Improved stern form for single- or multi-propeller ships with central propeller

Abstract

The invention relates to a stern form for a ship propeller, applicable to the hull of single- and multi-propeller ships with a central propeller, characterized in that the cross- sections of the ship's hull, referenced as sections 8, ½, and 9, are modified in the parts between the reference lines A and B of the lines plan, shifting aft of the propeller the bulge necessary to house a shaft and a supporting bearing for the propeller itself, allowing a reduction of the hull's wetted surface, a decrease in fuel consumption, and an improvement in overall propulsive efficiency.

Description

[0001] Title:

[0002] "IMPROVED STERN FORM FOR SINGLE- OR MULTI-PROPELLER SHIPS WITH CENTRAL PROPELLER”

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to an improved stem form for single- or multi-propeller ships with a central propeller.

[0005] PRIOR ART

[0006] As is known, numerous factors enter into the calculation of the fuel consumption of a ship as stated by the theory of naval hydrodynamics.

[0007] A brief description of the same is reported below:

[0008] □ CH hourly fuel consumption = PB x CS (kg / h)

[0009] □ PB Brake power required for the ship to advance at speed V

[0010] □ CS = Specific hourly consumption

[0011] □ PB = PE / qP

[0012] □ PE = Rt x V Effective power = power required by the ship without propeller to advance at speed V

[0013] □ Rt Total resistance of the ship without propeller

[0014] □ qP = (qH x qB) x (qm x qS) Total propulsion efficiency = (qH x qO x qR) x (qm x qS)

[0015] □ qH Hull efficiency

[0016] □ qO Open-water propeller efficiency

[0017] □ qB = qO x qR Efficiency behind the hull

[0018] □ qR Relative rotative efficiency

[0019] □ qM Mechanical efficiency

[0020] □ qS Shafting and bearing efficiency

[0021] The parameters forming part of the final formulation of PB of greatest interest for the present invention are two: a) Rt, Total resistance of the ship without propeller, which is, in basic form, the sum of two types of motion resistance: a.1 ) Frictional resistance, proportional to the hull surface and its roughness. a.2) Wave resistance, due to the creation of waves during advancement. Without intending to illustrate all the parameters leading to the complete determination of Rt, whether analytical or experimental, and focusing attention on Rf, the following relationship applies: Rf = Cf x 0,5 x p x VA2 x Sw (Sw-wet-surface-wetted, p-water density, Cf-friction coefficient, which is a function of the Reynolds number at which the hull moves).

[0022] As can be seen from the formulation of Rf, its value is directly proportional to Sw.

[0023] A percentage decrease X of Sw therefore corresponds to the same percentage decrease X of Rf and to a percentage decrease Y of Rt, which varies depending on the type and speed of the unit, and a consequent reduction in fuel consumption, which is the primary objective of this patent application. b) qB, Efficiency behind the hull.

[0024] As indicated in the formulation above: r|B = qO x qR where qR is essentially a reduction in the efficiency of the propeller behind the hull compared to that of the isolated propeller qO, which is determined through fluiddynamic calculations and experimental tests with a scale model in mechanical similitude, driven by a motor under full experimental control with the propeller immersed in water moving uniformly along its axis.

[0025] See Figure 1 , which illustrates the flow of fluid filaments at the propeller disk for a single- propeller ship.

[0026] The value of qR is notably increased, positively, by the solution of the present invention. Consequently, the value of qB is also positively modified.

[0027] The present improvement invention aims to enhance the importance and benefits of European patent application EP No. 88830294.0, which, however, limited its significance to a new stem structure for supporting the propeller bearing, see Figure 3 of that patent application.

[0028] Indeed, European patent application EP No. 88830294.0 (as indicated in its Figure 4) had identified the wake and vortices generated by the components located upstream of the propeller(s) as the main cause of the reduction in propeller efficiency, which, instead of operating in a uniform flow as in experimental tests or in appropriate fluiddynamic calculations, operates in a flow with radial and tangential velocity components of the fluid filaments that impair its optimal performance, see Figure 1 .

