Wave piercing bow of a monohull marine craft

Abstract

This invention provides an improved shape of the bow of a high speed ocean-going ship. It introduces a set of inverted and inclined surfaces that enclose the bow from above, and cause the hull to move through the waves rather than over them. These surfaces generate a downward lifting force that counteracts the displacement force. Displacement force causes a traditionally-shaped bow to lift above waves and initiate pitching movement. The new type of bow reduces or eliminates pitching movement and slamming loads on the hull, thus improving ride quality, and enabling designers to specify lighter structure under the existing rules. This in turn reduces the overall weight of the craft, enabling reduction in the power required to achieve the service speed, reduction in fuel consumption, and reduction in the associated capital and operating costs. It also improves ride quality for passengers, and reduces damage to cargo due to accelerations. 1U.S. Prior Application References5,184,561July 1993Nickell5,263,433November 1993Meyer6,116,180September 2000ThompsonForeign Prior Application References2,359,532November 2001Canada2,150,890July 1985United Kingdom2,230,717April 1991United Kingdom02,296,855June 1992Japan05,277,190May 1995Japan

Description

BACKGROUND OF THE INVENTION

[0001] This invention pertains generally to the hull shape of ocean-going ships. More specifically, this invention relates to the shape of the bow of a monohull high speed marine craft. The new and unique proposed shape of the bow includes several inclined top surfaces that replace the traditional forward deck, and are positioned to cause the hull of a ship to go through the waves, rather than over the waves.

[0002] A ship moving in waves is subjected to vertical accelerations. A traditional bow, having transverse sections that are the widest at the deck, is typically lifted up by its volume when it passes through a wave crest, and it falls into its trough. That movement is commonly referred to as “pitching”, and in certain conditions it results in high amplitude and acceleration levels. In extreme cases, at certain combinations of ship's speed, hull length and wave height, the hull will emerge from, and crash back into the water. To prevent damage to the hull, the rules governing structural design of ships, call for a suitably strong, hence heavy, supporting structure of the hull's shell. Structural strength requirement can be reduced under the construction rules in force only if the global loads (accelerations) and local loads (slamming) are reduced. In turn, these loads can only be lowered by reducing the level of hull's response to the waves. The benefits of reduced structural weight are significant. Firstly, the construction cost is reduced, as less material needs to be purchased and installed. Secondly, a lighter craft requires less power to achieve the required speed, further reducing the cost of building and operating such a vessel, as smaller engines need to be purchased and less fuel is consumed in service. Finally, reduced acceleration levels result in reducing damage to cargo and the incidence and severity of seasickness in passengers. This directly and significantly increases the revenue-generating potential of the ships. More so, when certain types of ships, such as passenger ferries or crew boats serving offshore installations, are often restricted in their operation by weather conditions. In heavy weather, speed may have to be reduced and course may have to be altered, increasing cost of operating a vessel. In some cases, ships are not permitted to operate above certain present or forecasted sea states. This invention is expected to eliminate or reduce those restrictions, and to produce the benefits associated with lower structural weight.

[0003] The described problem has been addressed in the past by introduction of several different types of marine craft, specifically designed to reduce response to wave action and to minimize pitch amplitude and accelerations. The known design solutions fall into two main categories: a passive and an active ride control. The former is based on the shape of the hull, or more commonly multiple hulls. The latter involves mechanically actuated and computer controlled moving surfaces, most commonly fins, which attempt to minimize vertical movement of the hull. Both are expensive to purchase and to use.

[0004] Multihull ships have the lowest payload to overall weight ratio, because of their heavy decks connecting two hulls. They are either twin hull catamarans, or one main plus two stabilizing hulls trimarans, or SWATH, an acronym for Small Waterplane Area Twin Hull, a vessel based on large entirely submerged torpedo shaped hulls connected to the decks with relatively thin vertical fins, which minimize effect of the waves on the vessel motion, as relatively little volume is offered to be displaced up when passing through the wave crest. These solutions work, but only up to a certain wave height. Above it, waves begin to hit the deck spanning the hulls, with often even worse effect than a conventional monohull, as slender twin hulls offer little movement damping effect. These solutions are also invariably expensive, for obvious enough reasons. Building a complex multihull craft with its heavy connecting deck, which has to accommodate all the payload, is more expensive than building a wider single hull, which can accommodate payload inside it.

