Salvage operation for tanker "Grigoriy Bugrov" that had 6138 t of cargo (masut) onboard at the moment of accident was completed successfully
On 25.10.2011 convoy with the emergency vessel arrived to the port of Astrakhan. At 17:45 "Grigoriy Bugrov" was moored at the berth No.3 that belongs to the special enterprise CJSE "ECO+".
On October, 13 at 14.32 tanker having onboard 6138 tons of cargo (masut) and stores (44 tons of diesel fuel, 1,5 tons of lub. oil, 5 tons of oily water and 30 tons of fresh water) has impacted at unknown underwater object. After collision in short time engine room has been flooded, vessel has stopped, electrical plant has failed. Vessel's list became of 27 degrees and simultaneously there was huge trim aft. In a result the tanker grounded by stern at the point with coordinates 44 dgr. 28'08" N, 48 dgr.12'06" E. (northern part of Caspian Sea, 75 miles from Volga mouth and 94 miles from port of Makhachkala). The crew in amount of 11 person has been rescued by dry cargo vessel "Amur 2515".
Cargo spillage was avoided, because tanker "Grigory Bugrov" in 2005 was significantly re-equipped under project of the Marine Engineering Bureau with full replacement of a cargo zone and hull renovation for 2SS level (hull strength corresponds to 10-years old vessel). After that re-equipment vessel fully complies with requirements of MARPOL Convention (including requirements due to double bottom and double sides).
For salvage operation coordination working group was organized at RosMorRechFlot such as Branch of eliminating accident fall-out in Astrakhan. Specialists from RosMorRechFlot, GosMorSpasSluzba, North Caspian Marine Salvage division, Novorossiyk Marine Salvage division, Baltic Marine Salvage division Marine Salvage division were included in this branch.
Captain of marine port of Astrakhan Magomed Abdulatyipov effected control for the whole salvage operation directly at the place of accident.
From 18:00 of October 13 Emergency Response group from Marine Engineering Bureau started providing tanker salvage with calculating service due to directive of Federal Agency of Marine and River Transport.
1577 prj. motor vessel "Grigoriy Bugrov" (L x B x H = 128.6 x 16.5 x 5.5 m) is a steel single-deck double-screw tanker of mixed river-sea sailing region of IISP class, with double bottom and double sides, with forecastle and poop, with trunk, with engine room and pump room located aft, with 8 cargo tanks.
Main watertight bulkheads are placed on fr. 27, 24, 61, 79, 97(133), 151, 169 and 196.
Frame space is of 400 mm in the fore end, 600 mm in the aft end and 660 mm in the cargo area.
During renovation part of vessel's hull in the region of fr. 34-169 was produced anew with alternated geometry in accordance with MARPOL requirements (double bottom height of 1100 mm in CL and of 1300 at inner bottom). Also 1500 mm height trunk was constructed. Section modulus of the middle part of the newly built hull had 16% reserve comparing with IISP class requirements. Hull elements' thickness in the middle part of the hull was increased in order to meet class requirements.
Unlike usual "Volgoneft" tanker "Grigoriy Bugrov" had got 4 groups (not 2 ones) of ballast tanks in the middle part of the hull. This moment facilitates vessel's position during accident.
Numerical model of the accident situation from the trim, stability and strength was worked out till 19:00 on 13.10.11. After numerical model was improved due to new information and subsequent prompt recommendations for the emergency branch were made.
Taking into consideration values of list and trim it was clear that due to bottom shell damage some tanks have been flooded, namely: PS ballast tanks 23, 11 and 13, ER and steering gear room, some poop compartments. Probably there was damages at ballast tank 9 PS.
At the beginning about 2800 tons of water flowed into vessel (about 1600 toms into ER, about 1200 tons into PS ballast tanks 25, 11, 13). Later on water flowed into compartments of poop and superstructure at PS, so list increased up to 30 degr. and total water amount was about 3000 tons.
Due to non-symmetrical flooding ship position was characterized by huge list (30 dgr. PS) and huge trim (4.5 m aft). Fore part of the vessel was afloat due to buoyancy reserve of the fore compartments and empty spaces within cargo tanks.
Stresses in the hull in such condition (without wave component) were within acceptable bounds. But situation was able to change in a cardinal way in case of storm.
The most dangerous zone was in the region of the pump room (in front of superstructure); still water bending sagging moment here was of about 59500 kNm. Bottom was tight, but it wasn't dangerous when moment was of such small value. But then hogging increased due to cargo discharge from aft tanks, so danger of hull breakage appear because this region is a weak place for "Volgoneft" vessels type.
Note. Vessel's cargo zone was newly built, but aft end of the vessel (beginning from pump room) was kept from the initial hull with transverse framing system and small thickness of hull elements.
Damage stability calculations showed real problems with dynamic stability (there was ability of vessel's overturning from waves impact).
