DESC:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

Title of invention:
A METHOD FOR EVALUATING ALIGNMENT OF A PROPELLER SHAFT OF A MARINE VESSEL IN A DRY DOCK

Applicant:
Mazagon Dock Shipbuilders Limited
A company Incorporated in India under the Companies Act, 1956
Under Ministry of Defence,
(A Govt. of India Undertaking)
Having address:
Dockyard Road, Mazagon,
Mumbai - 400010, Maharashtra, India

The following specification particularly describes the invention and the manner in which is to be performed.

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY
[001] The present application claims priority from Indian provisional application no. 201921006751 filed on 20th February 2019.
TECHNICAL FIELD
[002] The present subject matter described herein, in general, relates to a method for shaft alignment in marine vessels.
BACKGROUND
[003] Conventionally final alignment of shaft line system is done at 85% standard loading condition of the marine vessel. Till date marine vessel building yards wait for the vessel to attain the 85% loading condition post installation of underwater bearings (chock fasted) and stern tube bearings, so that marine vessel is embarked with actual equipment load due to self-weight and alignment is done at actuals without any estimations. Hull deflections which were a resultant of vessel load distribution was taken into account as it is at actual condition and alignment (optimisation of the bearings inside the hull) was done in afloat condition at draft values corresponding to standard loading conditions. It has been observed for earlier ships that the reference axis and the shaft line axis with the effect of hull deflection at deep load condition and at light ballast condition is eccentric (banana shape). This can primarily be attributed to the heavy loads imposed on the hull structure during launching, in afloat condition at 85% deep load displacement due to buoyancy force and at 85% light ballast displacement due to buoyant force. It has been observed in the earlier ships that the hull is deflected to banana shape due to the effect of launch induced forces and buoyancy forces at alignment conditions causing deflection in the pre-aligned reference shaft line axis. However, this method is time consuming as the time required to attain the alignment condition is approximately one year post installation of underwater bearings and stern tube bearings. Additionally three months were required for final alignment in afloat condition.
SUMMARY
[004] Before the present system and method are described, it is to be understood that this application is not limited to the particular machine or an apparatus, and methodologies described, as there can be multiple possible embodiments that are not expressly illustrated in the present disclosures. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present application. This summary is provided to introduce aspects related to a process for shaft alignment in marine vessels, and the aspects are further elaborated below in the detailed description. This summary is not intended to identify essential features of the proposed subject matter nor is it intended for use in determining or limiting the scope of the proposed subject matter.
[005] The present subject matter described herein, in general, relates to a method for shaft alignment.
[006] The present subject matter described takes into account the likely changes in the shaft line axis (based on hull deflection).
[007] The present subject matter described establishes design offset in bearings which are equal to the alignment conditions.
[008] The present subject matter described validates the load at alignment conditions.
[009] The present subject matter completes final alignment activity in dry dock in prevailing load conditions thereby saving idle man hours and waiting period for the vessel to reach the alignment condition.
[0010] The present subject matter reduces time required to build the vessel by twelve months as time required for alignment activity is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing summary, as well as the following detailed description of embodiments, is better understood when read in conjunction with the appended drawing. For the purpose of illustrating the disclosure, there is shown in the present document example constructions of the disclosure, however, the disclosure is not limited to the specific methods and apparatus disclosed in the document and the drawing:
[0012] The detailed description is described with reference to the accompanying figure. In the figure, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawing to refer like features and components.
[0013] Figure 1 illustrates a process of shaft alignment, in accordance with an embodiment of the present subject matter.
[0014] Figure 2 illustrates a process of shaft alignment, in accordance with an embodiment of the present subject matter.
[0015] Figure 3 illustrates a propulsion system.
[0016] Figure 4 shows effect of hull deflection on reference axis
[0017] Figure 5 shows hull deflection estimated by design-fdg from ship weight software and its relative response.
[0018] Figure 6 shows deck breakage readings taken in dry dock.
[0019] Figure 7 shows keel sighting records taken in dry dock.
[0020] Figure 8 shows boundary conditions for starboard shaft.
[0021] Figure 9 shows displacement influence number and bearing loads.
[0022] Figure 10 shows shear force diagram, bending moment diagram and elastic line for starboard shaft.
[0023] Figure 11 shows bearing load readings for port shaft in dry dock condition.
[0024] Figure 12 shows displacement influence numbers(stiffness matrix)
[0025] Figure 13 shows shear force diagram, bending moment diagram and elastic line of port shaft.
[0026] Figure 14 shows bearing load readings and displacement influence number (stiffness matrix) when the vehicle is water borne.
[0027] Figure 15 shows shear force diagram, bending moment diagram and elastic line of starboard shaft when the vessel in in wet borne condition.
[0028] Figure 16 shows readings of bearing load of port shaft at 66% load condition.
