WO1996020105A1

WO1996020105A1 - Means and method for dynamic trim of a fast, planing or semi-planing boathull

Info

Publication number: WO1996020105A1
Application number: PCT/SE1995/001582
Authority: WO
Inventors: Stanislav D. Pavlov; Serguej A. Porodnikov; Clas Norrstrand; Hans Eriksson
Original assignee: Marine Technology Development Ltd.
Priority date: 1994-12-23
Filing date: 1995-12-22
Publication date: 1996-07-04
Also published as: SE502671C2; AU4361796A; SE9404502L; SE9404502D0

Abstract

Mechanism for dynamic trimming of the floating position of a planing or semi-planing ship hull during operation thereof, including a plate (3) that is submerged transversely to the relative water flow directly behind the bottom of the hull for generating a vortex (V) having an upwardly and forwardly directed velocity component in front of the plate, thereby creating a water volume having an increased pressure that is acting upon the portion of the bottom which is positioned in front of the submerged plate. The plate (3) is continously adjustable to a desired depth through actuating members (8) and is vertically displaceable and supported in the lowermost portion of the stern plate of the hull.

Description

MEANS AND METHOD FOR DYNAMIC TRIM OF A FAST, PLANING OR SEMI-PLANING BOATHULL

The present invention relates to a mechanism for continous control and trimming of the floating position of a fast, planing or semi-planing ship hull during the operation thereof. The invention more specifically provides a mainly vertically adjustable foil, disposed at the stern of the ship hull. The foil is provided for a continous control of the pressure conditions in the water underneath the aft bottom portion of a single-hull or multiple-hull vessel. The invention therewith relates also to a new method for the dynamic trimming of a shiphull of said type.

High speed, sea-going vessels (planing or semi-planing) require a dynamic trimming of the vessel's floating position under operation, to achieve an optimum performance under variying conditions. The expression "dynamic trimming" is herein to be understood as a continuos, active counter acting to the pitching and rolling movements of the vessel in operation. In these kinds of hulls, the point of gravity is regularly displaced towards the aft of the hull, requiring a continous trimming of the floating position to counter act the increased liability for pitching movements. A continous trimming is also required to counter act the rise of the stem, caused under acceleration by the upwardly directed component of force of the water. For reasons of operation economy it is therefore of interest to force the hull into an optimum floating position as soon as possible. Other parameters which also affect the performance of the vessel, besides the placement of the point of gravity, are e.g. the operational speed, weather conditions, the course angle relative to wave and wind directions etc.

Known methods of dynamic trimming are e.g. the use of trim planes. Trim planes are commonly arranged behind the stern, or alternatively embedded under the stern as an extension of the bottom of the hull, or forming a part thereof. Trimming of the floating position is achieved by pivoting the trimplane upwards or downwards with the object to impart to the relative waterflow a vertically directed component of force, creating an increased or decreased pressure acting on the bottom side of the trim plane.

A drawback related to this known method is that the major part of the load that is added and used for changing the floating position, is transferred to the trim plane. This drawback is of significant disadvantage in connection with modern design implementations, wherein the trim planes are designed to swing continously in order to counter act pitching and rolling movements under operation. Serious problems of exhaustion have arised in these implementations, and the raised energy consump¬ tion reduces the efficiency of the method.

Another drawback related to the known trim planes is that the arrangement of the trim planes behind the stern or underneath the aft bottom of the hull will obstruct the reversed water jet of the power unit during retardation. Upon retardation the trim planes will also, due to their placement, take up excessive load from the water jet, the later being the most effective and common power system used for the type of vessels which is referred to. In order to withstand this excessive load, the trim plane and its associated actuating and supporting means can be over-sized. As an alternative, the working area of the trim plane can be under¬ sized, thereby permitting the trim plane to go free of the water jet. Naturally, this will reduce the efficiency of the trim plane, and will disadvantageously affect the operation economy.

The object of the present invention is therefore to provide a mechanism for the dynamic trimming of the floating position of a fast, planing or semi-planing ship hull, whereby the mentioned drawbacks connected with the known trimming devices are elimina¬ ted.

Another object of the present invention is to provide a new method for the dynamic trimming of the floating position for said ship hull. These and other objects are met with a mechanism and a method having the features listed in the attached claims.

The invention is disclosed more in detail by the following description, with reference made to the attached drawings, of which

Fig. 1 is an elevational view from behind showing a first em¬ bodiment of a trimming foil according to the invention, mounted on the stern of a planing or semi-planing ship hull,

Fig. 2 is a sectional view along the line II-II of fig. 1 , showing the trimming foil in a raised, resting mode,

Fig. 3 is a sectional view, showing the trimming foil of fig. 2 in a submerged, operational mode,

Fig.s 4a and 4b are side views of an alternative embodiment of a trimming foil in raised and submerged positions, respectively, and

Fig. 5 is a side view of another alternative embodiment of the trimming foil.

