[1]United States Patent Office 31467,050 3,467,050 STERN GEAR FOR SHIPS Colin Wray Herbert, Marske-by-the-Sea, England, assignor to The Glacier Metal Company Limited, Wembley, Middlesex, England Filed Feb. 21, 1967, Ser. No. 617,689 Claims priority, application Great Britain, Feb. 22, 1966, 7,827/66 Int. Cl. B63h 23132; F16c 33172; F16j 15140 U.S. Cl. 115-34 12 Claims ABSTRACT OF THE DISCLOSLTRE Stern gear for ships wherein a propeller shaft rotates within a stern bearing which is mounted in a stem frame tube wherein the stern bearing is secured axially' at its inboatd end only and removable inwardly enabling inspection, dismantling, or replacement of the bearing and access to the interior of the frame tube and including support means for the propeller shaft to support the shaft from the stern frame tube when the stem bearing is removed. The present invention Telates to stern gear for sbips. A com ' mon conventional stern gear has a stern bush which is pressed into the stern frame from inside the vessel and secured by an external nut. The stern bush contains two axially separated inner sleeves with lined bearing surfaces within which the propeller shaft runs. Lubricating oil is retained within the bearin.- by oil glands at the inner and outer ends of the stern bush. The oil glands are in the form of rotary seals, the outboard gland s.- rving to exclude seawater and sand. The propeller is mounted on the end of the shaft which projects beyond the outboard oil gland. The propeller shaft must be examined at regular intervals and with conventional stern gear this requires dockin.@ of the vessel so that the propeller shaft can be removed for inspection, the -propeller and outboard oil .-land having to be removed first. In accordance with the present invention there is provided stetn gear for ships comprising a stern frame tube, a stern bearing within which the propeller shaft rotates and which is mounted within and spaced from the frame tube, the stern bearing being secured axially at its inboard end only and removable inwardly, enabling inspection, dismantling or replace ' ment of the bearing and access to the interior of the frame tube, an outboard rotary seal between the propeller shaft and the stern frame tube, and support means for the propeller sbaft outboard of the stern bearing to support the shaft from the stem frame tube when the stern beating is removed. With this construction of the stern gear, inspection and routine maintenance can b,- carried out without the necessity of removing the shaft or docking the vessel. The support means may be in the form of a b,-aring ring fitted at the outboard end of the frame tube. The bearing ring may be supplemented by a hydraulic jacking system mounted within the bearing ring. In an alternative construction the propeller shaft can be drawn forward a short distance to bring it into at least partial enga,-ement with the bearing rin.-I which is conically tapered to centre the shaft. The drawing forward of the shaft also serves to engage a fixed auxiliary seal outboatd of the rotaryseal, enabling the rotary seal to be dismantled when the stern bearing is withdrawn complete with the static part of the rotary seal without the necessity of docking the vessel. The fixed auxiliary seal may alternatively take the form of an inflatable seal or seals. The outboard end of the stern bearing is preferably received within a mounting ring having a spherical or conical seating for the end of the bearing. 'Me bearing Patented Sept. 16, 1969 2 @ing for supporting the shaft may form part of this mounting ring. Preferably, the propeller boss is a hollow cylinder with an intemal flange which is secured to an end flange on the propeller shaft. The intetnal flange is set back from the forward end of the boss to the extent that the support means for the propeller shaft and possibly also the outboard rotary seal are contained wholly or partly within the boss. A shaft carrier bush can be mounted on the for10 watd face of the propelier shaft Range and may have an annular groove whose inner face or outer face mates with a bearing ring for the suppor-t of the shaft during removal of the stern bearing and whose inner or outer face engages a sealing ring forming, the fixed auxiliary seal referred to 15 above. The hollow cylindrical boss with the internal flange reduces the bending @noment on the propeller shaft by reducing the overhan- of the propeller weight. The bending moments can be further reduced if the boss has at its aft 20 end a buoyancy chamber providing a lifting moment acting in opposition to the weight of the propeller. The invention will now be described in more detail with the aid of an example illustrated in the accompanying