Cruise and ferry operators are attaching increasing importance to good manoeuvrability and looking for energy-saving systems
Strong manoeuvrability solutions are a must for both the cruise and ferry sectors, particularly in the fast-growing expedition market.
Propulsion pods are one growing trend within the expedition cruise market and their beneficial impact on vessel manoeuvring is useful in polar conditions.
Finnish naval architect firm Deltamarin has been working on polar/expedition cruise ship concepts recently and has highlighted propulsion choice as one area to focus on in a polar cruise vessel: whether to fit a traditional shaft system or pods.
Pods have strong benefits for manoeuvring in icy conditions. As Deltamarin sales manager Nina Savijoki told Passenger Ship Technology “Pods are much better in ice as they can be directed to flush and break the ice around the vessel.”
They are not just selected for manoeuvring; they have hydrodynamic benefits, since there are no shaft lines, and Ms Savijoki added that if an operator wanted a polar vessel to be more heavy duty, they could consider a DAC (double-acting cruiser) design.
This would be similar to the established double-acting tanker concept, which first went into service in Arctic waters in 2002. In this arrangement, a vessel has its aft region shaped and strengthened in such a way that it can operate stern-first in ice conditions with the propeller flow helping to ease the its hull through the ice.
“The benefit of this is that you have a good fuel efficiency in open water operations but still have a reliable solution to operate in heavy ice-conditions as well,” Ms Savijoki said. This solution can only be applied in a vessel that has azimuthing thrusters, she explained, such as Azipods or similar propulsion systems.
However, she said that a drawback is that a vessel would have to have a much more expensive wheelhouse as it must work “both ways”. In a cruise ship this would “most likely mean that there would have to be an additional smaller wheelhouse on the aft.”
Another growing trend for cruise and ferry manoeuvring solutions is to boost rudder efficiency.
Becker Marine Systems vice president sales and projects Henning Steffen told PST “There is a very high demand for good manoeuvrability when operating in ice conditions.” Also, expedition cruise ships “sail to very small ports in remote areas and need a very good rudder to carry out safe harbour manoeuvring in all weather conditions,” he said.
As a result, “we see a very high demand and a growing market here,” Mr Steffen emphasised.
In the past two years Becker has clinched contracts with US shipyard Nichols Brothers for a Lindblad expedition cruise ship and for another for an expedition ship being built by Chilean yard Asenav for Antarctica XXI.
Mr Steffen singled out Becker’s Flap Rudder as being especially appropriate for the expedition, cruise and ferry market. In contrast to a traditional rudder which consists of a single blade, a flap rudder consists of two parts: a main blade and a movable flap at its trailing edge to create a high turning force.
It has also seen demand for its Flap Rudder add-ons: a twisted leading edge and rudder bulb. “They reduce losses from the propeller which increase the efficiency of the vessel,” said Mr Steffen.
An example of this is a conversion on Norwegian Cruise Line vessel Norwegian Epic, for which Becker delivered new twisted flap rudders with bulbs.
The cruise ship and ferry rudder conversion market are a steady one, according to Mr Steffen. “We have had some projects with rudder refits where manoeuvrability was one of the main drivers to change something on the rudder.”
Mr Steffen also reported growing demand for state-of-the-art rudders in the ferry market. “Ferry operators went through a period of choosing traditional rudders,” he said, but they “now realise the importance of having a good rudder. It is a big issue as they have very tight sailing schedules, have to manoeuvre in small ports and this needs to be done in all weather conditions the whole year.” As a result, a high lift rudder is more or less a standard for new ferry designs, he said.
Indeed, the growing focus by ferries on manoeuvring can be seen in recent newbuild contracts, for example in November 2017, Voith revealed the latest order for the latest generation of its Voith Schneider Propeller (VSP), the VSP36RV6 ECS/285-2. Two of these thruster units will be fitted to each of three newbuilds for New York’s Staten Island Ferries, which is replacing two of its older ferries as part of a modernisation programme.
New York City Department of Transportation (NYC DoT), which owns the ferries, will decommission the two ferries and replace them with the three new ones, which will be built by Eastern Shipbuilding in Florida.
Voith’s propellers will both power and control the ferries and the manufacturer said in a statement that their “excellent manoeuvrability is a primary reason why the NYC DoT decided to use the VSP, because, in the very busy New York harbour, the ferries must be able to react promptly to new traffic situations.”
It also mentioned that the ferry service has to deal with difficult conditions such as strong currents, waves and ice conditions in winter, which it said was also a factor in why its VSP was selected.
In addition, Voith will supply four fill-controlled VTC 1150 TPZSRL turbo couplings. When these are drained, the engine can rotate without load, to enable gentle warming up and soft starting of the propulsion system.
When filled, these fluid couplings “eliminate torsional vibrations and provide the option of single engine operation mode when only one coupling is engaged,” Voith’s statement said. A single shaft then transmits the power to the VSP.
Norwegian company Servogear also won a significant contract in November last year: Ferry operator Norled ordered two 24 m battery hybrid catamarans from Norwegian shipyard GS Marine and chose to equip both vessels with a complete plug-in hybrid Servogear Ecoflow Propulsor solution.
This contract is said to be unique as it represents the first controllable pitch propeller (CPP) integrated plug-in hybrid solution on the market, with its accompanying HDE220 hybrid gearbox being deployed for the first time. It is built on the technology of Servogear’s HD220 gearbox, combined with the electronic technology. It has a maximum input of 900 kW at 2,250 rpm, an integrated pitch actuation mechanism, an oil cooler and remote duplex filter unit
Wärtsilä launches industry-first tilted steerable thruster
Wärtsilä has launched the Wärtsilä WST-24R, the industry’s first tilted steerable thruster with combined electric retraction and steering.
In a statement to mark its official launch during the Marintec exhibition in China in December, Wärtsilä said that it enables “excellent auxiliary manoeuvring in stationkeeping or dynamic positioning (DP) operations.” It also believes that the new device will provide “high reliability, easy installation, integration and maintenance.”
It particularly drew attention to the thruster’s gearbox, which has its propeller shaft tilted at 8°. This is said to significantly reduce thruster/hull interactional losses, producing up to 20% more effective thrust than conventional non-tilted thrusters and enabling lower fuel consumption. “This extra effective thrust directly contributes to the advanced DP capability of a vessel,” its statement said.
The WST-24R thruster offers more than 10% more thrust than Wärtsilä’s existing LMT 1510, which it replaces, giving it a higher power density. This, combined with improved hydrodynamics and Wärtsilä’s own thruster nozzle design, reduces the environmental impact of the propulsion system, the manufacturer’s note said. It can also be delivered to comply with clean notations and can be made compatible with the US EPA’s VGP2013 stipulations.
It also has fewer components than its predecessor, which Wärtsilä said improves its reliability. In addition, all its systems are easily accessible for maintenance, while the combined steering-retraction seals are designed to have no oil to water interface to reduce environmental risk. Its steering is electric, rather than hydraulic and its retraction system is to a new lightweight design that has self-locking electric actuation, boosting its safety, the company said.