A Rational Approach to FPSO Hull Configuration Selection
Authors: Wang Mark , McNelly Preston , Serratella Chris 
Published: October 2008

An important decision in development of a new-build shipshaped FPSO is to decide what hull internal configuration should be used. The choice can vary across the spectrum from a conventional single skin hull to a complete double hull. Selection of the most appropriate hull configuration requires consideration of many factors, some with conflicting requirements, which makes the selection process complex. This topic has been discussed frequently in various segments of the offshore industry with no conclusive path forward.

A systematic, rational methodology is presented in this paper to assist in making decisions in the selection of hull internal configuration. When utilizing this method, a number of factors are considered, including regional, international and Class Society regulatory requirements, project's functional needs, safety, collision and grounding risks, pollution control, hydrostatic stability, structural strength, construction cost, site environmental data, FPSO operation, inspection, maintenance, and repair requirements, historical experience with previous FPSO projects, etc...... The paper presents a step-by-step approach that should result in the most appropriate, fit-forpurpose hull configuration. In this method, effects of all of the factors are assessed in terms of cost, with both CAPEX and OPEX considered. Therefore, the selected hull configuration using this method is also optimally cost effective. All of the factors are extensively analyzed in this paper to provide some guidelines and useful information for the decision making process.

The method provides a useful tool that can be used to assist future FPSO projects in selecting a new-build hull configuration based on a rational approach and sound engineering principles. When the appropriate data is used, the method could also be used when considering between a single skin conversion candidate and a double-sided single bottom or double hull new-build.

Introduction

In general, hull configuration selection includes selection of external configuration (external hull form) and selection of internal configuration (inner part of hull). This paper actually addresses the selection of internal hull configuration. For the purpose of simplification, "hull configuration" is used here to represent "hull internal configuration".

Selection of the most appropriate, fit-for-purpose hull configuration is an important part of concept development when utilizing a new, purpose-built, ship-shaped Floating Production Storage and Offloading (FPSO) system as part of the field development solution. It is perhaps one of the most difficult subjects that most new-build FPSO projects must deal with. Each project may have particular features but the general procedures for the decision-making are similar. Unfortunately, to the best of our knowledge, there has been no systematic method or procedures published for such a decision making process.

The possible choices for hull configuration can be single hull (SH), double hull (DH), or double-sided single-bottom (DSSB) hull, and single-side double-bottom (SS-DB) hull. As shown in Figure 1, all four configurations can be found in the existing FPSO fleet.

Figure 1 below shows the percentage of the world's FPSO fleet by hull configuration (conversions and new-builds), based on an ABS date base. Although SH FPSO's still make up a large portion of the total FPSO fleet in operation, they are mainly those that were converted from trading tankers