OWS

Question 1

2. With reference to the disposal of bilge water from the machinery spaces: a) Explain when it is not permissible to discharge the bilge water overboard, even via an oily water separator; (8)
   b) State the maximum permissible oil content of the overboard discharge. (2) c) Identify the documentation to be completed and state by whom, following such an operation. (6)

Answer 1

a) When the vessel is alongside, anchored or at rest.
If the bilge water originates from cargo pump rooms.
If less than 12 miles off-shore.
If in a special area and no automated stop and logging controls are fitted.
This is to comply with MARPOL: Annex 1.
b) 15ppm.
c) Engine Room Log by watch-keeper and chief engineer.
Oil record book by watch-keeper, chief engineer and captain.
Vessel movements log and ships log by the captain.

Question 2

3. a) Describe the procedure for operating the oily water separator (12)
   b) State TWO ways that the separator could be made to operate more efficiently. (4)

Answer 2

a) Inform the bridge and C/E that you wish to discharge bilge water.
Fill the OWS with fresh water to flush, test the alarm ensuring the discharge stops during alarm state.
Sound bilge holding tank and record results.
Start drawing from bilge holding tank and record result, the separator must be in full auto control.
Log the time when the discharge commenced, the starting volume of tank and position of vessel.
After discharge quantity is reached, stop discharge and close discharge valve. Flush OWS with clean water.
Sound bilge holding tank and record in ER log book and oil record book.
Inform bridge and C/E operation finished.
b) Heat the bilge water to ait in the oil separation.
Auto logging and tracking in the OWS control system.

Question 3

4. a) Describe the operating procedure for using a static oily water separator to discharge bilge water overboard. (8)
   b) State the effect that EACH of the following would have on the efficiency of the separator: i) The addition of heat to the separator (4)
   ii) Agitating the bilge water before it is pumped. (4)

Answer 3

a) The main principle of operation works on gravity differential between oil and water. Generally, in an oily water mixture oil exists as a collection of small globules of varying size, the larger the higher rate of separation. The first stage is a coarse separating chamber, where oily water mixture flows over a series of baffle plates. Due to the movement of the fluid larger oil globules are filtered out and rise to the top where they collect and are discharged. Depending on the type of oil being separated, there will be heating coils in the first stage. The mixture leaves at around 100ppm and slows into the second chamber, where coalescent filters are used, which encourage the smaller remaining globules to join and increase the size. They they rise to the top of the second chamber where they’re discharged, meanwhile the remaining oily water mixture is going through the second set of filters ready to be discharged at 15ppm or lower.
b)
i) Heat added will increase the specific density differential of the oil and water and reduces the viscosity of the oil, which would aid in the separation.
ii) The larger the oil globules, the faster rate of separation. Agitating it will mix the water and oil making the globules smaller, making separation more difficult.