Safe transfer in the Elbe Estuary
Posted on June 08, 2017 by Dipl.-Ing Peter Pospiech, Images by ABEKING & RASMUSSEN, Dipl.-Ing Peter Pospiech
Trials success for new-concept pilot tender. The compact hull cylinder accommodates an mtu 10V 2000 M72 propulsion engine.
From SWATH to SWASH
With its solid tradition in shipbuilding and yacht construction, the globally renowned, high-tech A&R yard invested years of development work to bring the SWATH (Small Waterplane Area Twin Hull) vessel design to maturity for series production. Subsequent development leading to the SWASH concept was primarily undertaken for commercial reasons: Pilots operating on the River Elbe needed a lighter and more economically efficient type of transfer launch than SWATH designs allowed – but they did not want to give up any of the positive SWATH features.
According to A&R, SWATH boats cannot be supplied much smaller than around 25 meters in length: “Otherwise, the submerged hulls would not be big enough to accommodate the vessel’s propulsion system.”
The solution was provided by the EXPLORER, a 20-meter long, monohull, SWASH-design vessel with two trimaran-type stabilizing outriggers. “That makes the EXPLORER faster, more maneuverable and, most important, more economical to operate than a SWATH vessel,” explained the yard. The SWATH@A&R concept ensures secure pilot transfer even in extreme weather conditions. In addition, the vertical outrigger surfaces on the newly-developed SWASH vessel from ABEKING & RASMUSSEN mean it can dock with ocean-going ships as well as vessels with limited freeboard height between waterline and deck.
On the basis of its extensive experience building numerous SWATH units, A&R was so confident that the SWASH concept would exactly match the performance needed for pilot transfer in the Brunsbüttel area that the company took the unusual step (for a shipyard) of building the SWASH tender at its own expense and making it available to the operator for long-term trials. The SWASH concept is unique and its application in the EXPLORER is the first time it has been implemented in an intensive commercial context.
The SWATH concept
SWATH technology is used in virtually any situation needing an extremely stable platform that can be used under almost any wind and weather conditions. This covers pilot tenders and pilot station vessels but it also involves hydrographic survey vessels, support and service ships for the offshore sector, patrol boats and yachts.
SWATH@A&R pilot station vessels and pilot transfer tenders have been in operation throughout the North Sea area since 1999.
Physics at the extremities
Wave movements exert their greatest power on the surface and their power decreases as the water gets deeper. Vessels with only small surface areas that come into contact with the water obviously offer less surface for waves to act on and thus decrease their ability to rock the vessel. SWATH vessels only displace a fraction of the water displaced by catamarans and conventional monohull vessels that are forced to follow the movement of each individual wave. In heavy seas, vessels with SWATH technology achieve the same levels of stability as monohull vessels three or four times their size.
In contrast to SWATH vessels, the SWASH concept incorporates a hull connected by two slender struts with a cigar-shaped cylinder beneath the surface of the water. The cylinder provides the necessary buoyancy and also reduces the lifting power exerted by the waves. The buoyancy cylinder narrows towards the stern and is fitted with computer-controlled stabilizer fins at the bow end to further increase stability.
Hull houses entire propulsion system
Like its bigger sisters, the SWASH vessel has a diesel-electric propulsion system. With safety, reliability and efficiency as the prime design factors for the new submerged-monohull vessel, it was no surprise that the yard, the BMVI and the Pilotage Services Association all agreed on the selection of diesel engines from mtu in Friedrichshafen. The target that the pilots set for the engine builder was: “100% diesel engine reliability, 24 hours a day on every trip.” Any delay or downtime would necessarily involve huge consequential costs. The team at mtu’s Hamburg Center did not need to think too long: “mtu engines are designed to meet the toughest demands. That is what they do.”
The compact hull cylinder accommodates an mtu 10V 2000 M72 propulsion engine delivering 900 kW, and a special low-speed electric propulsion unit from Siemens. For pilot station operation, the electric motor means low fuel consumption and a permanently improved C02 balance. With this configuration and its 65 tonne displacement, the unusual trimaran can reach almost 20 knots – more than is needed for transferring pilots to large container vessels.
Surplus diesel power boosts electricity supplies
Propulsion power for the EXPLORER is generated by a diesel-electric hybrid drive from Siemens. Housed in the buoyancy cylinder, this ‘EcoProp’ system is capable of diesel and electric modes that facilitate economic operation for every duty profile. When the vessel is powered by its mtu diesel engine, any surplus power is fed into a generator that supplies on-board electricity for the entire boat. This option is particularly valuable on vessels such as the EXPLORER because pilot boats do not always travel at a constant speed. They frequently adjust speed to match the conditions prevailing at any given moment. This stop-and-go-type operation not only represents a high load factor for diesel engines, it is also energy inefficient.
EcoProp allows the engine to run at a constant level despite fluctuations in vessel speed and any surplus energy produced is fed to the generator. The outcome is longer engine service life and lower fuel consumption, which in turn means reduced emissions. The EXPLORER’s design also contributes to improving its energy balance: the vessel is relatively light and its two outriggers maximize stability even in heavy seas.