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SF exam > Ship Handling w/ Tugs > Flashcards

Ship Handling w/ Tugs Flashcards

1
Q

What are the 3 general categories of tugs used in shipwork?

A

Conventional, Tractor, and ASD

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2
Q

What are the 6 key elements in tug design?

A
  1. Towing Point 2. Propulsion Point 3. Propulsion and Steering 4. Maneuvering Lever 5. Hull Shape 6. Superstructure and Fendering
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3
Q

What is the towing point?

A

The last physical point on the tug that fairleads its line; or the point of contact between the tug and the ship when pushing.

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4
Q

What is the propulsion point?

A

The focal point of the tug’s application of horsepower under the water.

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5
Q

What is the maneuvering lever?

A

The distance between the towing point and the propulsion point.

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6
Q

Descibe the orientation of the maneuvering lever for a conventional tug.

A

towing point forward of the propulsion point - short lever

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7
Q

Describe the length and orientation of the maneuvering lever for a tractor tug.

A

Towing point aft of propulsion point - moderate lever

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8
Q

Describe the length and orientation of the maneuvering lever for an ASD.

A

Towing Point is forward of propulsion point, longest when towing point is the bullnose; shorter when the towing point is the bit.

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9
Q

What causes a tug to capsize when on a tow line?

A

The tug does not have enough leverage to counter the pull of the towline.

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10
Q

What advantage does a single-screw tug have over a twin-screw tug?

A

Efficency, since a single screw will develop 20% more thrust for equal horsepower.

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11
Q

What is the principal disadvantage of a single-screw tug?

A

Lack of maneuverability, inability to steer astern, and inability to maintain position when backing. Power astern is less than power ahead.

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12
Q

What advantage does a twin-screw tug have?

A

Excellent maneuverability, ability to maintain position when backing, and ability to steer astern.

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13
Q

What are the disadvantages of a twin screw tug?

A

May require a stern line when backing, is less efficent than a single-screw tug, backing power is less than ahead

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14
Q

What advantages does a tractor tug have over a conventional tug?

A

A tractor can steer when going astern, has omni-directional thrust and does not have the same risk of capsizing as a conventional tug when towing.

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15
Q

What advantages does and ASD have over a tractor tug?

A

Better sea-keeping ability, shallower draft, more efficent hp to bollard pull, can perform transverse arrest.

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16
Q

What are the 4 components of the steering and propulsion system?

A
  1. Power Source 2. Power Transfer and Control System 3. Hydrodynamic Driver 4.Thrust Directional Control Mechansim
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17
Q

What is the purpose of the power transfer and control system?

A

To transfer and control rotative force force to the tug’s hydrodynamic driver (typically a propeller).

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18
Q

What effect has the diesel engine had on the design of tugs?

A

Allowed smaller, more powerful tugs to be built, increased the range and power of tugs.

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19
Q

Describe the DR system of engine control

A

Direct Reversable - engine is directly connected to the propeller shaft and rotation is the same as the engine. Engine must be stopped and restarted to reverse directions. May have wheelhouse control.

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20
Q

What made DR systems obsolete?

A

Limited number of maneuvers, engine speed may not allow for most efficent sized propeller, vulnerable to failure to start or starting in the wrong direction.

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21
Q

Describe the DE system of engine control?

A

Diesel Electric - Consists of diesel engines running generators that supply current to the electric drive motors connected to the propellers. Direction and control of the propeller is determined by the current supplied from the generators.

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22
Q

What are the advantages to DE drive?

A

A wide range of speeds available from stop to full ahead or astern. The fact that the main engine runs at a constant speed.

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23
Q

What are the principle disadvantages of DE drive?

A

High cost, vulnerability to salt and dampness.

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24
Q

How does and SCR system differ from a conventional DE drive?

A

The SCR system employs an AC generator whose current is then converted by SCRs (Silicon control rectifiers) to DC current for driving propulsion motors.

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25
Q

Are there any particular advantages to the SCR system?

A

More modern, less expensive, and propulsion generators can provide ships supply power.

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26
Q

Describe the CPP system.

A

It is not only energy converting but is also a transmission. The amount of thrust is regulated by reducing or increasing pitich.

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27
Q

What maneuvering funtion is housed in the CPP?

A

Amount of thrust and reversing mechanisim.

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28
Q

What are the drawbacks of a CPP system?

A

High cost and susceptibility to damage. A vessels steering qualities are affected when in neutral pitch. Wheel is always turning so lines may become fouled.

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29
Q

How does a reverse reduction gear change propeller direction?

A

Through sets of additional gears and clutches; one for reverse one for ahead.

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30
Q

What factors effect propeller efficency?

A

Quality and velocity of water flow; number, pitch, shape, size, and speed of the propeller blades.

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31
Q

How do nozzles increase efficency?

