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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66 Proceedings Spring 2016 www.uscg.mil/proceedings A nswers Engineering 1. Note: The line fuses supplying a three-phase motor may be tested off-line using a voltage tester or a multi-meter set up as a voltmeter. A. The fuses must be removed from the circuit. Incorrect answer. To test the fuses on-line using a voltage tester, the fuses must remain in the circuit. B. The starter must be placed in the STOP position to stop and disconnect the motor. Correct answer. The motor must be stopped to prevent back-feeding of voltage to the bottoms of the fuses, which would result in errone- ous voltage readings. C. The three line connections in the motor terminal box must be disconnected and tagged. Incorrect answer. To test the fuses on-line using a voltage tester, the line connections to the fuses must be connected to the fuses and the line connections must be energized. D. Nothing need be done as long as the motor is running under a light load. Incorrect answer. The motor must be stopped. See explanation for choice "B." 2. Note: A salinometer is an instrument used to measure the chloride (salt) content of a solution. It measures the electrical conductivity of the solution, which is proportional to the chloride content. For accuracy, the salinometer reading must be corrected for temperature. A. pyrometer Incorrect answer. A pyrometer is used to measure very high temperatures, such as diesel engine exhaust and boiler stack temperatures. B. thermometer Correct answer. An ordinary thermometer is used to correct for the effects of temperature. C. hygrometer Incorrect answer. A hygrometer is used to measure the moisture content of the atmosphere. D. hydrometer Incorrect answer. A hydrometer is used to measure the specifc gravity of a liquid. 3. Note: While cold weather starting of diesel engines can be diffcult due to the thickness of the lubricating oil, this can be compounded by a reduction in torque that the starting system provides. A. direct cylinder admission air start Incorrect answer. The starting torque produced is primarily a function of the piston crown area and the starting air pressure, which are not signifcantly affected by cold temperature. B. hydraulic Incorrect answer. The starting torque produced is primarily a function of hydraulic motor piston area and the starting hydraulic pressure, which are not signifcantly affected by cold temperature. C. electric Correct answer. The starting torque is primarily a function of the battery's internal resis- tance and the specifc gravity of the electrolytes, which are signifcantly affected by cold temperature. D. air motor starting Incorrect answer. The starting torque produced is primarily a function of the air starting motor vane area and the starting air pressure, which are not signifcantly affected by cold temperature. 4. Note: Pitting on the inside of boiler tubes is generally the result of oxidation corrosion. A. waterside deposits are present Incorrect answer. Waterside deposits generally result when the mineral content of the boiler water causes hard scale formation. B. sludge is present Incorrect answer. Sludge accumulations are generally the result of soft precipitates forming in the boiler water as a result of boiler water treatment for scale control. Sludge settles to the bottom of the boiler. C. dissolved oxygen is present Correct answer. Excess dissolved oxygen in boiler water causes localized pitting corrosion in the boiler tubes. Excess dissolved oxygen can be caused by defective deaeration equip- ment or inadequate dosage with oxygen scavenger treatment chemicals. D. the tube metal acts as a cathode Incorrect answer. Galvanic corrosion in modern boilers is generally not problematic due to the avoidance of constructing boilers with dissimilar metals. Any corrosion, however neg- ligible, would be at the anode. The cathode would be protected.