Thrust measurement system for small planing watercrafts

FIELD OF THE INVENTION

The present invention relates to a thrust measurement system for small planing watercrafts, which is designed to measure the thrust of a small planing watercraft under the condition that the watercraft is received in a water pool in a floating condition.

BACKGROUND OF THE INVENTION

Japanese Patent Publication No. (SHO) 62-6173 discloses a method of measuring the thrust of a watercraft propulsion unit. The disclosed thrust measuring method, as illustrated here in

FIG. 8

, includes two strain gauge units

102

,

102

attached by bonding to an inner surface

101

a

of a casing

101

of the propulsion unit

100

in such a manner that the strain gauge units

102

,

102

are disposed in diametrically opposite relation to each other. Each strain gauge unit

102

has two strain gauge elements (not shown) which are connected with two strain gauge elements of another strain gauge unit

102

so as to form a bridge in a manner known per se.

During thrust measurement operation, the propulsion unit

100

is driven to rotate a screw-propeller

104

, and the amount of strain occurring in the casing

101

due to rotation of the screw-propeller

104

is measured by the bridge of the strain gauge elements. As is well known, there is a certain relationship established between the thrust of the propulsion unit

100

and the amount of strain of the casing

101

. Accordingly, by thus measuring the amount of strain of the casing

101

, a thrust of the propulsion unit

100

can be readily determined.

The conventional thrust measuring method discussed above is labor intensive because the strain gauge units

102

.

102

must be attached to and removed from the casing

101

each time the thrust measurement for one propulsion unit

100

is achieved. Furthermore, the conventional thrust measuring method is limited for use with a propulsion unit alone that is not installed in the hull of a watercraft. There has been a desire to realize a thrust measurement system which is capable of measuring the thrust of a propulsion unit as it is installed in the watercraft.

It is, accordingly, an object of the present invention to provide a thrust measurement system for small planing watercrafts, which is labor-saving, easy to conduct and capable of measuring the thrust of a propulsion unit as it is installed in the hull of a watercraft.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a thrust measurement system for watercrafts, comprising a water pool for receiving therein a watercraft in a floating condition, a bow holding apparatus disposed on an edge of the water pool for holding therein a bow of the watercraft during thrust measurement operation, a thrust measurement device mounted in the bow holding apparatus for measuring a thrust of the watercraft, and anchoring means spanning between the edge of the water pool and a hull of the watercraft for anchoring the watercraft in position against lateral swinging movement about the bow.

With the thrust measurement system thus arranged, the thrust of a propulsion unit used for propelling a watercraft can be measured under the condition that the propulsion unit is installed in the watercraft. This eliminates the need for a laborious manual operation which is employed in the conventional thrust measurement process of

FIG. 8

for the purpose of attaching or detaching the strain gauge units relative to a casing of the propulsion unit.

In one preferred form of the present invention, the bow holding apparatus includes a plurality of support columns, a carrier member slidably mounted on the support columns for vertical movement along the support columns, the carrier member carrying thereon the thrust measurement device, a cylinder actuator for moving the carrier member upward or downward along the support columns, a slide member slidably mounted on the carrier member for horizontal reciprocating movement in a direction toward and away from the water pool, a bow holding mechanism for holding therein the bow of the watercraft, the bow holding mechanism being connected to the slide member and held in contact with a probe of the thrust measurement device, and a balancing device that counterbalances to the weights of the bow holding mechanism, thrust measurement device, slide member and carrier member such that the bow holding mechanism, thrust measurement device, slide member and carrier member together form a floating structure that can move freely in a vertical plane.

By virtue of the floating structure of the bow holding apparatus, the bow of the watercraft is allowed to freely move up and down as the watercraft moves to drift in synchronism with heaving of the pool water surface.

