Bed plate.

There are different types of bedplates in slow-speed engines. They are completely enclosed on the underside, in order to form an oil sump, while the bearings for the crankshaft are supported by cross girders, which form part of the bedplate.

The Trestle type sits upon two parallel stools or raised portions of the ship's structure located in a fore-and-aft direction.
The Deep box type of bedplate is with a flat bottom, which enables it to be bolted to the ship's flat tank top.
Bedplates are usually fabricated from mild steel plates and steel castings, welded together; smaller engines may have cast-iron bedplates. The main advantage of the fabricated bedplate is its lightness and lower construction cost.
Bedplates made of Cast-iron are able to absorb vibration better than fabricated bedplates, due to the good internal damping characteristics of Cast-iron. Usually the larger engine bedplates are of the deep box pattern with a flat bottom. Smaller engines are either of the flat-bottom type or of the type that sits on stools forming part of the ship's structure.
All parts of an engine bedplate contribute to its strength. The parts are made from mild steel plates and steel castings, which are assembled and welded together so that the bedplate is strong longitudinally (fore-and-aft) and transversely (port and starboard) with good resistance to twisting along its length.
The longitudinal strength is obtained by making each side of the bedplate in the form of a Girder. These girders may be box formed with two flanges and two webs, or as a nomal girder with one web and two flanges The cross girders in which the main bearings are housed give the bedplate transverse strength. The cast steel cross girders are welded to the sides of the bedplate, to give good resistance to twisting.
The weight of the static engine parts is transferred to the bedplate through the A-frames. The sides of the bedplates, in way of the A-frame landings, are stiffened. Bedplates having the Deep box girder type construction have diaphragms between the webs and the flanges.
The transverse walls form the saddles for the main bearings. The strainer at the bottom prevents impurities from being carried over with the oil back to the sump. The sump contains the bulk of the lubricating oil, and its sounding is to be constantly monitored, so as to get a warming of oil leakage or contamination, which could adversely affect the engine.
Forces and stresses on a Bedplate
The Bedplate has to withstand and transmit the stresses arising due to the following forces:
1. The 'firing' loads transmitted through the Tie-rods.
2. Primary and Secondary couples of the reciprocating masses.
3- Centrifugal inertia forces occurring when the vessel rolls in a heavy sea.