This work was carried out at Odessa Maritime Training Centre. Presentation for the research conference "Modern technologies of design, construction, operation and repair of ships, marine engineering facilities and engineering structures” held in National Shipbuilding University (Nikolayev, Ukraine).

1. Tug Girting Assessment
Simulation results for a 50 tones BP ASD Tug
by Aleksandr D. Pipchenko

2. What is a tug escort and why is it necessary?

3. OOCL Hong Kong Breaks 21,000 TEU Mark,
Becoming ‘World’s Largest Containership’
15-May-2017

5.  Loss of control, contacts and
groundings represent the
majority incidents in EU waters
and on the EU flagged ships
according to EMSA Marine
casualties and incidents
annual overview 2016

7. What is the purpose of escort tug?
 An escort tug is supposed to provide assistance to and escort vessels in
dangerous and coastal waters, i.e., outside of safe harbors.
 While escort towing, the tug boat is intended to assist at high speed the
steering and arresting properties of a vessel to be assisted by means of a
tow rope coming from the towing winch and connected to the vessel
being assisted.
 While working in the harbour, the tug boat can be applied to normal
towing and buffering tasks.

8. Escort tug types
Tractor tug
ASD tug
VSP tug

9. When do the highest towing risks occur?

10. Higher the speed, higher the risk
As the speed of the vessel increases, the kinetic energy increases
geometrically, and the ability of the escort tug to affect the direction
of the vessel decreases.
 The kinetic energy is equal to one half the weight of the vessel
multiplied by the velocity squared (KE = ½ mV2 ).
 Simply put this means that at 10 knots the kinetic energy that the
tugs must control in an emergency is 100 times greater than that
generated at one knot.
 Also considerable part of a bollard pull that can be applied to a
vessel at zero speed is consumed on maintaining tug speed and
heading.

11. Available towing force for different
speeds
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 2 4 6 8 10 12 14
AVAILABLE TOWING FORCE
Tug speed 1 2 3 4 5 6 7 8 9 10 11 12 13
Available BP 50 49 48 46 44 41 37.5 34 29 24 19 12.5 6
% 100% 98% 96% 92% 88% 82% 75% 68% 58% 48% 38% 25% 12%

12. Speed to keep not to be overtaken by
the tow
Tug
heading,
deg
Tow speed, knots
1 2 3 4 5 6 7 8
10 1.0 2.0 3.0 4.1 5.1 6.1 7.1 8.1
20 1.1 2.1 3.2 4.3 5.3 6.4 7.4 8.5
30 1.2 2.3 3.5 4.6 5.8 6.9 8.1 9.2
40 1.3 2.6 3.9 5.2 6.5 7.8 9.1 10.4
50 1.6 3.1 4.7 6.2 7.8 9.3 10.9 12.4
60 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
70 2.9 5.8 8.8 11.7 14.6 17.5 20.5 23.4
80 5.8 11.5 17.3 23.0 28.8 34.6 40.3 46.1

13. Modes of operation and position
 The escort tug will render the greatest assistance to the vessel with
headway if the tug is utilized at the stern.
 When the tug is on the stern, it is at the greatest distance from the
pivot point of the vessel and thereby has a greater lever to work
with.
 Tug’s tow-point also matters, the greater distance between the tow-
point and the thrusters, the better.
 Hawser secured close to thrusters reduces tugs turning ability.
 Hawser secured close to midships indirectly leads to large heeling
moments.

14. Accidents with tugs
 According to the data of the European Maritime Safety Association
(EMSA), 23% of technical fleet ships' accidents are related to towing
[1]. In total, from 2011 to 2015, there were 236 incidents, 43 of which
were associated with significant damage or total loss of ships, as
well as with the death of crew members. This number includes 11
tugs capsized and sunk in European waters.
 Some of the renown accidents are:
Collision and capsize of Fairplay 22 11-Nov-2010;
Collision and capsize of Chiefton 12-Aug-2011;
Collision of Smit Polen on 13-Jan-2011;
Collision of Fairplay 2119-Nov-2009.

15. Common Reasons for Tugboat Accidents
@http://www.maritimeinjuryguide.org/
Capsizing: Capsizing is a real possibility with tugboats, and as mentioned
earlier, often happens when there are operational problems with the
vessel. Capsizing often leads to fatal injuries.
Mechanical breakdowns: Mechanical failure on tugboats such as loss of
power, broken ladders, and defective equipment can cause a host of
accidents and injuries.
Hazards on-board: Wet, slick surfaces, improper safety equipment, and
improper training while aboard a tugboat has led to numerous accidents.
Vessel collisions: Poorly maintained navigational gear and unqualified
personnel on the bridge have led to several deadly incidents. In addition,
tugboats are much smaller when compared to other vessels and can
easily be obstructed from view by a larger vessel, causing tragic collisions.

