GB2058678A - Semi-submersibles - Google Patents

Abstract

A semi-submersible catamaran comprises two lower hulls (11), always located below the waterline, which are parallel to one another and lie in the normal travel direction. Vertical plate-like struts (12) are mounted on the lower hulls (11) and an upper hull (13) is supported on the struts (12). The upper hull is always above the waterline. The invention provides particular ratios between the submergence depth (f) and the average diameter of the lower hulls (11) and between the height HL and width BL of the lower hulls (11). The invention also provides a particular fin arrangement (16, 16') provided on the lower hulls (11). The catamaran may be used, for example, as a passenger ship, a cargo boat or a floating factory ship. <IMAGE>

Description

SPECIFICATION A Semi-Submerged Catamaran (1) Field of the Invention The present invention relates to an improvement in generic properties of a semi-submerged catamaran.

(2) Description of the Prior Art: Significances of the properties required for ships ordinarily vary depending on the objects and conditions (for example, the marine climate in the navigation area and the depth of water in a harbor).

However, it may be said that the loading capacity, the speed characteristics and the navigation properties (inclusive of the motion characteristic and navigation stability) are important properties.

In conventional single-hull displacement ships, these requirements are often contradictory to one another, and therefore, designing of these ships is complex and difficult.

Accordingly, as a ship having improved speed characteristics and navigation properties, there has been proposed a so-called semi-submerged ship or catamaran comprising a hull for covering the majority of the displacement, which is located below the surface of water, and hull for storing cargos, which is located above the surface of water, that is, a ship comprising an upper hull and a lower hull which are separated from each other on the surface of water as the boundary and are connected to each other through thin poles.

A typical structure of the semi-submerged ship or catamaran constructed based on the above principle is illustrated in Fig. 1. In this structure, two lower hulls 1, 1 always located below the surface of water are arranged in parallel to each other with respect to the direction of advance, and an upper hull 3 (a space for cabins, cargos or factory stands) always located above the surface of water is connected to the lower hulls 1 through at least one relatively thin streamlined strut 2 mounted vertically on each of the lower hulls 1. In this semi-submerged ship or catamaran, either the full load draft or the light load draft (unload draft) is on the struts.

In principle, the semi-submerged catamaran involves a possibility that it will become a ship excellent in the speed characteristics and navigation properties. Furthermore, a broad deck area can be maintained and the loading and operation efficiencies can be improved. Therefor, it is expected that ships of this type will be effectively utilized in the marine transportation and ocean development in the future. However, since a ship of this type has a peculiar shape quite different from the shape of an ordinary ship, designing is complicated and difficult. In order to utilize or manifest excellent technical characteristics of a semi-submerged catamaran sufficiently, the configurations and dimensions of the lower hulls or struts should be appropriately set.Furthermore, since the configurations and dimensions of the lower hulls or struts have significant influences on the speed characteristics and navigation properties, it is required to establish a highly developed designing technique constructed while taking the respective properties and characteristics collectively into account.

There has recently been proposed a semi-submerged catamaran in which a strut 2 is divided into front and rear parts to decrease the water line area, as shown in Fig. 2. In this proposal, however, the ship's resistance including wave-making resistance is increased by interference of the front and rear struts during navigation, and the restoring force is small. Furthermore, since the entire length of the strut 2 is shortened, it is difficult to ensure spaces for tank and access sufficiently. Therefore, this proposal is not practical in many cases of design.

Summary of the Invention It is a primary object of the present invention to provide a semi-submerged catamaran in which the characteristics of the conventional semi-submerged catamaran are fully utilized, the motion characteristics are excellent, the force for damping the vertical rocking motion and the navigation stability is very good with a large lateral restoring force.

Another object of the present invention is to provide a semi-submerged catamaran in which a necessary power can be reduced, the wave-making resistance can be decreased and the navigation stability can be remarkably improved.

Other objects of the present invention will become apparent from the following description.

In accordance with one fundamental aspect of the present invention, there is provided a semisubmerged catamaran comprising two lower hulls always located below the surface of water and arranged substantially in parallel to each other with respect to the direction of advance, plate-like struts mounted substantially vertically on the upper portions of the respective lower hulls along almost the entire length thereof and an upper hull supported by said struts and always located above the surface of water, wherein the ratio (f/D) of the submergence depth (f) of the lower hulls to the average diameter (D) of the lower hulls is in the range of from 0.7 to 1.2.

In the present invention, it is preferred that the ratio (hit,) of the height (H,) of the lower hulls in the cross-section thereof to the width (BL) of the lower hulls be in the range of from 0.6 to 0.8.

In the above-mentioned semi-submerged catamaran of the present invention, good effects are attained when the maximum width of the struts at least in the central portion thereof on the draft level is 30 to 50% of the maximum width of the lower hulls at the same cross-sectional position.