[0029] However, that European patent application EP No. 88830294.0 did not explicitly address the stem form of a single-propeller ship, focusing only on the method of supporting the propeller weight with a bearing positioned aft of the propeller, and not forward of it, as is normal practice in current naval engineering.

[0030] Twin- propeller or multi- propeller ships without a propeller on the symmetry plane, considering their current stern hull forms, are not the subject of the present invention. For hulls of standard design for ships not having stem forms devised for special purposes, e.g., tugboats and the like, efficiency losses qR of 4-6% can be estimated, which directly affect the power values involved and, consequently, fuel consumption.

[0031] Document US 2,931 ,443 describes a hydraulic system for adjusting the pitch of controllable-pitch ship propellers (CPP). The propeller hub, which houses the controllable blades, is mounted on a fixed vertical support element extending from the stem of the ship. A bearing is provided that supports only part of the propeller’s weight, essentially serving as a guide for the aft part of the propeller hub. It is not indicated how easy installation and removal of this solution can be carried out, nor which measures are necessary to ensure the absence of disturbances caused by excessive proximity of the propeller blades to the new type of support structure.

[0032] Document JP 2012121370 A describes a ship propulsion system focused on the design of the propeller shaft support structure. The installation shown in the drawings clearly refers to a twin- propeller installation and, in any case, not to a ship with a central propeller.

[0033] The hull is incorrectly described as having a profile that slopes downward from bow to stem. The bearing supporting the weight of the propeller and its shaft appears to have the same longitudinal dimension as the support bracket, and such support bracket can be mechanically connected to the rudder structure. It is not indicated how easy installation and removal of this solution can be carried out, nor which measures are necessary to ensure the absence of disturbances caused by excessive proximity of the propeller blades to the new type of support structure.

[0034] One purpose of the present invention is therefore to create a stem form for propeller support that solves the problems of the prior art.

[0035] In particular, the present invention also allows a substantial elimination of such propeller efficiency loss as a result of the drastic reduction of disturbances to the fluid filaments at the propeller disk.

[0036] BRIEF SUMMARY OF THE INVENTION

[0037] These and other objectives are achieved by a stem form for a conventional propeller, applicable to the hull of single- and multi- propeller ships with a central propeller, in which it is currently common practice for the stem area of the hull to present a bulge intended to house the propeller shaft and its supporting bearing. The invention is characterized in that the cross-sections of the ship’s hull, in the stem area, are modified and shaped, from the extreme stem towards the bow, to fluidly conform with the external surface of the hull up to the sections no longer affected by the shaft sealing arrangement, thereby reducing flow discontinuity upstream of the propeller, and allowing a reduction of the wetted surface of the hull, a decrease in construction cost, a decrease in fuel consumption, and an improvement of overall propulsive efficiency.

[0038] An advantage of the invention is precisely that it allows a substantial elimination of such propeller efficiency loss through the drastic reduction of disturbances to the fluid filaments at the propeller disk.

[0039] Another advantage is made possible by the new stem hull form in the case of a single- or multi- propeller ship with a central propeller, which results, in addition to the above- mentioned improvement in propeller efficiency, in a reduction of the wetted stem surface of the hull.

[0040] Another advantage is due to the simplification of the hull plate curvatures in the affected stem area, with a consequent reduction in the relative construction cost.

[0041] Further features of the invention can be deduced from the dependent claims.

