, you only missed one. That gives you what, a strong B? :-) |
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