Abstract:
A wave reducing and eliminating ship hull including a generally triangular hull having a pointed narrow bow portion and a stern portion wider than the bow portion, the hull including generally rectilinear diverging sides extending substantially from the bow to the stern. The hull further includes a draft adjacent the bow deeper than the draft adjacent the stern, and the bow portion of the hull is generally free of depending structures.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to improvements on Transonic Hull (TH), and transonic hydrofield ( TH ), of application Ser. No. 08/814,418. More particularly, it pertains to certain relations between hydrostatic and hydrodynamic design parameters, to the relation between draft at the hull&#39;s stern, center of gravity position, speed regimes, effect of drag on hull&#39;s efficiency, and various other effects of draft at the hull&#39;s stern. The improvements have been established by means of TH/ TH  theory, and of tank and model testing, and have yielded important results for the utility of the TH invention. 
     2. Description of the Prior Art 
     Although certain vessels having triangular hull planform shape apparently similar in some respect to TH have been proposed in the past (for example, those cited by the Patent Office in the examination of application Ser. No. 08/814,418), these have been designed to have approximately equal drafts adjacent the stern and the bow, as in conventional ship design. The Japanese Patent 61-125981A of Mitsubishi Heavy Industries teaches, in all its embodiments, that the draft at stern and bow of this approximately triangular hull planform are approximately equal and the same as midbody draft. In this they followed earlier design criteria, even as far back as that of U.S. Pat. No. 23,626 of 1859, which also shows equal draft at bow, stern, and midbody. The deep stern drafts with broad beams at the stern are extremely inefficient. 
     In both the above-mentioned patents, the location of the center of buoyancy (CB) of their hulls, and therefore the location of their centers of gravity (CG) would be, by reason of their planforms and equal drafts, at or very close to their center of planform areas and waterplane, also known as longitudinal center of flotation (LCF), which is at 66% of water line length aft of the bow, unless a bow bulb is used. This proximity of CG, CB, and LCF is usual for conventional hulls. Moreover, such prior art does not consider the effects of CB and CG location on drag under forward motion. 
     In respect to proximity of CG, CB, and LCF, I have discovered that their proximity as in conventional hulls is not viable for TH, because it renders this type of hull with unstable tendencies in pitch under fast motion, when subjected even to a minor pitch disturbance. Such adverse behavior is similar to a phugoid self-sustained oscillation of aircraft when its center of gravity is close to its neutral point. In a ship, such oscillations not only increase drag, but are undesirable for structures, for cargo and for passengers, and may be dangerous. 
     Such fundamental problems are serious. The Mitsubishi patent teaches a solution to this problem by means of a bow bulb. Thus, it mixes a bulb technology which was developed and is useful for fat, slow ships, with a different type of hull. This adds drag, as well as volume, to their design, and the drag issue is not priority for prior art. 
     In contrast, TH and  TH  of application Ser. No. 08/814,418 make a totally different and innovative solution: it combines, in the submerged portion of TH, a deep draft forward and a shallow draft to the rear, which normal architectural ship design would consider dangerous with an inherent dive potential unless a bow bulb were used. However, following model tests, this writer confirmed that TH theory is correct in that dive tendencies are not determined on a triangular planform. The TH solution renders an inherent distance between LCF and center of buoyancy and therefore has a center of gravity substantially ahead of the LCF. Moreover, the quantitative aspects in the relation between CB, CG, LCF, and stern draft is dependent, I have discovered in relation to lack of dive tendency and established in respect to payload, with reference to the distinctions between the hydrostatic stern condition and the stern&#39;s hydrodynamic condition in the supercritical and subcritical regimes, as is done in the present CIP patent application in respect to limits of distances between LCF, CB, CB, and effect on static draft. Furthermore, these key relations are established in the present work in relation to the hydrodynamic drag consequence of entry and exit flow angles in its various speed regimes. 
     SUMMARY OF THE INVENTION 
     The invention pertains to transonic hull and transonic hydrofield. It relates to the static condition of the hull its dynamic conditions in the supercritical and subcritical regimes, by prescribing relations between the hydrodynamic entry angle of planform to exit angle in profile, and by relating the hydrostatic stern draft to center of gravity and longitudinal center of flotation in respect to hydrodynamic drag and pitch behavior in the supercritical and subcritical regimes, which are governed in important part by wake conditions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 ,  2  and  3  are views of the cover planform and profile view of TH, and planview of TH of the present invention; 
         FIGS. 4 ,  4 A and  5  cover specific quantifiable design parameters in accordance to present invention for the planview and profile view of TH, including relation of planform entry angle of flow and exit angle in profile of flow, and identify draft definitions; and 
         FIGS. 6A and 6B  specify the relation between stern draft, hydrodynamic drag, and center of gravity positions. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     1. Introduction and Conceptual Inquiry. 
