The launch and recovery system behind a new, high tech exploration ROV has been developed with a kind of minimalism in mind.
SuBastian, developed by the US-based Schmidt Oceanographic Institute, has been designed to reach into 4,500m depths and is capable of taking high resolution videos, seafloor mapping and sample collections – it is, by its nature, complex.
By contrast, the launch and recovery kit that will have to deploy the weighty 2,950kg ROV in harsh, remote regions needs to be as uncomplicated and robust as possible.
There was a snag: unlike most LARS which get designed and brought together as a whole, SuBastian is to be deployed and returned from a MacArtney 88kN SWL A-frame that is already installed at the aft of the MV Falkor. “We needed to make it work with existing equipment,” explained MacArtney’s Lasse Rasmussen, vice-president of Engineering.
The answer was surprisingly straightforward: MacArtney developed a MERMAC D 45 docking head to be directly connected to the A-frame top bar via a single existing mounting point: this meant there was no modification to the existing A-frame.
The docking head retains a few special features: a pneumatic pinchwheel helps feed the umbilical through to the top of the A-frame until the weight of the line on the deployment side starts to make its presence felt – the ROV itself, after all, is neutrally buoyant. There’s also a pneumatic locking function for safety.
The development may lead to others: the project “has helped us simplify our approach,” said Mr Rasmussen, and added the idea could be attractive to the price sensitive ocean science segment.
However, the umbilical itself is no small part of the entire system as it is has to provide the ROV with its power alongside a hefty datalink; as SuBastian is modular, it needs a versatile array of power and data interfaces to enable integration of a wide range of add-on instruments and samplers – plus it has to be able to handle the realtime output from those 4,000k video cameras.
Further, the line must also have the strength to cope with nearly 3 tonnes of ROV hanging from it as SuBastian rises out of the water and lands on the deck.
Handled by a single-drum MacArtney MERMAC oceanographic winch the umbilical is manufactured by combining five electrical lines for the power, five for the fiberoptic cable (wrapped in a polyethylene jacket), and laying a heft armour around them: this gives it strength and means it won’t start to twist under load. After manufacture it was tested firstly for power and short circuits, secondly for optic signal attenuation, and lastly a section was stretched to breaking point – it easily exceeded the necessary margins.
At time of writing the system has completed a number of launch and recovery operations and SuBastian itself has totalled over 100 hours underwater – with more soon to come.
By Stevie Knight