WO1987002958A1

WO1987002958A1 - Form stabilized low water plane area twin hull vessels

Info

Publication number: WO1987002958A1
Application number: PCT/US1985/002204
Authority: WO
Inventors: Terrence Wayne Schmidt
Original assignee: Lockheed Missiles & Space Company, Inc.
Priority date: 1985-11-08
Filing date: 1985-11-08
Publication date: 1987-05-21

Abstract

Vessel (2, 4, 6) that is form stabilized. The stability is achieved by the particular shape or orientation of the struts (8, 10) or both . In one embodiment (Fig. 2) the dihedral struts (8, 10) have a cambered cross-section area. In another embodiment (Fig. 7) the cross-section area of the struts (38, 40) are symmetrical and the struts (8, 10) are mounted in a toe out position.

Description

^~ι-

1 FORM STABILIZED LOW WATER PLANE AREA TWIN HULL VESSELS

2

^ 3 Technical Field

*^• 4 This invention relates to strut geometry for trim control of

Λ

5 small water plane area twin hull design watercraft. More

6 specifically, the configuration of the present invention

7 incorporates dihedral struts that are skewed relative to the

8 centerline of the vessel or incorporate camber shapes. 9

10 Background Art

11 Semisubmerged or small water plane area twin hull ships,

12 sometimes referred to as SWATH ships, have been developed for

13 high-speed operation at high sea states. U.S. Patents No. 3,623,444

14 and No. 3,897,744 issued to Thomas G. Lang, disclosed ships of this

15 configuration which have better operational characteristics than

16 conventional ships and can operate at much higher sea states.

17 The above-noted patents point out a number of configurations for

18 such vessels. One of these configurations include a rear stabilizer

19 and a forward canard for counterbalancing the sinkage and trim

20 forces exerted by the vessel itself. Because these control surfaces

21 must counterbalance these forces, their utility in controlling the

22 ship's motion and steerage is greatly reduced, or substantially

23 larger control surfaces must be utilized. Larger control surfaces

24 require additional machinery and degrade the overall performance of

25 the ship. 26

27 Disclosure of Invention

28 In accordance with the present invention, the vessel is form

29 stabilized. This is achieved by utilizing struts with a dihedral

30 angle that incorporate cambering of section or non-parallel -

31 alignment or both. 32

33 Brief Description of Drawings

34 Figure 1 is an isometric view of a vessel, of the present

35 invention.

36 Figure 2 is a sectional view of the vessel of Figure 1 taken

©UCSTSTJTE SHEET 1 along the line A-A illustrating the cambered shape of the struts.

2 Figure 3 is a sectional view of the vessel of Figure 2 taken

3 along the line B-B showing the negative dihedral angle of the strut

4 relative to the upper hull.

5 Figure 4 is a simplified depiction of the hydrodynamic forces

6 exerted on a vertical uncambered strut and submerged hull.

7 Figure 5 is a simplified depiction of the hydrodynamic forces

8 exerted on a cambered dihedral strut and submerged hull in

9 accordance with the teachings of the present invention.

10 Figure 6 is an isometric view of vessel showing another

11 embodiment of the present invention.

12 Figure 7 is a sectional view of the vessel shown in Figure 6

13 illustrating the toe out arrangement of the struts.

14

15 Best Method of Carrying Out the Invention

16 One form of the invention is depicted in Figure 1. A pair of

17 essentially tubular shaped parallel submerged hulls 2 and 4 provide

18 a buoyancy support for the upper hull 6 through a pair of dihedral

19 struts 8, 10, which are cambered in section. Each of the submerged

20 hulls 2 and 4 are made in the form of a long cylindrical shape,

21 including a rounded bow 12 and a tapered stern 14.

22 Individual propellers 16 are mounted on the aft end of each of

23 the submerged hulls 2 and 4. The propellers 16 are connected

24 through a suitable transmission to a single power plant, or two

25 individual power plants, to provide forward and reverse thrusts for

26 movement of the vessel.

27 For illustration, the upper hull 6 is shown as a platform and

28 includes a raised forward superstructure 18. Incorporated within

29 the platform are the necessary ship machinery, storage holds, crew

30 quarters, and the like.

31 By convention, when the angle between two objects exceeds 90 ,

32 the two objects are said to form a negative dihedral angle.

33 Conversely, when the angle between the two objects is less than

3 .4» 90o, the objects are said to form a positive dihedral angle.

