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118 Cards in this Set
- Front
- Back
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State the purpose of a marine transmission system
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Transmit power produced by the prive mover to the water as efficiency as possible thereby driving ships
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How was power transmitted to paddlewheels |
Directed connected to engine with gear and chains |
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Why are paddle wheels suck? |
Yawing
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What type of gearing system should be used in steam or gas turbine propulsion system and why? |
Double reduction because to reduce the spread of the output shaft |
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When was double reduction first used? |
1927 |
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What direction does the output shaft turn from in relation to the input shaft in |
A single reduction gearbox - different direction A double reduction gearbox - same
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State the fundamental law of gearing as a mathematical formula and as a statement. |
The speed ratio must always be the inverse of the diameter ratio....d1/d2=n2/n1 |
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Diametral pitch |
The ratio between the number of teeth on a g ear and the gear diameter , P=Nt/d |
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In a reduction gearbox, the input has the smaller g ear and the output shaft has a larger gear. what is these gears called? |
Pinion and gear wheel |
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The reduction ratio of a gearing system is limited for practical reasons, what is the max ratio and why? |
12;1 because the hardware becomes too large |
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What four different ways can the input and outpust shafts of a geaerbox be arranged? |
Concentric, parallel offset, right angle and shrewd |
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Double reduction gear is generally built with flex couplings between the first and second stage, waht is the name given to this ? |
Articulation and flexible coupling |
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The size of the double reduction gearbox can be reduced significantly by utilizing what type of gearing? |
Planetary
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List four major componets of a planetary gear set
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Planetary Gearing, Sun Gear, Planet Gears, and Planet Carrier |
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A duel tandem gearing arrangement requires torsional flexibility between stages. What is generally used for this purpose in naval vessels? |
Quill Shafts |
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What are pressure line and pressure angle? |
PL - Line of contact PA - angle between the line of contact and the tangent |
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Why are spur gears generally not used in high speed operation? |
They are limited in smoothness, noise, and vibration. Not suited for high speed operation |
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In comparison to spur gears why are helical gears preferred for marine reduction gearing? |
Less noise and better load sharing
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Name two advantages of dual tandem gearing? |
Half the stress on gears and gear reduction
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Why would you want to articulate a gear train? |
Offers resistance to shock loading, distributes power evenly |
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What are two ways to achieve articulation in a gearbox? |
Flexible coupling and quil shaft |
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What type of gearing is 'locked train' and what is considered as locked train? |
Gears with absolutely no backlock
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What is double helical gearing normally used in stead of single helical gearing? |
To reduce axial motion, and thrust balancing |
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How can reversing capability be proved for a ship? |
CRPP, Reverse shaft rotation,epicyclic gearing, reverseable reduction gear |
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Name five methods of producing gearing |
Die casting, cutting, stamping, extrusion, power centering |
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What materials are used in marine gearing and why? |
Carbon alloy steel |
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What methods are used to improve the heardness and wear resistance of metals |
Carburizing, carbo-nitriding, nitriding, Cyaniding |
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What is the purpose of bearings ina reduction gearbox? |
Hold the shafts
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Name two general types of hydrodynamic bearings |
Journal and Thrust |
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What name is giving tilting pad or pivoting shoe type thrust bearings |
Michel, kingsbury |
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What type of bearing is used to support radial loads? |
Journal |
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What properties of Babbit make it a good journal bearing material? |
Good embedability and conformability |
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What is forced lubrication used with hydrodynamic journal bearings? |
Helps create a oil wedge |
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What does Babbit consist of? |
Tin, lead, arcintic, copper |
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How do bearings in a plummer bearing differ from regular jounal bearings? |
Keeps the shaft plumb and has tilting pads |
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What functions are important in a gear case? |
Holding oil and bearings |
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How are bearings normally lubricated? |
Flooded |
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How are gears normally lubricated in the gear casing |
oil misters |
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What are solid coupling used for? |
Connecting 2 shafts with no freedom of relative movement of the shaft and better torque transfer |
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Can torque and thurst both be transmitted by a solid coupling? |
