NEW VESSELS Evolution of a tanker
SEVERAL months in operation affords an opportunity to review the design principles behind Lindenau’s new 40,500dwt tankers, which feature optimal hydro-dynamic characteristics
G
erman Tanker Shipping has now taken delivery of two of the four newbuildings -
hull numbers S272, S273, S274 and S275 – that represent an evolutionary step in tanker design. The newly developed 40,500dwt vessels offer loading volume capacities of 47,000m3
.
The general design and shape of the vessel were developed in close co-operation with the shipowner and the Hamburg Ship Model Basin (HSVA). The aim was to create a strategic advantage for the owner in a specific ship operational area by realising the following technical attributes:
•
• balanced trim for homogenous loads • • • •
low design draught for light load transport increased service speed
improved manoeuvring characteristics improved sea-holding
improved behaviour during ice operations In order to secure the contractually guaranteed
characteristics, comprehensive simulations, calculations and model tests were carried out at HSVA in March and April 2005. During resistance and propulsion tests the
vessels’ shape, optimised using a number of modern CFD design loops, demonstrated an excellent wave profile and very good propulsion characteristics right from the start. Contractually guaranteed speed of 15.5knots
on a design draught of 10m with main engine capacity of 8200kW, in accordance with the results of the resistance and propulsion tests, was expected to be exceeded by 0.5knots. Although deadweight was increased by about
25%, the new tanker type required almost the same engine output in sea trial conditions as its smaller predecessors to reach the guaranteed speed.
Although deadweight was increased by about 25% over its predecessor newbuilds, the new tanker type finding first form in Seatrout required almost the same engine output in sea trial conditions to reach its guaranteed speed.
The annual transport capacity of the Lindenau
newbuildings, depending of course on sailing profile, is said to be 10-15% higher than comparable modern newbuildings from Far East shipyards. In contrast to previous newbuildings, deployed
largely in the North European area, the newly developed types are seeing mainly global service, preferably in the Trans-Atlantic trades. Thus, special attention has been paid, in the
design of the bow sections, to the way in which the ships behave in heavy seas, both in respect of the forces exerted on them during bow-flare slamming and also in terms of speed lost during heavy sea operation. To complement CFD calculations and
TECHNICAL PARTICULARS SEATROUT
Length overall .............................188.33m Length between
perpendiculars......................... 179.50m
Breadth moulded.......................... 32,20m Side height to main deck............. 17.05m Draught, design............................ 10.00m Draught, max................................ 11.00m Deadweight min....................... 40.500dwt Loading tank volume................. 47.270m³ Main engine output ...................11.200kW Service speed ..............................16.00kn Classification
.....Germanischer Lloyd: GL 100 A5 E3 PRODUCT CARRIER OIL TANKER ESP ERS COLL 3 + MC E3 AUT INERT
simulations, tests were also carried out, using the free floating ship model, in irregular long-crested Force 4 seas (with significant wave heights of 2.8m) and in Force 6 seas (with significant wave heights of 5.4m). Compared to their smaller predecessors, the
number of ‘deck wetness events’ on the newly developed ships in the sea conditions tested could be significantly reduced. Additionally, the use of an optimal bow shape
reduced the danger of bow flare slamming. Compared to predecessor ships, the forces playing on the bow sections were reduced by about 40%. In the same way, it could be shown that,
because of the optimal bow shape, loss of speed in heavy seas, despite a 15% wider beam (32.2m instead of 28m), was no greater than with narrower predecessors. To improve manoeuvrability, the newbuildings
are equipped with high-performance flap rudders from Becker Marine Systems.
THE NAVAL ARCHITECT FEBRUARY 2007
Compared to the units in their predecessors, the
capacity of the lateral thrusters in the latest ships has also been increased by about 20% to 1250kW. Because of the danger that the ships’ main
dimensions and the speed required of them might cause yawing, a special stern section shape was designed to improve the yawing stability of the newbuildings. Manoeuvrability tests demonstrated that the yaw
stability criteria were significantly below those laid down by the IMO. The newbuildings comply with GL Ice Class E3
and Finnish/Swedish Ice Class 1A. In designing the underwater fore-ship lines,
meanwhile, attention was paid to ensuring that the ship’s form was suitable for ice operation both at ballast draught and in the range between design draught (draught = 10m) and fixed draught in fresh water (draught = 11.25m). In order to verify required engine performance
while operating in ice, tests were carried out in brash ice in the HSVA ice tank both at ballast draught and fixed draught. Compared to conventional newbuildings and
because of their special bow forms, these ships are not only able to break through relatively thin ice themselves, but also need considerably less installed power to be able to operate in icy waters. Indeed, because of their special bow shape and
controllable pitch propellers these newbuildings need only about a third of the capacity stipulated by Finnish and Swedish authorities for operation in ice at a speed of 5knots. Thus, the required ice operation performance of
these newbuildings is about 20-25% less than that needed for comparable modern newbuildings built in the Far East.
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