Abstract:
A marine vessel which uniquely combines tumblehome-like and trimaran-like attributes in an integrative form describing two underside channels comprises a medial major hull and a pair of lateral minor hulls. The port and starboard minor hulls, each generally describing an inverted triangular cross-section, have respective outside surfaces which slope in tumblehome fashion (downwardly outwardly). The major hull has port and starboard outside surfaces which can slope in any fashion, whether tumblehome or nontumblehome. The outside surfaces of the minor hulls are parallel to the vessel&#39;s centerline, whereas the outside surfaces of the major hull aftwardly slant toward the centerline. The minor hulls&#39; respective outside surfaces and the major hull&#39;s outside surfaces generally converge at longitudinally equivalent port and starboard locations, at which locations the major hull&#39;s outside surfaces commence to forwardly slant toward the centerline so as to generally converge at the vessel&#39;s bow tip.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to marine and naval engineering and architecture as pertains to shapes and configurations of ships, boats and other water vessels, more particularly to hull forms of such vessels. 
     The term “tumblehome” (alternatively spelled “tumble home” or “tumble-home”) refers to a property of a water vessel&#39;s hull wherein its topside, or some portion thereof, is inclined inward. Generally according to conventional tumblehome-type monohull designs, the two sides of the vessel are sloped, above the maximum beam (widest width or breadth), toward the middle or center of the vessel. These known monohull tumblehome hull designs typically are beset with certain undesirable characteristics. They have a poor righting arm, since the tumblehome feature decreases the water plane area as the ship heels (tilts to one side; lists). They have poor damage stability, because the above-water volume is limited by the tumblehome feature. They have restricted useable superstructure volume and width at the deck level. They are characterized by unusual sea-keeping responsiveness along with ongoing concern regarding the dynamic stability in a seafaring way; this is probably attributable to the broad transom (which has large above-water volume associated therewith) in combination with the wave-piercing bow (which has limited above-water volume associated therewith). 
     To some extent, trimarans are intended to reduce or eliminate the stability problems associated with conventional monohull tumblehome designs. A trimaran configuration includes three separate hulls, usually a main hull and two much smaller, pontoon-like or float-like hulls (sometimes called “outriggers”) on each side. A main drawback of a typical trimaran design relates to the fact that the large separation distance between the main hull and the outer hull amplifies the bending moment. Hence, each cross-structure connecting the main hull to an outer hull (outrigger) must be strong enough to handle the large bending moments caused by hydrodynamic loads. Consequently, the cross-structures represent significant increases in structural weight. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide a tumblehome-type hullform which is more stable than conventional tumblehome-type hull forms. 
     It is a further object of the present invention to provide a tumblehome-type hullform which is characterized by greater internal volume than is typical conventional tumblehome-type hull forms. 
     It is another object of the present invention to provide a tumblehome-type hullform which has better sea-keeping characteristics than is typical of tumblehome-type hull forms. 
     It is a further object of the present invention to provide a tumblehome-type hullform which is more stable than conventional tumblehome-type hullforms, but which is lighter than conventional trimaran hullforms. 
     Typically according to the present invention, a water vehicle such as a water transportation vehicle has a length, an imaginary lengthwise axis, a port side and a starboard side. The vehicle is about equivalently configured on each of its sides. The vehicle comprises a tumblehome outer surface, an inner surface and a junctional surface. The inner surface generally is located more proximate the lengthwise axis than the tumblehome outer surface. The junctional surface joins each of the tumblehome outer surface and the inner surface so as to generally be interposed between the tumblehome outer surface and the inner surface. 
     In accordance with many embodiments of the present invention, a hull comprises a back- section and a front section. The hull is characterized by a length and by an imaginary horizontal plane passing therethrough. The back section includes a pair of lateral fins and a medial portion between the lateral fins. The medial portion includes a pair of medial faces. Each fin includes a lateral tumblehome face and a crosswise face. Each crosswise face at least substantially is sloped at a smaller angle with respect to the imaginary horizontal plane than are the medial faces and the lateral tumblehome faces. Each crosswise face and a lateral tumblehome face form an at least substantially horizontal fin edge. Each crosswise face and a medial face form an at least substantially horizontal junctional corner. Each crosswise face at least substantially is sloped at an angle with respect to the imaginary horizontal plane which, to at least a substantial degree, gradually increases in accordance with the forward lengthwise direction of the hull. 