In the present invention, the struts may have such a draft line shape that a parallel portion is formed in the central zone of each strut and the length of this parallel portion has a length corresponding to 40 to 70% of the entire length of the strut. Each lower hull may include a propeller having a diameter (DP) corresponding to about 70 to about 100% of the height (H,) of the lower hull In the semi-submerged catamaran of the present invention, the foregoing objects can be attained also by disposing a front fin and a rear fin on the inside of each of the lower hulls. In this embodiment, it is preferred that the area of the rear fin be larger than the area of the front fin, and it also is preferred that the total area of the fins be 1 5 to 30% of the draft line area of the struts.Furthermore, there may be adopted a modification in which the respective fins are arranged so that they can be moved integrally, or another modification in which each fin is constructed by a movable portion and a fixed portion and the area of the movable portion is adjusted to 20 to 30% of the entire area of the fin.

As pointed out hereinbefore, the first characteristic feature of the semi-submerged catamaran of the present invention resides in the submergence depth of the lower hulls. As will become apparent from experimental data shown in Fig. 6, which will be described in detail hereinafter, by virtue of the feature that the ratio (f/D) of the submergence depth (f) to the average diameter (D) in the lower hulls is adjusted to 0.7 to 1.2, preferably about 1, both the total resistance coefficient (rT) on navigation but also the water-making resistance coefficient ('W) can be reduced. Accordingly, the power necessary for navigation can be reduced to aminimum level.

Accordingly, if the buoyancy of the lower hulls is controlled so that the submergence depth is in the above-mentioned range, the navigation efficiency can be remarkably improved.

The second characteristic of the present invention resides in the sectional shape of the lower hulls. In the present invention, by flattening the sectional shape of the lower hulls, the force for damping the vertical motion can be increased while maintaining the resistance of the lower hulls at a level as low as possible.

When the flatness degree (HiBL), that is, the height/width ratio, is controlled within the range of from 0.6 to 0.8, pitching and rolling movements of the ship can be reduced and the navigation stability can be remarkably improved.

The third characteristic feature of the present invention resides in the dimensions of the struts connecting the lower hulls to the upper hull.

In the present invention, one strut is formed on one lower hull continuously along the longitudinal direction of this lower hull and the width of this strut is adjusted to 30 to 50% of the maximum width of the lower hull. By this arrangement, the ship is made hardly synchronous with the frequency of waves and the navigation stability can be improved.

Furthermore, the front and rear parts of the strut are diminished in the size so that the strut has a ship-like shape, whereby the resistance can be reduced. If a parallel portion is formed in the central region of this shiplike strut, the resistance-reducing effect can be further enhanced. In this embodiment, it is preferred that the length of the parallel portion be 40 to 70% of the entire length of the strut.

If the strut is arranged so that the upper portion of the strut to be connected to the upper hull is enlarged, the connection between the strut and the upper hull can be strengthened, and if the enlarged portion is submerged in water by the list of the semi-submerged catamaran or for other reason, the lateral restoring force is increased.

In the case where a propeller is disposed in the rear portion of the lower hull, water flowing in the propeller is influenced by accompanying streams of the lower hull, but when a flat lower hull as claimed in the present invention, by adjusting the diameter (DP) of the propeller to about 70 to about 100% of the height (Hl of the lower hull, the propelling efficiency can be remarkably improved.

The fourth characteristic feature of the present invention resides in the posture control of the semi-submerged catamaran. In the present invention, fins are formed on the front and rear parts of each lower hull, and the area of the rear fin is made larger than the area of the front fin. If the total area of these four fins formed on the two lower hulls is adjusted to 1 5 to 30% of the draft line areas of the struts, the stability of the ship is improved. In addition, all the fins may be stationary, or all the fins or only the rear fins are movably arranged. In the latter case, if the area of the movable portions is adjusted to 20 to 30% of the total area of the fins, the stability of the ship can be improved and the posture of the ship can be controlled appropriately according to the speed or the wave or load condition.

Furthermore, by automatically controlling the fins so as to eliminate factors influencing the stability of the ship, such as waves, the stability of the ship can be further improved.

Even if any one of the above-mentioned four characteristic features of the present invention is adopted independently, the intended effects can be attained. However, if these characteristic features of the present invention are adopted in combination, the properties and capacities can be generally improved and there can be provided a semi-submerged catamaran in which the necessary power is reduced, the rolling and pitching movements of the ship are moderated and the navigation stability is remarkably improved.

Accordingly, the semi-submerged catamaran of the present invention can be effectively utilized as a factory ship cruising in a rough sea or the like or a military high speed ship.

Brief Description of the Drawings Figs. 1 and 2 are front and side views of a conventional semi-submerged catamaran.

Fig. 3 is a side view illustrating one embodiment of the semi-submerged catamaran according to the present invention.

