Bosch Rexroth makes distinct contribution to energy-efficient hybrid drive.
The AntiRoll from DMS is a roll stabilization system for 30-metre-plus ocean-going yachts. What makes AntiRoll unique is that the stabilization is highly effective both at sea and when moored, while the familiar disadvantages of comparable systems – significant drag in the water, leading to high levels of noise and fuel consumption – are kept to a minimum. This innovative solution lies in the biaxial elongated fins and the hybrid drive, in which Bosch Rexroth has ingeniously combined the advantages of hydraulics with the capabilities of variable frequency servo motors and control technology. The unique benefits for the maritime world of this solution have been recognized by the jury of the Maritime Innovation Award, who yesterday awarded the FIRST place to the design.
The Maritime Innovation Award was launched in 2000 by the Holland Marine Equipment Association, to raise awareness of the innovative power at work in the maritime and offshore supply industry. One of the aims is to stimulate innovative developments within the maritime cluster. This is an award which is awarded annually to a new product, process or service. In order to qualify, the entry must be broadly applicable within the maritime sector, commercially viable, and with sufficient export potential. Winner DMS easily met all these requirements.
At the helm of DMS are two experts with a passion for motion control in yachts: Patrick Noor and Arnold van Aken. Patrick Noor: “The inspiration for our development is the fact that yachts keep getting bigger and bigger, but the downside is it is no longer so easy to berth in every port. This means that skippers often drop anchor outside the port area and stay put there. However, the rolling motion of the boat then becomes a hindrance for many activities aboard the vessel. The various stabilizers that have been developed until now, without exception all uniaxial, have always had to compromise between the requirements of sailing, and those of lying at anchor.
This problem has now been solved by the use of biaxial fins that rotate while underway and make a flapping motion when the yacht is stationary. When sailing, the curved high-aspect fins generate 50 to 75% less drag in the water than traditional fins, resulting in a positive effect on both speed and fuel consumption. What’s more, the flapping motion of the fins has a much greater lifting effect than fins that only rotate when the vessel is stationary. Lastly, the fins can be folded against the hull, or alternatively partially rotated into a hull recess, making the system suitable for sailing yachts as well.
The underlying drive has been developed in close cooperation with Bosch Rexroth, with explicit attention given to energy efficiency and noise level. In the definitive solution, the motion specialist combined the high power density of hydraulics with a sealed, compact system powered by variable frequency servo motors. Two of these servo motors are built into the rotary actuators required on each side of the boat, where they control the direction and output of the hydraulic pumps. Each drive provides for both movements of a fin (rotation and flapping). A third, identical servo motor enables spikes in the energy demand to be intelligently accommodated. One benefit of this is that the drive system can be kept compact, while ensuring that a spare motor is immediately available if necessary for one of the actuators.
Moreover, the goal of an energy-efficient system as envisaged by the Bosch Rexroth 4EE Energy Conservation Program, has been fulfilled in every aspect. This is possible because, in contrast with most high pressure hydraulic systems, there is no hydraulic buffer. The only energy required is for the movement of the fins, and no energy is needed to keep a buffer pressurized. Furthermore, the energy drawn is also exactly the amount required by the frequency-controlled system, and the drives have been designed from the ground up with a view to energy efficiency.
At the time of the award ceremony, the mechanical part is fully assembled and the first tests are being performed at Bosch Rexroth with the complete system, including hydraulics, controller and servo motors.