[0005] Active ride control devices do work, but they represent not only high added purchase cost, but a significant risk as well. To work properly, articulated fins must be submerged and exposed to debris and other objects, including large fish and mammals. There are recorded cases of articulated fins being broken off or disabled in minor collisions, which otherwise have no effect on the hull itself. In many cases ships have been disabled and required assistance, as they were not designed to operate without said active ride control devices. Effectiveness of articulated fin based ride control devices is also limited, as they require water movement to operate, which renders them ineffective when the ship is moving slowly or when it is stationary, a common enough occurrence during docking or maneuvering around offshore installations.

[0006] Which leaves a monohull, the most cost effective configuration for an ocean going ship. To date, the only recorded attempts to reduce motions in waves, involve either design of longer and more slender single hulls, or, notably in Europe, single hulls fitted with a wave piercing bow. The former, adhering to the principle that a hull significantly longer than the wave length will respond less to it, are obviously more expensive to build. Not only the length itself adds to the cost, the structural strength requirements are the function of hull length (among many other factors) and a longer hull will have its section heavier than a shorter hull. The latter have been limited to very long, slender hulls, with needle shaped bows of generally round transverse sections, designed not to react to waves at all.

[0007] This invention represents a different approach.

BRIEF SUMMARY OF THE INVENTION

[0008] The concept behind this invention, which distinguishes it from all other existing forms of ship's bow, provides for the shape of a bow that reduces pitching motion of ship's hull at speed in waves by means of creating a dynamic lift force counteracting the forces that initiate pitching motion in waves.

[0009] The reduction of pitching is achieved by a new shape of the bow that causes the hull to move deliberately through the waves, rather than over them. This phenomenon is generally achieved by a bow that is shaped in such a manner that the center of the area of the transverse sections of the bow is located close to the water surface in normal operating condition, rather than high above it, as it is in a traditional ship's bow.

[0010] Wave piercing bows per se, are not new. Not to be confused with the early ramming bows, fitted to warships to enable them to ram an enemy's ship, wave piercing bows have recently been subject to extensive research worldwide. Based on the concept of preventing the initiation of pitching by eliminating the traditional bow's large volume above the waterline, the first wave piercing bows have been designed, optimized, and fitted to multihull vessels (primarily twin hulled, or “catamaran” ships), many of which are presently in service. There is a record of sporadic research into the wave piercing bows for a singe hull (referred to as “monohull”), but at the time of this writing, none yet in commercial service. The main reason is the difficulty of stabilizing a wave piercing monohull in waves. In the most simple terms, the volume of a bow above the waterline prevents the hull from diving (a desired effect), but it also causes the bow to lift over a wave, and then often crash into the next wave (not a desired effect). In the wave piercing monohulls researched to date, reducing that volume reduces both effects. The hull will not lift and crash, but it will dive easily. In multihulls, this problem has been solved by adding a third bow, positioned between and above the main two wave piercing hulls. In a monohull, it cannot be fitted.

[0011] This invention solves that problem by going beyond the passive elimination of the bow volume that causes pitching. Instead it introduces a new shape and distribution of volume in the wave piercing bow, to dynamically control and reduce the movement by balancing lifting forces produced by the interaction of the hull and the waves.

[0012] The main feature, which creates an improvement in hydrodynamic performance, is a system of surfaces enclosing the bow from above, forming the general shape of a wedge pointed forward, in the direction of the ship's movement. These upper surfaces are further inclined transversely to form a shallow inverted “V” (i.e., “Λ” shape) in the transverse section. At their aft, top end, the surfaces additionally curve outwards, deflecting the water and spray away from the wheelhouse and from the deck.

