SBT , BALLAST WATER MANAGEMENT , SHEAR FORCES AND BENDING MOMENTS - CAPT AJIT VADAKAYIL
Ballast water is used in tankers to increase the draft and thus the seaworthiness and stability. It also equalises stresses on the hull, and improves manoeuvrability and fuel economy.
Some ballast plans have the additional objective of reducing vibration underway. Vibrations of the PV stack can cause the Nitrogen blanket to escape.
To minimise hull stresses, ballast tanks should be filled in the order indicated by the ship’s ballast plan, and in proper coordination with the discharge/ load bar diagrams.
Normal ballast plans produce a trim of between one and three meters by the stern. Careful attention to the trim of the ship can add as much as 0.5 knot to the voyage speed. A good trim is essential for good draining while tank washing.
The master is responsible for selecting a ballast plan for a safe and economic passage, keeping in mind the seasonal weather. Slamming must be avoided and also ME rpm fluctuation ( and over speed trip ) due to airborne propeller.
Before ballasting/ deballasting check the air pipes to ensure free venting. These vents must be checked immediately after starting the operation to double check that the tanks are venting freely.
Whenever possible the initial filling of ballast tanks should be by running in ballast from the sea by gravity .
In general segregated ballast tanks are to be filled to one hundred percent (100%) full. Avoid overflowing the tanks. This can be achieved easily if 2 sets of tanks are ballasted together with off set soundings.
When segregated ballast has to taken in muddy rivers ,or polluted waters the ballast should, where practicable, be changed for clean sea water as soon as possible.
This is to —
Prevent accumulation of mud in DB tanks which are difficult to clean, they also choke the draining holes , thus increasing the ballast ROB. Most chemical charterers calculate the deadweight of the ship ,when the ship is constrained by draft restrictions or has to load to the loadline marks..
Achieve the full efficiency of cathodic protection systems in tanks which rely on this method of corrosion protection
SBT ballast shall not be discharged into the sea without first checking the contents using the sampling ports. The sampling hole should be a single screw type . Port State Control will not accept a sampling port where 4 nuts and bolts have to be removed with spanner. Use your sense of smell too.
If oil pollution of segregated ballast is found the discharge should only proceed when all appropriate precautions have been taken to ensure that no oil is discharged overboard.
Deballasting at loadport must commence immediately on berthing. Do not wait for surveyor to finish his rounds.
When ballasting/ deballasting is done bleeding off from Framo juice, make sure the cargo work is not affected by such diversion.
Ballasting ( SBT ) deballasting times must NOT be entered in the SOF.
No ballast tank must be entered unless the valve is lashed and a sign put---“ Do not open , men inside ”
Unlike oil tankers where the cargo ingress floats on top of sea water ballast, on parcel chemical tankers the cargo could be insoluble but heavier or fully soluble and invisible or partly soluble etc .
The sounding book on chemical tankers must have a column for pH value.
Unlike other types of ships , there are several small SBT ballast tanks on chemical tankers—please remember—the empty refill method is tedious.
As for the flow through method—bear in mind-- if the cargo is water reactive or having high MP ( cold interface ) or if tank preparation is going on elsewhere on ship astern , or riming takes place on deck in freezing weather with heated cargoes underneath, this effort may not be worth it. You may have to choose the lesser of the two evils.
The arrival SBT ballast shall be the minimum compatible with safe manoeuvring, the bow thruster must be fully submerged.
Modern chemical tankers have SBT tanks with overflow orifices ( with valves ) on ship side plating about 60 cms below the main deck plating. This prevents danger of tank rupture when overflowing the ballast.
BALLAST WATER MANAGEMENT
Ballast water log must be maintained in the highest California format on our chemical tankers.
Chief Officer is the ships Ballast Management Officer.
He is responsible for making out the Ballast water exchange plan , maintaining the BWM log and ensuring the ship’s BWMP is ship specific.
Ballast water exchange is mandatory since Feb 2004 in most countries.
The ballast water exchange form must be sent to the proper authority prior entering the territorial waters in the proper format—in USA the format is electronic and checking is automatic. If the form is not filled the right way, it will be returned by the shore computer.
The rules regarding depth of sea and distance away from land for exchange varies from country to country, check the BWMP and if in doubt ask the agent.
Canada and California USA has stringent rules with 200 miles / 2000 metres. In California the reporting has to be done to USCG as well as SLC. Some other countries have 50 miles / 200 metres.
