Finding efficient and safe ways to access turbines has preoccupied the offshore wind industry for years. Until now, most effort has been spent constructing and testing methods of landing near the access ladder. Engineers would then climb 15-20 metres to the turbine platform and access the nacelle through the tower. Vendors of such systems use different means of "connecting" the vessel to the transition piece and keeping the vessel as still as possible in relation to the wind turbine ladder.
The vessel can flank the turbine for direct access from the vessel to the ladder, or an access system can be used to lock the vessel to the outer frame of the ladder. Some companies propose a combination of these methods.
When the weather is particularly challenging, it is even more difficult to climb slippery ladders and make vessels stable without damaging either the vessel or the turbine — and without excessive risk to the crew.
Gangway access
Gangways present a new solution that removes the risk associated with the ladder access method. Uptime provides gangways in lengths from six to 25 meters, which are ideally suited to wind turbine access. The gangways are manufactured by Marine Aluminium, a vendor with 40 years’ experience, and others.
The telescopic arm of the gangway is aluminium, which combines strength, low maintenance requirements and reduced weight. A 20-metre telescopic gangway and an adjustable height pedestal allow the crew directly to access the platform. Advanced motion compensation enables access even in bad weather.
The internal aperture and strength of the gangway means several crew members can use it simultaneously. The closed roof reduces risk from falling objects such as ice, snow, parts and tools. Another advantage popular with users is that once contact with the platform has been made, access is continuous for as long as needed and the system is open for unimpeded access from the platform to the vessel.
Spares and tools can also be easily and safely transported from one end to the other. One of the accessories available is a custom trolley and pallet carrier that will facilitate transport of equipment through the gangway. With this carrier, equipment and parts too heavy for personnel to carry can be moved effortlessly. If this is integrated with an elevator system on the vessel, the use of cranes and hanging loads can be avoided. It is possible to transport goods up to a tonne through the gangway even when it is not landed.
Safe landing
The gangway can be supplied with two different transition solutions at the end: either a rubber-faced landing cone, which is landed onto the platform, or a bumper, which is pressed against the platform edge. With either solution, weight transfer and pressure can be set using appropriate software and monitored by pressure sensors.
Different types of adjustable pedestals have been developed to deal with problems arising from excessive tides and resulting variations in height. This ensures that the gangway can be connected with an initial neutral level (zero-degree incline), which increases comfort and expands the operating window with regard to weather and time.
Hydraulics, electric motors and the control system all have inbuilt redundancies or back-ups, ensuring that safety and operability is maintained even if the vessel loses power or propulsion. Using weather data and statistical information on vessel motion, gangway movement can be calculated and analysed to simulate possible operating windows for customers.
An operator manoeuvres the gangway from a cabin through an advanced onscreen display, multifunction handles and video surveillance. A radio remote is also available. This ensures that the best vantage position can be selected.
Svein Ove Haugen is marketing manager of access solutions provider Uptime International
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