(1) Field of Invention
This invention relates to vee-hull planning, semi-planning, and displacement boats incorporating a vee-hull bow shape with aft sponsons, sponsons, or external appendages.
(2) Description of Prior Art
Conventional vee-hull boats and ships are designed to cut through waves without pounding or slamming but sacrifice speed and transverse stability. The design of the forward vee-section of a boat hull determines the smoothness of the ride. In practice vee-hull boats and ships tend to be long and narrow and as a result they heel significantly from side to side. The Damen Sea Axe hull utilizes this concept where the vee hull is narrow and has little to no flair. The Damen hull sacrifices reserve buoyancy in the bow as a result. The Damen hull is inherently unstable in a following sea and requires active control fins to keep from broaching. Broaching typically happens when a vessel is riding along with a wave or racing down one.
Another vee-hull design is Austal's stabilized monohull used in Littoral Combat Ships (LCS-2). This hull has a long needle like bow that also provides little reserve stability and is shown to bury itself in large following seas. The LCS-2 hull also requires several sets of active control fins to remain stable in high seas. The LCS-2 hull also has amahs or outriggers to improve stability but the amahs contribute little to the vessel's overall displacement.
Another factor affecting hull design is weight distribution and interior accommodation, which are challenges in any vessel. The center of gravity of the boat must be located directly over the center of buoyancy of the hull at its designed waterline. If the two centers are not located in the same plane the boat will trim and list until the centers are properly located. If there is more weight to one side then the boat will list to that side. If there is more weight aft the boat will trim aft, i.e., sit lower in the water by the stern.
To achieve balance, conventional hulls have engines placed forward from the stern of the vessel. This encroaches on interior space and compromises the comfort of the vessel due to noise and heat from the engine. Also, lines must be run to the engine for cooling, intake air, and exhaust. Exhaust lines become quite hot requiring bulky insulation. An insulated housing is typically fashioned around the engine itself to deaden engine noise and contain heat. The insulated housing significantly reduces the available space for personal accommodation. This type of engine mounting also requires a propeller shaft to run from the engine normally under the boat or inside the hull to a stern drive propeller. If the shaft is under the boat, it is subject to damage should the boat run aground or hit debris in the water. Of course, any shaft configuration below the hull produces significant drag lowering the speed of the vessel and increasing operating cost. Both shaft configurations require bearing supports along the shaft length to ensure the shaft turns freely and does not vibrate.
Traditional semi-displacement hulls and modern interpretations thereof produce hulls that have little reserve buoyancy in the bow and are transversely unstable with a tendency to broach in high seas, especially following seas requiring active control fins to be stable. These vessels also require engine placement forward of the transom to achieve static balance in the hull necessitating long shafts to the propellers. The engine placement encroaches on valuable living or shop space in areas of the vessel. An alternate to traditional propellers is a jet drive. Jet drives are directly attached to the vessel's transom. The engines are still forward of the jet drives requiring long shafts as in the LCS-2 vessel to maintain proper vessel trim.
Broadly speaking, this invention provides a hybrid boat hull designed wherein the planning, semi-planning, or displacement of a hull having a conventional vee-hull forward transitions into outboard sponsons. The sponsons originate in the bow, forward, at, or aft of the forward perpendicular, in a vee shape and transition as they go aft. The sponsons also become wider as they transition aft. In application, the sponsons generally perform best when the aft sections have a constant width. When planning or semi-planning the proposed hull rides on the sponsons providing lift to the hull. The vee forward remains in the water but is also lifted thereby reducing wetted surface and drag, while cutting through waves enhancing the vessel ride. Air is trapped between the two sponsons and the water creates an area of buffered air adding lifting forces on the hull and further reducing drag at semi-planning speeds. This lifting force on the hull is augmented by water, which impacts the curved/cupped after sections of the vee-bottom of the hull and is deflected down. A ram air effect is also induced by the changing width of the outboard sponsons as they transition aft. The distance between the sponsons is greater in the bow creating a funnel for air. A large volume of air is trapped under the boat or ship enhancing the ride of the vessel. The buffered layer of accelerated air acts to increase the lift on the boat reducing the hull drag in the water.
