Comparison of Aluminium alloy and steel materials as deckhouses for offshore support vessels

Abstract

Aluminium alloy is a relatively more expensive material than steel although its weight is one-third of the steel. Thus the use of steel as a structure adds additional weight by 60%. This paper reviews the merit and demerit of Aluminium alloy and steel focusing on fabrication and assembly, and maintainability cost typical of a 60.0m offshore support vessel operating between Kemaman port and offshore oil rigs in the South China Sea. Mathematical equation was used to calculate the weight of the materials used to construct the deckhouses. Also, net present value and payback period calculations were performed to indicate the economic benefit between the two materials. The initial deckhouse construction cost for Aluminium and Steel are USD 45507 and USD 26808 respectively involving 23.5 metric ton for Aluminium and 67.0 metric tons for steel. In term of investment, offshore support vessels using Aluminium have shorter payback period of 7.9 years and 8.4 years for steel inclusive of the costs of maintenance and operation. This exercise indicates Aluminium alloy is more economical than steel as construction material for deckhouse of offshore support vessel due to its light weight, lower maintenance and increase earning capacity (more cargo).