Escort Tugs - Shiphandling Facts and Rules

Question 1

Escort Tugs - one conventional tug placement
(Henson)

Answer 1

use as rudder tug (Henson)

Question 2

Escort Tugs - conventional tug push/pull ship speeds
(Henson)

Answer 2

• pushing mode 3 - 4 kts
• Can’t pull until very low ship speeds or stopped
  (Henson)

Question 3

Escort Tugs - conventional tug on line aft ship speeds
(Henson)

Answer 3

impossible to move from one side to the other at speeds higher than 1 to 2 kts (Henson)

Question 4

Escort Tugs - omni / conventional placement at 4 to 5 kts
(Henson)

Answer 4

• use omni-directional aft and conventional forward
• safe at speeds 4 to 5 kts (Henson)

Question 5

Escort Tugs - steering forces - using indirect mode with speeds > 5-6kts
(Henson)

Answer 5

steering forces are higher
(Henson)

Question 6

Escort Tugs - powered indirect use with what ship speed
(Henson)

Answer 6

with ship speed between 3 to 7 kts (Henson)

Question 7

Escort Tugs - VS tractor steering forces
(Henson)

Answer 7

• can exert very high steering forces on a line at the stern (Henson)

Question 8

Escort Tugs - ASD braking forces
(Henson)

Answer 8

• can apply higher braking forces (Henson)

Question 9

Escort Tugs - indirect / direct performance relationship
(Henson)

Answer 9

• improving indirect mode performance can reduce direct mode performance (Henson)

Question 10

Escort Tugs - assisted turn tug positioning
(Henson)

Answer 10

in most cases it is better to assist a turn than oppose a turn (Henson pg 144)

Question 11

Escort Tugs - tug’s rudder lift forces with propeller stopped
(Henson)

Answer 11

approximately half when propeller stopped (Henson)

Question 12

Escort Tugs - ASD / VS indirect mode heeling
(Henson)

Answer 12

ASD heel more than VS Tractor when using indirect method (Henson)

Question 13

Escort Tugs - Tractor / ASD heeling w/ max side thrust
(Rowe)

Answer 13

Tractor heels more than ASD with max side thrust (Rowe pg 144)

Question 14

Escort Tugs - wave conditions and tug effectiveness
(Henson)

Answer 14

will reduce tug effectiveness (Henson)

Question 15

Escort Tugs - line force - indirect mode
(Henson)

Answer 15

line forces of 1.5x to 2x can be generated using the indirect mode (Henson)

Question 16

Escort Tugs - tug line passing
(Henson)

Answer 16

tug lines should be lowered to the deck of the tug by ship’s crew (Henson)

Question 17

Escort Tugs - ASD / Tractor tethered fwd at high speed
(Henson)

Answer 17

tethered at high speed is easier for ASD than tractor (Henson)

Question 18

Escort Tugs - when to fasten tugs
(Henson)

Answer 18

in all cases it is safer to fasten tugs as soon as possible (Henson)

Question 19

Escort Tugs - passive escort position
(Henson)

Answer 19

a good position is 4 points on the bow, 0.2nm off (Henson)

Question 20

Escort Tugs - ASD / VS tractor forward on line
(Henson)

Answer 20

• ASD better than VS forward on a line
• all tractor tug use forward is very limited by ship’s speed, “danger of tripping”
  (Henson)

Question 21

Escort Tugs - Conventional or ASD (towing from astern) vs. tractor - forward on line
(Henson)

Answer 21

Conventional or ASD (towing from astern) better than tractor forward on a line but “danger of girting” (Henson)

Question 22

Escort Tugs - tugs on a line relationship with ship’s speed
(Henson)

Answer 22

• tugs on a line forward tend to increase ship speed when assisting
• tugs on a line aft tend to decrease ship speed
  (Henson)

Question 23

Escort Tugs - braking force angle
(Henson)

Answer 23

braking force is higher when stern tug is at a small angle with ship’s centerline (Henson)

Question 24

Escort Tugs - ASD arrest modes at what ship speeds
(Henson)

Answer 24

• use transverse arrest > 8 kts
• use reverse arrest < 8 kts
  (Henson)

Question 25

Escort Tugs - optimal ship speed with harbor tug escorts

Answer 25

• max 5 kts
• allows for tugs to influence vessel movement in case of casualty

Question 26

Escort Tugs - ship speeds with purpose built escorts
(Henson)

Answer 26

• can be up to 10-12 kts