Fig. 4 is a view showing the section taken along the line lV-IV in Fig. 3.

Fig. 5 is a view showing the section taken along the line V-V in Fig. 3.

Fig. 6 is a diagram illustrating the relation of the submergence depth of the lower hull to the resistance characteristic in the semi-submerged catamaran.

Fig. 7 is a diagram illustrating the relation of the flatness degree of the lower hull to the resistance characteristic.

Fig. 8 is a diagram illustrating the flatness degree of the lower hull to the relation of the vertical motion amplitude.

Fig. 9 is a diagram illustrating the relation of the motion response of the semi-submerged catamaran to the wave length.

Fig. 1 O(A) is a diagram illustrating the distribution of accompanying steams at the propeller plane.

Fig. 10(B) is a diagram illustrating the distribution of accompanying streams at the propeller plane.

Fig. 11(A) is a diagram illustrating the force acting on a lower hull.

Fig. 11(B) is a diagram illustrating the force acting on a fin-attached lower hull.

Fig. 1 2 is a side view illustrating an instance of the fin including a movable portion.

Fig. 1 3 is a side view illustrating another embodiment of the semi-submerged catamaran according to the present invention.

Figs. 14(A) to 14(H) are side views illustrating bow portions in another embodiment of the semisubmerged catamaran according to the present invention.

Detailed Description of the Preferred Embodiments One embodiment of the semi-submerged catamaran according to the present invention will now be described with reference to Figs. 3, 4 and 5.

The semi-submerged catamaran shown in Figs. 3, 4 and 5 is of the so-called single strut per hull type in which a plate-like strut 1 2 is vertically mounted on each of two lower hulls 11 arranged in parallel to each other with respect to the lengthwise direction of the ship and the strut 12 is arranged to extend along almost the entire length of the lower hull 11.

As will be apparent from comparison of Fig. 2 with Fig. 3, the conventional semi-submerged catamaran shown in Fig. 2 is of the so-called twin strut per hull type in which front and rear struts 2 are formed on each lower hull 1 as shown in Fig. 2, while in the present invention, one strut, that is, a single strut 12, is adopted as shown in Fig. 3.

In case of the single strut type, the waterplane area is larger than iX case of the twin strut type, and therefore, the restoring force is large and the stability is increased.

The characteristic features of the present invention will now be described one by one.

(A) Relation between Resistance and Submergence Depth of Lower Hull: As one factor determining the propelling capacity of the semi-submerged catamaran, there can be mentioned the submergence depth (f) of the lower hull 11. By the term "submergence depth" is meant the distance between the center o of the lower hull 11 and the draft line during navigation.

As pointed out hereinbefore, in the lower hull, the larger is the submergence depth, the less is the wave-making resistance. Accordingly, increase of the submergence depth is advantageous for improving the propelling capacity.

However, since the upper hull 1 3 is connected to the lower hull 11 through the strut 12, there is caused another problem that the resistance is increased by the volume of the submerged portion of the strut 12.

In the case where the submergence depth is equal, when the strut 12 having a very small width Bs is employed, increase of the resistance by increase of the submergence depth is relatively small as compared with the entire resistance imposed on the ship, and therefore, the influence of increase of the submergence depth on the resistance is relatively insignificant.

As a result of various experiments made by us, it was found that there is a close relation among the resistance on the ship, the average diameter of the lower hull 11 1 and the submergence depth (f) thereof.

Fig. 6 illustrates the relations of the ratio (f/D) of the submergence depth (f) of the lower hull 11 to the average diameter (D) of the lower hull 11 to the total resistance coefficient rT and the wave-making resistance coefficient 'W. When the lower hull has not a circular section but has a flat section as described hereinafter, the value corresponding to 1/2 of the sum of the height H, and width B, of the lower hull is adopted as the average diameter (D). From Fig. 6, it is seen that if the f/D value is small, particularly smaller than 0.5, both the values rT and 'W are increased. In other words, with decrease of the submergence depth (f), the resistance of the lower hull 11 is drastically increased.

On the other hand, if the f/D value exceeds about 1.5, the rate of decrease of the resistance of the lower hull becomes lower than the rate of increase of the resistance by the strut, and the entire resistance tends to increase.

From the experimental data, it is judged that it is preferred that the f/D value be in the range of from 0.7 to 1.2, particularly about 1.0.

In order to design an appropriate semi-submerged catamaran, it is necessary to select an appropriate submergence depth for the lower hull. The submergence depth is influenced to some extent by the ratio (L/D) of the length (L) of the lower hull 11 to the average diameter (D) of the lower hull 11.

Data shown in Fig. 1 are those obtained by experiments made on lower hulls in which the VD value is adjusted to 10 to 1 5. With increase of the LID value, the submergence depth (f) tends to decrease.

