Double whammy of Aqualis expertise

Aqualis Aberdeen General Manager, Martin G. Brown and Marine Manager, Ken Roby, addressed the Marine Safety Forum (MSF) in Aberdeen on the 24th of November on “The Challenges Associated with Quayside Moorings for Drilling Rigs and Vessels”. 

During the present low oil price a number of drilling rigs (semis and drill ships), which would normally be drilling offshore, have been down manned and bought into shore for stacking until market conditions improve. These rigs are equipped with moorings systems which have been optimised for offshore mooring, but such spreads are far from optimum for inshore mooring. The presentation (click here to download) included examples of where semi-submersibles and ships have broken free of quayside moorings and caused significant damage to other vessels, bridges, breakwaters and quaysides. Clearly the potential for loss of life or possible pollution when any vessel is freely drifting in an enclosed area in poor weather conditions is high. 

Quayside mooring in general is difficult due to the following:

• Relatively short taut lines which can quickly lead to high tensions when vessels surge or heave
• High consequence of failure given the proximity to shore, other expensive assets and limited response time due to proximity
• Potential lack of suitable or degraded connection points on the vessel and onshore, e.g. bollards/bits
• Uncertainty in the calculation of environmental forces due to metocean data return period, wind shear effects, and shallow water blockage effects, etc
• Potential limitations on the ability to adjust moorings and balance the line tensions in adverse weather conditions
• Potential difficulty in knowing the actual tensions in the lines, in other words, a lack of instrumentation
• Potential for failures over time due to chafe points and abrasion including regular tidal range  
• Larger vessels may now be moored with stronger ropes on existing old and degraded bollards

Clearly there is a needed to have a two-pronged approach for quayside moorings, one which is suitable for trading vessels, which are not long term moored and are manned, versus rigs which may be unmanned and cold stacked. It is interesting to note that when rigs are moored offshore it is normal practice for a location approval certificate to be obtained in accordance with Underwriter requirements. However, when in inshore or quayside moored it does not appear to be standard practice to obtain a location approval, despite the inherent risks. 

Aqualis is keen to work with the industry to develop best practice for mooring operations both inshore and offshore. It seems the inshore side of rig mooring has been somewhat neglected when oil prices are high, hence the need to improve practice before any new serious incidents occur. 

For further information contact:  martin.brown@aqualisbraemar.com at Aqualis’s Aberdeen office, tel +44 (0)1224 443545