US20120042820A1

US20120042820A1 - Stepped boat hull

Info

Publication number: US20120042820A1
Application number: US13/032,433
Authority: US
Inventors: Kristian Brekke
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-22
Filing date: 2011-02-22
Publication date: 2012-02-23

Abstract

According to a preferred aspect of the instant invention, there is provided a boat hull that is an improvement over the state-of-the-art stepped hull. More particularly, in contrast to prior art designs, the instant steps are specifically constructed to have an opening/air passage situated on the side of each step. The air passage will be preferably placed on the side of the step closest to the surface of the water or farthest away from the keel of the boar. This feature tends to introduce more air under the boat, thereby reducing water drag on the hull and improving its overall performance.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/306,765 filed on Feb. 22, 2010, and incorporates said provisional application by reference into this document as if fully set out at this point.

FIELD OF THE INVENTION

The present invention relates generally to the field of recreational boating and, more particularly, to hull designs that are intended to reduce the drag of a boat in the water when the boat is in motion.

BACKGROUND OF THE INVENTION

It is well known that the shape of the hull of the boat can have a huge impact on the boat's stability and performance. One familiar modification to the generally streamlined shape of boat hulls is the stepped hull design. In short, a stepped hull is one that contains an abrupt step-like discontinuity in its surface. Typically, leading edge of the bottom surface of the “step” is conventionally flat or streamlined to match the remainder of the hull. The step then terminates on its aft face with a vertical wall that steps upward toward the bottom of the boat. The step would resemble a stair step down if the boat were turned upside down. Providing a boat hull with steps is generally believed to increase the efficiency of boat's movement through the water by pulling air underneath the boat, thereby reducing drag of the water against the hull when the boat is in motion.
Conventional hull steps are understood to operate by pulling air in behind the step from both sides of the hull. The force with which air is pulled underneath the boat is dependent on the speed of the boat and the size of the cavity behind the step leading to free air. Some steps are pointed forwards to get help from the dynamic pressure.
There are two conventional approaches to forming a stepped hull: solid steps and so-called ventilated steps. Solid-type steps are completely solid abrupt changes in the curvature of the hull surface, whereas ventilated steps are hollow and are open to the rear of the boat, but are closed on the sides.
Because conventional solid steps have a limited flow area with which to draw air under the boat, they may require a significant velocity to be efficient. Thus, this sort of step is mostly used for high speed racing boats to increase speed by reducing drag forces.
The lack of efficiency in pulling air under the boat has prompted the development of technology that utilizes forced air to increase the amount of air behind the steps. Typically, the air supply is increased through the use of an air pump that releases air proximate to the rearward face of the steps. However, force-air methods are expensive to implement and require a source of energy for the pump (e.g., electricity). Thus, solid steps—whether augmented with a force air supply or not—have not proven to be practical for common (e.g., low velocity) use. However, if the supply of air behind the step could be made more efficient in a natural and inexpensive way, the steps could be more widely used to save propulsion energy and reduce transportation time.
Heretofore, as is well known in the boating arts, there has been a need for a hull design that improves the efficiency of the traditional stepped hull. Accordingly, it should now be recognized, as was recognized by the present inventor, that there exists, and has existed for some time, a very real need for a stepped hull design that would address and solve the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of the invention within the ambit of the appended claims.

SUMMARY OF THE INVENTION

According to a preferred aspect of the instant invention, there is provided a stepped boat hull that is an improvement over the state-of-the-art stepped hull. More particularly, in contrast to prior art designs, the instant steps are specifically constructed to have an internal void that is in hydraulic communication with an opening/air passage on the side of a step that is closest to the surface of the water. The step will additionally utilize a rearward facing opening that is similarly in fluid communication with the internal void. This feature tends to introduce more air under the boat, thereby reducing water drag and improving its overall performance.
Another embodiment utilizes a stepped double hull configuration that conducts air that is captured by an air intake proximate to the prow of the ship. In the preferred arrangement, the air will pass between the double hulls (in some cases via one or more air conduits that are provided for that purpose) to the steps where the air is expelled.
The foregoing has outlined in broad terms the more important features of the invention disclosed herein, so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventors to the art may be better appreciated. The instant invention is not limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Additionally, the disclosure that follows is intended to apply to all alternatives, modifications and equivalents as may be included within the spirit and the scope of the invention as defined by the appended claims. Further, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 contains a schematic representation of a longitudinal cross section of a boat that includes one or more steps of the instant invention on hull.

