Seaway 7 has successfully installed a monopile foundation using dynamic positioning, clearing the way for the process to be used on the Hollandse Kust 1 & 2 and 3 & 4 offshore windfarms
Following what it described as a “multi-year innovation programme,” including extensive data collection during numerous monopile installation campaigns with floating crane vessels, the development and validation of a simulation model and the modification of vessel software, Seaway 7 said it has confirmed the feasibility of installing large monopiles using dynamic positioning (DP).
In a demonstration off the coast of The Netherlands, Seaway 7’s vessel Seaway Strashnov successfully installed and removed a 6.5-m diameter, 600-tonne monopile whilst in DP mode, remaining within inclination tolerances using a motion-compensated gripper.
DP is a technique used to automatically maintain a vessel in its position and/or heading or on a predefined track by use of its thrusters and/or rudders. Installing large monopiles from a floating vessel controlled by a DP system has long been a challenge because of residual vessel motions due to DP mode inaccuracy.
A number of solutions have been proposed, including using a motion-compensated ‘smart outrigger’ of the type used in the demonstration.
In April 2019, Seaway 7 was selected by Vattenfall to install the monopile foundations for the Hollandse Kust Zuid 1 & 2 offshore windfarms in the Netherlands, and Vattenfall has confirmed to OWJ that the monopiles for that project, and for Hollandse Kust 3 & 4, will be installed on DP.
Seaway 7’s envisaged scope of work under the contract includes transporting and installing 76 monopile foundations and laying the inter-array cables.
Monopile foundations are usually installed by a jack-up vessel or by a floating heavy lift vessel that is maintained in position by moorings.
A jack-up needs time to jack-up out of the water before installing a turbine and a heavy lift vessel needs time to anchor itself in position. This slows down the rate at which foundation installation can take place.
With monopiles increasing in size and with existing jack-ups coming close to their load-carrying limits, it has been argued that heavy lift from a DP vessel could be a more efficient choice for monopile installation.
Riviera Maritime Media will host the European Dynamic Positioning Conference in London on 4 February in 2020.