Tugs Flashcards by Ryan Finke

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?

Tractor is LESS effective than conventional

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

Tractor, ASD, conventional

Jeff, 13

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

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

Jeff 15

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What is the towing point?

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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What is the propulsion point?

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

Jeff 16

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Propulsion point is dictated by what three items?

Number of propulsion units
Type of propulsion
Location of propulsion units

Jeff 16

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Define maneuvering lever

The distance between towing point and propulsion point

Jeff 17

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

Conventional

Jeff 18

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

Forward

Jeff 19

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Conventional tugs maneuver best and apply strongest force when ______.

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

True.

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What are the two inherent weaknesses of conventional tugs?

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

45 to 60 percent

Jeff 20

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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

Half

Jeff 22

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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?

Rig a stern line, aka quarter line

Jeff 22

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

Submarines

Jeff 23

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

20 percent

Jeff 25

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

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

One third

Jeff 28

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

B) tractor

Jeff 30

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

21 degrees

Jeff p. 30

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

On the fore deck

Jeff 33

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

Study These Flashcards

The maneuvering lever (ML)

Jeff 187

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

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Turning lever (TL)

Jeff 187

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

Less thrust is required to keep the tug in position, therefore more thrust is available for pushing Jeff 187

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?

Center of hydrodynamic pressure, Shifting aft Jeff 188

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

3-4 kts Jeff 190

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

Aft Jeff 194

A gob rope is used to alter which point?

Towing point Jeff 197

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

Five to six kts Jeff 202

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

75 to 120 percent Jeff 202

Describe the jackknife maneuver

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

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

Line tension Jeff 209

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

Drag: parallels the water flow, Lift: transverse force Jeff 175-176

What are the four basic positions for tugs assisting ships?

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

What is the Center of Lateral Resistance of a ship?

The point on a ship where, if a lateral force is applied, will move the ship sideways with no rotation. Jeff 215

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?

1) Center of lateral resistance 2) pivot point 3) maneuvering lever Jeff 215

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

Trailing tug Jeff 247

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

1-3 kts *At slightly higher speeds, conventional tugs may assist steering, to ONE side only. Jeff 249

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

5 kts or less; Over 5 kts Jeff 249

What is the Assist Lever (AL)?

Distance between tug and ship’s pivot point. Jeff 222

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

Two Jeff 254

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

One Jeff 255

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?

Adjust angle to counter ships ahead motion. Jeff 255