EP0134767B1

EP0134767B1 - Hull configuration

Info

Publication number: EP0134767B1
Application number: EP84850227A
Authority: EP
Inventors: Roar Ramde
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-07-19
Filing date: 1984-07-18
Publication date: 1987-03-25
Also published as: NO153560C; DK352584D0; NO840609L; DK160471C; FI78650C; FI842794A0; GR82096B; NO153560B; EP0134767A1; ES534423A0; FI842794A; DK160471B; FI78650B; KR850001104A; DE3462769D1; ES8505599A1; DK352584A

Description

The invention relates to' a displacement-type hull configuration which makes it possible to improve a vessel's deadweight tonnage, transverse stability, navigational and sailing properties and to reduce stresses on the hull beam whether the vessel is sailing in quiet water or into the waves.
At given main dimensions of length, breadth and depth to the design waterline, conventional hull configurations can obtain greater deadweight tonnage by increasing the roundness of the underwater portion of the hull, thereby increasing the total displacement.
To improve the transverse stability of a conventionally formed hull, expressed as a higher initial metacenter, the breadth of the hull can be increased to obtain a greater moment of inertia at the waterline, optionally also raising the volumetric center of gravity of the underwater hull.
However, changes of this nature (increasing roundness and breadth), as demands for transverse stability and speed increase, will eventually result in an unacceptable increase in a conventional vessel's resistance to propulsion in quiet waters as well as in heavy waves.
To improve the seagoing properties of a conventional hull configuration, expressed as the vessel's angular movements about a transverse axis (pitching), vertical movements (heave) and the amount of increase in propulsion resistance compared to the resistance in quiet seas, one seeks to alter the vessel's natural frequency of pitching and heaving so that this frequency insofar as possible does not coincide with the frequency of the wave lengths which the vessel encounters.
In the case of conventional hull designs, structural alterations result in only slight improvements in the seagoing properties of the vessel, and extreme pitching and heaving movements and a great increase in the resistance to propulsion will occur when the ship is sailing into the waves when the prevailing wave length is approximately equal to the ship's length at the waterline.
Depending on the type of vessel and its rate of speed, such synchronous movements always make it necessary for a conventional ship to reduce speed or alter course in relation to the waves, thereby altering the cycles of encounter with the waves so that the wave period does not coincide with the natural frequency of the vessel's pitching and heaving.
Conventional hull configurations having an approximately rectangular displacement distribution will be subjected, as a function of increasing size, to bending and shear stresses which necessitate very large dimension materials and in special cases also restrict the distribution of cargo and/or ballast.
The present invention is defined in claim 1. In accordance with the present invention, the deadweight tonnage, transverse stability, seagoing properties and the magnitude of tolerable bending and shear stresses on the hull beam can all be improved without incurring the above drawbacks. The invention permits the hull to be made with rounder lines than conventional hull configurations, expressed by the term for leanness of line L/V^1/3, where L is the length of the hull at the design waterline corresponding to the depth T to the summer freeboard and V is the displacement volume of the hull at the design waterline, and where LN1¹³ can be about 3 or greater than 3 without increasing the specific resistance to propulsion compared to conventional hull configurations, while at the same time the hull breadth B can be increased such that the L/B ratio can be about 2 or greater than 2, where B is the maximum breadth of the hull at the design waterline, whereby the height of the metacenter of the hull can be more than doubled in relation to conventional hull configurations of the same length.
At the critical wave length/hull length ratio for conventional hull configurations sailing into the waves,-the seagoing properties of the hull configuration of the invention are improved, such that the hull's pitching and heaving movements are reduced compared to the movements of conventional hulls traveling at the same rate of speed, and these movements are also retarded such that the improved hull does not exhibit correspondingly large movements until the wave length/hull length ratio is more than twice as large, while at the same time the improved hull's resistance to propulsion is reduced to a similar degree.
According to a preferred embodiment of the invention, the displacement distribution in the longitudinal direction approximates a Rayleigh wave which with normal distribution of cargo will result in a reduction of the longitudinal moment of bending on the hull beam of around 50 % compared to conventional hulls. To obtain the abovesaid improvements, the hull configuration according to the invention must be formed with squarely cut off, approximately harmonic sinusoidal waterlines (dwl, 1, 2, 3) with extremity or stationary, points at the ends of the hull fore and aft, while at the same time the base lines of the waterlines (O_dli, 0₁, 0₂, 0₃) from the design waterline (dwl) and at increasing depths from this, gradually are displaced in the direction of forward propulsion and shortened so that an approximately oblique surface (s), which may be straight or approximately sinusoidal in longitudinal cross section and with extremity points around L/2 and at the hull's stern end, forms a wide, elevated surface (s) which comprises the stern half of the hull, and which thus permits utilization of a propulsion system characteristic for this hull configuration consisting of a support hydroplane (p) extending transversely in the horizontal plane across the full breadth of the hull, having a streamlined shape, and being fixed or rotatable about a horizontal axis in connection with supports (q), optionally provided with one or more horizontal rudders (h) at the aft edge, and wherein a plurality of propulsion units (f) are mounted at the fore or aft edge of the support plane, above or beneath it.
According to the preferred embodiment of the invention, a transverse section through the hull configuration below the design waterline (dwl) at a distance of about 0.15 L from the stern, will have a ratio between the breadth (B_i) at the design waterline and the depth (t₁) of the hull measured from the same waterline which will be about 3 or greater than the corresponding ratio for a section at L/2 where the breadth (Bv and depth (to are measured in the same way.
As a result of the invention, the hull parameter e = c_p/c_dwl will preferably be about 1 or greater than 1, where cp is defined as the hull's longitudinal prismatic coefficient expressed as the ratio between the displacement volume V to the design waterline and the volume of a body equal to the area of a transverse section up to the design waterline at L/2, designated A_L/2, multiplied by the design waterline L, which may be expressed by the equation cp = V/A_L/2 · L, and where c_dwl is the waterline coefficient for the design waterline, defined as the ratio between the waterline area A_dw, and the product L · B where B is the maximum breadth at the waterline, which may be expressed by the equation c_dwl = A_dwl/LB.
As a result of the invention, the design waterline's areal center of gravity (LCF) will be located around 0.2 L aft of L/2 and the improved hull's volumetric center of gravity (buoyancy) (LCB) at the depth of the design waterline (dwl) around 0.075 L forward of the areal center of gravity, which may be expressed as LCF - LCB = 0.075 L.
The hull configuration according to the inven- _ tion can in the region from the stern post and forward to about 0.3 L be provided with turbulence-controlling appendages which may consist of fixed or flexible fin-like means (v) in the streamline direction mounted approximately perpendicular relative to the hull and located approximately at the transition between the bottom and sides of the hull, or as longitudinal grooves in the form of pointed, rectangular or wave-like grooves (x) which decrease in depth in the direction of forward propulsion and which at about 0.3 L terminate in and coincide with the even portion of the oblique surface (s) and whose depth (d) will usually be about 0.02 B.
The improved hull configuration of an exemplary embodiment of the invention is shown in the accompanying figures 1, 2, 3, 4, 5, 6 and 7.