In the actual navigation of the semi-submerged catamaran, the submergence depth is changed according to the weight of the load. Accordingly, it is preferred that the submergence depth be adjusted by controlling the buoyancy of the lower hull.

(B) Sectional Shape of Lower Hull: The sectional shape of the lower hull is typically divided into a circular shape and a non-circular curved shape such as an elliptical shape. The surface area of the lower hull having a circular sectional shape is small and this lower hull is excellent with respect to the resistance owing to the surface area, that is, the so-called frictional resistance.

However, for the reason set forth above, the submergence depth should be maintained at a certain level. In case of the circular section, the draft is deeper than in case of the non-circular section, and the force of damping the vertical motion is smaller. Accordingly, the lower hull having a circular section is inferior in the motion characteristics.

In view of the foregoing, it is practicaily preferred that the lower hull should have a non-circular section.

One preferred example of the non-circular section is shown in Fig. 4. More specifically, a relatively flat non-circular section in which the height of the circle or ellipse is appropriately reduced so that the width (B,) of the lower hull at least in the central portion thereof is larger than the height H, of the lower hull.

When the section of the lower hull is thus flattened, the submergence depth is reduced as described above, and motion characteristics are improved.

When the ratio (HL/B,) of the height (H,) to the width (B,) in the lower hull is reduced and the section is extremely flattened, the shape resistance is increased in some case.

Fig. 7 is a diagram illustrating the relation between the ratio (FIR0) of the resistance (R) of the flat lower hull to the resistance (Ro) of the lower hull having a circular section (H,/B,=1.0) and the flatness degree (HlB,).

From Fig. 7, it is seen that as the H,/B, value is decreased, the R/Ro value is increased. In other words, as the flatness degree of the sectional shape of the lower hull is increased, the resistance is gradually increased. Accordingly, it is preferred that the H,/BL value be smaller than 0.6. It is recommended to select such as appropriate HiB, value that the increase of the resistance is within an allowable range while utilizing the advantage attained by the above-mentioned flattening.

Fig. 8 is a diagram illustrating the relation between the ratio (ZgZO) of the vertical motion amplitude Z in a flat lower hull to the vertical motion 4 in a lower hull having a circular section. From Fig. 8, it is seen that with increase of the flatness degree, the force for damping the vertical motion is increased and the Z/ZO value is decreased.

As is seen from Figs. 7 and 8, R/Ro and Z/ZO have characteristics contradictory to each other.

Accordingly, in order to reduce the vertical motion while maintaining increase of the resistance on the ship at a level as low as possible, it is preferred that the flatness degree be adjusted to 0.6 to 0.8.

In designing the flattened section for the lower hull, it is preferred to design a sectional shape by cutting off the upper and lower parts of a circle or ellipse by straight lines and connecting both the ends of the straight lines to each other by curved lines. In this case, the lower hull can be manufactured advantageously and the obtained lower hull is excellent in the strength.

(C) Shape and Size of Strut: The shape and size of the strut have most significant influences on various properties and capacities of the semi-submerged catamaran. In the present invention, the strut 12 is arranged so that it extends along the substantially entire length of the lower hull 11. In the embodiment shown in Figs.

3, 4 and 5, the rounded front edge 1 2b of the strut is located slightly backwardly of the front edge of the lower hull and a ladder shaft for driving a ladder 14, which extends backwardly beyond the rear end of the lower hull, can be supported.

As shown in Fig. 4, the width Bs of the strut 12 is substantially constant in the draft direction below the draft line at least in the central portion of the strut, but the sectional shape of the strut 1 2 has an upwardly enlarged area 1 2a in the upper portion thereof above the draft line. When this shape is adopted, the rigidity of said portion receiving a largest flexural moment of waves is increased and the connection to the upper hull 13 is reinforced. When the ship is greatly listed in the lateral direction, if the draft line at this listing includes this enlarged portion 1 2a, the lateral restoring force is increased.

Namely, the enlarged portion 1 2a has a function of increasing the stability.

The width Bs of the strut 1 2 has most significant influences on the motion characteristics and stability characteristics. The motion of the ship is determined by the external force which the ship receives from waves (the exciting force of waves). In case of the having motion, the exciting force Fzw of waves is represented by the following equation:: Fzw=(a3. pgA-a1M'w2)Z+a2N. 2w (1) wherein Aw stands for the waterplane area of the strut, M' stands for the added mass, p stands for the density of water, g stands for the acceleration of gravity, Nz stands for the damping coefficient, Zw stands for the rising height of the wave surface, Z w stands for the rising speed of waves, co stands for the circumferential frequency of waves, and a, 2 and ct; are coefficients.