drawings, in which: 2r) FIGS. IA and 1B are the two parts of a longitudinal section of a form of stem gear in accordance with the invention. FIG. 2 is a detail in longitudinal section of a modification incorporating a hydraulic jacking system for support30 ing the propeller shaft during inspection of the stem bearing. The stern gear shown has a stern frame tube 10 which is constructed as a rigid and continuous tube or cone and which encloses the stem bearing assembly. A mounting 35 ring 11 is pressed into a mechanical housing in a me ' mber 10a at the aft end of the frame tube 10. The mounting ring 11 is of corrosion-resistant material and is ma-. chined intemally to form a spherical seating 12 for the outer end of a stern bush 13 within which a propeller 40 shaft 14 rotates. The stern bearing 13 is a rigid tube of cast iron or steel carrying a seating ring 15 at its aft end which mates with the seating 12. At its forward end it carries a cylindrical flange 16. The bush 13 is lined with anti-friction material which forms the bearing in which 45 the shaft 14Totates. It may, alternatively, contain a roller contact bearing assembly. The stationary parts of an outboard rotary seal or oil gland 17 are attached to the seating ring 15 and engage a gland liner 18 attached to and rotating with the shaft 14. 50 A conventional oil gland is fitted at the inboard end of the stern bearing 13. The stern bush is held in position by bolts 19 securing the Range 16 to a stern frame membe-r 10b. The bolts 19 are axially loaded by hydraulicallytightened nuts 20. Arcuate wedges 21 are positioned and 55 secured to ensure positive radial location of the fiange 16 against the frame.member 10b. The use of spherical seating 12 for the aft end of the bearing 13 and mounting ring 15 allows adidtional provision to be made for bearing alignment that is not avail6o able with the conventional arrangement. Fine adjustment of the horizontal or vertical alignment of the bearing 13 relative to the shaft 14 can be made by adjusting the individual fore and aft positions, of the arcuate wedges 21. If a large angular offset from the optical centre line 65 is required this can be machined into the flange 16 during manufacture. The propeller shaft 14 is provided with a flanged coupling 22 at its aft end to which a propeller boss 23 is attached whilst a shaft carrier bush 24 is bolted to the 70 forward side of this flange. The bush 24 is of corrosionresistant material and together with the gland liner 18, forms a protective sleeve for the :aange 22 and shaft 14.
[2]3 The bush 24 also serves as a mounting ring for the gland liner 18. The bush 24 has a groove 25 in its forward face. The inner waR of the groove 25 forms a frusto-conical surface which rotates within a frusto-conical bearing ring 26 at the aft end of the mounting ring 11. A sealing ring 27 carried in the outside of the bearing ring 26 can engage the outer wall of the groove 25 when the propeller shaft 14 is displaced forwards and at the same time the inner wall of the groove will come into engagement with the bearing ring 26 (although corrosion and the build up of marine deposits may initially prevent complete engagement) so that the shaft is supported by the bearing ring. To enable the propeller shaft to be moved forward a spacer disc 28 is placed between a pair of flange connections 29 and 30 in the shaft line so that upon removal of the disc 28 the flange connections 29 and 30 can be directly coupled and the shaft 14 drawn forward. Alternatively, thrust pads (not shown) can be removed from the main thrust bearing thus allowing the shaft to be pulled forward. The propeller boss 23 is a hollow cylinder with an intemal flange 31 which permits attachment to the shaft flange 22 by studs 32 and nuts. The studs 32 are loaded by hydraulically-tightened nuts 33. The shaft carrier bush 24 is provided with 0-rings in its periphery to prevent ingress of sea water to the steel shaft. The periphery of the bush 24 and that of the shaft .flange 22 may be tapered as shown to facilitate mounting of the propeller. A principal objective of the arrangement is to perinit full examination of the stem-gear without removing the propeller or disturbing the shafting. In high power installations therefore the frame tube 10 is made of such diameter that when the bearing assembly is withdrawn a man may enter the annular space surrounding the shaft 14 to examine the surface of the shaft and the outboard gland liner 18. With the shaft diameters of 600 mm. or more this does not involve any penal increase in boss diameter. Diameters are such that if iiecessary the gland liner 18 may be withdrawn forward after removal of its securing bolts and the insertion