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The scope of a BWTS modification varies. Some modifications require replacing or adding components of the BWTS, such as replacing the filter element or adding additional sensors to monitor safe operation of the BWTS within its system design limitations (SDLs). For other modifications, only the system control software is updated without any physical changes to the BWTS. Some modifications are also made to implement improved technological designs for selected BWTS components, resulting in physical changes to the earlier approved BWTS.

An example of a typical modification is the upgrade of a BWTS, which was type approved based on the IMO G8 Guidelines adopted by Resolution MEPC.174(58), to comply with a later USCG type approval and/or IMO type approval based on the BWMS Code adopted by Resolution MEPC.300(72).

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