SMD has built a bespoke electric 6,000m wind and launch and recovery system for Shanghai Salvage
Hydraulic winches may have their advantages in terms of brute strength, but new improvements in technology mean that their electric cousins are quickly closing the gap. Moreover, electric systems have no requirement for large oil tanks, are remarkably quiet and consume very little power from the vessel whilst idling.
One company leading the charge is Soil Machine Dynamics (SMD), a major innovator in remote intervention equipment. Most recently, SMD completed work on a bespoke electric drive dual-purpose winch and launch and recovery system (LARS) to accompany an order from Shanghai Salvage for an SMD Quasar work-class ROV. As SMD explained to InnovOil, however, this is the first such system in the world with the ability to manage an umbilical with active heave compensation and under constant tension, to an operating depth of 6,000m.
The company, also known as China Ocean Engineering Services Shanghai, will be deploying the LARS and ROV for deepwater salvage operations around the world.
The winch will be provided with two interchangeable drums, SMD said: one spooling a 6,000m lightweight umbilical cable, and one 3,000m cable with TMS, which is capable of carrying heavier loads. These drums can be swapped whilst on the vessel to suit the requirements of the mission, without the need to return to shore – offering considerable savings in terms of time and expense.
The integrated launch and recovery system, comprising the A-frame and winches, has a safe working load of 12 tonnes up to Lloyds Sea State 6, requiring a design load of 2.5 x safe working load (SWL). The winch can pull up to 12 tonnes on the top layer when in 3,000m TMS mode, and the pull is limited when operating with the lightweight 6000m system.
Time is also saved in outfitting the vessel, as the integrated electric drive suite allows the entire system to be quickly mobilised onto a vessel of opportunity as one unit, via a single point lift. Moreover, the design can be integrated with the vessel’s electronics, meaning energy from the winch can be regenerated and used for other applications on the vessel.
Electric avenues The winch itself can operate using either AC induction or advanced synchronous reluctance motors. ABB’s SynRM motor technology also helps ensure compensation accuracy and response time, meaning the ROV can be safely launched and recovered during rough seas.
SMD is also providing a PLC control system, featuring auto-depth capability and power loss protection, as well as condition monitoring, remote diagnostics and data logging via cloud-based systems.
The Quasar, meanwhile, is a 3.5-tonne ROV capable of carrying payloads of up to 250kg and working at depths of up to 6,000m. Its isolated hydraulic system can run high-power tools, making it a sound choice for salvage operations, and a large payload capacity allows more tools to be carried to the work site, cutting down on additional trips.
SMD’s managing director of deck equipment, Paul Hatchett, explained to InnovOil: “Thanks to improvements in technology, electric winches are becoming an increasingly viable option. Electric drive technology for use in marine winches already exists and naturally improves as kit gets smaller, cheaper and offers better performance. In this case – with Shanghai Salvage – the existing offerings on the market would not meet the dynamics demanded for the application with dual drums.”
In designing the system, he added, it was not the length of the umbilical that proved a challenge, but rather the delicacy of the lightweight umbilical and the need to control this in an active manner. SMD’s approach reduces shock loading on the lighter umbilical, whilst simultaneously meeting the requirements for handling the heavier armoured umbilical.
Nearly all existing approaches regulate tension with a system that applies its control in a continuous single direction, where motors are generally running near to or at their most efficient speed (usually around 1500 rpm). Such single-direction systems are able to use reactive feedback, and react the loads to data after it is collected. In this application SMD needed to develop a system which actively changes tension on the fly, as data is collected, and which would apply control setpoints in a predictive manner.
“The application not only requires handling of a delicate umbilical, it has to do so in an unstable marine environment accounting from the pitch and roll of the waves as well as maintaining a constant tension on the umbilical to avoid slack,” Hatchett said. “This need translated into a forward and reversing drum operation at next to zero rpm, therefore demanding very high torque varying in direction. This is a challenging operating condition for any motor.” Recent improvements in motor technology proved to be the turning point in the design. “Synchronous reluctance motors were selected instead of servo or asynchronous motors, which also reduce wear, service intervals and the need for spare parts,” he said.
“A big advantage with this system is that we can apply ‘online’ changes to the fundamental operation; hydraulic systems inevitably need some mechanical hands-on to either increase or attenuate performance, whereas with our electric winch we can adjust performance without having to visit the equipment,” he continued.
In testing, the reactive performance of the motors exceeded expectations to a point where even minute changes in control would be seen at the motor. The motors’ low inertial quality also allowed for faster than anticipated direction changes, ideal in an active heave compensated system where accuracy to follow the wave – fast – is vital.
A by-product of the electrical motor operation is also electrical energy. The system becomes a generator in certain situations, e.g. when braking, and here the additional “regen” energy can be reused, stored or expelled as heat via resistor banks.
The added environmental and operational benefits of electric motors are pushing a change in the industry too. “Each improvement in the power density and performance of electric motors means a wider range of suitable applications. Operators consider the lower operating expense of electric motors to offset their higher capital cost, compared to hydraulic motors,” Hatchett told InnovOil. “The industry also seems to be a seeing a decrease in the amount of hydraulic expertise it has available, which is also lending weight to electric motor selection. With the increase in reliability and the ease with which electric motor drive units can be changed out and reprogrammed (with less specialised experience), [this] has made electric drive systems far more maintainable.”
Hydraulics are not going anywhere – they still provide a benefit for heavier applications and lower capital costs mean the economics are still persuasive for many operators. But for those that do, innovative applications such as these could prove to be valuable additions. In either case, SMD will be there to identify the best solutions for its customers.