Strict environmental regulations, passengers expecting a more comfortable ride and economic constraints are compelling cruise lines to work on the continuous improvement of their liners' efficiency and performance. There are many approaches, and that goes for stabilisers as well. As Andreas Bubbers from SKF Blohm + Voss Industries outlines, individual case analysis is always a prerequisite
Stabilisers have existed for many decades. From the beginning, this equipment was able to eliminate up to 90% of a ship's rolling motion. There's little room for improvement in this performance according to Andreas Bubbers, senior sales manager at SKF Blohm + Voss Industries, but more is still expected, not so much in terms of actual stabilisation but with a view to other technical conditions and changed fields of application.
Efficiency and environmental conservation are the operative words, explains Bubbers. "Rising energy prices are forcing operators to improve continuously across the board," he says. "Moreover, customers and the general public are pushing aspects such as conservation - demands backed by the environmental regulations of states and authorities. That's why we've paid closer attention to fluid dynamics in the various operating modes."
Working with specialist design consultants, SKF Blohm + Voss Industries has carried out thorough computational fluid dynamics analyses, observing the flow behaviour of stabilisers extended in different directions, and differences between one-piece and two-piece fins. Some variants make much better sense than others depending on the number of operating hours envisaged for the stabilisers. In some cases, the right design resulted in stabiliser operation economies of up to 8%.
"We are able to manufacture all these variants, but the right choice can only be made in dialogue with the customer," says Bubbers. "We can certainly supply facts and figures, but at the end of the day, it's about striking the right balance between cost-effectiveness and stabilisation performance - and that can't be done without input from the customer."
Another factor with implications for the types of stabiliser fitted is the US Coast Guard's Vessel General Permit (VGP) 2013, which applies to all vessels in commercial operation in US waters. It is therefore also applicable to all cruise ships inbound to the US. One requirement of the regulations is that these ships must use environmentally acceptable lubricants (EALs) at interfaces where oil may enter sea water. A stabiliser is one such interface.
"Of course, we can fit stabilisers compliant with VGP 2013," says Bubbers. "It is simply a matter of using special materials, compatible with the EALs to be applied, for certain components such as the sealing rings or coatings in the hydraulic oil tanks."
The conversion of stabilisers already in operation poses a major challenge, according to Bubbers; it requires precise analysis of which components are replaceable and need replacing, and how to convert the stabilisers to run on different hydraulic oil.
"In principle, we hold the plans of the equipment we convert," he says. "But we don't know the condition of the older models, which may have needed no maintenance for many years. This has to be worked out in detail with the customer."
Comfort is also playing an increasingly important role. There is growing demand from passengers for exclusive cruises in more remote waters, requiring the operation of medium-sized cruise liners. "People booking such cruises expect suitably luxurious amenities," explains Bubbers.
The ship's rolling motion should continue to be attenuated while she rides at anchor with guests still on board. Zero-speed stabilisers, which originated on luxury yachts, are able to achieve this, and SKF Blohm + Voss Industries also offers this technology.
"Our product is very compact and offers particularly effective roll reduction. This saves space and, ultimately, reduces operational energy consumption."
Bubbers sees consultancy services as increasingly important: "Selling stabilisers has always been a project business, as each piece of equipment must be custom-designed for the planned vessel. But ship operators face increasing demands, and we, as suppliers, have to recognise these demands and respond to them on behalf of our customers."