[0042] BRIEF DESCRIPTION OF THE FIGURES

[0043] Further features and advantages of the invention will become apparent from the reading of the following description provided by way of example and not limitation, with the aid of the figure shown in the attached drawing, in which:

[0044] - Figure 1 illustrates the flow of fluid filaments at the propeller disk for a single- propeller ship;

[0045] - Figure 2 illustrates the cross-sections of a stem form and a bow form in adjacent front view for a single- propeller ship, both belonging to the prior art;

[0046] - Figure 3 illustrates in side view a stem form for a single- propeller ship belonging to the prior art;

[0047] - Figure 4 illustrates the cross-sections of a stem form and a bow form in adjacent front view for a single- propeller ship, both belonging to the present invention;

[0048] - Figure 5 illustrates in side view a stem form for a single- propeller ship belonging to the present invention;

[0049] - Figure 6 illustrates in front view a stem form for a single- propeller ship belonging to the prior art; - Figure 7 illustrates in front view a stem form for a single- propeller ship belonging to the present invention;

[0050] - Figure 8 illustrates in front view, with detail highlighted, a stem form for a singlepropeller ship belonging to the prior art;

[0051] - Figure 9 illustrates in front view, with detail highlighted, a stem form for a singlepropeller ship belonging to the invention;

[0052] - Figure 10 illustrates in front view the detail of the stem form of Figure 8;

[0053] - Figure 11 illustrates in front view the detail of the stem form of Figure 9;

[0054] - Figure 12 illustrates in side view a stem structure for a single- propeller ship belonging to the prior art; and

[0055] - Figure 13 illustrates in side view a stem form for a single- propeller ship belonging to the present invention.

[0056] DETAILED DESCRIPTION OF THE FIGURES

[0057] The invention will now be described with initial reference to Figure 2, which illustrates a stem form 100’ and a bow form 200’ in adjacent front view for a single- propeller ship, both belonging to the prior art.

[0058] This Figure 2 should be compared with Figure 4, which illustrates a stem form 100 and a bow form 200, in adjacent front view for a single- propeller ship, both belonging to the present invention.

[0059] Figure 3 illustrates in side view the stem form 100’ for a single- propeller ship belonging to the prior art, to be compared with Figure 5, which illustrates in side view a stem form 100 for a single- propeller ship belonging to the present invention.

[0060] From these comparisons, note in particular, for the prior art, the bulge, see Figure 3, detail 10T, for the exit of the propeller shaft including the water seal and the propeller supporting bearing.

[0061] This bulge and the consequent stem forms are modified as shown in Figures 5 and 4, both in longitudinal view and in the stem cross-sections.

[0062] To fully highlight the differences between the two stem forms, see the comparison between Figure 6 (which illustrates in front view the cross-sections of a stem form 100’ for a single- propeller ship belonging to the prior art) and Figure 7, which illustrates in front view a stem form 100 for a single- propeller ship belonging to the present invention.

[0063] From the comparison of Figures 6 and 7, the following modifications between the current hull and the hull modified according to the invention can be identified: the cross-sections of the hull up to section no. 7 remain unchanged; the cross-sections of the hull marked: 8, 87, 9, are deeply modified in the parts between lines A and B, due to the elimination of the propeller bulge enabled by the redesign of the propulsion structure, as better illustrated below. the cross-sections of the hull marked: 97 and 10 remain unchanged.

[0064] Figure 8 illustrates in front view, with detail 110’ highlighted, a stem form 100’ for a single- propeller ship belonging to the prior art, and Figure 9 illustrates in front view, with detail 110 highlighted, a stem form 100 for a single- propeller ship belonging to the invention.

[0065] Furthermore, Figure 10 illustrates in front view detail 110’ of the stern form 100’ of Figure 8, and Figure 11 illustrates in front view detail 110 of the stem form 100 of Figure 9.

[0066] In these figures, in addition to the two complete stem forms, prior art and invention, the curves of the cross-sections affected by the patent modification are drawn: for sections 8, 8 , 9, below the reference lines A and B, called Lines Plan in naval technology.

[0067] As is known, the lines plan are surfaces that intersect the hull forms and are represented on the horizontal and lateral planes (not shown in the drawings) and are used to check the alignment of the hull surfaces, which could have small errors not visible in the normal front, lateral, or horizontal views.

