Marine cranes: Boosting efficiency with an overall hydraulic concept

Marine cranes: Boosting efficiency with an overall hydraulic concept
Marginal Column

November 2015


The development process for a marine crane involves many difficult decisions. But drawing upon a complete system, designed for individual adaptation, manufacturers like Tsuji can spare themselves many such decisions.

Anyone who is building a marine crane will often be confronted with a multitude of choices. Zhaorong Zou, the hydraulics engineer at Tsuji Heavy Industries, a manufacturer in China, knows this from his own experience. Just for the drive system alone, he often has to decide among many different approaches in order to achieve the best possible compromise between performance and energy efficiency. He was faced by a special challenge in the contract that landed on his desk at the beginning of 2014. The customer requested a crane in which the motor operated at a speed of 3,300 rpm – a considerable feat when handling large marine containers. In the past, Tsuji systems usually ran at below 2,800 rpm. But that was not all. Given rising energy prices, the amount of power drawn was to be no higher. It was quite clear to Zou that the former approach – assembling the drive system from components made by many suppliers – would reach the limits of feasibility whenever such demands were encountered.

New partner, new solution

Tsuji was looking for, and found in Bosch Rexroth, a new partner for the drives for his cranes. Yi Zhu, an application engineer for marine architecture at Bosch Rexroth in China, knew immediately that he could simply not take a solution off the shelf, but instead would have to design a new, complete solution, including the hydraulics, controls and piping in a closed circuit. “Our team put together and customized the hydraulic system with an additional pump,” Zhu recalls. His team used Rexroth components exclusively and achieved the maximum for all the factors that influence efficiency. But in the case of maximum fluid temperature, they achieved a minimum. At high ambient temperatures the fluid could exceed 80 degrees Celsius and viscosity in the circuit would suffer, resulting in a standstill. The new solution does not break out in a sweat even in tough climates, where the mercury hovers around 40 degrees. Thanks to an improved cooling system, the fluid temperature climbs no higher than 60 degrees. Another advantage is that the closed hydraulic system converts into electricity the energy generated when the load is lowered and returns it to the ship’s system. All in all, efficiency is boosted from 60 to 75 percent in this way. Power consumption, when compared with conventional systems, sinks by as much as 25 percent. And that means annual savings of about 42,000 euros per ship.

A successful premiere

In spite of the system’s complexity, only four months passed between receiving the contract and delivering the order. That is only half the time normally needed in such cases. The remaining requirements were also satisfied by Bosch Rexroth – one hundred percent. “With this complete solution, we were able to better respond to our customer’s wishes and even to satisfy high performance demands. This boosts Tsuji’s competitiveness,” according to Zhaorong Zou.