Yes |
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Can all flex couplings transmit torque and thrust |
Yes for torque and for thust... they can but normally don't |
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What are flex couplings used for? |
Articulation, and load sharing |
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What kind of flex coupling would you expect to find on a diesel and why? |
Rubber or elastomer type coupling allows some relative movement between shafts and act as a torsional vibration damper |
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What does a gear tooth coupling consist of? |
Male/female coupling |
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What is the purpose of a Turning Gear? |
The turning gears purpose is to position propulsion machinary without the use of the prime mover for various tasks |
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What is the difference between a clutch and a coupling? |
Clutch can synchronize shafts and disengage shafts |
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What are the main advantages of using a mechanical clutch instead of a friction clutch? |
Much stronger and doesnt slip |
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List two adv. of a fluid coupling/hydrolic clutch compared to a mechanical clutch. |
Articulation and Teperature regulation |
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Because of slippage of the hydrulic clutch what loss must be accepted? |
Efficiency loss |
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Name some applicaitons where a hydruliuc clutch is used? |
Auto transmission and diesel engine |
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What purpose does the shafting system fulfill in a main propulsion transmission system? |
Trasmit torque and thrust |
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What three factors affect the loading of a shaft? |
Weight of the shaft, bouyancy of the components outside the hull, and steadiness of the load |
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When the propeller turns it creates a thrust axially to itself which toehr direction will thrust be created? |
In towards the prime mover |
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What is the benefit of a hollow shaft? |
Stiffer and lighter |
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What is a shafts chritical speed and what causes it? |
Speed at which the shaft will go into resonance |
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What is the purpose of the thrust block bearing |
Keep shaft plumb |
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What is used as lubricant in a stern tube bearing? |
Sea water or oil |
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What are two types of bulkhead seals presently used in the navy? |
Soft packing type and face seal type |
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Where would a rope guard be fitted on a warship |
Just forward of the propeller to pretect the stern seal or A breaket |
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What components of a shafting system are subject to wear? |
Bearings, bulkhead seal, stern seal |
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How is an alignment carried out? |
Optical telescope or lasers |
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Shaft whirl |
Instabiltiiy |
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How is shaft alignment checked on a shaft already installed |
Bearing reactions |
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What is the name of the high pressure side of the prop |
Face |
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What is the name of the low pressure side |
Back |
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Pitch |
It is the distance the prop will advance for one revolution in an unyielding fluid |
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How does the prop blade generate lift |
With a pressure drop on the back and a pressure rise on the face the total pressure differential results in a net force on the blade |
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What is the advantage of using a variable pitch propeller |
Adaptable to the ships hull
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Advantage to controllable pritch prop |
Change speeds with chaging your shaft speed |
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What point is hte pitch of a variable piutch propeller blade given |
7/10 of the tip radius |
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Name three types of screw type propellers |
CRPP, CPP, Variable pitch, and constant pitch |
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What are two main reasons why a CRP or CPP prop would be used |
Increased flexability of operation and improved manuverability |
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The efficiency of a CPP propeller is slightyl lower than that of a fixed pitch propller at is design point. What? |
Because of the larger hub required to accomedate the blade control macheniery |
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What is the pilgrim nut and how is it used? |
It is used to apply hydraulic pressure to pull the prop. The nut is screawed to the prop shaft and the strong back over top.When hydraulic pressure is appliced to the NUt the rubber loading ring is inflated and pushes against the strong back displacing it and the prop astern so that the propeller comes free of the shaft. |
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How does cavitiation occur? |
The rapid formation and collapse of vapor pockets in a fluid flowing under very low pressure. |
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What are the types of cavitaition experienced on a prop |
Face, Tip Vortex, back cavitiaton |
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What design requirements must be met to fabricate a prop |
Hull and shaft vibration characteristics, manufactuability and transpotability |
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Properties of a efficicent prop |
Large diameter, wide thin blade, turns slowly, small angle of attack |
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Why is a marine prop wider than an aircraft prop |
Light loaded and still develop the required thrust |
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What is singing? When does it occur? |
Singing is the high frequency torsional oscillation about the blade axis from the root to tip before the onset of cavitiation. |