[0068] It is noted that the three sections affected by the modification have perimeter lengths: 9-CN-9, etc. (CN = Ship Center) significantly different, and consequently a hull surface Sw considerably different, resulting in the final reduction in fuel consumption from which the stem form of the invention benefits compared to current hulls.

[0069] This reduction leads to a decrease in the total wetted surface of the hull. A rough estimate may be 2-3%, and therefore, adding the two contributions — propeller efficiency and hull surface — it is possible to estimate a total power and, consequently, fuel saving of 6-9%.

[0070] The present invention increases the performance of single- or multi- propeller hulls with a central propeller currently used in naval engineering, improving their engineering characteristics; it is in fact evident the greater ease of design and construction of the proposed stem structures, which are more easily workable and producible than current ones (comparison of Figures 2 and 4 and Figures 3 and 5).

[0071] In fact, the construction and internal outfitting, especially for ships of considerable size, of a stem structure like the current one poses significant engineering and production problems, considering the need to perform mechanical work on various parts of the structure with difficulties in executing the necessary thick-plate curvatures and their alignment with the reinforcement structures within the hull and with the shaft exit from the hull.

[0072] Moreover, the present invention significantly simplifies the shape of a current stern with the corresponding shape and structure identified by comparison of Figures 2 and 4 and Figures 3 and 5.

[0073] In addition, the present invention reduces the interactions on the fluid filaments currently induced by the traditional stem, allowing a more uniform flow at the propeller disk, both in the traditional case and allowing an improvement of the flow at the propeller disk (see the comparison between Figures 6 and 7).

[0074] Furthermore, the present invention reduces the wetted surface of the hull without adding design or regulatory complications.

[0075] With reference to the comparison between Figures 6 and 7, the following modifications and the resulting constructional and hydrodynamic advantages become evident: the current hull presents shapes that are clearly complex in their geometry and therefore particularly costly to manufacture.

[0076] In current hulls, it is easy to notice the attempt to move the stern forms away from the propeller disk to reduce the disturbance effect on the fluid filaments induced by the current hull; this geometry improves the hydrodynamic operating condition of the propeller but is still more costly to manufacture than that shown in Figure 2 and Figure 3 in the part relating to the current hull.

[0077] The stem hull form of the invention therefore results in being: easier to design; simpler to construct; improved with regard to the use of the affected internal volumes; extremely useful for increasing qB and therefore overall propulsive efficiency, with a consequent reduction in fuel consumption; extremely useful for reducing the wetted surface of the hull, with lower resistance to advancement and, again, a consequent reduction in fuel consumption.

[0078] In essence, the hull of the invention for single- or multi- propeller ships with a central propeller allows a reduction in ship production costs, better utilization of internal spaces, and a reduction in fuel consumption.

[0079] It is also noted that the ship itself will not have an apparently different configuration or behavior in navigation / maneuvering requiring additional adjustments: it remains the same as before, even in the case of an already operational unit being modified from the prior-art hull to that of the invention at the same displacement.

[0080] Figure 12 illustrates in side view a stem form 100’ for a single- propeller ship belonging to the prior art, and Figure 13 illustrates in side view a stem form 100 for a singlepropeller ship belonging to the present invention.

[0081] In the prior-art stem form 100’ of Figure 12, the rudder 15’ and the bulge 50’ supporting the shaft 22’ of propeller 21 ’ are evident, whereas in the stem form of the invention 100 of Figure 13, the rudder 15 and a support structure 50 supporting the shaft 22 of propeller 21 are evident.

[0082] From the comparison between Figures 12 and 13, it can be seen that the distance D between the propeller 21 and the surface closest to it of the stem form 100 of the invention is more than double the distance D’ between the propeller 2T and the surface closest to it of the stem form 100’ according to the prior art.

[0083] Considering ship dimensions, speed, propeller dimensions, shafting dimensions, the distance between the propeller-bearing bearing and the shaft-seal bearing on the hull, the stem structure of the invention can be constructed with a solution using bent plates welded to each other and to the internal structures.