Fig. 1 shows the mechanism of the present invention that is generally referred to with reference numeral 1. The mechanism is mounted at the lower end of the stern of the ship hull 2. The illustrated embodiment includes the mechanism 1, that is from here on referred to as trimming foil 1, a substantially plane disc or plate 3, that is vertically adjustable and supported on a stern plate 104. The plate 3 includes, in the illustrated position, a downwardly extending edge 5. The adjustability of the plate 3 may be performed by guide pins 6 that slide within grooves 7, running in parallel and disposed in the trimming foil. The movements of the trimming foil are activated by hydraulic, electro-hydraulic or mechanical driving mechanisms that are not shown. The movements are transferred to the trimming foil 1 by bar members 8, 9. In the alternative, the movements may be activated directly by pistons 8, 9 of hydraulic piston/cylinder units.

The trimming foil has a length of 1 that substantially corresponds to the width of the lower edge of the stern plate. The foil is preferably split into two halves so that each half is adjustably attached so that the foils may be independantly submerged to a desired depth in the relative water flow below the bottom of the ship hull. The foils may be moved by drivable transferring members and/or directly by the driving members. The movements of each half of the trimming foil 1 may therefore be controlled together or independently to counter or reduce the pitching or rolling movements of the ship hull. Fins 10, 11 are attached to each side of the trimming foil 1. The fins extend mainly vertically in the longitudinal direction of the ship hull, at least from the trimming foil and forward. The fins have a height that at least corresponds to the height of the portion of the trimming foil that is submerged when the trimming foil is submerged to a maximum in the water flow. The length of the fins 10, 11 may be adapted to the shape of the ship hull. However, the length should not be shorter than the height of the portion of the trimming foil, that is submerged to a maximum, and is preferably longer than the height of this submerged portion. In the alternative, the fins 10, 11 may be attached to the ends of the trimming foil 1 or to the ship hull and preferably in the area of the bottom of the ship hull as shown in Fig. 1.

Fig. 2 shows the trimming foil 1 in a raised rest position so that the edge 5 is disposed at the same level as the bottom 12 of the ship hull or at least so that it does not extend below the bottom. The function of the fin 10, which may have a suitable shape with regard to the above mentioned dimensioning considerations, is described below in connection with Fig. 3. During movements in the direction of the arrow F in Fig. 2, a load is applied against the bottom of the ship hull when the water is transected by the ship hull. Thus, this load is gradually reduced toward to the stern of the ship hull. This is illustrated as a schematic in Fig. 2 by the arrows P that extend vertically against the ship hull.

Fig. 3 shows the trimming foil 1 in an operational position when the trimming foil has been lowered to a maximum so that the edge 5 protrudes below the bottom 2 of the ship hull at a depth A. The depth A may vary depending on the specific application. In the lowered position, the trimming foil presents a surface 5 ' that extends perpendicular to the direction of the relative water flow so that the water flow is slowed down against the surface. The fins 10, 11 therefore serve to prevent the water volume that has been slowed down from escaping the outer end areas of the trimming foil. In this way, the water volume that is caught is exposed to a compression or pressure increase. It may be realized that the submerged trimming foil 1 provides an increased drag during the operation of the ship hull. However, it has been shown in models and full scale tests that this increased drag is negligible and is outweighed by the overall improved energy efficiency of the ship hull due to the advantageous effects of the trimming foil. These tests have, however, indicated that it is advantageous that the depth A, that is the lowest depth of the edges 5 and surface 5' of the trimming foil, account for about 3% of the total length of the trimming foil 1 and preferably should, at a maximum, be about 2.7% of the length.

Fig. 3 illustrates a schematic of an embodiment of the trimming foil 1 that is arranged to slope at an angle a (alpha) in the vertical direction relative to the length of the ship hull so that the angle a is below determined relative to a line N that is the normal to the bottom of the ship hull. The angle a includes a shifting of the angle from the line N which, according to the tests and trials mentioned above, preferably should be within the interval of about 3 (three) to plus/minus 5 (five) degrees. That is, according to Fig. 3, this interval is within - 2 to +8 degrees as measured from the line N and toward the stem of the ship hull. By introducing a surface immediately behind the bottom of the ship hull that is perpendicular to the water flow L, a main vortex V is generated that has a velocity component that is directed upwardly and forwardly relative to the bottom of the ship hull. A plurality of minor whirls are also generated but are not shown. The main vortex V has the same length 1 as the length of the trimming foil 1 and extends between the fins 10, 11. The vortex rotates to create a water flow that is directed upwardly/forwardly below the bottom of the ship hull and in front of the trimming foil. In this way, a zone of increased pressure is created which is directed to the bottom surface as illustrated with P' in the schematic shown in Fig. 3. The magnitude of the pressure in the area of increased pressure depends on the velocity of the ship and the height of the submerged portion of the trimming foil 1.

