Cast iron shells IBOCS-FMGC

Ballast for subsea electrical cables developed by FMGC

Submarine cables are of critical importance for the safe transfer of power generated from wind or tidal turbines. They can be easily damaged by fishing, anchors, earthquakes, fish bites or drilling. The reliable protection of the submarine cables is essential for a stable and continuous power flow.


FMGC cast iron shells are the final product of the collaborative and innovative R&D project IBOCS and are especially designed to fulfill the specific requirements of the MRE sector. The aim of the project was to develop a full range of articulated cast iron shells that protect, ballast and stabilise subsea conducts (cables, pipes, etc) and a semi-automatic installation equipment.

SEM-REV installation

In August 2018, FMGC installed the cast iron shells (IBOCS) - developed to ballast subsea electrical cables - at a depth of 30 metres on the Centrale Nantes SEM-REV offshore test site. These tests are part of the FORESEA project and OCEAN DEMO project (Interreg Europe funding), which aims to help bring Marine Renewable Energy (MRE) technologies to market by providing access to the North-European network of offshore test sites, which includes SEM-REV.

The objective of the tests is to demonstrate the stability of the cables ballasted with these cast iron shells, including under heavy swell conditions. 

Several months of testing

The shells have remained on site for several months and be subjected to extreme winter conditions. These tests also provide comparative data, since three sections of test cables - two equipped with shells of different linear density and the third completely bare - were installed alongside each other.

Through regular on-site measurements, current measurements and cable movements, the impact of the cast iron shells can be easily assessed. The FMGC and SEM-REV teams observed how the shells bear up (resistance, corrosion, etc.) in order to gain unique feedback in an environment representative of offshore wind farm conditions.

Innosea, a Centrale Nantes spin-off, worked with FMGC on shell design methods to calculate the optimal mass required to ensure cable stability on the sea floor. FMGC also equipped the Floatgen foundation - the first offshore wind turbine in France - with clump weights, which are attached to the anchor lines, providing stability to the floating structure.
 
The FMGC is the third company to make use of the Centrale Nantes offshore test site, following on from NEREIS Environnement’s acoustic sensor and the Floatgen floating wind turbine - a European research project involving Idéol, Bouygues TP and Centrale Nantes.

IBOCS project dismantled after almost 4 years at sea

The IBOCS project aimed to test the stability of power cables fitted with cast iron shells during winter storms. To do this, 3 sections of cable were installed in line, equipped with shells of different weights, including an unshelled portion for comparison.  
Photos : Centrale Nantes & FMGC