[0029] Figure 17 shows readings of displacement influence numbers of port shaft.
[0030] Figure 18 shows shear force diagram, bending moment diagram and elastic line of port shaft.
[0031] The figure depicts various embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION
[0032] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising", “having”, and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary, systems and methods are now described. The disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms.
[0033] Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated, but is to be accorded the widest scope consistent with the principles and features described herein.
[0034] The invention, in general, relates to a method for installation and final alignment of shaft line axis of a marine vessel in dry dock for loading condition at undocked condition, for which the reference are alignment conditions.
[0035] The method involves use of tools such as Aveva Marine for estimation of hull deflections which is a resultant of load distribution on the vessel. The equipment loads are taken from binding documents of the OEMs and hull deflections at 85% standard loading conditions are derived. Further, these values are used in shaft designer software to get alignment parameters at alignment condition of the vessel and final alignment is completed in dry dock at 85% standard loading conditions itself during installation of underwater bearings and stern tube bearings using the alignment parameters estimated from shaft designer software. Furthermore, the alignment parameters are confirmed after the attainment of alignment condition of the vessel after 1 year by measuring the loads on bearings in afloat condition and alignment is completed.
[0036] Referring now to figure 1, shaft alignment activity requires establishment of correct bearing offsets to take into account the effect of hull deflection at various design load conditions.
[0037] Strain gauges are installed at bearing locations to measure hull deflection values which are required for alignment calculations and loading condition at undocking phase.
[0038] As per the method laid down by the classification societies, the final alignment of the shaft axis line is done on completion of 85% of deep displacement and 85% of light ballast(referred to as alignment conditions) of the vessel.
[0039] The alignment of condition for a vessel is reached after one year of cock fastening of ‘A’ bracket bearing and stern tube bearing after which the activity of final alignment of shaft line is undertaken.
[0040] The one year build period required to reach the alignment condition is compressed by verifying the bearing loads, obtained from the shaft design software, at alignment conditions (85% deep displacement and 85% light ballast) against OEM calculations, for hull deflection values, at 85% loading condition.
[0041] At the time of undocking, shaft alignment calculations for loading condition are done using hull deflection values, at the prevailing loading condition during vessel undocking and are compared with bearing loads at alignment conditions.
[0042] The bearing loads at alignment condition and at the time of vessel undocking are compared and bearing offset values are calculated for the final alignment condition of the vessel.
[0043] Shaft installation and alignment is done in dry dock. Bearing loads are achieved by giving offsets as per alignment calculations of OEM. Bearing loads, in afloat condition, for 66% loading condition is validated and loads are achieved as per the alignment calculations carried out in shaft design software.
[0044] Final validation of bearing loads is required to be done at alignment conditions(85% deep load draft and 85% light ballast draft)
[0045] Figure 2 shows a process of shaft alignment.
[0046] Figure 3 shows a propulsion system.
[0047] The main elements of the propulsion system include the following
a) Propeller
b) A-bracket with bearing
c) Stern boss with stern tube bearings
d) Intermediate bearings housed in plummer block
e) Thrust block with thrust bearing
f) Propeller shaft and intermediate shaft
[0048] Further, the invention can be used, but not limited to, in the following applications.
[0049] Figure 4 shows effect of hull deflection on reference axis
[0050] The alignment activity of shaft line in marine vessels calls for extreme precision due to its length and to minimize transmission losses.
[0051] Although, the actual shaft alignment commenced in the dry dock, a pre-aligned shaft line axis is established by carrying out the sighting on the slipway.
[0052] Post establishment of shaft line axis, A-bracket is welded to the stern region of the vessel by controlled welding. However, during launching, the pre-aligned shaft line axis is anticipated to be disturbed due to the moment created on account of buoyancy forces and reaction force on slip way. The deflection of hull in stern region is to be accounted in alignment calculations and also in the shaft alignment method.
[0053] As seen in Figure 4, the pre-aligned shaft line axis established on the slipway, resembles a banana shape, when it is docked for installation of shaft line elements. A-bracket, stern tube bearings, intermediate bearings, thrust bearing and reduction gear box axis are off-centered with respect to reference axis.
[0054] The factors influencing the establishment of elastic line at undocking condition are weight and maximum stern drop due to thermal stresses.
The alignment calculations for the shaft alignment in dry dock needs to be designed by taking the following factors in consideration (a) Stern drop due to thermal stresses on slipway
(b) Launching induced hull deflections
(c) Buoyancy force acting during the afloat alignment condition
(d) Buoyancy force acting during the afloat undocking condition
[0055] One embodiment of the invention can be used in ship building process i.e. hull construction and minor outfitting in wet basin and shaft installation in dry dock.