A

The propeller turns within a shroud which increases thrust 15 to 60 percent more than an open propeller.

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32
Q

What are the disadvantages of nozzles?

A

They present more drag and lateral resistance underwater, which hinders maneuverability and light tug running speed.

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33
Q

What 3 factors determine a rudder’s efficency?

A

Velocity of water flow, quality of water flow, and rudder shape.

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34
Q

What is the difference between a balanced and unbalanced rudder?

A

Balanced or semi-balanced rudders are constructed so that the leading edge of the rudder extends forward of the rudder post. This is done to provide more effective steering and a mechanical advantage to the steering gear.

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35
Q

What is a spade rudder?

A

A spade rudder is not supported at the bottom.

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36
Q

What is the difference between a steerable nozzle and a steerable propeller?

A

A steerable nozzle changes the angle of thrust by rotating the angle of the nozzle around a fixed propeller. A steerable propeller changes the direction of thrust by rotating the propeller around a vertical axis.

37
Q

Why are flanking rudders effective when operating astern?

A

Flanking rudders are installed ahead of the propeller, there are usually two of them for each propeller. They are more effective astern as they are on the discharge side of the propeller.

38
Q

Descibe the Voith-Schnider (VSP) cyclodial propeller.

A

The VSP functions like a CPP rotating around a vertical axis. The rotor turns while each vertical blade oscilates, changing its angle (pitch) at points along the circumference of the rotor casing track.

39
Q

What are the disadvantages of a VSP?

A

HP to Bollard Pull ratio is less for VSP than conventional or steerable propeller; VSP will have deeper draft than conventional or ASD, VSP systems are expensive compared to conventional or steerable propeller.

40
Q

Describe a steerable propeller system.

A

Engine power is transmited via shaft to the upper casing of the drive unit. A pnuematic or hydraulic clutch regulates engine output and drive unit input. A series of right angle gears and shafts converts the horizontal rotation of the propeller. The lower unit houses the propeller and can be rotated through 360 degrees.

41
Q

What are the disadvantage of a steerable propeller system?

A

Reversing thrust requires rotating the drive units 180 degrees; the unit may be thrusting through the entire rotation.

42
Q

What is bollard pull?

A

The pull in generated by a tug pulling against object. In conventional tugs it is estimated to be 1 long ton per 100 hp, depending on the configuration and whether nozzles are installed. Bollard pull can range between 22.5 and 38 lbs per HP.

43
Q

Describe the important aspects of the hull of a tug used for shipwork?

A

Heavily constructed hull with low freeboard. Should be “stiff enough so that a strain on a line will not capsize it. Bulwarks have tumble home to prevent damage.”

44
Q

Is the tug hull reinforced?

A

Yes, the bow of a conventional or ASD tug is heavily reinforced, the bow should have sufficent radius to distribute force. heavy rubrails are installed above the waterline to reinforce and protect the hull

45
Q

Why are structures set inboard on harbor tugs?

A

To prevent contact with the ship’s side when working under the flare of the ship or when both are rolling.

46
Q

What is a bullnose?

A

A large closed chock near the bow of the tug for both the head line and spring to run through

47
Q

What is a staple?

A

Functions as a tugs towing point, a closed chock that is connected to the tug’s internal frames, bulkheads and plating.

48
Q

Where are the bitts located on conventional American harbor tugs?

A

Fore and aft on the fore deck & athwarthships aft of the deck house. Quarter bitts installed augment the forward and aft H bitts.

49
Q

What are the strutural requirements for the bitts and deck fittings?

A

They must be large enough to belay the large sized working lines, and strong enough to take the heavy strain. The bullnose, forward cruciform bitt and quarter bitts must be set inboard so that they will not come in contact with the ship’s hull.

50
Q

What type of mast should be installed on a harbor tug?

A

A dipping mast should be installed so that it can be lowered when working under overhanging obstructions.

51
Q

With respect to visibility how should the wheelhouse be arranged?

A

So that the operator’s vision is as nearly unobstructed as possible. The helm andn throttles should also be located so that the view is unobstructed.

52
Q

Why are model single screw tugs prefered for assisting submarines?

A

They are less likely to do damage if they come in contact with the subs hull.

53
Q

What structural characteristics of a ship can make it dangerous for the ship assiting it?

A

Poorly located chocks and bitts installed to far forward or aft or beneath overhanging structures can damage or endanger the tug. External hull fittings on the ship’s side (sponsons, pipes, rub rails) can be a nuisance or hazard.

54
Q

What are pocket chocks or recessed chocks and why are they useful?

A

Set into convienent locations in the ship’s side in such a way that they have a bar or pin for the tugs lines to be secured to. They are particularly helpful in the case of some passenge vessels, container ships, and car carriers that have short forward and after decks.

55
Q

What are the three functions of fendering?

