Maximising marine efficiency

In today’s global fleet of increasingly specialised vessels, staying profitable means exploring every possibility for improvement, especially in light of rising fuel costs, increasingly stringent environmental regulations, and growing health and safety concerns. Ship operators need to maximise time at sea, reduce maintenance costs, and provide a safe working environment for the crew.

From enhanced shaft line transmission products to condition monitoring hardware and software, new innovations are cutting operating costs across the marine market while helping operators meet the challenges of reduced environmental impact and increased safety.

For example, a new method of coating couplings can achieve a 50% higher torque transmission capacity. These remarkable advances in coupling performance have been achieved by using advanced plasma technology to coat the inside of the inner sleeve. Plasma technology has superseded early experiments in high friction coating, which saw laser beams melting the surface and ceramic powder sprayed into the melted surface. This process gave a wear resistant surface and good friction but was an expensive, time consuming process that required an additional grinding stage. In contrast, plasma gives a wear-resistant surface and excellent friction properties but does not need any treatment after coating.

Plasma technology

Couplings produced using plasma technology can reduce the pressure needed to transmit the torque, and this development is of great benefit to OEMs. For example, these advanced plasma technology shaft couplings are enabling propulsion system manufacturers to remove the reinforcement sleeve inside the hollow shaft. The capability to produce shafts without the expensive reinforcement sleeve means cost savings for OEMs. The new couplings are also smaller and deliver a higher performance; a compact coupling saves space and reduces weight in the shaft line, while enhanced torque capacity means safer shaft connections.

Other recent innovations that have proven to be successful in the challenging marine environment are super-strength bolts, which provide an accurate fit for propeller shafts, enabling them to handle the high turning torques of today’s large diesel engine vessels. Factors such as low speed operation and bad weather can cause propeller loading to vary widely, meaning that shaft bending may occur because of ship hull deformation. Nevertheless, most of these failures have predominantly been due to the direct drive propulsion systems that have been built into most of the vessels that have been constructed in the last few years.

This design means that there is no gearbox and instead a large cathedral diesel engine drives the propeller directly. This does, however, mean that high torque forces are transmitted directly from the engine through the propeller shaft, and thus the associated flange bolts, rather than via traditional gearbox mechanisms. This can lead to extremely high levels of torque in the shaft arrangement, with problems typically manifesting themselves when the direction in which the engine is running is rapidly changed, as well at critical shaft speeds. As a result, torque loading is often distributed unevenly across the conventional flange bolts, so that a small number are subjected to most or all of the applied torque; in some cases, this can mean that the torque loading on individual bolts can more than double as a result of a change in direction of propeller rotation, causing bolts to fracture or shear.

An effective method of preventing shaft failures is through the use of the expandable SKF Supergrip bolt, which uses dedicated tapered bolts and sleeves, and is mounted and dismounted using hydraulic tools and a proven oil injection method. These new SKF Supergrip bolts are easier to install and remove, as well as being more cost effective than conventional bolting solutions, as the torque transmitted is mainly by the shear strength in the bolt, meaning fewer bolts are needed.