According to Regulation 11 of MARPOL Annex IV, sewage that has been stored in holding tanks shall not be discharged instantaneously but at a moderate rate while the ship is en route and proceeding at not less than 4 knots; the rate of discharge shall be approved by the Administration based upon standards developed by the Organization.
However, Regulation 11 has been amended by IMO Resolution MEPC.164(56) dated 13 July 2007 and the discharge rate shall now be approved by the Administration based upon IMO resolution MEPC.157(55).
The amended Regulation 11 is applicable from 1 December 2008.
Therefore, the discharge rate table shall be prepared in accordance with MEPC.157(55) and approved by the flag state government where untreated sewage that has been stored in holding tanks is to be discharged.

ClassNK may approve the discharge rate table for and on behalf of the Administration, for all vessels that have an ISPP Certificate issued by ClassNK.
The approval procedure is as follows:
1. Prepare the discharge rate table in accordance with MEPC.157(55)
(1) Calculate the maximum permissible discharge rate using the following formula:
DRmax = 0.00926VDB
where:
DRmax is maximum permissible discharge rate(m3/h)
V is ship's average speed (knots) over the period
D is Draft (m)
B is Breadth (m)
(2) Make a table using the results of the calculations
Average speed is to be recorded in 2 knot increments from 4 knots up to the maximum service speed.
Draft is to be recorded in 1m increments from the minimum operating draft up to the maximum summer draft.
(3) A sample discharge rate table is attached herewith.
2. Submit the discharge rate table to the ClassNK Machinery Department by E-mail (mcd@classnk.or.jp)

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