Figure 1 shows the improved hull configuration's squarely cut off, approximately harmonic sinusoidal waterlines around the design waterline (dwl) with extremity points around the hull's bow and stern ends, with the areal center of . gravity (LCF) about 0.2 L astern of L/2 and where the length/breadth ratio L/B of the design waterline is shown as being about 2.
Figure 2 shows the improved hull below the design waterline (dwl) in vertical section, where it may be seen that the base lines of the squarely cut off, approximately harmonic sinusoidal waterlines (0_dwl, 0₁, 0₂, 0₃) along an oblique plane surface (s), which are displaced in the direction of forward propulsion of the vessel, coincide with the base plane (g) at about L/2, and the distance between the areal center of gravity (LCF) and the buoyancy center of gravity (LCB) of the hull at the depth of the design waterline (dwl) is about 0,075 L.
Figure 3 shows the improved hull configuration of Figure 2 in horizontal projection with the waterlines dwl, 1, 2,3 and g, in the example with a U-frame at the bow end of the hull, but other known frame forms can also be utilized, as required.
Figure 3 also shows the characteristic ratio between breadth and depth for a section around 0.1 L from the stern and at L/2, where the respective breadths and depths are designated B₁ and B₂ and t₁ and t₂.
Figure 4 shows a vertical section near the center plane in the hull's aft-section with the base plane (g), oblique plane (s), support (q), support hydro-plane (p), horizontal rudder (h), propulsion units (f) and vertical rudder (r), in this case shown with the propulsion unit (f) positioned in front of and underneath the support plane (p), but the thrusters can also be mounted at the aft end or above the support plane.
Figure 5 shows a section parallel to and below the oblique plane (s), support plane (p), supports (q), horizontal rudders (h), the overlying contour of the design waterline (dwl) and the propulsion units (f), in this example four in number and mounted at the forward edge of the support plane.
figure 6 shows the improved hull configuration's design waterline (dwl). On the upper half of the figure, an example of placement of the fin-like appendages (v) mounted in connection with the oblique plane (s) may be seen. On the lower half of the figure, an example may be seen of the groove-patterned portion (x) of the oblique plane (s). Both of these are indicated by broken lines in the drawing. The line A-A in Figure 6 is a transverse section through the stern portion of the oblique plane (s), shown again in Figure 7 with turbulence-controlling, fixed or flexible appendages (v) on the left-hand side of the figure and an example of longitudinally oriented grooves or ridges (x) on the right-hand side, showing the approximate depth (d) of the grooves in relation to the oblique plane (s).