The boat hull has a forward center vee-section to ensure the boat will not slam or pound in a seaway and additional lift generated by buffered air under the hull ensures a measurably smoother and faster ride. In the preferred embodiment of the proposed hybrid boat or ship the hull incorporates a centerline vee-hull which becomes shallower as it transitions aft to further enhance trapping air under the vessel to provide lift.
The hull design provides outboard sponsons with sufficient width and depth for the engines and drive systems to be mounted inside the sponsons. Interior accommodation need not be encroached upon with the proposed design. The proposed design is ideal for placing water jets in the outboard sponsons since water jets require a flat surface for water intake and can be directly coupled to propulsion engines. Long propeller shafts are not required inside the hull or underwater. Since the vessel has no underwater propeller shafts there is no water drag on the shafting or supporting appendages. This enhances the efficiency of the proposed hull and consolidates the engine compartment to the extreme aft section of the vessel enhancing space utilization.
The buoyant sponsons allow the engines to be placed next to jet drives, or other propulsion devices. The vessel's buoyancy is matched to the designed weight distribution by adjusting the width and depth of the sponsons. This allows the propulsion machinery to be in one consolidated location. Jet drives enhance the dynamic positioning of a vessel making this configuration ideal for work vessels that have to carefully maintain station.
The hull is optimized for speed and comfort by changing the centerline vee and the outboard sponsons. The centerline vee section of the hull acts as a shock absorber deflecting waves. The wider the centerline vee section the more buoyancy that is provided, resulting in a stiffer, bumpier ride. Maximizing the depth of the centerline vee reduces speed but makes the ride smoother. A step can be added to the centerline vee to introduce turbulent flow in the water behind the step enhancing the water and air mixture trapped between the two outboard sponsons thereby reducing drag on the hull.
The outboard sponsons can be made deeper providing a more cushioned but slower ride. Alternatively, the sponsons can be made shallower and wider providing more lift for a faster ride. The width of the outboard sponsons is also critical in producing a wake at speed. The wake produced by the outboard sponsons and the centerline vee can be optimized to cancel each other at speed ranges just as a bulbous bow does on a ship. It is possible to reduce the wake of the hull configuration by adjusting the after sections of the centerline vee along with the width and depth of the outboard sponsons. The wake produced by the outboard sponsons can adjusted to be canceled by the centerline vee or by each other. The result is to produce a faster more efficient hull over a given range of speeds.
Additional advantages include variable fuel and water tanks that can be fitted below the deck centered over the vessel's design center of buoyancy. Tanks placed in this location do not affect the trim of the vessel regardless of how full or empty the tanks are. The added advantage is that nominal interior space is compromised to achieve this placement and safety is further enhanced over conventional vessels. A balance must be made between required buoyancy, outboard sponson draft, and outboard sponson width. Adjusting these variables allows for fuel and water tanks to be optimized around the vessel's center of buoyancy.
At low speeds the hull of this invention has increased drag over conventional boats and ships but the hull also has much greater transverse stability and the hull's natural frequency can be adjusted to significantly reduce motions. This makes the hull a breakthrough hull design for offshore work boats where station keeping is critical. At higher speeds the increased transverse stability keeps the boat from healing and the buoyant vee bow ensures the vessel does not broach in following seas.
Having described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be through and complete and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to the elements throughout.