35 The supporting struts 8 and 10 are formed with a negative

36 dihedral angle to the vertical and incorporate positive section

UTE SHEET camber. This would be best understood with the reference to Figure 2

2 and Figure 3. Figure 2 is a section taken along lines A-A of Figure

3 1 and shows the struts in section. The cross-sectional shape of the

4 struts is defined by the camber or inboard and outboard surface

5 curvature. When the curvature of the outboard surface 22 is greater 5 than inboard 20 as illustrated here, the strut is said to have

7 positive section camber. In Figure 2 the inboard surface 20 is g shown as an essentially straight surface but it could be curved if

9 desired provided its curvature does not exeed that of the outboard

10 surface. Figure 3 which is a cut-away view of Figure 1 taken along 1 the line B-B shows the negative dihedral angle of the struts 2 relative to the upper hull 6 and the submerged hulls 2 and 4.

13 An understanding of how the vessel is form stabilized can be J obtained by reference to Figure 4 and Figure 5. Figure 4 is a 5 simplified depiction of the pressure forces exerted on a single

1g submerged vertical strut and hull of a SWATH vessel by the movement

17 of the vessel through the water. It can be noted that the

2Q summation of the forces illustrated by arrows 24 produces a j resultant force, shown by arrow 26, in the vertical direction. This

2Q resultant force 26, which can be called a sinking force is

21 positioned forward on the hull causing the bow of the vessel to dive

22 unless counteracting forces are provided by foils or canards.

23 Figure 5 shows the pressure forces 28 exerted on a single

OΛ submerged hull and a cambered dihedral support strut in accordance

25 with the present invention. The summation of the forces on the

2g strut are shown by arrow 30. Arrows 32 and 34 show the vertical and

27 horizontal components, respectively, of the strut normal force. It

28 will be understood that since the forces acting on the other

2g dihedral support strut are symmetrical with the forces shown in Q Figure 5, the horizontal components cancel each other. As shown in

3 Figure 1, the vertical forces which are shown by arrows 36 and 26 2 add together and negate the vertical imbalance caused by the surface

33 piercing strut. The resultant vertical force being zero.

34 Another embodiment of the present invention is shown in Figure 6

35 and Figure 7. In this embodiment each of the dihedral struts 38 and 3g 40 are symmetrical in cross-section. The necessary vertical force

. _* _~~- ~~~ ~~~*

SUBSTITUTE SJ^ήΞE i needed to negate the vertical force imbalance caused by the surface

2 piercing strut is obtained by aligning the struts in a non-parallel

3 arrangement. In the embodiment, as shown, the distance between the

4 leading edges 42 of the struts is greater than the distance between

5 the trailing edges 44 of the struts, i.e., the struts are in a toe 5 out arrangement. it is understood that, if desired, the struts could be arranged g in a toe in arrangement. In such an arrangement the resultant g horizontal forces produced by each of the struts would be directed 0 inboard of the vessel. However, since the struts are still 2 symmetrical with each other, the horizontal forces produced by the 2 two struts will cancel each other out and leave a resultant force in 3 the vertical direction as set forth above. 4 Other modification and advantageous applications of this 5 invention will be apparent to those having ordinary skill in the 5 art. Therefore, it is intended that the matter contained in the 7 foregoing description and the accompanying drawings is illustrative 8 and not limitative, the scope of the invention being defined by the 9 appended claims. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6

SUBSTITUTE HEE

Claims

1 Claims: 2

^«*■■ 3 1- A form stabilized low water plane area twin hull vessel

4 comprising: a pair of substantially tubular shaped parallel y 5 hulls that provide buoyancy support for the vessel, a pair of

6 dihedral struts connected to said pair of parallel hulls and

7 adapted to support an upper hull, and an upper hull connected to

8 said pair of dihedral struts, wherein said pair of dihedral

9 struts form a negative dihedral angle with said upper hull and 10 wherein said struts include positive section camber.

11

12 2. A form stabilized low water plane area twin hull vessel

13 comprising: a pair of substantially tubular shaped parallel

14 hulls that provide buoyancy support for the vessel, a pair of

15 dihedral struts connected to said pair of parallel hulls and

16 adapted to support an upper hull, and an upper hull connected to

17 said pair of dihedral struts, wherein said pair of dihedral

18 struts each include a leading edge and a trailing edge and

19 wherein the distance between said leading edges is greater than

20 the distance between said trailing edges.

21 22 23 24 25 26 27 28 29 30 31 32 ^ 33 34 35 36

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