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Written exam > Tugs > Flashcards

Tugs Flashcards

1
Q

How does a tractor tug towing on a line forward, compare to a conventional tug, in giving steering assistance or creating sideways forces on a ship?

A

Tractor is LESS effective than conventional

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2
Q

What are the three categories of tugs used in ship handling?

A

Tractor, ASD, conventional

Jeff, 13

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3
Q

What are the 6 elements that interrelate with different tug designs?

A 
Towing point
Propulsion point
Propulsion and steering
Maneuvering lever
Hull shape
Superstructure and fendering

Jeff 15

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4
Q

What is the towing point?

A

The last physical point of the tug that fairleads its line to the ship; OR when pushing, the point of contact between tug and object being pushed

Jeff 16

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5
Q

What is the propulsion point?

A

The physical point of the tug’s application of horsepower, underwater

Jeff 16

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6
Q

Propulsion point is dictated by what three items?

A

Number of propulsion units
Type of propulsion
Location of propulsion units

Jeff 16

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7
Q

Define maneuvering lever

A

The distance between towing point and propulsion point

Jeff 17

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8
Q

What is The most common type of tug used worldwide in ship work?

A

Conventional

Jeff 18

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9
Q

On a conventional tug, when moving AHEAD, the towing point is ______ of the propulsion point

A

Forward

Jeff 19

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10
Q

Conventional tugs maneuver best and apply strongest force when ______.

A

Pushing ahead on its towing point, (and when on a towline, this occurs when PP is pushing on TP in direction ordered by pilot.)

Jeff 19

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11
Q

A conventional tug has a greater maneuvering lever when Pushing ahead than when on a towline, towing. T/F

A

True.

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12
Q

What are the two inherent weaknesses of conventional tugs?

A

1) Lack of astern maneuverability
2) Risk of capsizing while on the towline, especially when ship’s speed is excessive

Jeff 20

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13
Q

Conventional tugs, when backing on a headline, produce between ____% and ____ % of its ahead bollard pull.

A

45 to 60 percent

Jeff 20

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14
Q

When a twin screw tug is backing at a 90 alongside a ship that is moving ahead or astern (or with wind/current) it must twin-screw to stay in position. This results in backing power being less than _____ of its full astern power with both engines

A

Half

Jeff 22

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15
Q

If a conventional tug must back alongside at a 90 for extended periods or with full backing power, what must be done to maintain position?

A

Rig a stern line, aka quarter line

Jeff 22

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16
Q

Single screw conventional tugs are preferred for assisting what type of vessel?

A

Submarines

Jeff 23

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17
Q

When comparing horsepower of single vs twin screw conventional tugs, single screws are ____% more efficient.

A

20 percent

Jeff 25

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18
Q

The key difference between a tractor tug and a conventional tug is:

A

The orientation of the propulsion point and the towing point. The tractor tug has a longer and more effective maneuvering lever.

Jeff 25

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19
Q

A steerable propeller (ie: Z-Drive) can produce as much as _____ more bollard pull than a cycloidal drive, for a given HP.

A

One third

Jeff 28

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20
Q

Which type of tug has the deepest draft?
A) conventional
B) tractor
C) ASD

A

B) tractor

Jeff 30

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21
Q

When lying alongside a ship, delivering full thrust, A tractor tug may heel up to _____ degrees

A

21 degrees

Jeff p. 30

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22
Q

Where is an ASD tug’s primary towing point, as used for ship work?

A

On the fore deck

Jeff 33

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23
Q

What is the term used to describe distance between the towing point (TP) and the propulsion point (PP)?

A

The maneuvering lever (ML)

Jeff 187

24
Q

The distance between the towing point (TP) and the center of hydrodynamic distance (CHP) is know as _______.

A

Turning lever (TL)

Jeff 187

25
Q

What is the result of a longer maneuvering lever in relation to the turning lever?

A

Less thrust is required to keep the tug in position, therefore more thrust is available for pushing

Jeff 187

26
Q

A tug pushing alongside, as ship begins to move forward has to compensate for the increased leverage of water flow, resulting in a lengthening of the turning lever, due to a shift of which point, in which direction?

A

Center of hydrodynamic pressure,
Shifting aft

Jeff 188

27
Q

What ship speed is generally the maximum for a conventional tug pushing alongside?