of breaking screws which is accomplished with the aid of an extended ratchet brace. This bush would not nornially be expected to require removal during the Hfe of the vessel unless the vessel hab'tually trades for prolonged periods in waters containing abrasive media. To remove the bearing and the aft oil gland with the ship afloat in the normal attitude the shaft is first drawn forward as described above or the inflatable seal or seals are operated. The correct functioning of the auxiliary seal 27 is then checked by opening a test connection which drains the water-filled space between the main seal 17 and the auxiliary seal 27. The arcuate wedges 21 are first removed with the aid of breaking screws. The nuts 20 which retain the bearing in position are then removed. Extraction jacks are then fitted ;and coupled in parahel to a single hand pump. A standard jack is then placed beneath the shaft 14 forward of the bearing and loaded until it supports the shaft. Then by operation of the hand pump the bearing assembly is jacked forward until the forward flange 16 is clear of its housing within the frame tube 10. If it is required to remove the bearing when the ship is dry-docked it is unnecessary to carry out the preliminary operation of drawing the shaft forward or operating the inflatable seals. This being the case during the withdrawal process described above the aft end of the shaft assembly wiff be lowered some 3 mm. until supported by the shaft carrier bearing ring 26. Next the jack supporting the shaft at its forward end is removed and the bearing assembly complete with the aft oil gland 17 hauled forward on to a suitable carrier on which it may be rotated for inspection. With the ship in dry dock as a supplement to or as re3,467,050 4 placement to the support provided by the bearing ring 26 it is possible to provide bolts or a built-in hydraulic jacking system (see FIG. 2) for centering the forward part of the cylindrical propeller boss 23 with respect to the part 34. It will then be necessary for these to be brought into use from outside the vessel before the stem bearing 13 can be moved. The stem bearing 13 may be provided with plugged holes for measurement of wear-down and, if this is sus10 pected, then the gland assembly and seating ring 15 can be removed from the bearing 14 to facilitate inspection of the most highly-loaded section of the bearing surface. For inspection or maintenance purposes the flange 16 may be removed from the bearing 13 and the two halves 15 of the bearing separated. The bearing halves may then be removed for rescraping or relining or may be replaced by a spar@. To do this it is unnecessary to break the shaft line. For shaft inspection purposes a semi-circular plastic 20 cover with flanges to support the inspector's feet may be placed over the exposed shaft which may then be rotated slowly using the engine turning gear. Alternatively, the inspection may be completed by re-entering the annular space from beneath the shaft. It is further envisaged that 25 provision be made for the mounting of special honing equipment to permit lapping of the shaft in situ. The gland liner 18 may be removed as described above; this gives access to the surface of the highly stressed radius between the shaft 14 and flange 22. Thus with the 30 gland liner 18 removed the radius may be visuauy inspected, with the aid of a viewing instrument if necessary or a dye penetrant check for cracks may be carried out. Mounted on the aft end of the propeller boss 23 is a buoyancy chamber consisting of a closed hollow shell 35 35 of synthetic plastic reinforced with glass fibre, the sheu 35 being filled with a body 36 of foamed rubber or synthetic material having a closed cell structure. The shell 35 has metal Plates 37 embedded in it and is secured by bolts 38 to the aft end of the propeller boss 23. The buoy40 ancy chamber applies a lifting moment which helps to counter the weight of the propeher and thereby reduces the bending moment on the shaft 14. The shell 35 is of approximately frusto-conical form continuing the line of the slightly-tapering propeller boss. 45 In the modification shown in FIG. 2 the shaft carrier bush 24 has an annular groove 39 in its forward face which accommodates the aft end of the mounting ring 11. The ring 11 has on its inner face inflatable seals 40 to engage the inner wall of the groove 39 and thereby form nn the auxiliary outboard seal. A number of peripherally" spaced pistons 41 are mounted in the outer face of the ring 11 to form an intemal hydraulic jacking system and by supply of hydraulic fluid to their cylinders 42 can be driven outwards to engage the outer wall of the groove 39 .55 and thereby support the shaft 14.
