The Design of Rolling Bearing Mountings

61–62 Ship shaft bearings and stern tube bearingsThe propeller shaft of a ship is carried by so-called supportbearings. Since length variations of the shaft areconsiderable, particularly with long shafts, the bearingsmust have axial freedom. The last part of the shaft supportingthe propeller, runs in the so-called stern tubeor tail shaft bearings.Operating dataShaft diameter 560 mm; nominal speed of propellershaft 105 min –1 .Radial load from shaft and coupling 62 kN, no axialload – the propeller thrust is taken up by the propellerthrust block (figs. 63 and 64). With a supplementaryfactor of 100 % on the radial load (f z = 2), shocks orother dynamic forces are sufficiently taken into considerationwhen determining the bearing stress.Bearing selection, dimensioning, sealingSince the diameter of the ship shaft is specified, thebearings are overdimensioned for the loads to be accommodated.Thus the index of dynamic stressing f L rangesfrom 4 to 6 and therefore a high nominal life (L h ) is obtained.With very good cleanliness in the lubricatinggap, endurance strength is reached in the adjusted life calculation(L hna ) for ship shaft and stern tube bearings.A spherical roller bearing FAG 239/600BK.MB (dimensions600 x 800 x 150 mm, dynamic load rating C =3,450 kN) is used as ship shaft bearing. By means of thehydraulic method the bearing is attached to the shaftwith an adapter sleeve FAG H39/600HG and is locatedin a plummer block housing FAG SUC39/600H.1.....(fig. 61a). The housing is made of grey cast iron GG-25 and consists of a unsplit housing body with twosplit covers.The housing's sealing is provided for by the radial shaftsealing rings in the cover. For small quantities, weldedhousings are generally more economical than casthousings. Fig. 61b is an alternative ship shaft bearingarrangement made up of a spherical roller bearingFAG 23048K.MB with adapter sleeve H3048 and asplit plummer block housing S3048KBL.1.....(material GG-25).The ship shaft is surrounded by the stern tube at thestern. Fig. 62 shows a stern tube bearing arrangement,both bearings are designed as floating bearings. The tailbearing is also loaded by propeller weight and wave action.Spherical roller bearings are applied here alsowhose inner rings, with adapter sleeves, are attached tothe shaft. A special stern tube sealing protects the bearingsfrom seawater.Machining tolerancesThe inner rings carry circumferential load.Adapter sleeve seat on the shaft h8. Cylindricity toleranceIT5/2 (DIN ISO 1101); housing bore H7.Flanged housings are used for the tail shaft bearings.LubricationThe bearings are lubricated with a non-aging oil withEP additives (viscosity 150 to 300 mm 2 /s at 40°C). Thelower parts of the support bearing housings have viewingglasses or oil dip sticks on which the permissiblemaximum and minimum oil levels are marked. Thestern tube is filled with oil. The oil pressure is kept alittle higher than that of the surrounding water.61a: Ship shaft bearing; spherical roller bearing in SUC housingFAG 84