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needs to be checked carefully before committing to a surplus tanker for conversion.

The converted FPSOs often offer the shortest and the cheapest path to

initiating production. Their main limitations include a lack of ability to operate dry

trees, and technical feasibility of mooring in very deep water in harsh

environments. The turret assembly can become very complicated and difficult to

integrate with the hull.

6.1.1 FPSO Hull Design

There are four principal requirements that drive the size of a typical FPSO:

1. Provision of oil storage capacity compatible with the production rate and

offloading arrangements, i.e. shuttle tanker turnaround time

2. Provision of topsides space for a safe layout of the process plant,

accommodation and utilities.

3. Provision of displacement and ballast capacity to reduce the effects of
motions on process plant and riser systems.

4. Provision of space for the production turret (bow, stern or internal). and
the amount of hull storage capacity lost as a consequence (new-build or

conversion).
As water depths increase, the sensitivity of the FPSO mooring and riser

systems to wave frequency motions increases rapidly. The FPSO hull form can be

optimised to counter this by varying primarily the length, width, depth, draft and

mass distribution.

The hull length can be adjusted with respect to the expected wave lengths to

ensure that the extreme environmental conditions do not generate wave lengths

located in the range of the peak heave and/or pitching responses, thus reducing the

turret vertical motions and associated dynamic loads. The hull form can also be

adjusted in order to control rolling and pitching behaviour thus reducing riser

bend-stiffener design requirements, particularly for transverse conditions. This

optimisation also reduces the need for special topsides process equipment design

requirements such as baffles for separators.
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