Empirical Study on the Effect of Hydrofoils in a Hydrofoil-Assisted Trimaran
Ryno Moolman, Günther Migeotte, Volker Bertram

Study of Boundary Layer Over an Axisymmetric Hydrodynamic Configuration
P. Chougule, O.N.Ramesh, N. Banerjee, A. Saiju, Y. Veerachari

An Investigation into Process Outsourcing and Strategic Alliances for Shipbuilding in an Integrated Model
R. Sharma, O. P. Sha

Safety Assessment in Terms of Freeboard
Yoshitaka Ogawa, Shigesuke Ishida

Analytical Investigations on Double Hull Tanker Subjected to Impact Loads
Manu Mathew, Dr C G Nandakumar

Mathematical Modelling of Cathodic Protection of Hull Surface
A.Mathiazhagan

Hydrodynamic Stability of Fluid Flow through a Flexible Pipe with Outer Rigid Shroud by the Energy Method, Part-2: Axisymmetric Disturbances
Munendra Kumar, P.K. Sen, A.K. Raghav

BACK COVER – Vol 4, No. 1, January 2008

Empirical Study on the Effect of Hydrofoils in a Hydrofoil-Assisted Trimaran
Ryno Moolman, Günther Migeotte, Volker Bertram

ABSTRACT
Model tests and numerical simulations investigate the influence of hydrofoil assistance for trimarans, drawing on experience of foil-assisted catamarans. While foils are demonstrated to effectively decrease the resistance of trimarans, a comparison shows that a catamaran with similar displacement and same speed is still superior to the trimaran, with or without foils.

Keywords: hydrofoil, trimaran, catamaran, foil-supported catamaran, outriggers

Study of Boundary Layer Over an Axisymmetric Hydrodynamic Configuration
P. Chougule, O.N.Ramesh, N. Banerjee, A. Saiju, Y. Veerachari

ABSTRACT
In this study, Wind Tunnel experiments on the evolution of boundary layer flow over an axisymmetric body is presented. This geometry is typical of many hydrodynamic configurations. The boundary layer development over the cylindrical configuration is interesting from the fluid dynamics viewpoint for presenting a variety of complex fluid dynamic phenomena : the initial
stagnation region in the nose region, laminar separation after the shoulder, turbulent reattachment, development of an axisymmetric turbulent boundary layer under zero pressure gradient which finally undergoes an adverse pressure gradient development in its tail region due to a ramp-like shape. In view of these, the flow on the body was categorised into four different flow regimes. Measurements are reported here primarily for the constant pressure region. Mean and fluctuating velocities were measured using hot-wire anemometry. The resulting turbulent boundary layer was seen to be very similar to a canonical flat plate boundary layer developing under zero pressure gradient. This is attributed to the fact that the parameters governing the problem assume values which are typical of the flat plate limit wherein the flow structure is likely to be very similar to a flat plate flow under constant pressure. The variation of turbulence intensity also follows a similar behaviour with a peak occurring very close to the wall.

Keywords: axisymmetric body, axial flow, turbulent boundary layer, laminar separation, adverse pressure gradient

An Investigation into Process Outsourcing and Strategic Alliances for Shipbuilding in an Integrated Model
R. Sharma, O. P. Sha

ABSTRACT
The manufacturing process for a ship can be viewed as several independent manufacturing processes for different blocks, and later assembling these blocks for a complete ship. At times for ships, these blocks and their manufacturing processes do vary significantly in scale and nature. From a quality point of view, it is difficult for any ship manufacturing firm to achieve consistently high quality in every manufacturing process for each block. A shipyard is viewed as a structured manufacturing firm (i.e. consortium or group of companies) which consists of
separate small manufacturing companies and each of these are specialist in their own fields. In a company, if the manufacturing is focused and small (i.e. it will mean an efficient and sleek manufacturing process because process integration will be easy), then developing its particular skills on manufacturing and supplying high-quality components, structures and services to the shipyard becomes easy. In this work, we investigate into process outsourcing to explore which are the processes that can be outsourced in an integrated model. Additionally, though, it is well researched that the subsidies given in one particular country affect adversely the shipbuilding industry in another country; but still there is a no international law which governs shipbuilding industry. Also, since ships are assembled with materials and items that are manufactured independently, so shipbuilding falls also outside the World Trade Organization (WTO) multilateral rules governing unfair business and manufacturing practices. We investigate strategies for a medium scale shipyard to survive in the fiercely competitive world of shipbuilding. Finally, two case studies driven by real world data and applications are presented to show the applicability of the presented model, and ideas.