In the equation (1), the first term is a so-called buoyancy term, the second term expresses the force of inertia, and the third term expresses the damping force. When the damping force in the equation (1), which is much smaller than the other two terms, is omitted, since the added mass M' is deemed proportional to the plane projection area ALH of the lower hull, the equation (1) can be rewritten as follows: FZW/Zw-*C,AwC2ALHa) (2) wherein C1 and C2 are coefficients.

Furthermore, since the length of the strut is substantially equal to the length of the lower hull in the present invention, the equation (2) can substantially be expressed as follows: B5 Fz#w/Zw=C1BsC2B,2=C2B,(C3 a)2) (3) B, wherein Bs stands for the strut width, B, stands for the width of the lower hull, and C3 is a coefficient.

From the equation (3), the motion characteristic of the semi-submerged catamaran can substantially be defined by the relation between the strut width and the width of the lower hull.

Based on such knowledge and experimental data, the relation between the above-mentioned two factors has been clarified according to the present invention. In Fig. 9, the heaving motion is shown by plotting the ratio of the wave length A to the ship length Lt on the abscissa and the ratio of the amplitude Z of the heaving motion to the wave height S8 on the ordinate. In Fig. 9, curve Q)A shows results obtained when Bs/B, is nearly equal to 0.8. In this case, in spite of a semi-submerged shape, the motion characteristic is substantially as bad as that of an ordinary ship.Curve (ff) shows results obtained when the strut width B5 is much smaller than the width B, of the lower hull and the ratio Bs/B, is nearly equal to 0.2. In this case, the inherent frequency deviates to the longer wave length side, but on the shorter wave length side, since the value of s92 in the equation (3) is increased, the value of FZ\IZW (absolute value) is increased and the motion becomes rigorous in the region of short waves.

Curve DC shows data obtained when B5 is nearly equal to 0.4. from the data, it is seen that it is preferred that the value of BB, be in the range of from 0.3 to 0.5.

The width of the strut has influences on the propelling power and stability characteristic. As pointed out hereinbefore, increase of the width of the strut is not preferred because the resistance of the strut is increased if the submergence depth is in the range specified in the present invention.

Furthermore, if the width of the strut is diminished below the above-mentioned range, the lateral restoring force is drastically reduced and the stability is often degraded.

As shown in Fig. 5, in the present embodiment, it is preferred that the plane shapes of the strut 12 and lower hull 1 2 be parallel in the vicinity of the center and the sectional shapes be the same. The front and rear parts of the central portion are gradually slenderized toward the ends. The length of the parallel portion of each of the lower hull and strut is preferablyabout 40 to about 70% the entire length.

If the length of the parallel portion exceeds about 80% of the entire length, the shape should inevitably be changed abruptly in the front or rear part. If the length of the parallel portion is too short, the portion having a complicated curved shape is increased and the manufacturing cost is increased. Moreover, in this case, the displacement is reduced, resulting in decrease of the load. Therefore, too short a length of the parallel portion is not preferred.

(D) Dimensional relation between Lower Hull and Propeller: As is seen from Fig. 3, the semi-submerged catamaran of the present invention has a propeller 1 5 in the rear portion of the lower hull 11. The diameter of the propeller has significant influences on the propelling power of the semi-submerged catamaran.

The propulsive coefficient 77 is represented by the following equation: 71=77oxx7H x11R wherein rl, stands for the open efficiency of the propeller, rlH stands for the hull efficiency and 71R stands for the propeller efficiency ratio.

The value of 170 is determined by the propeller load, and generally, the lower is the propeller rotation speed (the smaller is the rotation number) and the larger is the diameter of the propeller, the higher is the efficiency 710. On the other hand, the hull efficiency TIH is determined according to the speeci of water flowing onto the propeller surface, that is, the accompanying stream of the propeller, by the following equation: 1-t t7H= 1-W wherein t stands for the thrust deduction factor and W stands for the wake fraction.

As shown in Fig. 10(A), in the distribution of wake W of the lower hull 11 alone, the value of W is large in a region spaced much inwardly from the circumference of the maximum diameter Accordingly, in a submarine or the like, if the diameter of the propeller is determined so that the propeller is located on this region where the wake are large, the value of rlH is increased and the propulsive efficiency can be increased. It is said that in this case, it is preferred that the diameter of the propeller be about 60 to about 70% of the diameter of the lower hull.

However, in case of a semi-submerged catamaran comprising a lower hull and a strut in combination, the wake distribution is as shown in Fig. 1 O(B) and is different from the above-mentioned wake distribution observed in case of the lower hull alone. As is seen from Fig. 1 O(B), in a semisubmerged catamaran, since the value of W is especially large in the upper portion of the lower hull, even if the diameter of the propeller is larger than in case of the lower hull alone, the propeller is operated in the region where the wake are large and the value of TIH is increased. Furthermore, since the diameter of the propeller is large, also the value of 110 is increased, with a result that the propulsive efficiency is improved.In the semi-submerged catamaran of the present invention, in order to attain this improvement, it is preferred that the diameter DP of the propeller be about 70 to about 100%, especially about 90%, of the height H, of the lower hull.

