Ballast system

BALLAST SYSTEM
System for ship stability :
• To keep draft position for safe maneuver (keep the center of gravity on safe position by filling-in seawater in ballast tank)
• Unloading condition ballasting
• Full load de-ballasting
• Calculation of ballast system= f (loading/offloading time)

COMPONENTS of BALLAST SYSTEMS
1. Sea chest (inlet)
2. Main Pipe
3. Branch Pipes (if manually operated)
4. Valves and fittings
5. Ballast Pumps
6. Ballast Tanks
7. Overboard

BALLAST TANKS
• Volume ~ 10% to 15% vol displ of ship
• Location : d/b tank, f/p tank, a/p tank, wing tank
• Cofferdam to be provided between ballast tank and f.o. or l.o. or drinking water tanks.
• For tankers: ballast tanks are to be separated from cargo tanks (in d/b tanks)
rules on segregated ballast tank

BALLAST PIPES
• Material: galvanized steel ref to BKI vol V (rules for material) sect 4.
• Thickness: category D (table 11.5 BKI vol III sect 11).
• Pipe joints: butt-weld, sleeve-weld, or flanges (table 11.11 and 11.12 BKI vol III sect 11).
• Pipes shall be provided with ‘flexible means’ (dresser coupling or U-bent) to overcome longitudinal deflection of the vessel and expansion due to change of pressure.
• Lay-out of pipes:
– Independent: branch pipes on each ballast tank lead onto ER.
– Ring Main System: one or two main pipe lead onto each ballast tank and further lead to ER.

LAYOUT OF BALLAST LINES
1. Type Independent (Main & Branch pipes 􀃆 manually operated)
• Each Ballast tank each branch pipe.
• Branch pipes are connected to main pipe that further connected to ballast pump. (Branch pipes are to be suction pipes or discharge pipes)
• Manually open-closed ballast valves in ER.
• Simple system (manual).
• Requires lots of pipes.
• Newest rules of ABS not allow the use of this system (leaks on branch pipes in the ballast tank may lead to additional seawater in unintended ballast tank, hence to change stability)

LAYOUT OF BALLAST LINES
2. Type Ring Main pipes
• All tanks connected to main pipe (as a ‘ring’)
• Suction / discharge directly connected to Ring Pipe.
• Each suction / discharge pipes in ballast tank to be equipped with remotely operated valve (using pneumatic or hydraulic actuators or mechanical).
• Remotely open-closed ballast valves to be located in ER or on Main Deck (Deck-stand valves)
• More complex system (due to the use of hydraulic/pneumatic or deck-stand).
• Less pipes to be used.
• Newest rules (ABS) recommend the use of this system.

SIZE OF BALLAST PIPE
• Din = f (Qballast, Vflow)
– Qballast= (total Volume of ballast tanks) / (duration to empty ballast tanks)
– Vflow= 2 ~ 4 m/s
• t pipe : category D (6,3 to 8,8 mm acc to Dout)

BALLAST PUMP
• Q = (total volume of ballast tanks)/( time to empty all ballast tanks)
• Time to empty = f (time to loading/unloading) typically 6 ~ 40 hrs
• Location: suction: in d/b , disch: on o/b
• Tot Head = Hz + Hp + Hv + tot H-loss
– Hz = (Hz suction in d/b) – (Hz disch on o/b) = (T+0.75m)
– Hp = (Pdisch– Psuct)/ρg
– Hv = (V2 disch– V2 suct)/2g ~ 0
– Tot H-loss = head loss total calculated on the longest Pipe

BALLAST PUMP
• Centrifugal pumps (self priming and electrically driven)
• Min 2 units
• Location: on tank top on E/R (usually fore of ER close to sea chest main pipe))
• Pay attention on NPSH of the pump

(diambil dari pipa udara blogspot)