PURPOSE: To facilitate the installation of equipment on an engine room inner bottom plate by making a void space or a cofferdam under the engine room inner bottom plate into a cooling sea water supply space so as to unnecessitate the disposition of a cooling water suction main pipe on the engine room inner bottom plate.

CONSTITUTION: A low sea chest 1 is provided at one board in an engine room, and a high sea chest 2 is provided on the other board, and a void space or a cofferdam under an engine room inner bottom plate 13 between the low and high sea chests 1, 2 is made into a sea water inlet space 3. The low sea chest 1 is communicated with sea water strainer 6 by a connecting pipe 4 with a stop valve interposed in between, and the sea water strainer 6 is communicated with the sea water inlet space 3 by the communicating pipe 4 with a stop valve 7 interposed in between. The high sea chest 2 is communicated with a sea water strainer 10 by a communicating pipe 8 with a stop valve 9 interposed in between, and the sea water strainer 10 is communicated with the sea water inlet space 3 by the communicating pipe 8 with a stop valve 11 interposed in between. Pipe seats 12 connected to the suction side of a sea water pump are fixedly provided on the engine room inner bottom plate 13 in the sea water inlet space 3.