METHOD FOR POSITIONAL SETTING OF CONSTRUCTIONAL COMPONENTS OF A SHIP'S PROPULSION UNIT

Abstract: The precise positioning of a component such as an engine bedplate (5) in a ship under construction is pre­ determined by making height measurements on the bed­ plate at a number of support positions before the bedplate is installed. A sighting line (ABCDEF) is established rela­ tive to the tank top (4) of the ship under construction by an optical sighting method and an optical sweep is made in a plane parallel to this sighting line to measure the dis­ tances from the sighting line of each of the bedplate sup­ port positions on the tank top so as to predetermine the height of individual bearing elements for the engine bed­ plate. Similar techniques are employed to establish the fore-and-aft and athwartships positioning of the engine bedplate before its installation. The positioning of machi­ nery in the ship can therefore be predetermined accurately without all the ancillary components having to be in place, and with minimal in situ adjustment.

Description: Positional setting of constructional components This invention relates to marine or building construction and in particular to the pre-alignment of components of a ship or building under construction. In ship construction the traditional methods of alignment of machinery and shafting in a ship require all the requisite components to be installed in the ship before final alignment can be achieved. Alignment of a propeller shaft with an engine is achieved by first establishing a line of sight, either optically or using piano wire, then boring out the stern frame in which the aft end of the propeller shaft is eventually supported. This is followed by machining and fitting of a stern tube and a propeller and shafting which are supported in the stern tube, and finally coupling the forward end of the propeller shaft with coupling flanges on the engine drive shaft, using mechanical means to adjust the setting of the engine to ensure alignment of the engine shaft with the propeller shaft. When aligning machinery by the traditional method any small alignment errors made either at the stern tube or at the engine will be very troublesome as the work of lining up the intermediate shafting proceeds, and it may be necessary to move the engine from its designed position. Furthermore, since alignment of the machinery depends on all the components being in position, delay in the delivery of any one component can delay the finishing of the vessel and possibly its eventual delivery. Ancillary work such as the building of ladderways and walkways cannot be completed, and the fitting of oil and fuel lines and cooling water pipes cannot even be commenced, until all the main propelling components of the ship's machinery are in place, so that even when alignment of the machinery has been achieved, completion of the installation work will then take several more weeks. An object of the present invention is to provide a method of construction in which alignment and positioning of. components of a structure, such as the machinery of a ship under construction, can be effected accurately without all the components having to be in place, and with minimal on-site adjustments. According to the present invention there is provided in one aspect a method of setting the position of a component in a structure such as a ship or building under construction, in which at least one measurement is made on the component before it is fitted in position to establish distances between at least two reference surfaces of the component, and at least one measurement is made on the structure itself, before positioning of the component, to determine the position in the structure at which one of the reference surfaces of the component is to be located, and the measurements on the component and the structure are combined to determine the size of at least one spacer or adjusting element which is positioned in the structure before the fitting of the component to predetermine the eventual position of the component in the structure. Once the or each spacer or adjusting element has been positioned the position of the component in the structure is predetermined and if necessary further construction and building work can proceed, even if the dependent alignment components are not actually installed - due, for example, to delay in the delivery of the component. Although the invention is particularly applicable to ship construction it is applicable in principle to building construction or any civil engineering structure in which components have to be positioned accurately. As applied to ship construction, with reference to which the invention will be further described, the method of the invention can be employed to predetermine the height, the longitudinal (forward and aft) position and the lateral (port and starboard) position of machinery in the hull of a ship under construction. The or each measurement made on the structure may be made using rules, but for the best results an optical alignment apparatus is employed. For example, optical sights may be located at selected positions in the structure at which measurements are made and may be aligned with each other using a telescope mounted on a table the axis of which is capable of tilt adjustment. An optical alignment method of the present invention is particularly advantageous in determining the height of machinery for installation on the tank top of a ship under construction, in which case a sighting line corresponding to the axis of a propeller shaft or an engine crankshaft is determined by an optical sighting method and an optical sweep