Tow Test Force Measurement System for the Ocean Cleanup

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Over 5 trillion pieces of plastic currently litter the ocean. Trash accumulates in 5 ocean garbage patches, the largest one being the Great Pacific Garbage Patch, located between Hawaii and California. If left to circulate, the plastic will impact our ecosystems, health and economies. Solving it requires a combination of closing the source and cleaning up what has already accumulated in the ocean.

Since the beginning Althen has been in contact with the engineering department of the Ocean Cleanup. It was known that the ambitious goal to design and develop a cleaning system could benefit of the right information when it is in place. For safety, for maintenance prevention, for testing. After having changed the design in an iterative way and after having conductive several scale models at Marin. The time has come to bring concepts into reality. 

The request from the Ocean Cleanup came to have a force monitoring system in place which could measure the forces that occur between the towing vessel and the system being towed. The forces where not expected to exceed 10 Tonnes but given many unknown factors and a complete new system that is being towed, it was decided to have a 12 Tonnes measurement range, with a breaking load of 300%. This means the load shackle would not break before 36 Tonnes. Since the marine environment would cause the shackle to be in the water, a submersible variant has been applied which can be submersed up to 10 meters. 

The load shackle being internally amplified has a 4-20 mA output signal since the cable length could potentially be quite long. In combination with Althen's Glet box module and a Graphtech GL240 datalogger a standalone battery powered measurement system was created. The data collected and monitored real time on the datalogger, can later be transferred via USB interface to a PC for further analysis. 

System 001 - Mission plan

In 2018 the Ocean clean up is planning to launch its first operational cleaning system. In the first 6 months of this year there have been several tow-tests in which a tow-ship has pulled out a 120 meter segment approximately 50 nautical miles offshore of San Francisco. The vessel has towed the unit in a multitude of directions in order to test the hydrodynamic behavior of the system. During this tow-test one of the very important parameters to monitor is the force that is applied on the linkage between the tow-vessel and the 120 meter long segment. In Q3 of 2018 the final 600 meter system will be towed approximately 240 nautical miles off the coast, where it will be launched in operational configuration for the first time. The systems behavior will be extensively monitored during this final rehearsal. After this trial, system 001 will be towed out to the Great Pacific Garbage Patch, approximately 1200 nautical miles offshore, where it will be launched in operational configuration and start the cleanup.


Althen's turn-key force monitoring system

During the multiple tow-tests that have been and will be executed it is very important that the forces on the connection between the system being towed and the towing vessel are under control. Due to rough sea conditions, current or wind the forces that will apply on the connection can increase significantly. To be able to adjust the towing speed and chance of reaching the final destination in one piece, a continuous force monitoring system has been put in place. The system consists of a IP67 12 Tonnes load shackle in combination with a standalone battery powered datalogger which is capable of logging all measurements over a longer period. When the system is measuring it is possible to see forces increase and to take action when needed. With the first large tow-test being successfully completed even in rough conditions, there is big confidence that the full 001 system will be out in the great pacific cleaning by the end of 2018.

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