SRI vessels, indispensable for offshore wind

Subsea rock installation (SRI) vessels are widely used in the offshore industry, stabilising and protecting subsea pipelines, cables and other structures at the sea bed. For the offshore wind industry, SRI vessels also lay protective coverings of rock around turbine foundations, to avoid scouring.

Ulstein has a proven track record in developing these highly specialised vessels, the most recent reference being the highly innovative DP3 fall-pipe vessel ‘Bravenes’. It is the latest fleet addition for the Netherlands based contractor Van Oord, featuring the unique ULSTEIN X-BOW® design and capable of handling a wide range of rock sizes (1-3», up to 60-300 kg) down to 1,000 metre water depth.

The vessel is equipped to perform three different types of rock installation:
- via a flexible fall pipe through the moon pool for deep water operations
- via a flexible fall pipe over the side for medium water depths
- via a tremie pipe over the side

The latter configuration allows the vessel to install rock very close to offshore structures in shallow water, such as turbine foundations.

Besides its high flexibility in operational rock dumping modes, it is the lay-out of the vessel that makes a big contribution to the innovative nature of the vessel design. It is the only vessel in its class that features an open top notation, an achievement that Ulstein is especially proud of and rarely seen in offshore vessels.

Together with Van Oord, Ulstein also developed the main Fall Pipe Deployment system (including skidable automatic flexible fall-pipe tower), putting a strong focus on simplicity. By mechanizing the systems as much as possible, higher levels of safety and control and minimising human interaction is achieved when deploying and recovering the fall pipe. The result has been a truly integrated ship design, fully optimised for its core operations: installing rocks subsea.

The rocks are transferred by conveyor belts below the holds to the central hopper, from where the rock enters into the flexible fall-pipe. Using a fall-pipe ROV to accurately steer and position the fall-pipe, the rock is placed at the pre-determined location.

Bravenes has been built at Sinopacific Shipbuilding’s Ningbo yard in China and was designed by Ulstein Design & Solutions B.V. in the Netherlands.

Previous fall-pipe references include the 'Flintstone' vessel.



Subsea rock installation vessel, suitable for installation of a wide range of rock sizes through a fallpipe in the moonpool, through a fallpipe over the side or through a tremie pipe over the side. With a DW of 14,000t, a length of 154 m and a beam of 28 m, the vessel can operate in depths of more than 600 metres.

Main dimensions
Feasibility studies
Feasibility studies

Feasibility studies

Ulstein carries out multiple studies, one of which is feasibility studies. A feasibility study provides the insight for selecting the best solution towards CAPEX, OPEX and environmental impact. Here's an example of how we can carry out an energy storage feasibility study.

Feasibility studies

Please contact us for more information

Marketing and sales manager Nick Wessels
Nick Wessels

Marketing & sales manager

Tel: +31 620 43 0465