Preferably, the bow holding mechanism has a bow hold member having a recessed portion of a configuration snugly receptive of the bow of the watercraft, a vertically disposed thrust board connected to the slide member for movement in unison with the slide member and held in contact with the probe of the thrust measurement device such that a movement of the slide member in a direction away from the water pool causes the thrust board to push the probe of the thrust measurement device, and a ball joint articulately interconnecting the bow hold member and the thrust board. interconnecting the bow hold member and the thrust board.

With this articulate coupling using the ball joint, the bow hold member can take various postures relative to the thrust board, which may occur when the watercraft undergoes pitching, rolling, steering and accelerating.

The bow holding mechanism may further have a plurality of compression coil springs acting between the bow hold member and the thrust board and arranged at regular intervals around an axis of the ball joint. Furthermore, the bow holding mechanism may also have adjustable spring retainers each supporting one end of a respective one of the compression coil springs, the adjustable spring retainers being movably mounted on one of the bow hold member and the thrust board and separately movable in a direction to change a preload applied to the individual compression springs. Preferably, the adjustable spring retainers each comprise a stepped round bar having a thread-free small-diameter portion, a threaded large-diameter portion, and an annular flange separating the small-diameter portion and the large-diameter portion, the annular flange supporting thereon one end of each compression coil spring with the thread-free small-diameter portion received in an internal space of the compression coil spring, and the threaded large-diameter portion being threaded through an internally threaded portion of the thrust board. The bow hold member may have a plurality of recessed portions arranged around the axis of the ball joint and each receiving therein the opposite end of a respective one of the compression coil springs.

The anchoring means preferably comprises a first wire rope having one end connected to a first edge portion of the water pool and the other end adapted to be connected to a central portion of a stern of the watercraft, a second wire rope having one end connected to a second edge portion of the water pool diametrically opposite the first edge portion and the other end adapted to be connected to the central portion of the stern of the watercraft, and a third wire rope having one end connected to a third edge portion of the water pool diametrically opposite an edge portion where the bow holding apparatus is disposed, the other end of the third wire rope being adapted to be connected to the center of the stern of the watercraft. It is further preferable that the first, second and third wire ropes each have two hooks at the one end and the opposite end thereof, and means for adjusting the length of the wire rope.

With the wire ropes thus arranged, the stern of the watercraft is anchored in position against lateral oscillation about the bow being held in the bow holding apparatus. The wire ropes permit vertical movement of the stern during thrust measurement operation.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will hereinafter be described in detail, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1

is a perspective view of a thrust measurement system according to an embodiment of the present invention;

FIG. 2

is an exploded perspective view of a portion of the thrust measurement system including a bow holding apparatus and a thrust measurement device built in the bow holding apparatus;

FIG. 3

is a vertical cross-sectional view showing a part of the bow holding apparatus;

FIG. 4

is a diagrammatical side view, partly in cross section, of the thrust measurement system showing a small planning watercraft set in a measurement position inside a water pool;

FIG. 5A

is a diagrammatical side view, partly in cross section, of the thrust measurement system, showing one mode of operation in which the small planing watercraft is driven to run in a straightforward direction;

FIG. 5B

is a diagrammatical plan view of

FIG. 5A

;

FIG. 6A

is a view similar to

FIG. 5B

, but showing another mode of operation of the thrust measurement system in which the small planing watercraft is steered to make a left turn;

FIG. 6B

is a view similar to

FIG. 5B

, but showing still another mode of operation in which the small planing watercraft is steered to make a right turn;

FIG. 7

is a view similar to

FIG. 5A

, but showing a further mode of operation in which the small planing watercraft is accelerated to take an elevated position with its stern sinking deeper and bow rising higher; and

FIG. 8

is a diagrammatical side view showing a conventional thrust measurement method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and

FIG. 1

in particular, there is shown a thrust measurement system

10

for watercrafts (small planing watercrafts, in particular) according to an embodiment of the present invention. The thrust measurement system

10

generally comprises a water pool

20

of a rectangular configuration for receiving therein a small planing watercraft

11

in a floating condition, a bow holding apparatus

30

disposed on a front edge portion

21

of the rectangular water pool

20

for holding a bow

13

of the small planing watercraft (hereinafter referred to, for brevity, as “watercraft”)

