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ESCORT TUG GIRTING ASSESSMENT

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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).

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ESCORT TUG GIRTING ASSESSMENT

  1. 1. Tug Girting Assessment Simulation results for a 50 tones BP ASD Tug by Aleksandr D. Pipchenko
  2. 2. What is a tug escort and why is it necessary?
  3. 3. OOCL Hong Kong Breaks 21,000 TEU Mark, Becoming ‘World’s Largest Containership’ 15-May-2017
  4. 4.  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
  5. 5. 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.
  6. 6. Escort tug types Tractor tug ASD tug VSP tug
  7. 7. When do the highest towing risks occur?
  8. 8. 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.
  9. 9. 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%
  10. 10. 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
  11. 11. 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.
  12. 12. 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.
  13. 13. 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.
  14. 14. 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
  15. 15. 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.
  16. 16. 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.
  17. 17. “Towing system”: conventional towing
  18. 18. “Towing system”: bow-bow mode
  19. 19. “Towing system”: towing from stern
  20. 20. “Towing system”: girting simulation
  21. 21. “Towing system”: girting simulation
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. “Towing system”: girting simulation
  27. 27. 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
  28. 28. 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
  29. 29. Thank you for your attention! Visit my website: www.BoNMarine.net and fellows www.Key4Mate.com

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