16. Girting, girding or tripping (GGT)
 The term refers to the situation when a tug,
is towed broadside by a towline and is
unable to manoeuvre out of this position.
 This phenomenon is known to all tug
masters. It is the most prevalent reason for
tugs to capsize and can cause fatalities. This
occurs at either end of the tow and can
happen very quickly. Rarely does it happen
slowly enough to allow all of the crew to
leave the tug before it capsizes. Tug
masters must be aware of the phenomenon
and understanding the quick release to the
tow wire is essential if disaster is to be
averted.
 *Tug and Tows – A Practical Safety and Operational Guide by SHIPOWNERS

17. Stability during towing
The heeling moment can be caused:
 a) By the tow – tow tripping, this
happens when the tug is dragged
by the tow, via the towline at a
certain speed and certain course
through the water.
 b) By the tug – self-tripping, the
heeling moment is then caused by
the combined action of rudders,
propellers and the towline force or
hydrodynamic lateral force on the
hull. Decisive are the thrust forces or
bollard pull of the tug.
 c) By a combination of tow and tug.

18. Stability during towing
 d as tow tripping arm (ABS, BV,
GL) – center of effort as function
of the lateral area (1/2 T or VCB).
 d as self tripping arm (USCG,
DNV, IACS) – center of effort is in
the center line of the propellers.

19. “Towing system”: conventional towing

20. “Towing system”: bow-bow mode

21. “Towing system”: towing from stern

22. “Towing system”: girting simulation

23. “Towing system”: girting simulation

24. Statements
 During escort service tug has to
keep heading close to the tow’s
heading to maximize towing
capacity and to reduce
probability to be overtaken by the
vessel
 Towline under tension tends to turn
the tug inline with itself
 If no steering applied, or if it’s
insufficient vessel will go into girting
at any speed / power setting
Towing mode: stern-to-bow
Thrust: 80%
Speed: 4 knots
Steering: NO

25. Statements
 During escort service tug has to
keep heading close to the tow’s
heading to maximize towing
capacity and to reduce
probability to be overtaken by the
vessel
 Towline under tension tends to turn
the tug inline with itself
 If no steering applied, or if it’s
insufficient vessel will go into girting
at any speed / power setting
Towing mode: stern-to-bow
Thrust: 80% / Speed: 8 knots
Steering: Heading autopilot, both thrusters steer
Max azimuth: 50 / Heading setting: 0

26. Statements
 In order to prevent girting towline direction has to be carefully monitored
Towing mode: stern-to-bow
Thrust: 80% / Speed: 8 knots
Steering: Heading autopilot, both thrusters steer
Max azimuth: 20 / Heading setting: 10
Towing mode: stern-to-bow
Thrust: 80% / Speed: 8 knots
Steering: Tow direction autopilot, both thrusters steer
Max azimuth: 20 / Heading setting: 10

27. Stern-to-bow towing
 Synchronous steering mode with no limits may lead
to a capsizing
 Asynchronous steering mode with no limits may lead
to large list angles
 In stern-to-bow mode its reasonable to keep one
thruster for pushing and another for steering
 On speeds close to 8 knots thruster’s azimuths should
be limited to 40-50 max.
 Heading has to be close (±10) to a towed vessel’s
heading
 Higher the speed, higher the list encountered by a
tug. In girting case it may reach 40 and above on 8
knots, and about 15 on 4 knots with one thruster
pushing sideways. Both thrusters pushing against the
tow rope during girting may provoke capsizing
Stern-to-bow towing risk matrix
Tug
heading,
deg
Towline heading, deg
10 20 30 40 50 60 70 80
0 8 8 8 8 6 6 2 2
10 6 6 6 6 2 2 2 2
20 2 2 2 2 2 2 2 2
30 2 2 2 2 2 2 2 2
40 2 2 2 2 2 2 2 2
50 2 2 2 2 2 2 2 2
60 2 2 2 2 2 2 2 2
70 2 2 2 2 2 2 2 2
80 2 2 2 2 2 2 2 2
- stability risk zone
- caution zone, situation may lead to a large heel
- safe zone
- confidence zone
Number in the cell defines maximum safe speed at which towing can be performed

28. “Towing system”: girting simulation

29. Statements
 The key to a stable towing is the ability to keep sideways speed
 In this particular case sway is above 2.0 knots
Towing mode: bow-to-bow Thrust: 80% / Speed: 4 knots
Steering: Heading autopilot, synchro mode - both thrusters steer Max azimuth: 40 / Heading setting: 210

30. Bow-to-bow operations risk matrix (girting)
Towing mode: bow-to-bow
Thrust: 80%
Steering: Heading autopilot, synchro mode - both thrusters steer
Max azimuth: 40
Bow-to-bow towing risk matrix
Tug heading,
deg
Towline heading, deg
10 20 30 40 50 60 70 80
0 8 8 8 8 8 8 8 8
10 8 8 8 8 8 6 6 6
20 6 6 6 6 6 6 6 6
30 6 4 4 4 4 4 4 4
40 4 4 4 4 4 4 4 4
50 2 2 2 2 2 2 2 2
60 2 2 2 2 2 2 2 2
70 2 2 2 2 2 2 2 2
80 2 2 2 2 2 2 2 2
- stability risk zone
- caution zone, situation may lead to a large heel
- safe zone
- confidence zone
Number in the cell defines maximum safe speed at which towing can be performed

31. Thank you for your attention!
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