11

during thrust measurement operation, a thrust measurement device

34

mounted or assembled in the bow holding apparatus

30

for measuring a thrust of the watercraft

11

, an anchoring means

75

spanning between a hull (stern

14

in the illustrated embodiment) of the watercraft

11

and remaining edge portions (a left side edge portion

22

, a right side edge portion

23

and a rear edge portion

24

) of the water pool

20

for anchoring the watercraft

11

in position against lateral swinging movement about the bow

13

, and a display unit

95

for indicating thrust data measured by the thrust measurement device

34

.

The thrust measurement device

34

preferably comprises a load cell which is designed to measure an applied load or thrust by a change in its properties, such as a change in resistance (strain-gage load cell), pressure (hydraulic load cell), etc. The thrust measurement device

34

has a probe

34

a

against which a load or thrust is applied. When the thrust measurement device

34

is comprised of a hydraulic load cell, the probe

34

a

is formed by a piston.

The water pool

20

has a hollow rectangular space open upward and defined by a rectangular bottom wall

25

, front and rear walls

20

a

and

20

b

extending vertically upward from opposite end edges of the rectangular bottom wall

25

(FIG.

4

), and left and right side walls

20

c

and

20

d

extending vertically upward from opposite side edges of the rectangular bottom wall

25

. The water pool

20

holds therein an appropriate quantity of water

26

. An upper opening of the water pool

20

has a size sufficiently larger than that of the watercraft

11

so that it can receive or accommodate the watercraft

11

in a floating condition.

As shown in

FIG. 2

, the bow holding apparatus

30

includes four support posts or columns

31

(three being shown), a carrier member

35

slidably mounted on the columns

31

for vertical movement along the columns

31

, a cylinder actuator

41

operative to move the carrier member

35

upward and downward along the support columns

31

, a pair of laterally spaced slide members

43

,

43

slidably mounted on the carrier member

35

for horizontal reciprocating movement in a direction toward and away from the water pool

20

, a bow holding means or mechanism

45

constructed to hold the bow

13

of the watercraft

11

while allowing movement of the bow

13

in all directions relative to a thrust axis, the bow holding mechanism

45

being mounted to the slide members

43

,

43

for movement in unison with the slide members

43

,

43

for thrusting the probe

34

a

of the thrust measurement device

34

, and a balancing device or balancer

71

that counterbalances to the weights of the bow holding mechanism

45

, thrust measurement device

34

, slide members

43

,

43

and carrier member

35

. The thrust measurement device

34

is fixedly mounted or carried on the carrier member

35

. The thrust axis is formed by the axis of the probe

34

.

The support columns

31

stand upright from four corner portions of a rectangular base plate

32

which is secured to the front edge portion

21

of the water pool

20

. A rectangular top plate

33

is attached to upper ends of the respective support columns

31

. The carrier member

35

is normally disposed centrally between the base plate

32

and the top plate

33

. The carrier member

35

comprises a hollow rectangular frame formed jointly by two rectangular end blocks

35

a

and

35

b

each mounted slidably on two adjacent ones of the support columns

31

, and upper and lower horizontal plates

35

c

and

35

d

extending between the end blocks

35

a

,

35

b

so as to define, together with the end blocks

35

a

,

35

b

, a hollow rectangular space

36

. Each of the end blocks

35

a

,

35

b

has a pair of vertically spaced guide grooves

37

extending horizontally in a direction parallel to a longitudinal axis of the rectangular water pool

20

. The guide grooves

37

have a dovetail shape and open into the hollow rectangular space

36

of the carrier member

35

. The thrust measurement device

34

is disposed centrally between the slide members

43

,

43

within the hollow rectangular space

36

and firmly secured in position against movement relative to the carrier member

35

.

Each of the slide members

43

,

43

has a pair of vertically spaced guide rails

44

,

44

of a dovetail configuration slidably fitted in the guide grooves

37

,

37

of a respective one of the end blocks

35

a

,

35

b

, so that the slide members

43

are movable in a horizontal plane toward and away from the water pool

20

.

