I am having difficulty in understanding the solution to the problem described below and illustrated by a rather crude Paint sketch I made:(adsbygoogle = window.adsbygoogle || []).push({});

“Each propeller of the twin-screw ship develops a full-speed thrust of 600kN. In maneuvering the ship one propeller is turning full speed ahead and the other turning full speed in reverse. What thrust P must each tug boat exert on the battleship to counteract the turning effect of the ship’s propellers?”

This is the answer:

P = 600 * 12 / (120 – 50) = 102.86kN

Surely the distance of the tug boats from the thrusters should matter (easier to combat the turning force of the ship’s propellers the farther away the tugs are from it, so as to take advantage of leverage / mechanical advantage)? And does not the precise location of the center of thrust of the ship’s propellers matter?

I assume one tug is pushing and the other pulling.

Also, how does the answer and solution provide the amount of thrust for each tugboat and not just a figure of total force needed to counter the turning effect of the ship’s propellers?

Another point: The question and answer only seems to care about the difference that each tug has in relation to each other from a reference point, which in this case is a plane perpendicular with the bow of the ship (70m). But should the tugs be the same distance from this reference point then the moment of the ship’s propellers would be divided by zero, which of course would render zero as the final answer! Obviously, in real life, the answer would not be zero if the two tugs were the same distance from the reference point.

I am having a very hard time trying to understand thissimpleproblem. Any explanation to help clear my brain fog would be much appreciated!

Edit: Direct link to diagram, as attachment is pending approval:

http://img440.imageshack.us/img440/3025/staticsshiplq6.gif [Broken]

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# Homework Help: Force Couple Problem (Thrust of Ship)

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