A
  1. Absorb and disipate energy 2. Enhance or reduce traction 3. Create spacing between the tug and the ship
56
Q

What are the three components of a towline?

A
  1. Working lines 2. Fastening/Release mechanisims 3. Best Practices
57
Q

What types of synthetic lines are used in shipwork?

A

Nylon, Polyethelyne, Polypropolene Blends, HMPE and Aramid

58
Q

Are 100% nylon lines used in shipwork?

A

Not as a stand alone line - they are much too elastic. However, short sections of nylon may be used in composite lines.

59
Q

What are Dacron lines used for primarily?

A

Slings, Mooring, Working Lines

60
Q

What are polypropolene and polyethylene lines used for?

A

Light work where a floating line is best.

61
Q

What are blended lines used for?

A

All applications because they are stronger than poly lines but lighter than Dacron. Also they float.

62
Q

What are two common names for HMPE?

A

Spectra and Dyneema

63
Q

What purpose do wire rope penants serve?

A

They protect the working lines from chafe as they lead through the chocks on the ship. They are generally 15 to 25 feet in length.

64
Q

What are the five most common rope construction patterns?

A

3, 6, 8, 12 strand and double braid.

65
Q

What types of wire rope are sutiable for penants and working lines?

A

6x19 or 6x37 IPS or EIPS

66
Q

What are the purposes of a composition line?

A

Abrasion resistance, Disposable component, Accommodation of dynamic loading, Creation of a weak link, Provide flexibility and softness to working ends

67
Q

What are the four important characteristics of a winch?

A

Breaking capacity, Maximum line pull capacity, Slack line speed, Remote release

68
Q

What are the two main operational Best Practices?

A

Choose the right rope for the job. Use the rope properly.

69
Q

List the common items of auxiliary equipment.

A

Heaving lines, Tag lines, Gob lines, Quick release straps

70
Q

Describe the heaving lines commonly used on tugs.

A

They are usually about 15 fathoms in length and 1” to 1/2” to provide a handhold for the deck force on the ship.

71
Q

Describe and explain the purpose of a tag line.

A

A length of line 30 to 40 feet long about 1 inch in diameter. It is attached to the outboard end of the working line to facilite heaving it aboard.

72
Q

Can tag lines be made of manila?

A

Yes, beacuse it provides a good handhold. Slippery lines such as poly should be avoided.

73
Q

What is a gob line and what is its purpose?

A

A gob line is a stout line used to tie down the towline of a tug when the tug is doing a towline job. Its purpose it to secure the towline nearer to the stern of the tug and restrict its arc of movement so that the tug will not be girted or tripped. It is especially useful when the tug is being towed stern first.

74
Q

What is a quick release strap and how is it used?

A

A relatively short length of line secured to the after ‘H’ bitts on a tug that is rove through the eye of a hawser used as a towline. Its purpose is to provide a safe method of slipping “the towline without endangering the crew.”

75
Q

A conventional tug when going astern only produces _______ % - _______ % of its ahead thrust

A

45% to 60%

76
Q

A steerable propeller tug can produce up to ______ more bollard pull per HP than a VS

A

1/3

77
Q

ASD can walk sideways faster than a Tractor Tug. T/F

A

False - VS less nimble than a tractor tug when moving sideways

ROWE says that ASDs “side stepping ability not as good”. Just something to note

78
Q

Backing power of a fixed propeller in a nozzel is assumed to be

A

50%

79
Q

Backing power of a VS is assumed to be

A

90%

80
Q

Steerable propeller backing power is assumed to be

A

100%

81
Q

Traditional rudders give maximum rudder angles up to ______ - ________ degerees. Towmaster system (shutter rudders) permit angles up to ________ degrees.

A

35-40* / 60*

82
Q

Steerable nozle maximum angle is

A

25* - 30*

83
Q

A good headline has an eye spliced in each end, is attached to a winch and is what length?

A

150 - 200 ft

84
Q

A towline should float and is a similar strength to the headline or springline. What is the length?

A

200 - 250 ft

85
Q

Polyamid can elongate ____ to ______ under strain

A

30 to 40 %

86
Q

Aramid lines are also known as :

A

Kevlar or Twaron

87
Q

The center of lateral resistance determines the resultant proportion of ________ vs _________ force of an applied lateral force to the ship

A

Lateral vs rotational

88
Q

The ship handler is more interested in the practical definition of the center of lateral resistance (CLR) which is?

A

The point the ship where the application of a lateral force results in the ship moving sideways with no rotation. When a lateral force is applied away from the CLR the CLR acts a fulcrum of a lever that simultaneous rotates the ship and moves it sideways.

89
Q

ASD and tractor tugs can maintain effective pushing forces at higher speeds. This is due to?

A

Their omni directional propulsion, a CHP located further forward, and the lift produced by the hulls resistance.

SF exam (14 decks)

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