is then made in a plane substantially parallel to the sighting line to measure the distances from the sighting line of a number of machinery suppport positions on the tank top, measurements are made on a support base of the machinery before its installation to establish the height relative to the sighting line of the machinery base at each support position, and bearing height adjustment elements are selected, each having a height determined from said measurements on the support base and from the optical sweep measurements, the said adjustment elements being located at the appropriate support positions to predetermine a correctly aligned position of the machinery upon the subsequent installation of the machinery base on the tank top. Preferably the measurements made on the machinery support base before its installation include measurements at a forward and aft reference position, these measurements being subtracted from the height of the sighting line at these positions measured in the optical sweep to obtain forward and aft reference heights of the base above the tank top. When carrying out the method of the invention on a vessel under construction the hull construction must be sufficiently far advanced to permit of alignment checks without danger of subsidence or settlement. Typically this would apply when the hull has been fully welded from the top of the stern frame to the main deck level and for about three holds or compartments forward of the stern. The position or alignment checking method should be completed before preparations are commenced to transfer the weight of the vessel from keel blocks onto launching ways, such preparations being usually started about two weeks before launch. The invention will be further described, in its application to shipbuildingf and by way of example, with reference to the accompanying drawings, in which: Figure 1 is a purely diagrammatic longitudinal section of part of the hull of a ship under construction showing positions at which optical alignment sights are located; Figure 2 is a longitudinal section, on an enlarged scale, of part of a bedplate on which machinery is supported in the ship's hull; Figure 3 is a plan view of the bedplate showing machinery support points and a suggested position of an optical scanning device; Figure 4 is an exaggerated longitudinal section illustrating the optical alignment method for determining the base height and bobbin measurement of the machinery and its bedplate in the ship's hull; ; Figure 5 shows diagrammatically side elevations of three different types of element which may be used in the method described with reference to Figures 3 and 4; Figure 6 is a diagrammatic longitudinal section of part of the hull of a ship under construction illustrating a method of determination of the forward and aft position of the machinery in the hull; Figure 7 is a diagrammatic sectional view of one of the adjustable stoppers used in the positioning of an engine bedplate by the method of the present invention, and Figure 8 is a longitudinal section, on a grossly enlarged scale, of part of the stern frame of a ship under construction, illustrating a method of correcting for misalignment of the bore in the stern frame relative to the axis of the propeller shaft. At a stage in the construction of a ship after the welding of the hull from the stern to the main deck level at least two holds or compartments forward from the stern, optical sights are set up at a number of points, labelled A to F, between the after end A of the stern frame 1 to the forward end F of the main propulsion unit 2 (Figure 1). A special adaptor is used to ensure that the sight at F is coaxial with the sight line AF, while another special adaptor at E is fully adjustable in all directions, enabling it also to be set coaxial with the with the sight line AF. Optical alignment of the sights at A to F along a line coinciding with the propeller shaft and the drive shaft of the propulsion unit is effected by means of a telescope, laser beam or other optical means, before the mounting of machinery on the double bottom 3 of the hull of the ship under construction, to establish a number of height measurements of the sight line above the upper surface 4 of the double bottom 3, usually referred to as the 'tank top'. Before machinery such as the propulsion unit 2 is installed in the ship measurements are made upon the bedplate 5 which supports the unit 2. The bedplate 5 is made up of a number of interconnected sections the base surfaces of which are usually machined at an early stage of manufacture of the engine and are not in general coplanar. The distance of the axis of the propulsion unit drive shaft, that is, the crankshaft where the propulsion unit is a reciprocating engine, above the base surface 6 of the bedplate 5 is measured by mechanical or optical means at the after and forward points of the bedplate. These distances are subtracted from the height of the points E and F above the tank top 4, as obtained from a preliminary optical sweep of the sights set up at points A to F to obtain forward and aft bedplate clearance dimensions X and Y (Figure 1) which will in general be different from each other. Two special distance gauges 7 and 8 (Figure 8) are set up on the tank top 4 with optical sights at points E and F. These gauges 7 and 8 are aligned with each other optically and for this purpose the gauge 7 includes an optical telescope (not shown), fixed table, enabling the gauges to be aligned with each other along the line EF, coinciding with the bore line of the engine drive shaft. Each of the gauges 7, 8 supports a respective target 10, 11 supported