10. Tug use in Port 10-15% pg 17

Question 1

Various ————– tug are discussed in a general way, addressing the diversity of design, propulsion, steering and manoeuvring capabilities.

Answer 1

types of harbour

Question 2

A ——— is presented first of factors which affect operational requirements for a harbour tug, such as the different tasks for which they are used, the particulars of a port, the environmental conditions and ships calling at the port.

Answer 2

general review

Question 3

After reviewing ————, tug types are considered in more detail, including the performance of different types of tug resulting from the location of propulsion devices, towing point and lateral centre of pressure. Tug capabilities, limitations and effectiveness with respect to different assisting methods and operating positions relative to a ship are discussed.

Answer 3

assisting methods in use worldwide

Question 4

The —– required to handle a vessel safely is frequently a topic for discussion between pilots and shipmasters. This important subject is discussed taking into account the effects of wind, current, shallow water and confined waters. The number of tugs and total bollard pull used in several ports around the world is mentioned.

Answer 4

number of tugs

Question 5

Much attention is given to —— for tugs, such as interaction and girting, and to environmental conditions such as fog

Answer 5

dangerous operational situations

Question 6

—— is dealt with, particularly in relation to safe and efficient shiphandling.

Answer 6

Towing equipment

Question 7

——-, being a subject of specific interest nowadays, is dealt with separately.

Answer 7

Escorting and escort tugs

Question 8

Proper —— for a tug captain and crew is essential in order that they handle the tug safely and efficiently. The same applies to the pilot and/ or master for shiphandling with tugs. Training is therefore an important subject in the book, including simulator training and research

Answer 8

training

Question 9

——— in ports and port approaches around the world differ due to local conditions and specific situations and have often grown from long standing customs and traditions. These differences in assistance methods and practices are often reflected in the requirements for the tugs and hence in the development of a range of tug types.

Answer 9

METHODS OF ASSISTANCE PROVIDED BY TUGS

Question 10

The operational requirements that harbour tugs must conform to with respect to ship assistance are mainly determined by the following factors:

Answer 10

• The kind of port or harbour and approaches, foreseeable future developments and the existing geographical environmental conditions.
• The type of ships calling at the port.
• The services required in and around the port and, if relevant, at offshore locations, e.g. SPMs, F(P)S0s or oil rigs.

Question 11

The method of assistance used by tugs will depend on:

Answer 11

• Port, jetty, terminal layout and/ or offshore installation.
• Types of ship.
• Environmental conditions.
• Navigational complexity of river, channels and port approach.
• Whether bridges and locks have to be passed.
• Often on tradition.

Question 12

So the following types of tug can be seen, all belonging to one or both of the above groups:

Answer 12

•	Conventional tugs.
•	Tractor tugs with azimuth propellers or Voith propulsion.
ASD-tugs.
•	Reverse-tractor tugs.
•	Combi-tugs

Question 13

Conventional types of tug

Answer 13

The largest number of tugs still belong to this type

Question 14

Three aspects are important in manoeuvring a normal single screw conventional tug:

Answer 14

• The aft location of the rudder and propulsion.
• The transverse effect of the propeller when turning for astern.·
• The low astern power.

Question 15

Conventional tugs have certain advantages and so do reverse-tractor tugs. ASD-tugs are nearly the same as reverse-tractor tugs but are designed in such a way that they can operate like a reverse-tractor tug as well as a conventional tug, thus combining the advantages of both.

Answer 15

Azimuthing Stern Tugs

Question 16

—– is independent of ship’s speed as long as engine propeller revolutions or propeller pitch match a ship’s speed but is dependent on rudder angle applied.

Answer 16

Turning diameter

Question 17

The ——- is an imaginary floating point, situated somewhere in the vertical plane through stem and stern, around which a vessel turns when forced into a directional change. The form of the submerged body, rudder size and type, trim, underkeel clearance and direction of movement all affect the position of the pivot point of a vessel. The exact location of the pivot point is therefore not stationary but variable

Answer 17

pivot point

Question 18

The —— is that point from where the line goes in a straight line from the tug towards the ship. For tugs pushing at a ship’s side the contact point or pushing point is of importance. Before discussing the capabilities and limitations of different tug types the towing and pushing point in relation to the location of propulsion and centre of pressure are considered.

Answer 18

towing point

Question 19

—–, one of the basic design requirements, is of great importance for harbour tugs due to the nature of their work. Conventional tugs, when towing on a line as a forward or after tug, can experience very large athwartships towline forces. The same applies to ASD-tugs when towing on a line as a conventional tug.

Answer 19

Operational stability