Alternative Double Hull Design for Tankers Offering Advanced Manufacturing and Safety Features (AVIF-No. A 234)

Responsible research centre: Rostock University (Prof. Röhr)

Time period: 01.01.2006 - 30.08.2008

Final report: CMT 13/2008


Project summary:

 

Double skin structures in the area of bottom and sides of the ship hull require a considerable effort in manufacturing connected with high costs. The main task of this type of structures is to ensure a qualified standard of structural safety especially for tankers.

The overall aim of the project has been to develop an efficient concept of manufacturing and assembly as well as to create an improved design for the secondary system of stiffener against collision, grounding as well as against ice pressure.

The structural design proposed enables to combine the advantages of a so called “Divided Modular Assembly Concept” (DMAC) for double skin structures with a novel structural system of stiffeners mounted at the outer shell of the double skin structure.

The basic idea of the developed concept for the assembly of double skin structures is based on a dividing of the conventional double skin structure in two stiffened open panels by means of a suitable located so called “mounting-plane”. The both open sections are assembled by fitting along the mounting-plane. This process of assembly makes it possible to transfer several operations of manufacturing from closed narrow compartments into open structures (stiffened panels) before the double skin structure is closed.

The verification of the practical effort of manufacturing of the DMAC succeeded by the construction of a prototype of a double bottom section in DMAC and simultaneously on the conventional way for a product tanker of the Lindenau Safety Class 2010. This large scale manufacturing test has shown the evidence of the advantages of the DMAC compared with the conventional mounting process.

The result of the investigations regarding improved structures of stiffeners for tankers is an alternative stiffener system - the so called “Plate Reinforced Profile Stiffener” (PRPS) - which increase the resistance of the side structure of the hull against collision and ice pressure significantly. From the point of view of manufacturing the novel stiffener system can be integrated compatible in the DMAC, if it will be fitted at the outer shell of the side structure.

The main feature of the proposed PRPS concept bases on a reinforcement of conventional stiffeners - as transverse or longitudinal profiles at the outer shell - by covering with plane and cylindrical curved plating, respectively. It has been designed regarding the demands to avoid considerable interventions in the conventional double skin structure as well as to ensure the inspection and maintaining of the PRPS structures.

Comprehensive systematic non-linear FEA proof the significant enhanced ultimate load behaviour by the PRPS under extreme in-service conditions - as collision and ice pressure - in comparison with conventional stiffener systems. Compared with the significant growth in ultimate strength the additional effort of material related to the total steel mass of the hull is of marginal order.

This novel concept of PRPS Design designed especially for tankers is likewise suitable for seagoing ships and inland vessels as container ships and bulk carrier as well as for offshore applications.

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