It is to be understood with reference to the above descrip¬ tion that changes of the depth of the submerged trimming foil directly affect the trimming position of the ship at velocities above a certain critical limit.

Extensive tests have thus shown the above characteristics relating to the operational depth of the trimming foil and the slope of the foil relative to the bottom of the ship hull. The same tests have shown that the drag that is generated by a trimming foil that is formed according to the present invention, is negligible. The test results show an increased effectiveness that may be calculated for all ship sizes that are operated at a FNL value that is higher than 0.6. The FNL value refers to the dimension free Froude value which takes the constant of gravity into account and depends on the length of the ship and the velocity thereof.

With reference to Figs. 4a and 4b, a schematic of an alternative embodiment of the trimming foil of the present invention is shown. In this embodiment, a trimming foil 1', having a bow shaped cross section, and a surface 5'', that is turned in the direction of the movement of the ship hull, are secured to a peripheral end of a rotatable rod member 13 to transfer a peripheral movement to the trimming foil 1 ' . In this way, the rod member 13 may be mounted into a recess 14 disposed in the stern plate of the ship. It should be understood that a certain number of rod members 13 are required to provide stable rotatable attachment and movement of the trimming foil 1 ' although only one rod member is shown in the figure. The trimming foil 1' is formed so that it may rotate about a pivot point 15 so that its radius is a distance R. The pivot point 15 may be attached to the sides or to a bottom 16 disposed in the recess 14. The rod member 13 may be controlled to raise or lower the trimming foil 1' to the position, as shown in Fig. 4b. This movement may be performed by hydraulic, electro-hydraulic or mechanical driving mechanisms not shown. In this way, a piston/cylinder unit may, for example, be attached within the recess 14 or extend to the outside of the stern plate as is known to the person of ordinary skill in the art. Naturally, the alternative embodiment of the trimming foil 1 ' must be designed so that the portion of the trimming foil 1 ' that is submerged in the water flow satisfy the geometrical requirements regarding length, sloping angle, and depth in the water as was determined above for the trimming foil 1. Similar to the trimming foil 1, the trimming foil 1 ' cooperates with fins attached to each side of the foil 1' . Also, the foil 1' preferably is divided into two halves which are individually movable by separate driving members.

It should here be pointed out that the gap 17 that may be created between the stern plate and the trimming foil in all applications should be kept to a minimum to prevent water from escaping through an opening which would lower the efficiency of the increased pressure that is generated in front of the trimming foil.

With reference to Fig. 5, yet another embodiment of the trimming foil of the present invention is shown. In this embodiment, the trimming foil l' ¹ includes a bow shaped surface 5' ' ' that is turned in the direction of the movement. A rod 24 is adapted to transfer peripheral movements to the surface 5' ' ' by being rotatably attached to a pivot point 18. The trimming foil 1^? ' is shown as having two separate halves that are each rotatably attached to holding devices 19, 20, respectively. The holding devices 19 are shown with dotted lines in the figure. To create enough space for the discharge portion of the driving device, both of the inner holding devices 19 extend away from the stern plate 4 at a certain angle. Both of the halves of the trimming foils are maneuvered individually by rotatably attached piston/cylinder units 22, 23 respectively. These units shift the trimming foil 1'' in a bow shaped path about the peripheral end portion of the rod 24. It should be understood that the two separate and individually maneuvered halves of the trimming foil provide continuous counter force to rolling movements or lateral movements of the ship. By coordina¬ ting the activation of both of the halves, the pitching movements or movements in the longitudinal direction of the ship may be reduced.

Obviously, the activation of the trimming foils may, in all embodiments, be controlled automatically to counter act the movements of the ship which are detected by for example a gyro. This detection is then converted into control signals for the driving mechanism of the trimming foil.

In the latter embodiment, the pivot point 18 should be positioned so that the operational position of the bow shaped surface 5'¹ ' of the trimming foil 1' ' is adapted to achieve the expected effect of desirable length, sloping angle and depth so that the parameters outlined above also apply to the trimming foil 1 ' ' . A detailed description of the dimensions are not going to be provided here because it is up to the person of ordinary skill in the art to adjust, for each specific application, the dimensions of the trimming foil including its suspension and rotation members to achieve the desired results based on the above description of the invention.

