Installing redundancy systems, reducing vibration and employing automation can help mitigate the risk of steering failure
Loss of ship steering and the potentially fatal consequences that can ensue are of keen interest to ship insurers. UK P&I Club risk assessor Ansuman Ghosh says ship operators and onboard crew need greater awareness of what can cause a loss of steering.
“Failure of transmission systems between the navigation bridge and the steering gear, or breakdown of the electrical or hydraulic power supply systems, are often the cause for loss of steering,” he explains.
“Often, aft-end vibrations can loosen components of control systems, leading to breakdowns over time,” says Mr Ghosh.
Crew need to identify the cause of such problems and be trained to regain control in the event of a catastrophic loss of steering.
“A ship’s crew must be aware of the means to regain control quickly in an emergency situation,” says Mr Ghosh. “This is especially crucial when the vessel is sailing in restricted waters, as there is limited time available,” he says.
He expects seafarers to be trained to quickly regain control in an emergency: “As with most systems on a ship, close monitoring, regular maintenance, continuous crew training, realistic drills and familiarisation are the key elements. Simplification and clarity of the emergency changeover procedure is vital.”
The risks of steering failure can be mitigated during the design and construction phase of ships. This is the responsibility of naval architects and shipyard engineering departments.
“Design improvements to reduce vibrations will assist in reducing failures,” says Mr Ghosh. Vessels also need extra equipment, in case of a failure in the primary system, installed during construction. “Ships are required to have at least two independent steering control systems designed with built-in redundancy,” says Mr Ghosh.
Kongsberg Maritime director for energy solutions Erling Johannessen says owners’ requirements for cost-efficiency and space-saving also affect steering design.
“This has led to the evolution of more compact, lightweight and simple-to-install hydraulic and electro-hydraulic steering systems,” he explains, adding, “ease of maintenance has also been a defining influence.”
Mr Johannessen says a collective drive for improved system reliability has resulted in the inclusion of more numerous and accurate alarms on steering system control panels.
Efficient steering can also help benefit the environment, a key concern behind the evolution of hybrid and/or electric propulsion systems.
With this in mind, Kongsberg has developed its Autocrossing system for ferries, which “constantly monitors and adjusts the power distribution and steering angle between the forward and aft thrusters on a ferry,” explains Mr Johannessen. Autocrossing is installed as an integrated package of control systems and propellers, or it can be retrofitted. It has been fitted on two fully-electric double-ended car ferries operated by Fjord1 in Norway.
Operational efficiency and frictional forces need to be considered when designing and selecting a steering system, says Wärtsilä Marine director for propellers and gearboxes Elias Boletis. This includes the impact on energy efficiency design and operational indexes.
“The efficiency improvement impacts the vessel EEDI and EEOI and the vessel’s lifecycle operational expenses,” he explains. “The noise and the manoeuvring impact the ability of the vessel to operate under certain conditions, in the vicinity or within ports.”
Wärtsilä has developed different rudder technologies to improve performance and efficiency of a ship and its manoeuvrability. Energopac propeller and rudder integration was introduced in 2019’ Mr Boletis says it, “improves the hydrodynamic performance of the propeller and rudder together”. “We promote propulsion integration and include the rudder and steering as part of our commercial package.”
Wärtsilä now offers a gate rudder in its integrated packages. This was developed in Japan in collaboration with Kuribayashi Steamship Co Kamome Propeller, the National Institute of Maritime, Port and Aviation Technology and Yamanaka Shipbuilding.
“We are introducing this new type of rudder in the market under licence,” says Mr Boletis. “We are providing a few system enhancements relative to the initial concept, in combination with our digital portfolio tools and the machinery room integration capabilities.”
The gate rudder includes rudder elements located at both sides of the propeller and at the same propeller longitudinal position.
“There is increased redundancy in the system,” says Mr Boletis. “Due to the careful location of the blades and the selected geometry, the gate rudder becomes a thrust generator, easing the work of the propeller. In parallel, it reduces the propeller signals generated by the propeller blades.”
For optimised efficiency, the gate rudder and propeller need to be selected and sized together. “There is no longitudinal constraint (as there is no downstream rudder anymore), meaning the propeller location can be further optimised,” says Mr Boletis.
Other considerations in designing steering systems include stricter class rules and azimuth propulsion, according t azimuth propulsion builder Steerprop.
It notes a growing interest in condition monitoring and an increasing need to keep steering systems protected against cyber threats where ship controls are connected to the internet.
It has developed Steerprop Care condition monitoring which “provides predictive maintenance oversight that enables service scheduling to help eliminate the need for emergency repairs,” it says.
It has also developed Steerprop W ducted propulsors and an economic version of its contra-rotating propeller, where the propulsion load is divided between two propellers.
“Simplification and clarity of the emergency changeover procedure is vital”
Schottel has also invested in remote monitoring technologies for its rudder propellers, according to vice president for sales Roland Schwandt. Its MariHub IoT gateway is for data acquisition, remote monitoring and condition-based maintenance. “It also offers 24/7 onboard surveillance of the propulsion system and can significantly improve service and maintenance scheduling,” says Mr Schwandt.
Shallow draught solutions for inland waterway vessels
As water levels fall worldwide, vessels need to be designed with shallow draught steering and propulsion systems. Veth Propulsion has developed propulsion and steering technology for shallow draught ships, which operate in water depths sometimes less than 2 m. Veth Propulsion manager of projects and product manager for thrusters Bastiaan van Zuijlekom says shipping needs to take note of falling water levels. “Now is the time to act. We should be prepared for less rain and limited operations with ships and technology with shallow draught solutions,” he says.
The issue involves maintaining efficiency in shallower waters, as water depth can affect rudder and propeller size. Veth designed its propulsion to be enclosed within the ship’s hull, instead of free hanging below the hull.