A

3-4 kts

Jeff 190

28
Q

When a tug is breasted or on-the-hip, it is important to have propulsion units ______, in order to maximize leverage

A

Aft

Jeff 194

29
Q

A gob rope is used to alter which point?

A

Towing point

Jeff 197

30
Q

Direct towing for tractor and ASD tugs is effective at ship speeds _______

A

Five to six kts

Jeff 202

31
Q

Powered indirect towing, working a tug at 90 degrees to a ship’s centerline in relation to the towline, allows a tug to apply ____ to ____ percent of the tug’s rated bollard pull

A

75 to 120 percent

Jeff 202

32
Q

Describe the jackknife maneuver

A

When a tractor or ASD tug quickly repositions from indirect to direct towing (typical for continuous steering forces applied while a ship reduces speed)

Jeff 205

33
Q

Tug thrust is equal to pulling force at any hawser angle. __________, however increases dramatically with increases of hawser angle.

A

Line tension

Jeff 209

34
Q

What are two components of the Center of Hydrodynamic Pressure (CHP)?

A

Drag: parallels the water flow,
Lift: transverse force

Jeff 175-176

35
Q

What are the four basic positions for tugs assisting ships?

A

1) leading tug, towing on a line
2) tug alongside, pulling on a line or pushing
3) breasted or on-the-hip
4) trailing tug, pulling on a line or pushing

Jeff 174

36
Q

What is the Center of Lateral Resistance of a ship?

A

The point on a ship where, if a lateral force is applied, will move the ship sideways with no rotation.

Jeff 215

37
Q

What are the three basic ship handling principles that must be taken into account in order to have a clear vision of the ship’s behavior?

A

1) Center of lateral resistance
2) pivot point
3) maneuvering lever

Jeff 215

38
Q

What is the best tug position for steering a vessel, (moving ahead)?

A

Trailing tug

Jeff 247

39
Q

Conventional tugs can provide steering assistance as a trailing tug at what speed?

A

1-3 kts

*At slightly higher speeds, conventional tugs may assist steering, to ONE side only.

Jeff 249

40
Q

When tractor or ASD tugs are acting as trailing tug, indirect towing is used as speeds ______, and direct towing at speeds_______.

A

5 kts or less;
Over 5 kts

Jeff 249

41
Q

What is the Assist Lever (AL)?

A

Distance between tug and ship’s pivot point.

Jeff 222

42
Q

A ship is stopped. When a tug pushes on one end, the ship is turned in approximately _____ ship’s length (s).

A

Two

Jeff 254

43
Q

When tug forces are applied to both ends of a stopped vessel, the ship is rotated in approximately _____ ship’s length.

A

One

Jeff 255

44
Q

A ship with no headway uses steering and propulsion to turn, with a tug on the bow (pushing or pulling to assist turn) To counter forward motion generated by ship’ propulsion, what must the tug do?

A

Adjust angle to counter ships ahead motion.

Jeff 255

45
Q

Transverse arrest can be performed by which type of tug(s)?

A

ASD or tractor (only with steerable nozzles)

Jeff 274

46
Q

At what speed does reverse arrest start to lose braking force effectiveness, and transverse arrest becomes a better option?

A

7 knots

Jeff 360

47
Q

In ship escort, what is the most effective tug position?

A

Tethered ASD or tractor, to ship’s stern

Jeff 357-358

48
Q

What is the basic signal to instruct a tug to “come ahead on your engines,” if stopped?

A

One short blast

Jeff 366

49
Q

What is the signal given to a tug to instruct “stop” if they are going ahead or astern?

A

One short blast

Jeff 366

50
Q

What is the whistle signal to a tug, instructing to “back your engine?”

A

Two short blasts

Jeff 366

51
Q

What is the ship to tug whistle signal for “more speed.”

A

Three very short blasts

Jeff 366

52
Q

What is the whistle signal for a tug, for “slow speed?”

A

One prolonged blast

Jeff 366

53
Q

A ship signaling to a tug to “let go or shift,” is:

A

One long blast, followed by two short blasts

Jeff 366

54
Q

Inward turning twin screws are better for _______, whereas outward turning is better for ________.

A

Inward walks better
Outward turns better

Livingstone 5

55
Q

Tugs tend to creep which way while walking

A

Ahead

Livingstone p.5

Written exam (13 decks)

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