     The important TH improvements of the present invention are related to TH and  TH  of my patent application Ser. No. 08/814,418 and can be best understood by a brief review of that application and the conceptual inquiry this review raises. Accordingly,  FIG. 1 , taken from that patent application, is a side view of TH having a hull  1  with a submerged hull portion  3  of length L, the undersurface of which is at a negative angle of approximately 3.5° relative to water level  5 , with the deep draft forward. An alternative deeper submerged portion  7  makes a larger angle  1  of approximately 7°. Larger angles can also be used, for example 11°. However, the submerged portions are shown to have a shallow and virtually zero draft in side view at stern  9 , in all cases exhibiting a substantially triangular profile shape of the submerged portion of the TH. 
     Accordingly, the planview of TH of  FIG. 1  as is shown in  FIG. 2 , has a waterplane is substantially triangular, and the centroid of its area, also called (for reasons unclear to this writer) longitudinal center of flotation LCF, is inherently at one third the length of the waterplane forward of the stern. The semi-angle of entry at bow is of small magnitude 7.1°, as shown in the drawing, even though the length-to-beam ratio is large, i.e. 4:1. The entry angle could be larger up to about 11°. 
     The center of gravity positions shown in  FIG. 2  are ΔXCG for angle β, and a larger distance ΔX 1 CG for larger angle β 2 , both distances forward of LCG, but undefined in magnitude. 
     The teachings above corresponding broadly to patent application Ser. No. 08/814,418, but does not cover important subjects related to hull efficiency. For example:
         a. What is best stern draft in static case to obtain best efficiency with forward motion?   b. What are best CG positions ahead of LCF to obtain optimum efficiency as related to stern draft?   c. Until the present analysis, what is the important optimized relation between the angle of entry of the planview, which minimizes formation of bow wave, and undersurface exit angles β and β 1 , which counter the formation of a stern wave?       

     Consider  FIG. 3 , which shows the two hydrodynamic regimes of TH in motion, the supercritical  TH  regime, with rays  17  and flat wake  21 , corresponding to a speed/length greater than approximately 1.25, and the subcritical  TH  regime with wake transition borders shown as dash line  19 , corresponding to a speed-to-length less than approximately 1.25. The speed-to-length ratio is in knots divided by square root of length in feet, and the values mentioned are somewhat dependent on ratio of weight-to-length, in which weight is in tons and length is actually the third power of length in feet divided by 100. These different speed regimes have important relation to static draft at stern, and in turn to weight-to-drag ratio, i.e., hydrodynamic efficiency; that is, it depends on CG position and stern draft. 
     2. TH/ TH  Design Parameters of the Present Invention. 
     Theoretical considerations, backed up by test data of models, establish in the present invention my discovery that there are important quantifiable relations between LCF, CB, CG, stern draft, planform angle of entry and exit profile angle, stern draft and performance of TH, as is specified below in reference to  FIGS. 4-6 .
         a)  FIG. 4  shows depth of transom  21  in static conditions, which in turn depends on CG&#39;s location relative to LCF shown in  FIG. 5 , and alters angle of undersurface to, say, β 11  value shown in  FIG. 4 , which is different from hydrodynamic β 1  or β in earlier figures.   b) The relation LCG-LCB=ΔXCG shown in  FIG. 5  governs to an important extend the speed-to-length ratio at which transition from subcritical to supercritical occurs, as dependent on length  23  in  FIG. 3 , and on beam  25  in  FIG. 5 , thus establishing lower speed regime range and upper speed range of efficient operation of TH.   c) Moreover, there is a critical minimal distance ΔXCG between CG and LCF, shown in  FIG. 5 , which governs ΔZ in  FIG. 4  and is thus related to the performance parameter weight/drag. Moreover, there is another minimum value of ΔXCG called herein ΔXCG critical, which is equivalent to determining a neutral point for pitch stability, in analogy to the neutral point which governs pitch stability of aircraft. If for TH&#39;s archetype ΔXCG in  FIG. 5  is made too small, pitch oscillations similar to phugoids in aircraft will be excited by minimal external pitch disturbances.   d) Another relation of importance in respect to stern wake, ΔZ, and drag is the shape relation of in planform and profile of TH, as these also govern, ΔZ, ΔXCG, LCF, etc., and the hull shapes are governed by two important angles: the planform entry angle α* and the exit profile angle β*.       

     Thus, in my discoveries, according to  TH  theory and  TH  experiment, I have established and confirmed through TH model tests the critical relation of ΔZ in static conditions such as is shown by draft  21  on static TH  24  in  FIG. 4  with undersurface angle β, to location of center of CG forward of centroid of area at a distance ΔXCG, as shown in  FIG. 5 . The distances in respect to the stern are shown in  FIG. 4  as LCF of L/3 and LCG as somewhat larger, all these distances measured from stern forward, which respond to the inherent formulation of TH, rather than from forward post to the rear, as is usual for conventional ships. 