FIG. 2 depicts a magnified view of the rear portion of the boat cross section of FIG. 1.

FIG. 3 depicts a cross sectional view of the embodiment of FIG. 2.

FIG. 4 an illustration of a preferred embodiment that makes clearer the nature and configuration of the side openings of a preferred embodiment of the instant invention.

FIG. 5 contains another preferred embodiment which is double hulled, with at least a portion of the space that separates the two hulls being used to transport air from the front of the boat to the portion of its hull that is under water.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein the reference numerals indicate the same parts throughout the several views, there is provided herein a system for improving the performance of a boat via a modification to its hull shape. In the preferred embodiment, and as is discussed below, the instant invention will utilize a plurality of hollow steps that are positioned on or incorporated into the hull, with the steps having at least one opening on the side nearest the surface of the water and being opened toward the rear of the boat.
Turning first to FIGS. 1 and 4, in a preferred embodiment the underside of the boat 105 will have a plurality of notches or steps 100 which might be made integral to the boat 105 hull during its manufacture or added onto it after the fact. As can be seen in this figure, each step 100 will be substantially hollow and have a side aperture 120 which is preferably located on the side of the step 100 remote from the centerline of the boat. Said another way, the side aperture 120 will, in most cases, be the side of the step 100 that is nearest to the surface of the water 110. Note that this feature is critical to the operation of the instant invention.
Additionally, each step 100 will preferably be oriented transversely to the centerline of the boat, wherein “transverse” should be broadly understood to mean that the rearward face of the step 100 generally extends away from the centerline of the boat, as opposed to the more restrictive “orthogonal” meaning for transverse that is occasionally seen in other contexts.
In some embodiments, the steps 100 will be angled to create a chevron-type pattern on the underside of the boat. Further, each step 100 will have a downward facing (i.e., when the boat is in an upright position) lower face 150 that is preferably impermeable to the flow of water and, in the preferred embodiment, substantially flat or shaped to create a streamlined lower surface. Of course, it is not inconceivable that the lower face 150 might have one or holes therethrough, but preferably that surface would be solid.
Additionally, the step 100 will be at least partially defined by a lower surface of the hull of the ship 105 or by a separate upper face (e.g., wall 310 in FIG. 3), depending on whether the step 100 is added onto an existing hull or made to be integral to a hull during the boat's construction. Those of ordinary skill in the art will recognize how a step 100 such as that taught herein could be added to an existing hull or formed along with it.
FIG. 2 contains a magnified view of the embodiment of FIG. 1. As is made clearer in this figure, the rearward facing portion of each step 100 will preferably be open to the water via aperture 120. Although it is preferable that a single aperture 120 that occupies the entire side of the step 100 be utilized, in some preferred embodiments less than the entire side of the step 100 might be used and/or multiple openings might be placed in the side of the step 100. For example, a plurality of smaller openings of different shapes (e.g., round, square, rectangular, triangular, etc.) might be used instead. However, generally speaking it is believed to be preferable that the side of the step 100 be as open as possible to facilitate the flow of air into and through the step 100.
Turning next to FIG. 3, this figure contains a cross sectional view of the embodiment of FIG. 2 which illustrates that the rear (aft-facing face) of each step 100 will preferably be largely open to the water. That being said, in some preferred embodiments instead of the single large aperture 130 a plurality of smaller apertures might be utilized. In some instances, one or more internal reinforcing partitions 135 might be utilized for purposes of, for example, strengthening the step. In any case, it is preferred that the opening(s) provided on the rearward face of the step 100 be as large as possible to encourage the flow of water therethrough. Further, in the preferred embodiment the internal partitions 135 (if any) will also have openings therein to allow free flow of water and air bubbles from the outermost/air gathering aperture to the innermost step which is located nearer the centerline of the boat. In the preferred embodiment, each of the steps will be in fluid communication with the other through the one or more openings in each internal partition 135, thereby making it possible for air bubbles to move transversely between adjacent steps.
In practice, as the boat 105 moves forward through the water 110, air will tend to enter the into the aperture 120 defined by the step 100 that is situated furthest from the centerline of the boat when the boat is in motion. This will tend to create a cushion of air bubbles that are pushed by the force of the water through the rearward opening 130 of each step. The air bubbles will tend to reduce the friction between the boat lower surface and the water, thereby reducing drag and decreasing the amount of power that is required to move the boat. The mechanism by which air bubbles reduce friction is well known to those of ordinary skill in the art.
Preferably the steps will be positioned near the prow of the boat but exact placement of the steps 100 that provide optimal advantage may need to be determined on a trial and error basis. As has been suggested previously, in a preferred embodiment, each step 100 will be open at the side and at the rear (see, e.g., FIG. 4), thereby creating an aperture 120 within. It is especially important for purposes of the instant invention that the sides of the steps 100 nearest the waterline be open to the water. Further, any steps not adjacent to the waterline will preferably have one or more openings in their sidewalls to allow movement of water and air between adjacent steps. This concept is discussed more fully below.