(E) Posture Control of Lower Hull: As shown in Figs. 4 and 5, fins 1 6 and 16' having a blade-shaped section are mounted on the front and rear portions of the lower hull 11 in the semi-submerged catamaran.

The plane shape of the fin is tapered so that the chord length of the end close to the lower hull (fixed end) is longer than the chord length of the other end (free end), whereby flexural stress owing to the flexural moment acting on the fixed end is moderated.

In the present embodiment, four fins as a whole are mounted on the front and rear portions of the two lower hulls. The shapes and sizes of these fins are selected after due consideration of the characteristics and properties of the semi-submerged catamaran.

By provision of fins in a semi-submerged catamaran, there can be attained effects of increasing the force of damping the motion and improving the lateral stability during navigation, but a defect of increase of the resistance is caused by fins. Accordingly, fins are designed after due consideration of these merits and demerits.

In case of a semi-submerged catamaran, the motion damping force by the hull alone is smaller than in an ordinary ship. By the term "motion damping force" is meant a force of dumping the rocking motion when the ship rocks among waves. Namely, reduction of the kinetic energy possessed by the ship by generating waves on the rocking movement of the ship results in generation of the motion damping force. In case of a semi-submerged catamaran, because of a specific configuration thereof, the wave-making phenomenon is moderated and therefore, the motion damping force is small.

Accordingly, the motion characteristic of the semi-submerged catamaran is such that a large rocking motion is caused in waves in the vicinity of the point of synchronism. Accordingly, if fins are not disposed, it is apparent that excellent navigation properties inherent of the semi-submerged catamaran cannot be attained. On the other hand, if fins are disposed, since the resistance of the fins owing to the vertical movement of the fins acts as the motion damping force, the motion is reduced and in the semisubmerged catamaran where the damping force is small in the vicinity of the point of synchronisms, the effect of the fins is increased. From results of experiments, it has been found that best results are obtained when the total area of the fins is about 1 5 to about 30% of the waterplane area Aw. If the area of the fins is too large, friction resistance and induced resistance owing to the presence of fins are increased during navigation, and increase of these resistances is especially conspicuous when the Froude number Fn exceeds about 0.35.

What should be taken into consideration in arranging fins is the relation between the area of the front fin and the area of the rear fin, which is concerned with the longitudinal stability of the semi submerged catamaran. More specifically, the longitudinal stability moment M, of the semisubmerged catamaran is represented by the following equation: M(longitudinal restoring moment)-(unstability moment based on dynamic lift of lower hull) In an ordinary ship, since the waterplane line area is large and the longitudinal restoring moment is very large and since the longitudinal stability moment is positive and is sufficiently large, the longitudinal stability need not be especially taken into account. However, in case of a semi-submerged catamaran, since the waterplane line area is small, the longitudinal restoring moment is reduced.

Furthermore, as shown in Fig. 11(A), the lower hull generates a dynamic lift during navigation, and since the point of generation of the dynamic lift is in the front of the gravity center G, when the lower hull is in the bow-rising state as shown in Fig. 11(A), the moment acts in a direction further increasing the trim. In other words, the unstability moment acts on the lower hull. Accordingly, when the unstability moment based on the dynamic lift of the lower hull in the above equation becomes larger than the restoring moment, the longitudinal stability moment comes to have a negative value, and the semi-submerged catamaran comes to have an unstable posture. This longitudinal unstability is effectively prevented by provision of fins.

Although a fin 1 6 mounted on the lower hull 11 generates a dynamic lift during navigation as shown in Fig. 1 1 (B), the front fin 16 located in the front of the gravity center G generates an unstability moment Mff as in the above-mentioned lower hull as is apparent from Fig. 1 1 (B), the rear fin 1 6 generates a stability moment Mf (the moment of restoring the posture of the ship). Accordingly, in order to improve the stability of the semi-submerged catamaran by fins, it is preferred that only the rear fin be disposed or the area of the rear fin be made larger than the area of the front fin. However, if the area of the rear fin is made too much larger than the area of the front fin, no good balance of the damping force is attained between the rear and front fins, resulting in increase of the pitching motion.

Accordingly, a good stability is obtained when the area of the rear fin is made appropriately larger than the area of the front fin. As a result of experiments made by us on dimensions of fins, it has been found that it is preferred that the area of the rear fin be about 1.5 to about 3 times, especially about 2 times, the area of the front fin.

The fins may be fixed or one or both of the rear and front fins may be movable. Movable fins act as a stabilizer and can perform the posture control of the semi-submerged catamaran during navigation or the motion control in waves.

The entire area of the fins is often determined so that a sufficient damping force is obtained.

However, if the fins are moved, a smaller area is advantageous from the viewpoint of the driving power.

