Design and Installation of Large Advanced Class Saturation Diving Systems on Semisubmersible Fire Fighting and Dive Maintenance Vessel
Authors: Miller Keith 
Published: October 2008

A review is undertaken of the major features of three saturation dive complexes installed by Sea forth Engineering Limited on semi-submersible fire fighting, rescue and dive maintenance vessels for operations in the Northern North Sea. The paper outlines the evolution of the design from the Phillips SS which was the world's first such maintenance and firefighting vessel through the MSV Tharos to the latest semi-submersible Multi-Function Service vessel currently being built in Finland for Shell/Esso. The design of the chamber complex and associated ancillary equipment is highlighted.

The design of the handling system for launch and recovery of the submersible diving chamber or bell is a key factor in ensuring a low level of system downtime and the results of computer modeling is discussed. The special arrangements for handling the swimming manned tethered vehicle "Mobile Diving Unit" MDU from the MSV Tharos and the free swimming diver lockout submersible from the Shell/Esso MSV is also discussed.

Each of these submersibles incorporates a hyperbaric Rescue Chamber in the design and the operation philosophy, launching technique and overall concept design development is discussed.

The installation of such large and complex systems within a shipyard represents a number of problems particularly in respect to pipe work and associated penetrates through ship's bulk heads. Experience with performing and precommissioning of such systems to eliminate shipyard activity is discussed.

Introduction

The recently perceived requirement for semi submersible vessels for firefighting and rescue operations in the exposed location in the Middle and Northern North Sea has created an opportunity, by exploiting the favorable motion characteristic and availability of surplus space and deck loading, to provide an extensive saturation diving capability. Each operator has a widely differing requirement for underwater activities and the emphasis placed on the diving complex as a part of the overall multifunction role varies considerably. Differences would appear to be related to numbers of platforms serviced and their type, water depth and weather, requirements for other "competing" functions such as accommodation, workshops and heavy lift facilities. Each vessel therefore reflects an assessment of the utility of these different functions and an optimized choice between these; this has been discussed more fully by others1.

A discernable trend has been the increasing size and complexity of the living complexes, handling systems and submersible vehicle systems, as can be seen from Figure 1.

Living complexes

The design evolution of the semi-submersible maintenance vessel type is a major study in its own right and the changes between individual vessel reflects differing operational philosophies as well as changes due to development in diving operations1.

The Phillips SS diving system has a 12 man living complex consisting of an 8 man living chamber attached by a side man-way to a transfer lock which is in turn side mated to a 12 man twin lock rescue chamber which has an alternative role as a 4 man living chamber. The 2 man submersible diving chamber bottom mates to the top of the transfer lock and the overall system 1ayout is shown in Figure 3.