Proceedings Of The Marine

SPR 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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96 Proceedings Spring 2015 www.uscg.mil/proceedings A nswers Engineering 1. Note: A single-phase capacitor start induction motor has two sets of windings shifted by 90 mechanical degrees: a run (main) winding and a start (auxiliary) winding. On an attempted startup, if the motor hums without starting, usually one of these two winding circuits is open-circuited. The humming noise is the result of current passing through one winding and not the other. A. an open start capacitor. Correct answer. A start capacitor is wired in series with the centrifugal switch and the start winding. If the capacitor has failed open, the start winding circuit has a permanent open-circuit condition, thus producing motor hum with no starting torque. The motor will fail to start. B. a tripped cir- cuit breaker. Incorrect answer. If the circuit breaker is tripped, neither winding will pass current. On a start-up attempt, the motor will not start, nor will a humming noise be produced. C. a shorted centrifugal switch. Incorrect answer. The centrifugal switch is wired in series with the start capacitor and the start winding. If the centrifugal switch has failed shorted closed, the motor will successfully start but will trip the circuit breaker on excessive current shortly after startup because, the centrifugal switch is incapable of dropping out the start winding circuit as the motor accelerates up to rated speed. D. a blown fuse. Incorrect answer. This scenario is similar to a tripped circuit breaker. If a supply fuse is blown, neither wind- ing will pass current. On a start-up attempt, the motor will not start, nor will a humming noise be produced. 2. Note: When the drill size marking has been worn off the drill shank, a micrometer may be used to measure the drill. A. margins. Correct answer. You should measure from the outside of one margin to outside of the other margin at the point of the drill (not be confused with the dead center). This corresponds to the actual drill size. B. futes. Incorrect answer. The futes are the spaces between the webs. C. shank. Incorrect answer. On a straight shank drill, the shank diameter is slightly less than the actual drill size (margin-to- margin diameter). D. web. Incorrect answer. The webs are the metal columns between the futes. The web diameter is slightly less than the margin-to-margin diameter, thus providing the body clearance necessary for drilling. 3. Note: Lube oil analysis is a powerful diagnostic tool used to determine the following: condition of the lube oil and whether or not it should be replaced, type and level of contamination present, and the condition of the components of the machine being lubricated. A. the air fltration is inadequate. Incorrect answer. Inadequate air fltration will allow excessive amounts of dust and dirt to contaminate engine lubricating oil, resulting in a high silicon content. B. engine coolant is leaking into the lube oil. Correct answer. Sodium nitrite is a corrosion inhibitor found in many closed-loop cooling water sys- tems. As such, the presence of this chemical in a lube oil analysis indicates engine coolant is leaking into the lube oil. C. fuel oil is leaking into the lube oil. Incorrect answer. Fuel oil leaking into the lube oil would result in "fuel dilution" of lube oil. Depend- ing on the type of fuel, this would be indicated by a change in viscosity and fash point of the lube oil. D. the piston rings are excessively worn. Incorrect answer. Excessively worn piston rings results in cylinder blow-by, allowing the by-products of combustion to enter the lubricating oil. 4. Note: Carbon dioxide extinguishes fres mainly by smothering. Halon 1301 is a gaseous "Clean Agent" that extinguishes fres by chemically disrupting combustion. A. A cylinder is considered satisfactory if its weight is within 10% of the stamped full weight of the charge. Incorrect answer. While this is true for carbon dioxide extinguishing systems, the criteria for Halon 1301 is within 5% of the stamped full weight of the charge. Refer to 46 CFR Table 91.25-20(a)(2). B. If a protected space is ventilated mechanically, the ventilation system must be automatically shut down by the release of the agent. Correct answer. For a carbon dioxide extinguishing system, 46 CFR 95.15-35(a) states the following: "Where mechanical ventilation is provided for spaces other than cargo and similar spaces which are protected by a carbon dioxide extinguishing system, provisions shall be made so that the ventilation system is automatically shut down with the operation of the system to that space." For a fxed clean agent extinguishing system, 46 CFR 95.16-30(a) states the following: "If mechanical ventilation is provided for in a protected space, the ventilation system must automatically shut down prior to discharge of the system to that space." C. To avoid confusion during an emer- gency situation, there should be only one action necessary (such as a single pull box) to activate the system. Incorrect answer. Activating a carbon dioxide and Halon 1301 fxed extinguishing sys- tem requires two independent actions. Refer to 46 CFR 95.15-10(d) for carbon dioxide systems and 46 CFR 95.16-5(c) for "Clean Agent" systems. D. All of the above. Incorrect answer. Choice "B" is the only correct answer.

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