at an accurately defined distance below the line EF equal to the respective distance, previously measured, of the axis of the propulsion unit drive shaft from the base surface 6 of the bedplate 5, so that the two targets 10, 11 are located at the distances Y and X respectively above the tank top 4 and are aligned with each other in a datum plane 12 (Figure 2) for the base surface of the bedplate 5. The irregularities in the base surface 6 of the bedplate are shown exaggerated in Figure 2. Each engine support point on the bedplate 5, indicated by an asterisk in Figure 3, is marked carefully on the tank top 4. With the targets 10 and 11 set up in the datum plane 12 representing the level of the base surface of the bedplate above the tank top 4, an optical sweep is now made in the datum plane by means of a telescope mounted upon a turntable 13 located inside or outside the bedplate area (Figure 3). Height measurements above the tank top 4 (the irregularity of which is exaggerated in Figure 4) are made at each previously marked engine support point by aligning the telescope in turn with each of these points and reading off through the telescope a height on a height measuring gauge such as a graduated scale located at each engine support point in turn. The height measurements thus obtained relate to the height of the datum plane 12 above the tank top at each engine support point, and are corrected by taking into account the actual height of the bedplate 5 at each engine support point, measured by means of a suitable caliper gauge 15 (Figure 2) to give actual clearance heights of the bedplate base surface 6 above the tank top 4 at each engine support point. These clearance heights will be the heights of respective bobbins which have to be located on the tank top 4 at each engine support point to ensure that when the engine bedplate is seated on the tank top the axis of the engine drive shaft will be at the designed shaft centreline height coinciding with line AF. Normally this shaft axis of centreline will be horizontal, but at this stage allowance can be incorporated for deliberate sloping, "hogging" or "sagging" of the engine shaft axis. Allowance can also be made at this stage for deflection or compression of the ship's bottom due to the weight of the propulsion unit. Examples of the different kinds of bobbin 15 which may be manufactured for each engine support position are illustrated in Figures 5(a), (b) and (c). The bobbin 15 shown in Figure 5(a) has parallel end faces and is designed to support an engine bedplate parallel to the ship's bottom, while the bobbin 15 shown in Figure 5(b) has a bevelled upper surface and is designed to support a bedplate having an inclined base surface, or to support a bedplate on a sloping tank top 4. In each case, the engine support points at which the bobbins are located coincide with vertical stiffeners in the engine bedplate structure, as shown diagrammatically in Figure 5. Figure 5(c) illustrates a multi-purpose bobbin 15 having a standard upper portion 16 with a bevelled upper face, designed for re-use, and a lower portion 17 of appropriate height keyed to the reusable upper portion. To allow for fine height adjustment of each bobbin, the bobbins illustrated in Figures 5(a) and 5(b) are deliberately manufactured with a height which is a predetermined amount less than the required height, and a standard tinplate shim 18 having a thickness of this amount is affixed to the bottom of the bobbin. If, due to a miscalculation or minor error, the height of the bobbin has to be corrected, it is not necessary to scrap the entire bobbin, but merely necessary to substitute a shim 18 of a different thickness. Further fine height adjustment may be achieved by taking advantage of the fact that in practice the base 6 of the engine bedplate 5 will in general be inclined to the tank top 4, so that by moving the bobbins 15 along the surface of the tank top small height adjustments of the engine bedplate can be achieved. The bobbins 15 allow the propulsion unit or engine and its bedplate 5 to be dropped into the correct predetermined position in the hull of the ship, before other components have been fitted, and to maintain the engine in its correct position of alignment until the engine is supported and chocked in the usual manner. A similar procedure is used to predetermine the forward and aft position of the engine or propulsion unit 2 before it is located in the ship. As a first step, the exact distance between the coupling face 20 of the coupling flange of the engine drive shaft (Figure 6) and the aftermost edge of the engine bedplate 5 is measured by means of a suitable mechanical gauge, while the engine and its bedplate are "ashore". The gauge, indicated diagrammatically at 22 in Figure 6, is then located on the tank top 4 in the ship's hull, at the approximate position of the engine shaft coupling. A steel tape or other similar measuring device is then used to measure the distance from the face of the gauge 22 which coincides with the eventual coupling face 20, to the outside of the stern boss 23 in the stern frame 1 through which the propeller shaft will eventually pass. This distance, indicated by H in Figure 6, is measured at a convenient height, usually the height of the bottom dead centre of the stern boss and the bottom of the engine coupling face 20. Having measured the distance H, the position of the gauge 22 is then adjusted in a forward and aft direction so that the eventual distance H is about 10 mm proud of the combined propeller gland and propeller shaft length, thereby leaving about 10 mm on the after face of the stern boss 23 for subsequent