Tug Use in Port - Cap 4 Tug Capabilities and Limitations

Tug Use in Port - Cap 4 Tug Capabilities and Limitations

1. 4.1 -Introduction

2. 4.2 - Basic priciples and definitions

   • 4.2.1 - Pivot Pint
   • 4.2.2 - Towing point, pushing point and lateral centre of pressure. Direct Towing and indirect towing. Skegs
     • The lateral centre of pressure
     • The lateral centre of pressure
     • Direct and indirect towing method
     • Pushing point
     • Skeg and their effect
   • 4.2.3 Stability
     • High GM and good dynamic stability
     • Reducing transverse resistance of the hull
     • Reducing de height of the towing point
     • Reducing the height of the pushing point
     • A towline with good shock absortion characteristics
     • Tug freeboard being such that the deck edge is not immersed at too small a heeling angle

3. 4.3 - Capabilities and limitations

   • 4.3.1 Capabilities and limitations of the tug
     • Tugs towing on a line
       • forward tugs towing on a line
       • Stern tugs towing on a line
     • Tugs opeting at a ship`s side
       • Pushing mode
       • Pulling mode
       • Stopping assistance
     • Summary
       • Conventional tugs
       • Tractor and Reverse-tractor tugs
       • ASD tugs
   • 4.3.2 Effectiveness of tug types
     • Performance diagrams
       • Performance of a conventional and ASD-tug when pushing at a ship underway at speed
       • Performance of a ASD and VS tug while towing on a line
     • Speed control - braking assistance
   • 4.3.3 Effective tug position
   • 4.3.4 Towing on a line compared with operating at a ship`s side

4. 4.4 - Operational limits

5. 4.5 - Design consequences

6. 4.6 - Conclusions regarding tug types

7. 4.7 - Some other pratical aspects

   • Coperation
   • Communications between pilots and tug captains
   • Tug use
   • Speed
   • Decreasing effectiveness of tugs when a ship gathers speed
   • Ship´pulled or pushed around by a bow tug gathers speed