     The effect of static ΔZ on hydrodynamic drag under forward motion is shown in  FIG. 6A , with relative drag changes in the vertical axis, and the static stern draft ΔZ in the horizontal axis, expressed as fractions of stern&#39;s beam  25  in  FIG. 5 , that is, as ΔZ/B. 
     The corresponding relation between the position of center of gravity and stern&#39;s draft is shown in  FIG. 6B , in which the adverse case of old art, namely, equal drafts at bow and stern is numerically equal to ΔZ/B=0.081. 
     It is seen in  FIG. 6  that if static draft is equal to 0.08 of beam to which corresponds a CG at the centroid of waterplane area for equal stern and bow draft, the hydrodynamic drag is very large, and the concepts of subcritical and supercritical hydrodynamic regimes of TH would not apply or make sense. 
     In accordance to the test data of this invention, in the supercritical regime at v/√{square root over ( )}L≈1.45, the static draft should be reduced by a factor of 4 from 0.08 to approximately 0.02. Then the hydrodynamic payoff is a drag is reduction by 34%, which is extremely important for range and speed, apart from the large gains of stability in pitch. Further reductions of stern draft at v/√{square root over ( )}L≈1.45 show an increases of drag. 
     And in accordance to tests of the TH invention, in the subcritical regime at v/√{square root over ( )}L≈1.05, the static draft should be reduced from 0.08 to 0.01, a factor of 8 compared to old art. The hydrodynamic drag payoff is then a reduction of drag by approximately 51%, again extremely important for range and speed, apart from the stability gains, also very important. 
     As the parameters described in  FIGS. 4 to 6B  are dependent on planform and submerged profile angles which govern volume distribution, it is very important to maintain the proper relation between planform entry angle shown in  FIG. 5  to the dynamic exit angle alpha* that applies corresponds to the exit angle shown in  FIG. 4   a , between the rearmost portion  31  of TH&#39;s undersurface, adjacent the stern, and a line which, parallel to the water level, intersects the lower corner of the transom in the design speed envelope of TH. The α*β* relationship that provides the most efficient hydrodynamic results covers β* values from approximately one half α* to higher value which approximate α*. However, β* can be increased for hulls of large displacement in which a forward portion of the undersurface is parallel to the static waterline due to draft limits in harbors, for example, as shown in FIG. 13C of application Ser. No. 08/814,418. In such a case, β* can exceed α*. 
     The range of stern draft of ΔZ/B 0.01 to 0.02 for best hydrodynamic performance of  FIG. 6B  correspond to longitudinal position of the center of gravity which varies from about 0.44 L for smaller stern draft to about 0.41 L for the larger stern draft, but in both cases with a significant negative angle in TH&#39;s undersurface, as shown in  FIGS. 4 and 4A . This range has the added and important benefit of having increased pitch stability. 
     It is possible to extend the range of LCG forward from that of  FIG. 6B , for example to 0.48 L, by accepting an angle larger than angle β in  FIG. 4 , if draft forward is not excessive, for example, in relation to water depth. 
     It is also possible to use a shorter LCG from stern, for example, to 0.385, but such choices start running into pitch stability problems, and those depend on mass distribution on a full size boat which need not be that used for model tests, and therefore the pitch stability area should be investigated and tested full size by a licensed boat builder as his responsibility. 
     The numerical values of the design criteria mentioned above are representative for the hull characteristics reviewed, and may be adjusted for specific TH hull shapes, thrust line positions, and other design features. 
     The present invention pertains to hydrodynamic conditions that require propulsion systems to achieve the specified speed-to-length ratio with which the draft variations and related parameters are attained. One important ratio is 1:25. Accordingly,  FIG. 4  shows an engine  31  driving by means of inclined shaft  33  a propeller  35  with a thrust line approximately parallel to the remote waterplane. In the higher speed regimes, for example, approximately at or above ratio of 1:45 shown in  FIG. 6A , water jets can be used. This alternative is shown in  FIG. 4A  having a bottom water intake  39  for water jet  37  which exits at  41 , in this case ahead of transom to decrease for military purposes white water in wake, which would occur if the exit of the water jet is at or above water level  31 . 
     The specifications and drawings pertain to hydrodynamics, TH shapes and propulsion and does not cover structures or controls. Model tests are not sufficient for determining stability of full size manned TH of unknown weight or other safety related matter. These matters should be investigated and determined solely by licensed manufacturers, who have the sole responsibility in such matters and are obviously outside the scope of the present patent application and its claims, presented below. 
     Finally, it is to be understood that changes can be made on the drawings and specifications without departing from the teachings as covered in the claims of the invention.