machining whilst boring out the stern boss 23 should this be necessary. Having established the distance H and thereby located the precise position of the coupling face 20 when the engine is eventually fitted, the previously determined distance K from the coupling face 20 to the after edge of the engine bedplate 5 is marked on the tank top 4. A special heavy duty end stopper is next welded to the tank top 4 at a position which is 10 mm less than the distance H from the outside of the stern boss 23. A second end stopper is also welded to the tank top 4 at the forward position of the bedplate 5, the distance between the two stoppers being adjusted to the bedplate length minus 1 mm. The two stoppers define a forward and aft containment position at which the engine bedplate unit will be located as it is lowered into position. A similar method is used for positioning the propulsion unit and the engine bedplate 5 laterally, that is in a port and starboard direction. The width of engine bedplate is first measured "ashore". A minimum of two pairs of heavy duty port and starboard adjustable stoppers are then welded to the tank top 4, a first pair at the forward end and a second pair at the aft end of the engine position. The width between the port and starboard stoppers of each pair is adjusted so as to be approximately 0.5 to 1 mm less than the engine bedplate width, the stoppers of each pair being set symmetrically on opposite sides of the sight line EF. Plumblines dropped from hangers at points E and F to provide corresponding reference points El and F1 at the tank top level (Figure 1). El and F1 must be marked before launch. The engine bedplate 5 is now lowered into a "nest" formed by a minimum of six heavy duty stoppers that is, the forward and aft stoppers and at least four port and starboard stoppers. Fouling of lubricating oil drop pipes and the like is avoided by suitable location of the stoppers. An example of an adjustable stopper is illustrated in Figure 7, comprising a pivoted stop block 24 adjustable by means of a screw 25, the support for the stop block 24 being welded to the tank top 4. The final and precise positioning of the engine bedplate 5 to ensure that crankshaft axis is aligned with the sight line EF is now carried out, using a tramn ltype arm and clock gauge, located from the bearing on special telescope fixtures at points E and F. The clock gauge is adjusted to make contact with the engine crankshaft coupling flange or any suitable surface concentric therewith. Work on the final installation of ancilliary fittings, including lubricating oil pipes, water pipes, ladders, pipes, floors and the like can now commence, without waiting for any further alignment work to be carried out. To provide a means of detecting any vertical change in the engine bedplate position with respect to the tank top during the subsequent engine building stages a series of gauging points are now established between the lower surface of the bedplate and the top surface of the tank top. Dome ended screw-threaded studs are passed through the bedplate lower flange and set to be approximately 26 mm above the tank top. After setting these studs accurately at 26 mm above the tank top with the aid of a 25 mm cube block and feeler gauges, the studs are welded in position, and can be used to make allowance for any deflection of the tank top during the subsequent engine build programme. Thus any changes in the distance between the tips of the studs and the tank top can be monitored and if necessary corrections can be undertaken. Having set the propulsion unit 2 and the engine bedplate 5 in position on the bobbins 15 the "boring out" of the propeller shaft bearings between the propulsion unit 2 and the stern frame 1 commences, along the line ABCDEF previously established by means of the optical sights. Boring out can proceed either before or after engine positioning. The sight at position E can be used to establish the shaft axis ABC for the purpose of marking concentric rings on the stern tube bore faces or aft peak bulkheads. These rings to be used when positioning steadies for a boring bar used for boring the stern frame by affixing targets at B and C to be co-axial with the line of sight EA and then substituting the target with a metal disc having a female centre hole. A concentric ring can now be marked on the bore faces and bulkhead using scribing trammels. Another use of the sight line EA is to measure any misalignment of the final size of the bored stern frame, enabling allowances to be made for such misalignment by suitably machining the stern bearing tube 26 subsequently located in the bore of the stern frame boss, as illustrated exaggeratedly in Figure 8. Misalignment of the stern frame boss 23 is shown exaggerated in Figure 8. In addition to the stern bearing tube 26, the outer oil seal, carried by an annular gland carrier 27, is also machined with an eccentric outer surface so as to fit into the stern frame boss 23 while maintaining accurate coaxial alignment with the internal bore of the bearing tube 26, such alignment being checked by mounting a telescope at point E (Figure 1) and checking the alignment through the bore of the bearing tube 26. For the purpose of making accurate optical alignments by the procedures described above a telescope sight is used which, as illustrated diagrammatically in Figure 4, comprises a rigid support 28 surmounted by a circular bearing ring 29. A table 30 carrying telescope mounts 31 rests on the bearing ring 29, the table 30 having a bevelled lower face 32 which bears against the inner edge of the bearing ring 29 to afford an annular bearing surface.

