Section 13 Machinery and raft seatings

13.1.1 Main and auxiliary engine seatings are to be effectively secured to the hull structure. The scantlings of such seatings are to be adequate for the intended purpose, with due account taken of the gravitational, thrust, torque and vibrating forces together with the load increases resulting from sea motions and shock which may be imposed upon them.

13.1.2 In determining the scantlings of seats for engines, consideration is to be given to the general rigidity of the engine itself and to its design characteristics with regard to out of balance forces.

13.1.3 The longitudinal girders forming the engine seatings are to extend as far forward and aft as practicable and are to be adequately supported by transverse floors or brackets. The webs of the longitudinal girders are to be welded to the bottom shell plating.

13.1.4 The seats are to be so designed that they distribute the forces from the engine(s) as uniformly as possible into the supporting structure. Longitudinal girders supporting the seatings are to be arranged in single or double bottoms, and are, in general to extend over the full length of the machinery space. The ends of the girders are to be scarfed into the bottom structure for at least two frame spaces. Adequate transverse brackets are to be arranged in line with floors. Half floors, transverse brackets or hanging brackets will in general be required under the top plate in way of holding down bolts.

13.1.5 Where rafts are proposed for supporting the main and auxiliary engines the arrangements of such rafts are to be in accordance with Vol 2, Pt 1, Ch 3 Requirements for Design, Construction, Installation and Sea Trials of Engineering Systems

13.1.6 Welding in way of all machinery seating is be double continuous and where appropriate full penetration.

13.1.7 Large areas of unstiffened flat plate are to be avoided.

13.1.8 The number openings of lightening holes in the seating structure are to be kept to the minimum necessary for access essential for maintenance, etc. Lightening holes are to be as small as practicable and are in no case to be greater than one half of the corresponding dimension of the plate in which they are positioned. Lightening holes with dimensions which are in excess of one third the corresponding dimension of the plate in which they are positioned are to be suitably edge stiffened by spigots or other equivalent means.

13.1.9 Machinery seatings are additionally to be examined for compliance with the bottom stiffening requirements as appropriate for their location, with due account taken of both local and global loadings.

13.2.1 In determining the scantlings of seats for engines, consideration is to be given to the general rigidity of the engine itself and to its design characteristics in regard to out of balance forces.

13.2.2 In the case of higher power engines or turbine installations the seatings should generally be integral with the bottom structure. The tank top plating in way of the engine foundation plate or the turbine gear case and the thrust bearing should be substantially increased in thickness, see Figure 3.13.1 Machinery and raft seatings, Type 1.

13.2.3 If the main machinery is supported on seatings of Type 2 as shown in Figure 3.13.1 Machinery and raft seatings, these are to be so designed that they distribute the forces from the engine as uniformly as possible into the supporting structure. Longitudinal members supporting the seating are to be arranged in line with girders in the double bottom, and adequate transverse stiffening is to be arranged in line with floors, see Figure 3.13.1 Machinery and raft seatings, Type 2.

Figure 3.13.1 Machinery and raft seatings

13.2.4 In ships having open floors in the machinery space the seatings are generally to be arranged above the level of the top of floors and securely bracketed to them, see Figure 3.13.1 Machinery and raft seatings, Type 3.

13.3.1 Seats are to be so designed as to provide effective support for the turbines and ensure their proper alignment with the gearing, and (where applicable) allow for thermal expansion of the casings. In general, the seats are not to be arranged in way of breaks or recesses in the double bottom.

13.4.1 Boiler seats are to be of substantial construction and efficiently supported by transverse and horizontal brackets. These should generally be arranged in line with plate floors and girders in a double bottom or with suitable deep beams or transverses and girders at boiler flats. Suitable allowance is to be made in the design of the supporting structure for the variation in loading due to thermal expansion effects.

13.5.1 Auxiliary machinery is to be secured on seatings, of adequate scantlings, so arranged as to distribute the loadings evenly into the supporting structure.