The trimming foil of the present invention provides a mechanically simple and reliable, effective and easily maintained mechanism at a moderate investment cost. The invention enables continuous, dynamic trimming of a fast moving ship hull while counter acting rolling and pitching movements during the operation of the ship. Some of the desirable results can be summarized as follows:

- Quick response and low energy requirements.

- High efficiency of the trimming energy provided.

- Low mechanical load of the moving parts.

- No disturbance of a reversed water jet stream.

Furthermore, by way of a rotatable trim plane being substituted by a vertically adjustable trimming foil, a fixed trim plane can likewise be substituted by a fixed trimming foil. The disclosed trimming foil can also be used in cooperation with other types of known devices, e.g. hydrofoils, for dynamic trimming of the floating position under acceleration and operation of a fast vessel.

Claims

1. Mechanism for dynamic trimming of the floating position of a planing or semi-planing ship hull during operation thereof, c h a r a c t e r i z e d by a surface (S'-S'^S'''), submerged transversely to the relative water flow directly behind the bottom of the hull and facing the operational direction of the hull, generating at least one main vortex (V), said vortex having an upwardly and forwardly directed velocity component in front of said surface to create a water volume having an increased pressure that is acting upon the portion of the bottom which is positioned in front of the surface.

2. Mechanism according to claim 1, c h a r a c t e r i z e d by the surface (S'-S'^S''') being submerged to a continously adjustable depth (A) that corresponds to about 0-3 % of the length of the surface, preferably up to a maximum of 2,7 % of the length.

3. Mechanism according to claim 1, c h a r a c t e r i z e d by the surface (5' ,5'' ,5''') extending along a substantial part of the width of the hull, preferably along the total width of the hull bottom or bottom halves.

4. Mechanism according to claims 1 and 3, c h a r a c t e ¬ r i z e by two fins (10,11), enclosing the surface (5',5'' 5' ' ' ) and positioned in association with the resp. outer ends of the surface, preferably attached to the bottom of the hull.

5. Mechanism according to claim 1, c h a r a c t e r i z e d by the submerged surface (5' ,5' ',5''') sloping in a vertical plane along the longitudinal section of the hull, the slope (a) advantageously being in the range of -2 to +8 degrees and preferably +2 to +4 degrees relative to a normal (N) to the bottom of the hull, when measured from stern to stem.

6. Mechanism according to claims 1 and 2, c h a r a c t e - r i z e d by a plane disc or plate ( 1), linearly displaceable and supported in the lower part of the stern plate (4), the side of the plate that is facing the operational direction (F) forming said surface (5' ), the plate ( 1) being continously submergeable to a desired depth (A) through associated hydraulically, electro- hydraulically or mechanically powered actuating members (8,9).

7. Mechanism according to claims 1 and 2, c h a r a c t e ¬ r i z e d by an arcuate disc or plate (1 ' , 1 ' ' ), rotatebly supported in the lower part of the stern plate (4) , the side of the plate (l',l'' ) that is facing the operational direction (F) forming said surface (5' ' , 5' ' ' ), the plate (1' , 1 * ' ) being continously submergeable to a desired depth (A) through associa¬ ted hydraulically, electro-hydraulically or mechanically powered actuating members (13,24).

8. Mechanism according to claims 1,2 and 7, c h a r a c t e ¬ r i z e d by the plate (1' ) being attached to the outer, aft end of a pivotable bar (13) that is mounted in a recess (14) in the stern plate (4).

9. Mechanism according to claims 1,2 and 7, c h a r a c t e ¬ r i z e d by the plate (l¹ ' ) being attached to the outer, forward end of a pivotable bar (24 ) that is mounted behind the stern plate (4).

10. Mechanism according to claim 1, c h a r a c t e r i z e d by the surface (5', 5' * ,5''') being split in halves, the resp. half being individually submergeable to a desired depth (A) through separately associated hydraulicaly, electro-hydraulically or mechanically powered actuating members (8,9,13,24).

11. Method for dynamic trimming of a fast, planing or semi- planing ship hull, c h a r a c t e r i z e d by - generating a water volume having an increased pressure that is acting on the aft bottom portion of the hull by submerging, directly behind the bottom of the hull, a surface (5', 5' ', 5' ' ' ) transversely to the relative water flow and facing the operatio¬ nal direction of the hull, and

- continously adjusting the submerging depth (A) in response to the movements of the ship.

12. Method according to claim 11, c h a r a c t e r i z e d by the surface (S^S''^''') being submerged to a depth (A) that corresponds to about 0-3 % of the length of the surface, preferably to a maximum of 2,7 % of the length, and sloping (a) within a range of -2 to +8 degrees, preferably +2 to +4 degrees relative to a normal (N) to the bottom of the hull, when measured from stern to stem.