Claims: CLAIMS 1. A method of setting the forward-and-aft position of a component such as an engine bedplate (5) in a marine structure such as a ship (3) under construction, characterised in that at least one length measurement is made in the forward-and-aft direction on the component before the latter is fitted in position to establish the distance longitudinally between at least two reference end surfaces of the component, and at least one measurement(H) is made on the structure itself, before positioning of the component, to determine the position in the structure at which one of the reference surfaces of the component is to be located, and the measurements on the component and the structure are combined to determine the size of forward and aft end stoppers (22) which are positioned in the structure, with the distance between the stoppers substantially equal to the said measured length of the component, to predetermine the forward-and-aft position of the component in the structure before said component is fitted. 2. A method as claimed in Claim 1, in which optical sights (10, 11) are located at selected positions in the structure at which measurements are to be made and are aligned with each other using an optical instrument (7) mounted upon a table (30) and capable of vertical and horizontal displacement and of tilt adjustment, the table being rotatable for sweeping of the instrument in a plane. 3. A method as claimed in Claim 1 or Claim 2, in which the width of the component for installation in a ship under construction is measured before its installation and at least two pairs of port and starboard adjustable stoppers (24) are then fixed to the structure (4), in different transverse planes along the sighting line, the distance between the said stoppers being adjusted to be equal to or slightly less than the said width, before the component is fitted. 4. A method of determining the mounting height of propulsion machinery (2) for installation on the tank top (4) of a ship under constructidn in which a sighting line (ABCDEF) corresponding to the axis of a propeller shaft or an engine crankshaft if determined by an optical sighting method and an optical sweep is then made in a plane substantially parallel to the sighting line to measure the distances from the sighting line of a number. of machinery support positions on the tank top, measurements are made on a support bedplate (5) of the machinery before its installation to establish the height relative to the sighting line of the machinery bedplate at each support position, and bearing height adjustment elements (15) are selected, each having a height determined from said measurements on the support bedplate and from the optical sweep measurements, the said adjustment elements being located-at the appropriate support positions to predetermine a correctly aligned position of the machinery upon the subsequent installation of the machinery bedplate on the tank top. 5. A method as claimed in Claim 4, in which the measurements made on the machinery support bedplate before its installation include measurements at forward and aft reference positions (, E), these measurements being subtracted from the height of the sighting line at the positions measured in the optical sweep to obtain forward and aft reference heights of the bedplate above the tank top (4). 6. A method as claimed in Claim 5, in which optical sights (8, 7) are established at the forward and aft reference positions, the aft sight being concentric with the shaft axis, sighting elements (11, 10) being carried by the forward and aft sights and supported at positions corresponding to the forward and aft reference heights of the base above the tank top, an optical sweep of the machinery support positions being made with the said sighting elements to obtain height measurements for each bearing height adjustment element (15). 7. A method as claimed in Claim 4, Claim 5 or Claim 6, in which reference studs or screws are affixed to the lower surface of the support base, projecting a distance towards the upper surface of the tank top (4) such as to be spaced by a common reference distance therefrom upon the initial installation of the support base, measurement of said distance enabling subsequent deflections of the tank top to be monitored.

Inventors: BEST, WILLIAM JOHN
Applicants: THE RANK ORGANISATION LIMITED
Application year: 1980
Main classification: B63B9
IPC codes: G01C15, B63B9, G01B11, B63H21