Unique simultaneous lifting operation of sunk floating dock No. 154 and tanker "Volgoneft-263" is completed
On September 8, 2011 at Ilychevsk Ship-repairing Yard simultaneous lifting operation of sunk double-wall steel floating dock No. 154 (length of 225.4 m, width of 45 m, top deck height of 18.05 m, height of pontoons of 5.75 m, dock light weight of 8224 tons) and tanker "Volgoneft-263" (length of 132.6 m, width of 16.5 m, depth of 5.5 m, light weight of 1700 tons) from depth of 17 m was successfully completed.
Full duration of lifting operation was of 3 hours. Lifting velocity specially was not accelerated especially in order to align list and trim of the dock on-the-fly and to avoid appearance of dangerous general deformations of the dock. Same time tanker's position relative to pontoon deck has to be controlled.
During lifting operation all ballast tanks of the dock have been involved. For decrease the risk of excessive pressure onto pontoon deck compressed air was forwarded to the drained tanks when ballast pumps worked. Such decision facilitated pumps' work and created counterpressure onto pontoon deck simultaneously.
It was taking into consideration that during lifting operations there was a real danger of dock's breakage, special attention has been given to ensuring of dock's strength.
During lifting operation water discharge from watertight (aft) part of the tanker was carried out. When sinking vessel was shifted so there was danger of overturning of the tanker during lifting. In order to avoid overturning additional support column bases were arranged under vessel's hull.
Shipyard's chief engineer Igor Baranov was a head of lifting operation. For underwater works fulfillment and help in lifting works "SPTR" company was involved (Sergey Kuvshinov is a director, Roman Shulevskiy is a chief engineer). "SPTR" company has significant experience of lifting and diving works.
The lifting project has been developed by company "Kosatka" (Oleg Lukyanenko is a director).
Several variants of lifting scheme were considered during operation preparing. As a result variant was accepted that included lifting of the dock together with the tanker kept on the pontoon deck. Lifting forces have to be produced by recovering water-proof of dock's and tanker's hulls with further water discharge from these hulls.
Dock's strength and stability were checked by Emergency Response Service group from Marine engineering Bureau (Alexander Nilva, Ph. D and Andrey Solov'ev, Ph.D). Behaviour of dock modeling was carried out. Strength and stability calculations were been made for different lifting variants.
For the operative control of dock's strength experts of the Bureau and Shipyard have manufactured and placed mechanical tensometers (with one-rev indicator) onto dock's top-deck.
Totally 10 tensometers were arranged on top-decks of Stb & PS walls. Tensometers were placed at the every interpontoon joint. Thus it was provided on-line control of dock hull's strained condition in order to avoid hull's breakage.
Large amount of preparing works was fulfilled with the hulls of both objects in way to close holes that corrupted objects' watertightness. Air pipes of all dock's ballast tanks have been restored. Watertightness of StB safety deck also was restored. Electric wiring and ballast pumps' gears were replaced.
Now the floating dock and the tanker are surveyed and prepared for repair.
Some word of history. On May, 22nd, 2011 at the night time from Sunday to Monday outside water inflow has started into last two dock's pontoons (5th and 6th). The dock has got trim of about 5 degrees and touched ground by its aft end.
The dock' sagging has increased, so decision to fill all ballast tanks with outside water in order to place dock fully onto ground was accepted. This decision kept dock from breakage.
Approximately by 04:30 on May, 23rd the dock has been placed onto ground. Only top deck was kept above waterline (at average height of 0.5 m).
Tanker "Volgoneft-263" that was in the dock has sunk together with dock due to technological cuts at the fore and aft parts of the vessel's hull. After sinking the vessel stayed in the dock but has shifted in the longitudinal direction and turned across dock. Only single tier of the vessel's deck-house was kept above waterline.
Due to sinking dock's engine room (in the right side wall) was flooded. All electric wiring and ballast pumps' gears were destroyed.