[0056] Final shaft alignment in dry dock is carried out using the following steps
a) Alignment calculations in dry dock: The stern drop readings are incorporated in the alignment calculations and bearing loads at reference axis are calculated by using shaft designer software. This calculation gives reference axis for afloat condition. Intermediate bearings (plummer blocks) and thrust block are loaded as per the alignment calculations.
b) Alignment calculations at alignment condition: Beating loads at 85% deep load draft and at 85% light ballast condition draft are to be done with estimated values of hull deflection in FE based shaft designer software and elastic time is to be drawn. This elastic line is compared against reference axis with stern drop values and elastic line obtained at 66% condition, is the undocking condition.
c) Alignment calculations at undocking condition: The bearing load calculation at 66% of full draft condition is done by using calculations of shaft design software. The loads on intermediate bearings (plummer blocks) and thrust block are verified and adjusted as per alignment calculations. The elastic line is drawn at this condition. Bearing offsets with reference to alignment calculations are derived and incorporated to achieve the final alignment condition.
d) Measurement of hull deflection by using strain gauge method: Hull deflection values at bearing locations could be derived by using strain gauges at bearing location. This could be used for alignment calculations as they represent actual values for the hull forms.
[0057] Figure 5 shows the estimations considered using design engineering to forecast the elastic lines at the given loading conditions
[0058] Figure 6 shows deck breakage readings noted to incorporate structural deflection in dry dock in alignment calculations in dry dock.
[0059] Figure 7 shows keel sighting readings noted to incorporate structural deflection in dry dock in alignment calculations in dry dock.
[0060] Figure 8 shows shaft modelling with point loads and moments at connecting locations like OKF coupling, hydraulic coupling and sound insulation coupling. The load on the standard shaft is described in the figure.
[0061] Figure 9 shows displacement influence number and bearing loads.
[0062] Figure 10 shows shear force diagram, bending moment diagram and elastic line for starboard shaft.
[0063] Figure 11 shows bearing load readings for port shaft in dry dock condition.
[0064] Figure 12 shows displacement influence numbers (stiffness matrix).
[0065] Figure 13 shows shear force diagram, bending moment diagram and elastic line of port shaft.
[0066] Figure 14 shows the bearing loads for the vessel when the vessel is water borne and is loaded 66% with respect to deep load draft.
[0067] Figure 15 shows shear force diagram, bending moment diagram and elastic line of starboard shaft when the vessel in in wet borne condition.
[0068] Figure 16 shows readings of bearing load of port shaft at 66% load condition.
[0069] Figure 17 shows readings of displacement influence numbers of port shaft.
[0070] Figure 18 shows shear force diagram, bending moment diagram and elastic line of port shaft.
[0071] One embodiment of the invention can be used in shipyards which includes public and private shipyards where equipment delivery is uncertain.
[0072] Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include those provided by the following features.
[0073] Some object of the present invention reduces build period of the vehicle by at least twelve months.
[0074] Some object of the present invention results in reduced idle man hours.
[0075] Some object of the present invention enables timely delivery of vessels.
[0076] Some object of the present invention provides for commencing of the shaft line activity even before completion of 85% construction of the vessel.
[0077] Some object of the present invention provides for unfollowing the conventional method of 85% deep load displacement, for commencing shat line activity, provided the hull deflection values has minimum error.
[0078] Some object of the present invention provides for checking bearing load and carrying out minor corrections at 85% alignment condition, using a plummer block, for fine tuning the alignment.
,CLAIMS:
1) A method for evaluating alignment of a propeller shaft of a marine vessel in a dry dock comprises:
determining a reference axis for afloat condition by simulating alignment in dry dock based on stern drop on slipway due to thermal stresses, induced hull deflections, buoyancy force acting during the afloat alignment condition and buoyancy force acting during the afloat undocking condition;
determining an elastic axis by simuating alignment conditions based on consideration of bearings at 85% deep load draft and at 85% light ballast condition;
determining hull deflection at various location of bearings; and
evaluating the propeller shaft alignment by comparing the determined reference axis and the determined elastic axis.
2) The method for alignment of a propeller shaft of a marine vessel in a dry dock as claimed in claim 1, wherein said elastic axis is determined by calulating alignment at 66% loaded condition.
3) The method for alignment of a propeller shaft of a marine vessel in a dry dock as claimed in claim 1, wherein the hull deflection at various location of bearings is configured to be measured using straing guages.
4) A system for alignment of a propeller shaft of a marine vessel in a dry dock comprises:
a gearbox for transmission of power;
a thrust bearing configured to support an output shaft of the gearbox;
an intermediate bearing configured to support a propeller shaft;
a stern tube bearing located on the body of the hull section and configured to support the propeller shaft;
a bracket with a bearing located outside the hull section is configured to support the propeller shaft; and
a shaft configured to pass through the engine gearbox, the thrust bearing, the intermediate bearing and the stern tube bearing, wherein the bearings are offset according to the determined hull deflection to achieve alignment of the shaft.