The bow holding mechanism

45

is essentially comprised of a vertically disposed thrust board

47

firmly connected at an upper end portion thereof to the slide members

43

,

43

by means of screws

46

, and a bow hold member

65

designed for holding therein the bow

13

of the watercraft

11

, and a ball joint

51

articulately interconnecting the bow hold member

65

and a lower part of the thrust board

47

.

The thrust board

47

includes a rectangular plate

48

forming a body of the thrust board

47

, and a reinforcement frame

49

of a hollow rectangular shape provided on a front surface

48

a

of the plate

48

for reinforcing the plate (thrust board body)

48

. The thrust board

47

has an upper end portion bolted to the slide members

43

,

43

, Aback surface of the plate

48

is held in contact with the probe

34

a

of the thrust measurement device

34

, as shown in FIG.

3

.

The thrust board

47

and the bow hold member

65

are pivotally connected by the ball joint

51

, and four compression coil springs

61

are interposed between the thrust board

47

and the bow hold member

65

. The compression coil springs

61

are arranged at regular intervals around the axis

56

a

(

FIG. 3

) of the ball joint

51

such that two compression coil springs

61

are disposed on each of the upper and lower sides of the ball joint axis

56

a.

The bow hold member

65

includes a vertically disposed support plate

66

and a holder body

67

attached to a front surface of the support plate

66

. The holder body

67

has a recessed portion

68

formed in a front surface thereof. The recessed portion

68

has a profile or configuration complementary in shape with the profile of the bow

13

of the watercraft

11

, so that the bow

13

of the watercraft

11

can be snugly received in the recessed portion

68

of the bow hold member

65

.

As shown in

FIG. 4

, the cylinder actuator

41

is disposed vertically at a position behind both the thrust measurement device

34

and the balancing device

71

. The cylinder actuator

41

has a cylinder body

41

a

connected to the upper plate

35

c

of the carrier member

35

and a piston rod

41

b

connected to the base plate

32

of the bow holding apparatus

30

. With this arrangement, when the cylinder actuator

41

operates to extend its piston rod

41

b

, the carrier member

35

moves upward along the support columns

31

. In this instance, since the bow holding mechanism

45

is connected to the carrier member

31

via the slide members

43

, the bow holding mechanism

45

also moves upward together with the carrier member

35

. Conversely, when the cylinder actuator

41

operates to retract its piston rod

41

b

, the carrier member

35

moves downward along the support columns

31

. In this instance, the bow holding mechanism

45

moves downward together with the carrier member

35

because the carrier member

35

and the bow holding mechanism

45

are connected together via the slide members

43

. Thus, by properly adjusting the forward or backward stroke of the piston rod

41

b

of the cylinder actuator

41

, it is possible to place the bow holding member

65

of the bow holding mechanism

45

in a desired vertical position.

The balancing device

71

is disposed between the thrust measurement device

43

and the cylinder actuator

41

. The balancing device

71

is connected to the carrier member

35

so as to cancel out or counterbalance the weights of the bow holding mechanism

45

, thrust measurement device

34

, slide members

43

and carrier member

35

. By thus providing the balancing device

71

, the bow holding mechanism

45

, thrust measurement device

34

, slide members

43

and carrier member

35

together form a floating structure that can move freely in a vertical plane.

