Guidance on DP jack-ups and use of dumb barges for offshore renewables sector from IMCA

Published on 16 May 2013

An increasing number of members of the International Marine Contractors Association (IMCA) are involved with the offshore renewables sector and for this reason the association has published ‘Guidance for the Positioning of Dynamically Positioned (DP) Jack-up Vessels on and off the Seabed” (IMCA M 223) and an updated version of their information note The Inspection and Auditing of Manned and Unmanned Barges’. Both are aimed at ensuring and enhancing offshore safety.

“The aim of IMCA M 223 is to provide the owners and operators of dynamically positioned (DP) jack-up vessels with guidance to create procedures for going onto and leaving location,” explains IMCA’s Technical Director, Jane Bugler.”A DP system interfaces with the vessel’s propulsion systems to hold the vessel in position against external forces (such as wind and waves) that are acting to move the vessel.

For DP vessels with jack-up capability – when a vessel moves into position on DP but intends to undertake the work on location as a jack-up vessel – there can potentially be excessive stresses induced into the legs during the transitional period from being on DP to ‘leg touchdown’ to soft pinning of the legs. The first leg contact with the seabed will restrict the vessel’s motion which may indicate a position error to the DP system. This could the lead to an increase of thrust of the vessel’s positioning propulsion systems and consequently may impart these excessive stresses on the legs.”

IMCA M223 has sections on Risk Analysis (vessel characteristics; environmental conditions and loading; site specific assessment integrity; and DP specification and performance); Background Material (that encompasses company procedures; vessel procedures; and information for each location); and covers Procedures for a DP Jack-up Vessel Going on and Leaving Location.

Like all IMCA guidance it is free to download from the IMCA website for members and non-member alike. Printed copies can be purchased at £5.00 for members and £10.00 for non-members via the IMCA website at legacy.imca-int.com and from publications@legacy.imca-int.com.

Update of dumb barge information note
IMCA published ‘The Inspection and Auditing of Manned and Unmanned Barges’ as an information note in Autumn 2012. A so-called ‘dumb barge’ is a vessel that is unmanned during transits, does not have its own propulsion and must be either towed or pushed to its destination.

This has now been updated to include a new short section on ballast arrangements and further information on anchoring. This information is also available for download from the IMCA website