12 and that the barges 1 2 extend along opposite shorter sides of the jacket in the particular example shown each of the trusses 3 4 lies adjacent to four respective legs 15 of the jacket parts of the trusses 3 4 are then engaged with portions of the legs 15 of the jacket 12 the legs of the jacket and any diagonal bracing are cut and the part of the jacket above the line of the cut together with the deck 13 lifted by the trusses 3 4 and the barges to a position vertically clear of the remaining lower part of the jacket 12 that stage in the procedure is shown in fig5 it will be appreciated that the cutting of the jacket legs and raising of the upper part of the structure is a critical part of the procedure and a more detailed description of it is given later once the upper part of the structure has been lifted clear as shown in fig5 the vessel 10 is manoeuvred back away from the remaining lower part of the jacket using the dynamic positioning system the upper part of the structure is then carried on the vessel to a quay 20 of a yard the vessel being towed by suitable towing tugs which may be replaced by harbour tugs in the vicinity of the yard an advantage of the vessel 10 being formed principally of the barges 1 2 is that the draught of the vessel can be reasonably small enabling the vessel to be docked at various yards fig6.