Better check with the local agents well in advance-- be careful--fines are heavy.
More countries are jumping into the Ballast exchange bandwagon--like ROPME.
Any change in the status of tanks after the first report must be followed up by an amended report prior arrival port. Failure to comply can result in huge fines—especially in USA, Australia, Brazil, Canada , Europe etc.
All officers shall read the Company ballast water management plan and also the class approved ballast water management plan which is ship specific and contains the pumping plan.
The entire crew shall read and understand the various BWM posters stuck in the alleyways.
Samples may be drawn from the approved sampling points and tested ashore for salinity, micro-organisms etc –to verify that the exchange is indeed done.
Training records with signatures must be filed in the BWM plan. The training record shall have the following columns—
Date/ Name/ Rank/ Sign/ Verified by/ Status ( on board / signed off )
No deballasting shall be done at port unless the BW exchange plan has been acknowledged by the ballast water authority.
Ballast exchange can be done by –
1) Sequential method or Empty-Refill: Empty and refill tanks. The SF/BM of the ship shall be recorded by the Chief officer . Undue list and slamming must be avoided for safety of life/ ship. This procedure is a weather permitting procedure. If weather does not allow safe exchange the parameters for distance / depth are reduced . This information must be obtained from the relevant source.
2) Flow through method: Overflow tanks using the approved means, without structural damage. Minimum 3 times exchange is required . The capacity of the pump and the volume of the tank must be considered.
3) Treatment with Sodium Hypochlorite or Alternate Method —100 gms / ton or Calcium Hypochlorite 14 gms/ ton. Usually done in rivers of Argentine compulsorily—even if exchange has been done at sea.
Ballast tanks having excessive mud must be cleaned out in the ocean.
Rinse anchors and anchor chains prior entering sensitive ports.
The BW log is different from the ship’s sounding book.
The BW log must have the following essential information:
Separate page for each and every Ballast tank—a running page with information for last 2 years.
Name of ship/ Flag/ IMO number/ Ballast tank number/ Ballast tank capacity on the header.
The columns are—
Start and End point date
Start and End point time
Start and End point Location Lat/ Long ( make sure it is allowable distance )
Volume
Operation of pump Ballast or Deballast ( Load/ Discharge/ Internal transfer )
Exchange method –Empty-Refill or Flow-through
Temperature of sea water in Celsius.
Specific Gravity of ballast water in tank – NOT outside sea-water.
Sea Depth ( make sure it is more than allowable depth )
Signature of Chief Officer
Remarks— a) >300% flow through
b) Internal transfer to correct list.
Each ballast movement must be in a separate line.
The BW exchange form submitted in written or electronic form must have all the relevant columns filled like—
Date
Port of Arrival
Agents name
Total number of ballast tanks
Capacity
Quantity of Ballast on board
The number and identity of tanks to deballast
If any alternate method is used like treatment/ filtration.
History of Ballast water source
History of BW exchange
History of Ballast water to discharge---wrt ---Tanks/ Date/ Posn of ship/ Volume/ Temp/ Method / Sea depth/ SG / % exchanged
The ships Ballast water management plan shall include the following contents—
International, Federal and state ( California )regulations
Discussion on how the ship will comply with the law
Vessels ballast schematics including location of sampling points
Indicate location of BW posters
Training log
Familiarisation contents—pumping plan/ sounding and air pipe plan/ flow through release/ safety precautions/ recording of soundings and stresses.
Safety precautions:
No over pressurisation / Vacuum in tanks
Free surface effect
Riming precautions and cold weather precautions
Stability
Shear forces and bending movements
Torsional forces
Min/ Max drafts ford and aft
Wave induced hull vibrations
Contingency procedures for pump failure , loss of power
Time taken to complete the job
Continious monitoring.
Understanding when ballast exchange should not be done—for ship safety.
The ship is not required to deviate from or delay its voyage in order to comply with the above requirements and should not be required to carry out ballast water exchange if it would threaten the stability or safety of the ship or its crew.
Weather conditions should be such, that in the Master's judgement, the ballast exchange can be safely accomplished without adverse effects of vibrations or sloshing.
In the event of actual or anticipated heavy weather, it may be necessary to alter course, reduce speed and/or heave-to, in order to avoid these conditions, if the timing of ballast exchange operations cannot be changed.
-------CAPT AJIT VADAKAYIL
29 YEARS IN COMMAND
0 comments:
Post a Comment