As a result first priority tasks were defined, as follows: decrease aft draught (making vessel's afloat) and list decreasing with simultaneously strength control at the area of pump room.
Main aim was to get vessel's conditions with maximal draught less than 4.2-4.3 m (for providing ability of tanker's towage to Astrakhan.
Action variants were analyzed, as follows.
1. Hermetic sealing flooded compartments and their discharging:
• poop compartments (because of big free water surface;
• ER and steering gear room compartments (because of big aft trim, huge stability and buoyancy loss and, as main, for significant hogging moment that was dangerous for hull in the area of the pump room);
• ballast tanks (11, 13 and 25) because of list.
2. Cargo discharging.
3. Combination of above two methods.
Prompt calculations were effected. They showed that it was necessary to work out variants 1 and 2 simultaneously.
After discharging cargo tank 7PS (846 tons of cargo) hogging moment in the dangerous zone increased up to 85900 kNm. It was permissible value but noticeable. More over there was bottom damage with unknowable sizes (at the moment of calculations work out).
After discharging tank 7 PS it was necessary to discharge tank 5PS in order to decrease list. Thus hogging moment decreased down to 42000 kNm; list decreased significantly and dynamic stability became better.
So recommendations were issued as follows:
• to discharge cargo tank 7PS for maximal level;
• to provide discharging cargo tank 5PS (it was noted that during this stage list to StB should appear, and after such moment discharging tanks 5PS and 8StB should be done simultaneously till reaching necessary draughts and list eliminating);
• to press water out of ballast tanks 11 and 13, then 25 and 9; then out from ballast tank 12 (later water in ballast tank 12 was discovered; evidently this tank was flooded after accident as a result of air pipes damage during storm on October, 19-21);
• to provide hermetic sealing and discharge poop, steering gear room and ER compartments.
It was foreseen to unload cargo from tanks 6 and 8 (symmetrical ones for tanks 5 and 7) in order to eliminate list.
When stern started moving up further water discharging from ER was accomplished with cargo transfer from tanks 3 and 4 to the tanks 5 and 6. Aim of this transferring was avoiding vessel's fore trim.
During operation recommendations were corrected in connection with getting actual data on damaged compartments (e.g. ballast tank 12 flooding and breach at the forecastle) and on actual capacity equipment (the pump temporarily placed in a cargo tank 5 had the essentially greater capacity than the one in a cargo tank 7), etc.
Actual dimensions of breakages were detected later when vessel started to float up. Early vessel has "laid" on these breaches.
On October 21, at about 22:00 first breach was discovered. It was placed through the bottom shell in the shoulder region of the ballast tank 9. It dimensions was as follows: 5.5 m length and up to 35 cm width.
Further five breaches have been detected and sealed, as follows: in area of forepeak PS, in area of a ballast tank 9, between ballast tanks 25 and 13, between ballast tanks 13 and 11, and also on the bottom of ER. Lengths of breaches were from 4 to 8 meters with breadth up to 35 cm.
Thus, the tanker has suffered from bottom damages PS on a length of about 96 m (72 % from vessel's overall length) and about of 3000 tons of water flowed into vessel (28% of summer freeboard displacement). Taking into account, that there was onboard also 6138 tons of a cargo and about 80 tons of stores, it is necessary to recognize, that vessel's condition was extremely dangerous and operation with such object was very hard (as they say, "on the verge of possible").
In a result, salvors provided vessel afloat (in the morning on October, 22), heel and an significant trim were avoided, an intact stability was recovered also the hull strength was not damaged.
Till 19:45 of 23th of October all main survivability actions including masut discharge were completed. Amount 4405 cub.m. of cargo was discharged.
On October, 20 Marine Engineering Bureau developed and approved at the Astrakhan RS branch Grounding of tanker towage (2 variants, conveyance to the port of Astrakhan or Makhachkala). Document was developed due to order of Branch of eliminating accident fall-out. Conclusion of this document included, as follows:
1. Wind-wave conditions in the region allow one-time trip in the form of towage by wire without crew with permissible 3% probability wave height of 2.5 m.
2. Damage trim and stability of the vessel during one-time trip meet RS Rules requirements for all inspected cases.
3. During one-time trip vessel's strength with account of damages meet RS Rules requirements with restriction of 3% probability wave height of 3.5 m.
4. For one-time trip restriction for permissible 3% probability wave height of 2.5 m is set. This will provide additional strength reserve.
Such one-time trip was successfully carried out beginning at 24.10.11 at 03:0 and completing at 25.10.11 at 17:45.
Active participation in the salvage operation took newly built marine diver vessel "Stolniy grad Yaroslavl". Vessel was built due to Marine Engineering Bureau project in 2010 by Yaroslavl for North-Caspian Branch of Salvage, Towage and Underwater Service. Customer is RF Federal Agency of Maritime and River Transport.
In a result of salvage operation vessel's crew isn't suffered, cargo spillage is avoided, vessel "Grigoriy Bugrov" is rescued.