Claims

1. A hull of the displacement type, having squarely cut off, longitudinally approximately sinusoidal waterlines defining a half wavelength at each side of the hull with stationary points of the curves at or adjacent the hull's fore and aft end points, and wherein the waterlines' base lines (0_dwl, 0₁, O2, 0₃) gradually, with increasing depth from the design waterline (dwl), are displaced in the direction of forward propulsion until they become tangential with the base plane (g) at about L/2, whereby an approximately oblique surface (s) through the base lines (0_dwl, 0₁, 0₂, 0₃) forms a broad termination at the stern half of the hull, under which there is mounted in the horizontal plane, transversely positioned, and fixed or rotatable about a transverse axis, a support hydro-plane (p) provided with propulsion units (f) distributed across the width of the support plane, mounted above or below said plane at the forward or aft edge thereof.

2. A hull according to claim 1, wherein the displacement in the longitudinal direction is distributed approximately.on a Rayleigh curve.

3. A hull according to claims 1 and 2, wherein the hull parameter e = c_p/c_dwl is about 1 or greater than 1, where cp is defined as the longitudinal prismatic coefficient expressed as the ratio between displacement volume V to the design waterline (dwl) and the volume of a body constituted by a cross-sectional area corresponding to that of a transverse section up to the design waterline (dwl) and passing through its half- length L, designated A_L/2, multiplied by the length L of the design waterline, and where c_dwl is defined as the waterline coefficient expressed by the ratio between the area enclosed by the design waterline and the maximum length L of the design waterline multiplied by its maximum breadth B.

4. A hull according to claim 1, wherein the number representing leanness of line L/V^1/3 is about 3 or greater than 3, wherein L is the length of the design waterline and V is the displacement volume of the hull configuration below the design waterline (dwl) to the maximum depth (T) for which the hull is designed.

5. A hull according to claim 1, wherein the ratio between the hull's maximum length and the breadth measured at the waterline at the maximum depth (T) for which the hull is designed is about 2 or greater than 2..

6. A hull according to claim 1, wherein the ratio between a transverse breadth (B_i, B₂) and depth (t₁, t₂) is at least three times larger at a section measured at about 0.15 L from the stern than at U2, where L is the length of the waterline at the depth for which the hull is designed.

7. A hull according to claim 1, wherein the oblique surface (s) in longitudinal section is formed approximately as a sine wave with stationary points at L/2 and the hull's stern end.

8. A hull according to claim 1, having one or _ more, fixed or flexible, plateshaped appendages (v) mounted approximately perpendicular relative to the surface of the hull on both sides thereof at the transition between the bottom and sides of the hull, mounted in the streamline direction within about 0.3 L from the stern end of the hull.

9. A hull according to claim 1, wherein the aft portion of the oblique surface (s) is made with longitudinally oriented, pointed, rectangular or wave-like grooves (x) which at about 0.3 L terminate in and become coincident with the oblique surface (s).