[0013] An added advantage of this invention is the reduction of resistance and power at speed in calm water, as compared to a standard raked bow. The tip of the proposed wave piercing bow is located much closer to the waterline, and the resulting length at the waterline is greater than that of a hull of the same overall length, fitted with a standard bow. Hydrodynamically, a hull of the same displacement and greater waterline length will inevitably require less power for the same speed in calm water.

[0014] That benefit is shared by all wave piercing bows. However, wave piercing bows developed to date tend to be very long and narrow, consequently increasing the overall hull length, and hence cost of a vessel. The present concept attempts to produce the desired hydrodynamic effects without adding to the overall length. In fact, in order to create the upper surface producing a downward lifting force, the proposed new type of bow has to be relatively wide, resulting in a hull which has more usable space inside than traditional narrow high speed hulls.

[0015] The reduction in accelerations and wave impact loads on the hull also enables the designer to specify a lighter internal structure for a ship fitted with the proposed new wave piercing bow. Weight is one the most important factors affecting the economics of a cargo ship. In simple terms, the less weight built into the design, the more payload can be carried in the same hull, to generate revenue. There is a certain minimum structural strength required to safely operate an ocean going ship, a minimum safeguarded by the recognized authorities by enforcing compliance with their rules. These classification societies examine and approve the design before a ship can be built.

[0016] High speed craft, to which the application of the proposed new wave piercing bow would primarily apply, have their internal structure designed to so called High Speed Craft (HSC) code. Under HSC code, the scantlings (thickness of the plates or size of the stiffeners) depend primarily on the accelerations and impact loads. These, in turn, are based on empirically determined maximum loads measured on high speed ships, and inevitably produce a heavy structure. Lighter structure is allowed only if lower loads are proven through model testing. Lighter structural weight not only results in lower construction cost, but it also requires lower power for the same speed and payload. Alternatively, the difference in weight may be exchanged for a higher payload and revenue. This weight reduction is the primary benefit of the present invention.

[0017] The inventor has funded a comprehensive research and development program, involving comparative model testing of the standard and wave piercing bows on the same hull, and the design of a lighter structural arrangement. This preliminary R&D work has fully confirmed the benefits claimed herein.

[0018] The form of the ship's bow described above creates a unique and improved concept. This bow takes advantage of the waves to stabilize the hull at speed, resulting in lower accelerations, lower structural weight, lower power requirements, lower capital and operating costs, and higher payload and revenue.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1—Isometric view of a hull fitted with the proposed wave piercing bow, showing the overall

[0020] FIG. 2—Comparison of the profile (side) views of a hull fitted with the proposed wave piercing bow and a hull fitted with a standard bow.

[0021] FIG. 3—Profile (side) view of the proposed new wave piercing bow showing key surfaces.

[0022] FIG. 4—Plan (top) view of the wave piercing bow, showing key surfaces.

[0023] FIG. 5—Body plan (front view) of the wave piercing bow, showing key surfaces and a section.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Referring to the drawings showing FIGS. 1 through 5, the numbers 1 through 9 indicate the following portions or features of the new bow.

[0025] 1. Standard bow shown to illustrate the difference in waterline length,

[0026] 2. General outline of the proposed wave piercing bow,

[0027] 3. Waterline length with a standard bow,

[0028] 4. Waterline length with the wave piercing bow,

[0029] 5. Waterline,

[0030] 6. Hull draft, shown to illustrate the relation to the height of the wave piercing bow tip above waterline,

[0031] 7. Height of the tip of the wave piercing bow tip above waterline,

[0032] 8. A pitch reducing reverse lifting surface,

[0033] 9. Wave and spray deflector,

[0034] 10. Typical transverse section of the proposed wave piercing bow

[0035] FIGS. 1 through 5 illustrate the preferred embodiment of this invention. The specific features that are unique to this invention and their hydrodynamic effect are shown on the drawings and described in detail hereinafter, although it should be understood that the invention is not confined to any strict conformity with, or limited by the accompanying drawings, but it may be modified to optimize the hydrodynamic performance, so long as one or all the essential features are present within the limits specified below and in the claims.