Referring back to

FIG. 1

, the anchoring means

75

includes a left wire rope

81

having hooks

82

,

82

at opposite ends thereof, a right wire rope

84

having hooks

85

,

85

at opposite ends thereof, and a rear wire rope

87

having hooks

88

,

88

at opposite ends thereof. The hook

82

at one end of the left wire rope

81

is hooked on an anchor ring

77

provided at the left side edge portion

22

of the water pool

20

, and the hook

82

at the other end of the left wire rope

81

is hooked on an anchor ring

76

provided at the center of the width of the stern

14

. Similarly, the hook

85

at one end of the right wire rope

84

is hooked on an anchor ring

78

provided at the right side edge portion

23

of the water pool

20

, and the hook

85

at the other end of the right wire rope

84

is hooked on the anchor ring

76

of the watercraft

11

. The hook

88

at one end of the rear wire rope

87

is hooked on an anchor ring

79

provided at the rear edge portion

24

of the water pool

20

, and the hook

88

at the other end of the rear wire rope

87

is hooked on the anchor ring

76

of the watercraft

11

. The left, right and rear wire ropes

81

,

84

,

87

each have a means for adjusting the length of the respective wire rope

81

,

84

,

87

. The rope length adjusting means may be a turnbuckle

83

,

86

, and

89

that can adjust the length of each wire rope within a certain range of distance.

The left and right wire ropes

81

,

84

have substantially the same length, and the length of these wire ropes

81

,

84

is set such that, when the left and right wire ropes

81

,

84

are hooked at opposite ends on the anchor rings

76

,

77

,

78

with the bow

13

of the watercraft

11

being received in the recessed portion

68

of the bow hold member

65

, each wire rope

81

,

84

extends substantially straight without sagging between the anchor ring

76

on the watercraft

11

and a corresponding one of the anchor rings

77

,

78

on the pool side. By thus setting the lengths of the left and right wire ropes

81

,

84

, lateral movement or oscillation of the stern

14

does not occur.

The length of the rear wire rope

87

is set to be somewhat longer than the distance between the anchor ring

79

of the pool side and the anchor ring

76

on the stern

14

so that when the wire rope

87

slightly sags down when hooked at opposite ends on the anchor rings

76

,

79

. This permits forward movement of the watercraft

11

when the watercraft

11

is driven forward, which is due for pushing or thrusting the probe

34

a

(

FIG. 2

) of the thrust measurement device

34

via the thrust board

47

(

FIG. 2

) of the bow holding mechanism

45

.

Additionally, the wire ropes

81

,

84

,

87

that are hooked on the anchor rings

77

,

78

,

79

at the pool edge portions and the anchor ring

76

at the center of the stern

14

of the watercraft

11

permit vertical movement of the stern

14

to some extent.

As shown in

FIG. 3

, the ball joint

51

is composed of a first or male member

52

having a ball

56

at an end thereof, and a second or female member

53

having a socket

57

at an end thereof. The ball

56

and the socket

57

are coupled together so that relative movement between the male and female members

52

,

53

is permitted within a certain angle in all planes passing through a line. The male member

52

is secured to the plate

48

of the thrust board

47

by means of a threaded faster which is composed of an externally threaded shank portion

52

a

of the male member

52

and a nut

54

threaded around the shank portion

52

a

. The male member

52

has an annular flange

55

disposed on the opposite side of the nut

54

across the plate

48

of the thrust board

47

. The female member

53

is secured by screws

69

to the support plate

66

of the bow hold member

65

.

The compression coil springs

61

interposed between the thrust board

47

and the bow hold member

65

are stably held in position against displacement by and between adjustable spring retainers

63

and recessed portions

65

a

formed in the bow hold member

65

. The adjustable spring retainers

63

each comprise a stepped round bar having a thread-free small-diameter portion

63

a

and a threaded large-diameter portion

63

b

separated from each other by an annular flange

63

c

. The annular flange

63

c

supports one end

61

a

(right end in

FIG. 3

) of the compression coil spring

61

with the thread-free small-diameter portion

63

a

of the adjustable spring retainer

63

received in an internal space of the compression coil spring

61

. The threaded large-diameter portion

63

b

is threaded through an internally threaded bush

62

firmly secured by welding to the plate

48

of the thrust board

47

. The opposite end

61

b

(left end in

FIG. 3

) of the compression coil spring

61

is held in abutment with a bottom surface of the recessed portion

65

a

of the bow hold member

65

. The internally threaded bush

62

forms an internally threaded portion of the thrust board

47

.