The hybrid boat hull of this invention has a forward center vee-section of the hull to ensure the boat will not slam or pound in a seaway and additional lift generated by buffered air under the hull ensures a measurably smoother and faster ride. Existing vee-hulls have a higher wetted surface, while semi-planning, creating more drag and providing less lift at speed. Conventional vee-hulls are also notably less transversely stable. The hull of the boat or ship incorporates a centerline vee-hull which becomes shallower as it transitions aft to further enhance trapping air under the vessel to provide lift as shown in
An example of a 200-ft high speed shallow water patrol boat is shown in
The side view of a 200-foot patrol boat is shown in
In reviewing the wave pattern shown in
The increase in width of the outboard sponsons 3A and 3B as they transition aft, shown in plan view of hull bottom (
The combined advantages of increased stability lift on the hull, and accelerated fluid flow between the outboard sponsons dramatically increase the attainable speed of the hull and comfort for the passengers. The hull design of this invention represents a significant advance in the technology.
The distribution of underwater volume shown in these figures is accommodated by machinery weight and the weight of the hull itself. A profile view with general arrangements of the 200-ft patrol boat is shown in
Note in
The bow can also have a single chine forward of the forward perpendicular (FP). This allows the deep vee in the bow to be fuller having move volume and buoyancy. A fuller deep vee increases reserve buoyancy making the boat dryer. In this configuration there is a single chine forward of the FP and the sponsons are blended into the deep vee for a longer length in the bow. The sponsons don't develop until aft of the FP as shown in
The 150-ft patrol boat example in
The ability to adjust the resonant frequency of the hull is critical to ensure reduced motions. Even a small wave with the proper size and height can excite a hull to roll and pitch if it falls in the resonant frequency of the vessel. The induced roll and pitch can be so large as to make operations unsafe or impossible. The ability to move the natural frequency of the vessel away the excitation period of waves gives the hull of this invention a unique advantage over other hull forms.
The aft view shown in
The plan view shown in
Comparison of an Existing Vessel with the Hybrid Vee-Hull
The difference in draft and beam are notable and the ramifications of the differences are significant. The draft of the Damen vessel does not include the propeller below the hull. Equipped with jet drives the hybrid vee hull is capable of traveling in significantly less water and has increased interior space with greater stability. The shallower draft greatly increases the range of the vessel especially in regions like the Caribbean.
The hybrid vee-hull has significant improvements over conventional vee-hulls in stability, performance, accommodation, sea-keeping and station keeping. The hybrid vee-hull SEV has greatly improved transverse stability inherit in the added width of the outboard sponsons and increased possible width of the hull. The metacentric height of a vessel represents the initial stability of the vessel. It is the height about which the vessel heels like a pendulum on a clock. The higher the metacentric height the more stable a vessel is. Note the extreme difference between the Damen vessel with a metacentric height of 1.52 meters compared to 7.65-meters for the hybrid vee-hull of a similar size and displacement. The hybrid vee-hull has over five times the initial stability of the Damen Stan 4207. This illustrates the Damen vessels tendency to broach in following seas and the inherent stability of the hybrid vee-hull.
Increased lift on the hull provides a smoother ride and greater obtainable speed as a result of the wing-in-ground effect, which is augmented by the shape of the outboard sponsons. The centerline vee-hull ensures good motions in a seaway. Maintaining proper fore and aft balance, regardless of fuel level, is designed into the hull by adjusting the width and depth of the sponsons coupled with the centerline vee-hull, taking into account engine weight and placement. Additional items such as active control fins which are an absolute requirement on long slender vessels to keep them from broaching in following seas are not required to achieve proper balance which represents a savings in cost and complexity of the vessel. It is also a significant safety imperative no competing vessel can claim such inherent stability. Inboard engines can be fit into the hybrid vee-hull outboard sponsons and can be adjacent to stern drives, long propeller shafts and the complexity they entail are not required, thereby consolidating machinery space while preserving interior and accommodation space. Also, interior space can be increased while maintaining improved performance.
In addition to the advantages of the hybrid vee-hull invention already mention and in summary, there is provided:
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the inventions are not be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included with the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
The contents of Provisional Application U.S. Ser. No. 61/997,046 filed May 21, 2014, on which the present application is based and benefits claimed under 35 U.S. C. §119(e), is incorporated by reference.
Number | Date | Country | |
---|---|---|---|
61997046 | May 2014 | US |