Keywords: lean shipbuilding, process outsourcing, strategic alliances

Safety Assessment in Terms of Freeboard
Yoshitaka Ogawa, Shigesuke Ishida

ABSTRACT
For further improvement of ship safety, the safety level of a current regulation should be verified. Because some requirements of the regulation had been provided empirically, it is important to verify the safety level in terms of freeboard, which is one of factors for the safety of a ship. In particular, there has been a significant change in terms of ship types and its size after the provision of the current international regulation of the freeboard. It is important not only for conventional ships but also for new type of ships to clarify the safety level and the technical background in the current regulation. Based on this background, the safety level in terms of freeboard and sheer was assessed by means of a series of model tests and an analytical study. It was confirmed that a freeboard, which is provided by the current regulation, ensure the adequate safety level in terms of deck wetness. It was also confirmed that there is room for the modification of a standard sheer in the current regulation.

Keywords: freeboard, load line, safety, deck wetness, wave response, standard sheer

Analytical Investigations on Double Hull Tanker Subjected to Impact Loads
Manu Mathew, Dr C G Nandakumar

ABSTRACT
Tankers are used for carriage of oil and other liquid cargo in bulk. If any damage occurs to side or bottom shell it will cause oil spillage and the subsequent pollution will have catastrophic impact on marine environment. As a remedy, double hull tankers are being used, in which the cargo spaces are protected from environment by a double hull dedicated to the carriage of ballast water. This double hull not only makes the structure leakproof to a great extent but also enhances the strength of the hull structure in bending and shear. But when subjected to impact like explosive loads, even this double hull structure may fail. Tankers subjected to explosive loads are becoming a subject of great interest due to increasing public awareness about ship safety and potential harm to the environment. Tankers are likely to be subjected to impact loads like standoff explosion of mines actuated by proximity fuses and torpedo warheads. So the impact loads generated by the underwater explosion and the subsequent effects of it on the double hull is taken up for detailed study. Numerical investigations are carried out on a double hull tanker designed as per LRS. The double hull structure is modeled using thin plate elements and the finite element analysis of the double hull structure is performed using finite element software NISA. Linear elastic analysis is carried out for the structure to study the effect of impact load due to underwater explosion. The ultimate strength of the double hull is estimated based on geometric nonlinear analysis. Free vibration and transient dynamic analyses are carried out and dynamic response has been reported.

Keywords: stiffened Plates, impact Loads, Finite Element Method, geometric nonlinearity, transient dynamic analysis.

Mathematical Modelling of Cathodic Protection of Hull Surface
A.Mathiazhagan

ABSTRACT
The use of sacrificial anodes on ship hulls has become standard practice in order to preserve the structure and to protect coatings. However corrosion protection may be inadequate due to improper anode distribution / location, inadequate anode numbers, or unsatisfactory level of anode current output. This paper deals with basic principles of cathodic protection, design of sacrificial anodes for ship's hull and presents a simple mathematical model for deciding anode placement to ensure adequate corrosion protection.

Keywords: Cathodic protection, sacrificial anodes, current density, protective coatings.

Hydrodynamic Stability of Fluid Flow through a Flexible Pipe with Outer Rigid Shroud by the Energy Method, Part-2: Axisymmetric Disturbances
Munendra Kumar, P.K. Sen, A.K. Raghav

ABSTRACT
In this paper we study the stability of compliant pipe flow, considering a visco-elastic pipe with an outer rigid shroud and with Hagen-Poiseuille flow through the pipe. Here axisymmetric disturbances are considered. The coupled fluid-solid equations have been solved numerically by the Sen and Arora method. Stability of surface flow of a ship can be used to set up criterion for drag reduction on such bodies, requiring special surface materials. Energy methods have been rigorously developed, both for the fluid-side and for the solid-side, for the axisymmetric disturbances. The importance of the various terms in the energy equations are analyzed.

Keywords: Stability, flexible pipe, visco-elastic material, drag reduction, normal + tangential (N+ T) compliance.