It should be further noted that in some preferred embodiments the steps 100 will be configured to allow air and water to move from steps on one side of the boat to steps on the other. By way of explanation, consider the walls 325 between two adjacent steps in FIG. 3. In some preferred configurations, the adjoining walls 325 (which, of course, might actually be formed from a single piece of wood or other material) would have one or more openings therein to make it possible to have air move across the centerline of the boat in some circumstances. For example, this might be especially desirable when the instant invention is utilized with sail boats that have keels, where it might be desirable to pull in air from the up side of the boat when it is leaning.
Turning next to a technical discussion of the features of the instant invention, it should be remembered that the ventilated steps 100 of the instant invention are hollow rather than solid and contain an opening on their rearward (stern facing) surface. In some embodiments, the steps will also have an internal opening in their leading edge as well that places them in fluid communication with the step or steps that are closer to the bow of the boat. By way of explanation, consider the walls 125 between two adjacent steps 100 in FIG. 2. Those of ordinary skill in the art will readily understand how a passage way might be created between these two steps 100.
A key objective of the instant invention is to increase the area through which air can flow into the step and under the hull. In addition to flowing in from the side of the boat behind the steps, in another preferred arrangement air will be able to also flow in through the step itself and out through the open rear part of the step. The suction that the water creates when flowing across the steps provides the energy needed to pull the air in underneath the boat.
According to some preferred embodiments, existing boats can be retrofitted with steps of the sort taught herein. Instead of distinct hollow steps, the hull could also be made as a double hull with the two hulls being separated a uniform distance apart all along the boat. Thus, in this variation the invention would appear to be a traditional boat hull with an extra layer of hull material arranged at a certain fairly constant distance away from the inner hull. There will preferably be an opening between the two hulls all along length of the boat (e.g., the side portion of each step) that lets air in from the sides of the boat into the space between the hulls. The bottom hull closest to the water (or closest to the bottom of the body of water when the boat is in an upright orientation) will preferably have holes in it behind each step, the holes being designed to provide additional suction force to pull air out of that step and through the hull toward the aperture on the rearward portion of the step. In some preferred embodiments, these holes could also be arranged in a corrugated fashion that is integral to the steps. These stepped openings/slots could either be small or large and could be arranged in any number of ways along the hull. The two arrangements can also be combined.
According to still another preferred embodiment, there is provided a double hull boat configuration that utilizes air that is drawn from the front of the boat and conveyed to the portion of the hull that is under the water, thereby introducing air bubbles to the underside of the boat and reducing drag on the hull. FIG. 5 contains an illustration of a preferred double hull boat configuration 800 in cross section. As is indicated in this figure, this embodiment may not utilize distinct steps but instead might utilize a matrix of air discharge orifices 810 situated on the outer hull 815. One or more air intakes 820 will preferably be provided on the front of the boat proximate to the prow, although it is certainly possible that the air intake could be located, say, amidships, with air ducts conveying the air from its intake point to the underside of the boat where the air can be released within the steps 100 to replace or augment the air that originates from air intake 820. Further, and in some preferred embodiments, the air intake 820 will wrap around both sides of the boat 800 and might extend its entire length or some part thereof. Additionally, in some embodiments there will be multiple small air intakes 820 that are situated at various locations near the prow of the boat 800 and/or along its sides. All that is important is that one or more of the air intakes 820 be above the waterline when the boat 800 is in motion.
Note that in some preferred arrangements, the double hull configuration 800 might have a hull with many small steps (or even corrugations) rather than the larger steps that were preferred in the previous embodiments. The inner 805 and outer 815 hulls will preferably be separated by a near constant amount throughout, although the amount of separation that is best for a particular vessel may need to be determined on a trial and error basis and may or may not utilize a constant separation distance. In FIG. 5, one or more spacers 830 have been illustrated as an example of how the hulls might be kept apart. Preferably, the separators 800 will be designed so as to not impede the flow of air between the hulls either laterally or horizontally so that air can move the length of the boat 800 and from side to side if the boat is tilted while it is maneuvered. As is illustrated, the spacers 830 might be chosen to allow air to flow through them. Those of ordinary skill in the art will be able to readily devise alternative means for keeping the two hulls separated such that air is free to flow in between.
In some preferred embodiments, the passively gathered air from air intake 820 will be passed between the hulls to one or more of the steps 100 that are made to be in hydraulic communication therewith. This additional air (i.e., in addition to what is picked up through the open sides of the steps 100 at the water line) will then be released through the steps as is indicated generally in FIG. 6. This might further be augmented by, for example, routing all or a portion of the engine exhaust via exhaust conduits to the steps 100. Additionally, and preferably in some circumstances, the outer hull 815 might be corrugated and/or slotted with a multiplicity of openings therein to assist in the passage of air therethrough. Finally, in some preferred embodiment one or more air conduits will be used to conduct air from the air intake 820 to the steps 100 where it will be released into the water.