Since the rear fin is very important for attaining a good longitudinal stability, it is difficult to reduce the area of the rear fin and a trouble is often caused when all the fins are rendered movable.

The above problem is solved by adopting, for example, a fin structure shown in Fig. 12. The fin 16 comprises a fixed portion 1 6a and a movable portion 1 6b (flap). Ordinarily, it is preferred that the area of the movable portion 1 6b be about 20 to about 30% of the area of the fin 16.

In the embodiment shown in Fig. 3, the front edge 1 2b of the strut 12 is located backwardly of the front end 1 a of the lower hull 11. Fig. 1 3 illustrates another embodiment of the semi-submerged catamaran in which the front edge 1 2b of the strut 12 is located forwardly of the front and 11 a of the lower hull 11.

Generally, a semi-submerged ship is excellent in the high speed navigation capacity, but when the Froude number Fn represented by the following formula:

wherein Fn stands for the Froude number, v stands for the velocity of the ship, g stands for the acceleration of gravity, and L stands for the length of the lower hull, is about 0.3 or in the range of from 0.4 to 0.6, the wave-making resistance is drastically increased. Accordingly, when the normal speed of the semi-submerged ship corresponds to the above-mentioned Froude number owing to other necessary design conditions, the power of the main engine should be increased and an economical disadvantage is caused.

This problem can be solved by locating the front edge 1 2b of the strut 12 forwardly of the front end 11 a of the lower hull 11. More specifically, by this arrangement, the wave-making resistance, which occupies about 50% of the total resistance of the semi-submerged ship when the Froude number is about 0.3 or in the range of 0.4 to 0.6, can be remarkably reduced, with a result that the necessary power of the main engine can be reduced.

From results of experiments made by us, it has been found that the longer is the distance I between the front edge 1 2b of the strut 1 2 and the front end 11 a of the lower hull 1 the smaller is the wave-making resistance. However, if in order to increase the distance I, the strut portion is elongated, the friction resistance is increased by increase of the dipping area and the effect of reducing the wave-making resistance is cancelled by this increase of the friction resistance. Furthermore, if the strut is located extremely forwardly, a problem is caused concerning the structure or arrangement of the upper hull 13. Accordingly, from the practical viewpoint, it is preferred that the value I be 5 to 30% of the entire length L of the lower hull 11.

Figs. 14(A) to 14(H) are diagrams illustrating still another embodiment of the present invention where the front edge 1 2b of the strut 12 is formed to have a vertical, inclined, curved or other shape. In designing a semi-submerged catamaran, an appropriate shape is chosen so that the wave-making resistance can be minimized.

The semi-submerged catamaran of the present invention may be applied to a passenger ship, a cargo ship, a factory ship or the like while appropriately arranging the structure of the upper hull.

Moreover, the capacity, shape, size, scale and other factors of the semi-submerged catamaran of the present invention can be determined according to the intended use. Therefore, dimensions and configurations of the strut and lower hull may be defined by ratio values such as mentioned above, ratherthan by specific numerical values.

Accordingly, relative values (ratio values) are adopted for defining the respective elements in the present invention. For better illustration, examples of specific values are shown in the following Table.

Item Size, displacement 200-400 tons Submergence depth f (m) 1.5-3.1 Lower hull average diameter D (m) 2.1-2.6 height H, (m) 1.8-2.2 width B, (m) 2.4 3.0 length L (m) 25.0-31.0 Strut draft line area (m2) 40-60 maximum width (m) 1.0-1.2 entire length (m) 26-32 length (m) of parallel portion 12-1 5 Diameter DP (m) of propeller 1.5-1.9 Fins area (m2) of front fin 1.0-1.5 area (m2) of rearfin 3.7 4.7 area (m2) of movable portion 1.0-1.2 The present invention is not limited by embodiments specifically shown in the accompanying drawings or numerical values shown in the above Table, but various changes and modifications can be made without departing from the scope defined by the following claims.

Claims (22)

Claims

1. a semi-submerged catamaran comprising two lower hulls always located below the surface of water and arranged substantially in parallel to each other with respect to the direction of advance, plate-like struts mounted substantially vertically on the upper portions of the respective lower hulls along almost the entire length thereof and an upper hull supported by said struts and always located above the surface of water, wherein the ratio (f/D) of the submergence depth (f) of the lower hulls to the average diameter (D) of the lower hulls is in the range of from 0.7 to 1.2.

2. A semi-submerged catamaran as set forth in claim 1 wherein the ratio (LID) of the length (L) of the lower hulls to the average diameter (D) of the lower hulls is in the range of from 10 to 1 5.

3. a semi-submerged catamaran as set forth in claim 1 wherein the ratio (hit,) of the height (HL) to the width (BL) in the cross section of the lower hulls at mid length is in the range from 0.6 to 0.8.