[0036] The first significant and unique feature not applied thus far to the design of a high speed marine monohull craft, is the lifting surface (8), a panel forming the top of the proposed new wave piercing bow, shaped to generate, upon the bow entering a wave, a lifting force directed down, opposite to the displacement force generated by a submerged volume of the bow, which typically initiates the pitching movement by lifting the bow up over the wave. Panels (8), shown in FIGS. 1 through 5 only in a generic form, will have their size, shape and angle optimized for the size of the craft and the design speed, to counterbalance the displacement force and to minimize the pitching motion while moving through the waves. The height (7) of the point of origin of panels (8) will also be optimized in terms of its ratio to the draft (6). Introduction of the reverse panels (8), which counterbalance the forces causing pitch motions, and reduce said motions and the associated loads affecting the structural weight required under the rules, represents a significant improvement in the art of ship design.

[0037] An additional improvement resulting from lowering the tip of the bow to the distance (7) closer to the waterline (5) than in a standard bow, is an increase in the waterline length (4) as compared to the waterline length (3) of a ship of the same overall length, as shown in FIG. 1. As a rule, resistance of a marine craft hull and the associated power required to move the hull at a required speed, is an inverse function of the waterline length, i.e., the longer the waterline length, the lower the resistance and power at the same hull displacement. An increase of the waterline length, inherent to the present invention, again represents an improvement in the art of ship design.

[0038] An adverse effect of the water and spray being carried over the bow moving through the wave, rather than over it, is admittedly a trade-off for all other improvements listed here. As expected, the initial tests confirmed that overall amount of water and spray displaced by a wave piercing hull was lower than that displaced by a hull fitted with an ordinary bow, but a standard hull crashing into the wave displaces water and spray away from the hull, while the wave piercing hull causes it to move over the bow and onto the aft deck, where equipment or payload may be stored. This undesirable effect is controlled by the spray deflectors (9), a curved upper portion of the reverse surfaces (8), deflecting water sliding up the surface (8) to the side and away from the hull centerline. This effect may be further controlled by the operator, by slowing down the craft when particularly adverse sea conditions are encountered.

Claims

1. A sea-going ship's hull form, in which the bow is enclosed from the top by a surface extending longitudinally from the tip of the bow located at a point vertically closer to the waterline than the deck, to said deck level further aft, said surface also inclined transversely sloping down from the center plane of the hull towards the sides of the hull, said surface having at least half of its area, in which straight lines tangent to the points on longitudinal sections through said half of the area, are at angles of no less than 0 degrees and no more than 30 degrees to horizontal, and in which straight lines tangent to the points on transverse sections through said half of the area, are at angles of no less than 0 degrees and no more than 30 degrees to horizontal.

2. A sea-going ship's hull form as defined in claim 1, in which said top bow enclosing surface has shape symmetrical port and starboard.

3. A sea-going ship's hull form as defined in claim 1, in which shape of said top bow enclosing surface is composed of plurality of panels separated by knuckles.

4. A sea-going ship's hull form as defined in claim 1, in which said top bow enclosing surface has an additional panel having horizontal transverse sections, at the center portion of said top bow enclosing surface.

5. A sea-going ship's hull form as defined in claim 1, in which one or more portions of said top bow enclosing surface is of a conical shape.

6. A sea-going ship's hull form as defined in claim 1, in which one or more portions of said top bow enclosing surface is flat.

7. A sea-going ship's hull form as defined in claim 1, in which shape of said top bow enclosing surface is composed of plurality of panels, some of which are displaced vertically in relation to one another, and joined with additional panels of height not exceeding 10% of the total length of said top bow enclosing surface, and inclined no more than 45 degrees from vertical.

8. A sea going ship's hull form as defined in claim 1, in which said top bow enclosing surface is further twisted below said deck to deflect the flow of water and spray to the sides, away from the hull.

9. A sea-going ship's hull form as defined in claim 1, in which said top bow enclosing surface is fitted with one or several recesses to accommodate mooring and other fittings and/or equipment.