Technical Discussion: CFD Modeling

Preliminary computational fluid dynamics (“CFD”) modeling results have been obtained calculated for the instant invention. A comparison was made between the performance of the hollow ventilated step technology of the instant invention with that of solid steps which represent known technology.
The boat hull that was used in the simulations was modeled after a Norwegian 18 ft. mahogany runabout that has been modified to include the new hollow ventilated step technology. A propulsion force of 5000 N was applied and the boat was assumed to have a weight of 1000 kg with a center of gravity located 2 m from the bottom rear point of the boat. In this simulation, the first two steps and the last step are taken to be traditional solid steps that have been used in some race boat designs. However, in this example steps #3 and 4 (counting from the front of the boat) are of the new and more efficient hollow inventive design.
It should be noted that it is the part of the hull located behind a step that benefits most from the air pulled in under the hull by the step. Thus, for the simulation boat, only the hull behind step 3 will have full benefit from the new and hollow steps, while the hull behind step one would benefit from air pulled in behind the old solid steps.
Based on the results of this simulation, air is most efficiently pulled in through and behind the new hollow steps (behind step 3) while almost no air is pulled in behind the solid steps at the velocities investigated in this study, i.e., at velocities less than about 13 m/s or approximately less than 26 knots. In fact it can be shown that traditional steps do not work well at these speeds while the hollow steps of the instant invention supply the entire downstream hull with air at velocities above 10 m/s or 20 knots. This comports with the conventional wisdom that solid steps are most useful at high speeds. Thus, it can be seen that the instant invention would be especially useful for relatively slow moving boats such as, for example, sailboats.
Thus, the present invention is well adapted to carry out the objects and attain the end and advantages mentioned above as well as those inherent therein. While the inventive device has been described and illustrated herein by reference to certain preferred embodiments in relation to the drawings attached thereto, various changes and further modifications, apart from those shown above or suggested therein, may be made therein by those of ordinary skill in the art, without departing from the spirit of the inventive concept the scope of which is to be determined by the following claims