4. A semi-submerged catamaran as set forth in claim 1 wherein the maximum width of each strut at least in the central portion thereof on the draft level is 30 to 50% of the maximum width of each lower hull at the same cross-sectional position.

5. A semi-submerged catamaran as set forth in claim 1 wherein the struts have such a draft line shape that a parallel portion is formed in the central zone and the length of said parallel portion has a length corresponding to 40 to 70% of the entire length of the strut.

6. A semi-submerged catamaran as set forth in claim 1 wherein each lower hull includes a propeller and the diameter (DP) of said propeller is about 70 to about 100% of the height (HL) of the lower hull.

7. A semi-submerged catamaran as set forth in claim 1 wherein front and rear fins are disposed on the inside of each lower hull and the area of the rear fin is larger than the area of the front fin.

8. A semi-submerged catamaran as set forth in claim 7 wherein the total area of the front and rear fins is 1 5 to 30% of the draft line area of each strut.

9. A semi-submerged catamaran as set forth in claim 7 wherein the area of the rear fin is 1.5 to 3 times the area of the front fin.

1 0. A semi-submerged catamaran as set forth in claim 7 wherein each fin comprises a fixed portion and a movable portion and the area of the movable fin is 20 to 30% of the total area of the fin.

11. A semi-submerged catamaran as set forth in claim 1 wherein the front edge of each strut is located forwardly of the front end of the lower hull.

12. A semi-submerged catamaran comprising two lower hulls always located below the surface of water and arranged substantially in parallel to each other with respect to the direction of advance, plate-like struts mounted substantially vertically on the upper portions of the respective lower hulls along almost the entire length thereof and an upper hull supported by said struts and always located above the surface of water, wherein the ratio (hit,) of the height (H,) to the width (B,) in each lower hull is in the range of from 0.6 to 0.8.

1 3. A semi-submerged catamaran as set forth in claim 12 wherein the maximum width of each strut at least in the central portion thereof on the draft level is 30 to 50% of the maximum width of each lower hull at the same cross-sectional position.

14. A semi-submerged catamaran as set forth in claim 1 2 or 13 wherein the struts have such a draft line shape that a parallel portion is formed in the central zone and the length of said parallel portion has a length corresponding to 40 to 70% of the entire length of the strut.

1 5. A semi-submerged catamaran comprising two lower hulls always located below the surface of water and arranged substantially in parallel to each other with respect to the direction of advance, plate-like struts mounted substantially vertically on the upper portions of the respective lower hulls along almost the entire length thereof and an upper hull supported by said struts and always located above the surface of water, wherein front and rear fins are disposed on the inside of each lower hull and the area of the rear fin is larger than the area of the front fin.

1 6. A semi-submerged catamaran as set forth in claim 1 5 wherein the area of the rear fin is 1.5 to 3 times the area of the front fin.

1 7. A semi-submerged catamaran comprising two lower hulls always located below the surface of water and arranged substantially in parallel to each other with respect to the direction of advance, plate-like struts mounted substantially vertically on the upper portions of the respective lower hulls along almost the entire length thereof and an upper hull supported by said struts and always located above the surface of water, wherein front and rear fins are disposed on the inside of each lower hull and the total area of the front and rear fins is 1 5 to 30% of the draft line area of each strut.

1 8. A semi-submerged catamaran as set forth in claim 17 wherein each fin includes a movable portion and a fixed portion and the area of the movable portion is 20 to 30% of the entire area of the fin.

19. A semi-submerged catamaran comprising two lower hulls always located below the surface of water and arranged substantially in parallel to each other with respect to the direction of advance, plate-like struts mounted substantially vertically on the upper portions of the respective lower hulls along almost the entire length thereof and an upper hull supported by said struts and always located above the surface of water, wherein the ratio (f/D) of the submergence depth (f) of the lower hulls to the average diameter (D) of the lower hulls is in the range of from 0.7 to 1.2, the ratio (HIB,) of the height H, to the width B, in each lower hull is in the range of from 0.6 to 0.8, front and rear fins are disposed on the inside of each lower hull, the area of the rear fin is larger than the area of the front fin and the total area of the front and rear fins is 1 5 to 30% of the draft line area of each strut.

20. A semi-submerged catamaran as set forth in claim 1 9 wherein the area of the rear fin is 1.5 to 3 times the area of the front fin.

21. A semi-submerged catamaran as set forth in claim 19 wherein each fin includes a movable portion and a fixed portion and the area of the movable portion is 20 to 30% of the total area of the fin.

22. A semi-submerged catamaran substantially as described herein with reference to Figures 3 to 14 of the accompanying drawings.

Amendments to Claims Filed on 18.8.80.

Claims 1 2-1 8 deleted, claims 1 9-22 renumbered and appendancies thereof corrected.