Proceedings Of The Marine

WIN 2015

Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.

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64 Proceedings Winter 2015–2016 www.uscg.mil/proceedings A nswers Engineering 1. Note: A hand-cranked analog megohmmeter is used to evaluate insulation resistance by imposing a relatively high DC voltage across a conductor and the framework of the apparatus (ground). The response of the pointer while performing this nondestructive test is used to determine the condition of the insulation. Assuming that constant DC voltage is applied while cranking, the measured resistance is inversely proportional to the leakage current. A. dipping toward zero, then raising slowly Incorrect answer. This response pattern is the result of the capacitance of good, dry insula- tion and is especially seen when testing the insulation of large machines. B. continually rising as test voltage is applied Incorrect answer. This response pattern is seen when testing good, dry insulation, and the resistance will continue to climb to the true resistance value. C. kicking slightly down scale as voltage is applied Correct answer. This response pattern is caused by leakage of current along the surface of dirty insulation. D. fuctuating around a constant resistance reading Incorrect answer. This is not a typical response pattern. 2. Note: Using a steam-heated fuel oil heater and associated control system as an example, the fuel oil heater fuel oil outlet temperature is the quantity or condition being measured and controlled, and is known as the controlled variable. A. controlled variable Correct answer. The controlled variable is that quantity or condition that is being mea- sured and controlled, as explained in the note above. B. manipulated variable Incorrect answer. The manipulated variable is the variable of the process acted upon to control the output (controlled variable) at the desired value. In the example cited in the note, this would correspond to the fuel oil heater steam inlet fow. C. set point Incorrect answer. The set point is the desired value of the controlled variable. D. control point Incorrect answer. The control point is the actual value of the controlled variable at any given time. 3. Note: The side clearance between a piston ring and its groove should be suffcient to allow for thermal expansion but not so great as to allow the ring to reciprocate within its groove excessively and cause pounding. A. expand excessively under operating temperatures Incorrect answer. The thermal expansion rate of piston rings is a function of ring metal- lurgy and the piston operating temperature, not piston ring side clearance. B. scuff the cylinder liner excessively Incorrect answer. Excessive scuffng of the cylinder liner is primarily the result of inad- equate cylinder liner, piston, and piston ring lubrication. C. hammer the piston land above the ring Incorrect answer. Though excessive side clearance does cause the ring to reciprocate within its groove excessively, due to fring pressure, the resulting pounding causes the piston land below the ring to be hammered, not the land above. D. hammer the piston land below the ring Correct answer. Excessive side clearance causes the ring to reciprocate within its groove excessively. Due to fring pressure exerting downward, the resulting pounding causes the piston land below the ring to be hammered. 4. Note: A vessel is subject to six freedoms of movement, three of which are linear motions and the other three rotational motions about a specifc axis of rotation. A. yaw Incorrect answer. The yaw motion is a rotational motion where the vessel rotates about a vertical axis. B. sway Incorrect answer. The sway motion is a linear horizontal motion where the direction of movement is to port or starboard. C. heave Incorrect answer. The heave motion is a linear vertical motion where the direction of movement is up or down. D. surge Correct answer. The surge motion is a linear horizontal motion where the direction of movement is forward or aft.

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