some operations although the techniques are not always proven so jack-up vessels are still likely to be used.


Table 5.23 Envelope of dimensions for jack-up vessels Dimensions Jack-up Vessel


Length Breadth Draught (max.) Number of legs Deck area Spud can area (m2) Types of leg Max. allowable leg penetration 110 – 165m 42 – 50m 6.0 – 8.0m 3 – 6 2,500 – 4,500m2 50 – 200m2 each leg Cylindrical, triangular, truss leg, lattice Site specific, typically 0.5–15m


240. Dynamic Positioning Heavy Lift Vessel: If used at the East Anglia THREE site a heavy lift vessel would need to be capable of lifting heavy loads such as transition pieces and nacelles into place.


241. DP is a computer-controlled system which is used to automatically maintain a vessel's position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors and gyro compasses, provide information to the computer pertaining to the vessel's position and the magnitude and direction of environmental forces affecting its position.


242. DP vessels often make use of azimuth thrusters whereby the propeller is placed within a pod or a duct to allow rapid repositioning of the thruster in response to changes in vessels position. This enables the vessel to stay in a precise location.


243. Accommodation vessel: One or more accommodation vessels could be used as a temporary home to the workers who install and commission the wind turbines and electrical infrastructure at the windfarm. These types of vessels are sometimes known as “flotels”.


244. Windfarm service vessel: Windfarm service vessels are typically much smaller than the jack-up, heavy lift and accommodations vessels and are usually no greater than


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 5 Description of the Development Page 55


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