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What effects does prop vibration have? What causes prop vibraiton? |
Noise and excess drag A flow disturbance in the wake can cause vibration |
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What practice is used to change a prop natural frequency? |
Adding mass by load drilling |
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What is propeller material |
Cast Iron Cast steel Manganeese-bronze aluminum stainless steel |
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What properties are consdered to be important when choosing the material used for making a prop |
strength, controlibility, corrosion resistance, cavitation erosion resistance |
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What is the benefit of a kort nozzle compared to a conventional prop |
The Kort has low speed, high power, and better directional capability |
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On what type of vessel would a Kort nozzle be fitted? |
Tugboats and oil rigs |
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What advantages does a jet type propulsion system and what ship would you find it on? |
Jet has the ability t operated in very shallow waters and its very manuverable |
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What is a contra-rotating prop? |
It is two mounted propellers with the 2nd prop using transitional thrust |
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What is the normal ship speed for a vessel employing a super cavitating prop? |
30-80 knots |
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Describe the general operation of the CRPP system and components |
A propeller that has blades that can be rotated far enough to give a negative pitch angle which would produce reverse thrust |
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Give 3 adv. for using double helicat gears rather than spur gears |
- Less noisy - can take higher load - oblique line of contact |
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What is the purpose of modfiying the tip, flank ,and crown of the gear tooth? |
Removing interference, contact loading, quieter, and reducing line |
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What is the purpose of using a seversible converter coupling? |
To be able to have a fluid coupling |
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What is the name of the shaft arrangement used by planetary gearing? |
Concentric epicycle gearing |
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What part of a planetary gear system would have to be held stationary in order to achieve an output which is in a direction opposite to an input? |
Carrier |
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Give three improvements that are nescessary to allow a gear train to transmit more power? |
- increases face width of teeth - increases material hardness - increase diameter of pinion |
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In the interest of cutting the most accurate teeth, what method would you use to cut a gear? |
Hobber
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When would you choose to nitriding over carburizing for improving the physical properties of gears? |
Proper alloy and want hard teeth without quenching |
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What is hte disadvantage of using a buricant with too high a viscosity in the gearbox? |
Does not get rid of the heat properly, and components get too hot |
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Give two functions of a turning gear |
- gear inspection - position propellor for a dry dock |
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Give 3 conditions which you would find acceptable for gear tooth inspection |
- frosting - light wear - light pitting
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Give two conditions which would condemn gearbox teeth |
- spalling - cracking
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WHen connecting external gearbox couplings, why is it necessary to dial gauge the opposing shafts? |
Minimize eccentric imbalance |
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Give two adv. of using a mechanical clutch over a friction clutch |
Stronger, no slips, longer life |
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Under which condition will a SSS clutch disengage a prime mover? |
When the counter torque is larger than the input torque |
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Give two sources of periodic loading of a shaft system |
Speed variances and changing torque loads |
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What is the meaning of the phrase "The critical whirling speed of the shaft"? |
Speed at which the shaft will go into resonance |
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List three modificaiton that can be made toa shaft design in order to increase its critical whirling speed |
- larger polor moment of inertia - shorter shaft sections - increase G - lighter/stiffer material |
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What is the purpose of the thrust block |
Take thrust from the intermediate shaft/prop shaft and transmit it to the hull |
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Why are shaft thrust blocks never mounted to rafts? |
- A hard mount is required to transfer the thrust fully to the hull - A raft would dampen the transfer of thrust |
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What is the fuction of an A bracket bearing? |
To support the propeller shaft outside the hull |
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WHich two types of shaft bearings incorperate Michell tilting pads? |
Thrust and Journal |
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Which type of bulkhead seal uses grease for lubrication? |
Self-aligning seals |
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What is the purpose of eddy plates? |
Prevent eddy currents |
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What is the name of the stern tube seal used on the CPF |
Crane M series gland |
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List 3 characteristics of an efficient prop |
- large diameter - thin blade -light weight -stiffness |
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Provent cavitation |
-Larger area of blade - decrease camler |
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How does a kort nozzle achieve more thrust than a single prop under the conditions of low advance and high power? |
By utilizing the forward thrust of the aerofoils with the convergent duct surrounding the prop. |
