New deck grillage system maximises efficiency on short term mobilisations

Design and engineering consultancy, Houlder, was contracted by power cable installation and repair specialists Global Offshore, part of the Global Marine Group, to design and deliver a new deck grillage system for the Q1400 Subsea Trencher system. The aim of this project was to maximise efficiency, reducing mobilisation time and costs for short term trenching projects.

Global Offshore’s current Trencher system comprises of a 47Te SWL A-frame, umbilical winch, snatch limiter, supporting equipment and associated container modules. To integrate the system onto a vessel, it usually requires a set of deck grillages. Currently, grillages are designed specifically for each major Q1400 component and for each charter vessel on which the system is mobilised. Underdeck stiffening is often required, adding significant time and cost to each mobilisation. During mobilisation, all parts are lifted, installed individually and then electrically and hydraulically hooked up, requiring significant vessel time and high utilisation of the vessel’s crane. Global Offshore recognised the need to reduce mobilisation times and by taking the majority of the work off the critical path, efficiency increases.

Houlder responded to the engineering challenge by developing an innovative concept design which minimised the charter vessel time alongside during mobilisation. Additionally, Houlder ensured the system fitted the primary vessel but also the sister ship and any vessel of opportunity, guaranteeing the system was modular and adaptive for multiple projects. The deck grillage system was also designed to be road transportable, stackable for storage, and with reduced seafastening to ensure more efficient mobilisations.

Houlder provided underdeck checks for the vessel which were submitted to DNV GL and the entire system installation has been class approved. No underdeck stiffening was required, a significant cost and timescale benefit. In addition, the winch system lift has been designed in accordance with DNVGL-ST-E273 standard as a portable offshore unit.

Houlder deployed the full breadth of its service offering working hand in hand with Global Offshore,  from concept design consultancy through to installation support. The concept design, fabrication and installation was developed within a twelve week period and the system is now in operation on the vessel, the Normand Cutter.

James Smith, Senior Structural Engineer, Houlder, commented: “Using our expert knowledge and problem solving experience has been key to providing an efficient solution for Global Offshore. The value in a specialist consultative approach is crucial to a successful project and our significant experience in marine and offshore engineering has enabled us to design a solution which meets our clients’ needs – flexible, efficient and reduces cost and time for all parties. The first installation of the new system has taken place and it is great to see the system in action.”

Martyn Drye, Engineering Director, Global Marine Group, added: “To go from a concept design to fabrication, approval and installation in a matter of twelve weeks, considering the current COVID-19 circumstances, is particularly impressive and it is a credit to the team at Houlder for their hard work, expertise and collaborative approach. The quality of the design, fabrication and installation has exceeded expectations and we are very pleased with the final solution. We reduced the vessel mobilisation time by 40% and future mobilisation costs by approximately 50% as the grillage system is re-usable for other projects and vessels..”

Houlder is ideally placed to support its clients and partners in providing innovative engineering consultancy with an 80-strong team of experts with a wide variety of experience from numerous industries. Houlder has supported challenging offshore, marine and subsea construction projects for over thirty years from offshore wind farm projects to vessel life extension, highlighting the  breadth and depth of expertise.