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Marine Towing  -  Dynamic Tension Control

- At 9 p.m. on 19th November 2001 the towline (a 2" 335-ton steel cable) between the tug DE DA and the 900-foot oil tanker ATIGUN PASS parted in a storm 96 miles off Newport, Oregon.  Six days and a broken emergency tow line later the tanker was eventually under control before it was grounded. - 19th November 1997 M/V GREEN LILY was lost off the East Coast of Bressay, Shetland in force 7 increasing to force 10 winds. Three tugs, two connected towlines (which parted after 51 and 5 minutes respectively) and one successfully connected anchor cable (which also parted) were not able to save the vessel.
- Ships will continue to need towing and rescue in the future... ...but the towline will not need to fail.

Towing a ship, an oilrig or a barge in bad weather or in strong currents is one of the most difficult and hazardous operations to undertake. The kinetic energy generated when two heavy vessels suddenly are forced by the waves in opposite directions is often enough to part the towline regardless of its thickness. The consequences can be catastrophic, as can be seen on the news from time to time.  Disasters will happen again.  

Automatic dynamic tension control ensures that the tow line does not break in strong winds and big waves

The so-called "constant tension winches" used onboard tugs sound good in theory but these only measure and react to the force in the tow line and will attempt to adjust the pull force accordingly. However, it is too late to react when the tow line tension exceeds the limit. A fraction of a second later - before the "constant tension winch " has had time to react - the line will have snapped.

DFDInstruments have developed a hydraulic technology which ensures that the towline tension truly is constant regardless of the pull force variation pattern.  

The system actively heaves in and pays out tow line instantly in such a manner that e.g. two large vessels can tow each other successfully with a tow line much thinner than normally required for towing, should that be needed.

Innovative aspects of dynamic tension control:

Instead of reacting to tension stresses in a towline, this system ensures in a dynamic way that the towline tension never exceeds, or, if required, never goes below certain pull force limits, even if the tow line stress changes are sudden and unpredictable.

As an emergency mesure towing can be done successfully with a thin tow line.Main Towing Advantages:

  • Safe towing can take place in bad weather.
  • Increased maneuverability for tanker escorting
  • Considerably more tug flexibility with regards to the ratio of Breaking Load/Effective Bollard Pull, minimum towline length and other, traditionally, restricting towing limitations.
  • Sea rescue operations will be able to take place in currently impossible weather conditions to avoid environmental disasters
  • Significantly reduced consumption of tow line!
  • As an emergency towing system onboard commercial ships the technology will improve the ability of these ships to rescue each other, or at least hold each other without parting the towline until rescue tugs arrive. Currently two large vessels cannot successfully tow each without the towline parting due to the very high kinetic energy generated by the movement of each of the ships.
  • As a mooring system this technology will prevent oilrigs, ferries and other vessels from pulling loose in bad weather.

Current stage of dynamic towing technology

Small scale modeling of the hydraulic principle has been carried out.

The concept is ready for full scale prototype development. The prototype should ideally be placed on board a tug but any vessel will be able to demonstrate its capabilities.  

Target Markets

Immediate primary market

The various maritime towing operations currently undertaken every day around the world. Vessels like tugs, supply vessels, anchor-handling vessels, rescue vessels, etc. are potential users of this dynamic towline tension control technology.

Secondary markets
  • As emergency towing system onboard commercial ships
  • Mooring systems with dynamic tension control for vessels
  • Rescue and evacuation systems for oilrigs, ships or onshore uses

               Interested parties please contact DFD Instruments for more details 

 

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