Installation solution for tidal turbine - First Marine Solutions

Overview

Tidal turbine developer Nautricity Ltd approached FMS in order to provide an installation solution for its prototype grid connected 500kW tidal turbine unit, which was to be installed at the European Marine Energy Centre full scale test site.

This unique device consisted of a gravity base mooring structure with ballast units attached onto the export cable head and a neutrally buoyant turbine nacelle which was mounted onto a swivelling midwater connection point.

FMS’ scope of work was the entirety of the installation – from loadout design and mobilisation through to retermination and connection of the berth cable onto the structure, ballasting the gravity base and finally connection of the turbine generation system.

Approach

Due to the highly tidal nature of the installation site, FMS was required to develop a number of innovative solutions to allow the DP construction support vessel to utilise works-class ROVs during the vanishingly short slack water periods between tides. All operations had to be completed within about an hour, otherwise there was significant risk to the ROV and client assets.

FMS provided Nautricity with a full consultancy package, working with Nautricity engineers to develop the mobilisation and deployment plans, engineer the sea-fastenings and design the mechanical elements of the turbine subsea connection. This required some “outside the box” thinking in order to keep the scale of the operations achievable during the limited number of slack water periods within a neap tidal period.

FMS leveraged its unique position as a supplier of mooring products to provide key components of the mooring system, whilst drawing upon its sister companies, Mooring Systems and First Subsea, to provide logistical and technical support to Nautricity.

Operations

From its fully equipped shore-base in Montrose, FMS assisted in the final assembly and mobilisation of the Nautricity turbine nacelle and mooring ballast, along with the required survey and ROV spreads onto the heavy lift construction support vessel to be used in the works during two phases of the offshore campaign.

Once on site in Orkney, FMS managed the high voltage export cable head modifications, cable connection onto the base and deposition onto the seabed of the gravity base assembly, final ballasting with 300 tonnes of chain, and then connection of the tidal turbine generator.

These operations were conducted during ROV interventions which had to be scheduled around the four, one – two hour slack water periods each day. By bringing significant vessel selection and operation experience to the job, FMS comfortably completed the installation within the approx. 100 hours ROV flight time available over two neap tidal windows. This was achieved despite the fact that wind and swell conditions at the somewhat exposed site were approaching the limit of the vessel crane capabilities.

Results

This operation represented the first stage in a series of turbine proving activities for Nautricity. Ultimately, the holistic approach to marine works – including the equipment delivered by FMS – was demonstrated to be reliable, safe, expedient and cost effective.

FMS provided a hands-on, turnkey service to Nautricity while operating in the financial and time constraints imposed on a renewable energy start up.

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