With this arrangement, when a movement of the watercraft

11

occurring during thrust measurement operation causes the bow hold member

65

to pivot or turn upward about the ball

56

of the ball joint

51

, the upper two compression coil springs

61

are axially compressed while the lower two compression coil springs

61

are allowed to expand. Conversely, when a movement of the watercraft

11

occurring during thrust measurement operation causes the bow hold member

65

to turn or pivot downward about the ball

56

of the ball joint

51

, the upper two compression coil springs

61

are allowed to expand while the lower two compression coil springs

61

are axially compressed.

The initial position of the bow hold member

65

relative to the thrust board

47

can be changed by properly adjusting the amount of preload applied to the necessary one or ones of the compression coil springs

61

by axially displacing the corresponding one or ones of the adjustable spring retainers

63

relative to the bush

62

. For instance, when the bow support member

65

is to be inclined upward relative to the thrust board

47

, two adjustable spring retainers

63

that are positioned below the ball joint

51

are turned in a direction to cause forward movement of the same spring retainers

64

toward the bow support member

65

. Conversely, when the bow support member

65

is to be inclined downwardly relative to the thrust board

47

, two adjustable spring retainers

63

that are positioned above the ball joint

51

are turned in a direction to cause forward movement of the same spring retainers

64

toward the bow support member

65

. Similarly, when the bow hold member

65

is to be tilted leftward or rightward relative to the bow hold member

65

, two adjustable spring retainers

63

that are disposed on a right side or a left side of the ball joint

51

are turned in a direction to cause forward movement of the same spring retainers

63

toward the bow support member

65

.

FIG. 4

is a diagrammatical vertical cross-sectional view of the thrust measurement system

10

of the present invention, showing the condition in which the watercraft

11

is in a thrust measurement position with its bow

13

and stern

14

held by the bow holding apparatus

30

and the anchoring means

75

, respectively.

When the watercraft

11

is in the thrust measurement position of

FIG. 4

, the bow

13

of the watercraft

11

is fitted or snugly received in the recessed portion

68

of the bow hold member

65

of the bow hold apparatus

30

, and the stern

14

of the watercraft

11

is stably held or anchored by the left, right and rear wire ropes (only the rear wire rope

87

being shown) of the anchoring means

75

spanning between the corresponding edge portions (only the rear end edge portion

22

being shown) of the water pool

20

and the anchor ring

76

at the center of the stern

14

of the watercraft

11

.

For setting the watercraft

11

in the thrust measurement position, the bow

13

of the watercraft

11

is held in the recessed portion

68

of the bow hold member

65

and after that the stern

14

of the watercraft

11

is anchored by the wire ropes

81

,

84

,

87

(FIG.

1

). In this instance, since the bow holding mechanism

45

and the carrier member

35

are connected together via the slide members

43

, it is readily possible to place the recessed portion

68

of the bow hold member

65

in a position substantially the same in level or height as the bow

13

of the watercraft

11

merely by moving the carrier member

35

upward or downward along the support columns

31

through operation of the cylinder actuator

41

.

During thrust measurement operation, the watercraft

11

undergoes pitching and rolling movements, which necessarily involve vertical movement of the bow

13

and stern

14

of the watercraft

11

. In order to accommodate vertical movement of the bow

13

, the bow holding mechanism

45

is required to move up and down in synchronism with vertical movement of the bow

13

which is received in the recessed portion

68

of the bow hold member

65

. According to the present invention, since the balancing device

71

provided in the bow holding apparatus

30

counterbalances to the weights of the bow holding mechanism

45

, thrust measurement device

34

, slide members

43

and carrier member

35

, these components

45

,

34

,

43

and

35

jointly form a floating structure that can move freely in a vertical plane. By the floating structure thus provided, free vertical movement of the bow

13

during thrust measurement operation is permitted.

Vertical movement of the stern

14

is also permitted to some extent because the left, right and rear wire ropes

81

,

84

,

87

spanning between the anchor rings

77

,

78

,

79