Claims

What is claimed is:

1. An apparatus for reducing the drag between a hull of a vessel and the water through which the vessel is moving, said vessel having a bow end and a stern, said apparatus comprising:

(a) at least one step positionable to be affixed to the hull of the vessel in an orientation that is transverse to a centerline of the boat, wherein

(i) each of said at least one step extends at least partly across a width of said hull transverse to a center line of said hull,

(ii) each of said at least one step is substantially below the water line when the vessel is not in motion, and,

(iii) each of said at least one step step has

(1) an internal void in fluid communication with the water through which the vessel moves,

(2) at least one side aperture on a side of said step furthest from a centerline of the vessel, and at least one side aperture within a stern-facing face of said step, said side aperture and said stern-facing aperture being in fluid communication with each other at least through said internal void, and

(iv) at least one of said at least one side aperture is above the water at least intermittently when the vessel is in motion.

2. A stepped boat hull having at least one step forming at least a portion of a lower surface of said hull, said hull having at least a bow and a stern, each of said at least one step being oriented transverse to a longitudinal centerline of said hull and extending at least partially across a width of said hull, each of said at least one step being substantially below the waterline when said hull is at rest in the water and being above the waterline at least intermittently when the hull is moving through the water, at least one of said at least one step comprising;

(a) a substantially solid lower surface, said lower surface forming at least a portion of a lower surface of said hull;

(b) a substantially solid upper surface internal to said step;

(c) a side remote from said hull center line, said side containing at least one aperture therein, said at least one aperture being situated to acquire air when the boat is in motion; and,

(d) a substantially vertical rearward facing wall, said wall having at least one aperture therein, said lower surface, said upper surface, said side and said rearward facing wall cooperating together to define an internal void in said step, said at least one aperture in said side and said at least one aperture in said rearward facing wall being in fluid communication with each other through said internal void.

3. The stepped boat hull according to claim 2, wherein said substantially solid upper surface internal to said step is a lower surface of said hull.

4. A stepped boat hull boat, comprising:

(a) an inner hull, said inner hull being substantially impervious to the flow of water therethrough;

(b) an outer hull containing at least one air intake situated above a waterline when the boat is in motion in the water, said outer hull being spaced apart from said inner hull and containing at least one step formed therein, said inner hull and said outer hull cooperating together to create a void therebetween, at least one of said at least one step being in hydraulic communication with said at least one air intake, at least one of said at least one step comprising:

(b1) a substantially solid lower surface, said lower surface forming at least a portion of a lower surface of said hull;

(b2) a side remote from said hull center line, said first side containing at least one aperture therein, said at least one aperture being situated to acquire air when the boat is in motion; and,

(b3) a substantially vertical rearward facing wall, said wall having at least one aperture therein, said lower surface, said side and said rearward facing wall cooperating together to define an internal void in said step, said at least one aperture in said side and said at least one aperture in said rearward facing wall being in fluid communication with each other through said internal void and said internal void being in hydraulic communication with said at least one air intake.

5. The stepped boat hull boat according to claim 4, wherein said outer hull and said inner hull are maintained in a spaced apart configuration by a plurality of spacers.

6. The stepped boat hull boat according to claim 4, wherein there are a plurality of air intakes, at least of one air intakes being proximate to a prow of the boat, and at least one of said air intakes being positioned apart from said at least one air intakes proximate to the prow of the boat.