[0084] The material to be used and its surface treatment will be those typical of naval structures of this type.

[0085] In general, the materials to be used should have the following characteristic: corrosion resistance: to withstand exposure to salt or fresh water; tensile strength: to withstand hydrostatic pressures and stresses due to ship motions; toughness: to absorb stresses resulting from collision with other ships or mooring structures or submerged objects such as logs or ice; weldability: essential for assembling the various parts of a ship in a robust manner; flexibility and formability: they must be adaptable to the different shapes of naval components, from hulls to decks and superstructures.

[0086] By way of example only, steels such as AH36, DH36 and EH36, normally used in shipbuilding, or equivalents, may be used.

[0087] As indicated above, the geometric modifications of cross-sections 8, 8 , and 9 reduce the interactions on the fluid filaments induced by the stem, optimizing the flow toward the propeller disk and improving propeller efficiency. In the stern form 100, the distance between the propeller and the closest surface of the stem form is increased by at least double compared with the prior art, further reducing hydrodynamic interference.

[0088] The structure 50 of the stem form 100 of the invention can be designed, constructed, and used in a dry dock as support for the ship’s weight.

[0089] The stem form 100 can also be used for naval units having single- propeller or multipropeller hulls with a central propeller of current type that are under construction and also for units already in operation.

[0090] To the present invention, a person skilled in the art, in order to satisfy contingent and specific requirements, may make further modifications and variations, all of which are nonetheless contained within the scope of protection of the invention as defined by the following claims.

Claims

CLAIMS1 . A stern form for a ship propeller, applicable to the hull of single-propeller and multipropeller ships with a central propeller, of the current type in which the stem area of the hull presents a bulge intended to house the shaft and the supporting bearing of the propeller, characterized in that the cross-sections of the ship’s hull, in the stern area, are modified and shaped, from the extreme stem towards the bow, to fluidly conform with the external surface of the hull up to the sections no longer affected by the shaft sealing arrangement, reducing flow discontinuity upstream of the propeller, allowing a decrease in construction cost, a reduction of the hull’s wetted surface, a decrease in fuel consumption, and an improvement in overall propulsive efficiency.

2. A stem form for a ship propeller according to claim 1 , wherein the modifications made result in a reduction of the total wetted surface of the hull, generally compared to the same unmodified hull in the stem area, significantly contributing to the reduction of fuel consumption.

3. A stem form for a ship propeller according to claim 1 , wherein the modifications made compared to the same unmodified hull in the stem area result in a reduction of fuel consumption of up to 9%.

4. A stem form for a ship propeller according to claim 1 , characterized in that the geometric modifications of cross-sections 8, 8 , and 9 of the hull, compared to the same unmodified hull in the stem area, reduce interactions on the fluid filaments induced by the stem, optimizing the flow toward the propeller disk and improving the propeller efficiency behind the hull.

5. A stem form for a ship propeller according to the preceding claims, characterized in that the distance between the propeller and the closest surface of the stem form is significantly increased compared to the same unmodified hull in the stem area, further reducing hydrodynamic interference.

6. A stem form for a ship propeller according to the preceding claims, characterized in that the shape of the stem area allows the use of the form with conventional propulsion and steering systems, without substantial changes to the positions of the propeller and the rudder.

7. A stem form for a ship propeller according to the preceding claims, characterized in that the said form can be designed, constructed, and used in a dry dock as support for the ship’s weight.

8. A stern form for a ship propeller according to the preceding claims, characterized in that the configuration of the stem area allows the application of the form both during the construction of new naval units and as an adaptation element on existing hulls, without substantial modifications to the overall hull configuration or to the alignment of the propulsion system.

9. A stem form for a ship propeller according to the preceding claims, wherein said stem form is made using steels of the type AH36, DH36, and EH36, or equivalents.

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