Feeder vessels, the smaller container ships that connect smaller local ports to larger international hubs, need high manoeuvrability for their frequent port calls and good energy efficiency to comply with increasingly stringent emissions regulations. The combination of a Wärtsilä controllable pitch propeller (CPP) and shaft generator system – easily integrated with any brand of 2-stroke engine – answers both these challenges while also providing increased flexibility for future upgrades like hybridisation.
The hub-and-spoke distribution model and the increasing size of ocean-going container vessels – the largest now exceed 24,000 TEU ¬– make feeder vessels a vital link in the maritime transport chain. With large vessels only able to call
at big regional hubs, it is the feeders’ role to ferry containers to and from smaller local ports. Feeders can be anything from 800 to 6,000 TEU, though the most are in the lower half of that scale. They typically operate on fixed schedules
and routes, making multiple port calls to load and unload goods in synch with the larger vessels’ schedules.
Manoeuvrability is the key to making feeder operations as safe and efficient as possible. Their high number of port calls means that the more they can do independently, without tug assistance, the better. Manoeuvrability is also critical when navigating
busy hubs and sailing on rivers and canals.
Of course, the feeder vessel segment is subject to the same increasingly stringent regulations as the rest of the global maritime fleet – for example, compliance with the IMO’s Energy Efficiency Design Index (EEDI) and Carbon Intensity Indicator (CII) requirements. In order to avoid having to limit engine power to comply, which is unattractive for vessels that need to stick to strict schedules, minimising emissions (and therefore fuel use) is essential.
While many feeder vessels operate with fixed pitch propellers, the need for increased manoeuvrability and fuel efficiency is driving many owners and operators to weigh up the advantages of switching to controllable pitch propellers (CPPs) instead.
CPPs allow a vessel to accelerate faster from a standstill and stop more quickly. They improve vessel manoeuvrability by allowing the drive train to be continuously on standby to provide instantaneous manoeuvring thrust and water flow on the rudder. The
propeller blades can be adjusted to the optimal pitch to enable higher thrust and propulsive efficiency at varying load levels, thereby providing flexibility and saving both time and fuel. Another big efficiency bonus is that they are typically integrated
with a shaft generator system. Using power from the main engine is a more fuel-efficient and cost-effective way of generating onboard electricity than using the auxiliary engines. Combining a CPP and shaft generator system also provides more flexibility
for the future as they are easier to integrate with hybrid or fully electric systems.
With the potential to improve a vessel’s energy efficiency by three to five percent and reduce both emissions and fuel costs, shaft generator systems typically have an ROI of around two to four years depending on system power. They also have a positive impact on a vessel’s CII rating. Over 650 vessels sailing today already use Wärtsilä shaft generator systems.
Wärtsilä has decades of experience with CPPs and shaft generator systems and, perhaps more importantly, integrating them with the entire shaft line. “The shaft line itself is made up of several complex components that all need properly integrating to get the most out of the whole. People often have the wrong idea about where the real challenges lie for 2-stroke driven CPP installations. The main engine and shaft line can be seen as two separate building blocks, and in reality the challenges are related to proper design of the shaft line rather than to the connection with the main engine. Wärtsilä’s CPPs can, and have many times been, successfully connected with any brand of 2-stroke engine. Naturally, if the entire propeller shaft line is provided by one supplier it greatly simplifies optimisation, maintenance and repairs over the vessel’s lifetime. In addition, working with one supplier will also mean that the propeller blades are optimally designed using computational fluid dynamics for the individual vessel and its operating profile,” says Piet van Mierlo, Team Leader, Product Team Propellers at Wärtsilä.
But getting the most out of a CPP and shaft generator system is not just about careful integration of mechanical moving parts – all that power needs controlling. The Wärtsilä Energy Management System (EMS) controls power generation and
distribution onboard to ensure there is enough power for propulsion and manoeuvring – optimising performance and reducing the risk of blackouts. The system has several advanced options that reduce distribution losses, increase energy availability
and save space and installation costs.
The Wärtsilä Propulsion Control System (PCS) is a comprehensive system of control devices, displays, indicators and modules integrated with the main shaft line to control both the main engine and the pitch of the propeller. It connects the signals from the main engine, shaft generator system and propeller into one system for better control and safer, more efficient operations.
The tunnel thrusters of feeder vessels probably see more action than those on many other types of merchant ship, so it’s important that they are also properly integrated. “By designing and integrating the entire shaft line from engine flange
to propeller, as well as the shaft generator system and thrusters, we make it as easy as possible for both shipyards and vessel owners,” explains van Mierlo. “Yards get the convenience of having the components supplied with guaranteed
interoperability from one manufacturer, while owners get peace of mind from the knowledge that their entire shaft line has been tailored for their specific vessel and reliable service support is available anytime, anywhere.”
Going one step further, beyond the propeller, GATE RUDDER™ by Wärtsilä significantly reduces a vessel’s fuel consumption by replacing the drag of a traditional rudder system with a thrust-generating arrangement. The arrangement also further enhances manoeuvring capabilities and improves the vessel’s noise and vibration signature. “Placing the high-lift rudder foils on either side of the propeller enables better course keeping under real environmental conditions, turning at higher speeds, independent manoeuvring in confined ports, faster mooring and quicker crash stops,” van Mierlo points out. “Its application will also manifest itself in a better CII performance as gate rudder technology has proven to work exceedingly well in real operational conditions.”
“Wärtsilä can of course supply all the needed components, but where we bring real value is in our years of experience of optimising propeller designs, integrating shaft lines and shaft generator systems, and connecting them to any brand
of engine. We also supply fixed pitch propeller systems that can be fully integrated with energy-saving technologies like GATE RUDDER™ and pre-swirl devices,” explains van Mierlo. “Ultimately, putting a little more emphasis on design
and optimal integration in the early stages of a vessel’s life will lead to more reliable and efficient performance over its twenty years or more of service. And with the role of feeders only set to expand and get busier, it’s hard to
put a price on that.”
Read about Wärtsilä CPPs
Read about Wärtsilä shaft generator systems