     In accordance with the present invention, the medial faces can be sloped in a tumblehome or conventional (nontumblehome) fashion. According to some of the embodiments wherein the medial faces are sloped in tumblehome fashion, the medial tumblehome faces and the lateral tumblehome faces at least substantially are sloped at at least substantially the same at least substantially constant angle with respect to the imaginary horizontal plane. 
     A typical hull configuration according to this invention has an imaginary centerline and comprises a stern surface, an outer starboard tumblehome surface, an inner starboard surface, an outer port tumblehome surface, an inner port surface, a starboard obliquely downfacing surface and a port obliquely downfacing surface. The outer starboard tumblehome surface, the inner starboard surface, the outer port tumblehome surface, the inner port surface, the starboard obliquely downfacing surface and the port obliquely downfacing surface each extend from the stern surface in a generally forward direction. The starboard obliquely downfacing surface connects the outer starboard tumblehome surface and the inner starboard surface. The port obliquely downfacing surface connects the outer port tumblehome surface and the inner port surface. The outer starboard tumblehome surface and the outer port tumblehome surface are each approximately parallel to the centerline. Proceeding from the stern surface in a generally forward direction, the inner starboard surface tumblehome and the inner port surface diverge from the centerline in approximately equivalent fashion. 
     The inner starboard surface and the inner port surface are each disposed: (i) vertically (i.e., in nontumblehome fashion); or, (ii) nonvertically, equivalently and oppositely angled upwardly away from the centerline (i.e., in nontumblehome fashion); or, (iii) nonvertically, equivalentsly and oppositely angled upwardly toward the centerline (i.e., in tumblehome fashion). According to some embodiments wherein the inner surfaces are tumblehome surfaces, the outer starboard tumblehome surface, the inner starboard tumblehome surface, the outer port tumblehome surface and the inner port tumblehome surface each define approximately the same tumblehome angle. Generally, according to inventive embodiments wherein the inner surfaces, as welt as the outer surfaces, are tumblehome surfaces, the outer starboard tumblehome surface, the starboard obliquely downfacing surface and the inner starboard tumblehome surface define, from an aft perspective, an approximate N-shaped starboard profile wherein the outer starboard tumblehome surface reaches a greater elevation than does the inner starboard tumblehome surface; the outer port tumblehome surface, the port obliquely downfacing surface and the inner port tumblehome surface define, from an aft perspective, an approximate reverse N-shaped port profile wherein the outer port tumblehome surface reaches a greater elevation than does the inner port tumblehome surface. Proceeding from the stern surface in a generally forward direction, the N-shaped starboard profile and the reverse N-shaped port profile each narrow in breadth in approximately equivalent fashion. 
     The present invention uniquely features a dual (both-sided) tumblehome, trimaran-like, integral hullform design. According to typical inventive embodiments, the inventive hullform includes a medial hull and two outrigger-analogue hulls which are integrally associated with the medial hull. According to typical inventive practice, there are no cross-structures for connecting the outrigger-analogue hulls to the medial hull; all three hulls are closely integrated into what is essentially a monohull hullform. According to many inventive embodiments, the inventive hullform is characterized by two tumblehome surfaces (one port, one starboard); one tumblehome surface is described by each outrigger-analogue hull, and two nontumblehome surfaces are described by the medial hull. According to other inventive embodiments, the inventive hullform is characterized by four tumblehome surfaces (two port, two starboard); two tumblehome surfaces are described by the medial hull, and one tumblehome surface is described by each outrigger-analogue hull. 
     The inventive dual tumblehome monohull hullform affords greater sea-keeping, stability and capacity (space or volume) vis-a-vis the conventional tumblehome monohull vessel, while also affording lesser structural weight vis-a-vis the conventional trimaran vessel. In comparison with conventional hulls, the inventive hull features a relatively moderate transom width; effectively in certain respects, the inventive hull&#39;s transom width is the width of the transom at the rear of the inventive medial hull. Stability and seakeeping are furthered by the inventive vessel&#39;s combination of the two lateral outrigger-analogue hulls and the medial hull characterized by a moderate transom width. The double (two-sided) tumblehome arrangement, on both sides of the inventive vessel, serves not only to reduce signatures but also to architecturally render, together with an upper portion of the medial hull, a kind of curtain over two mirror-image tunnels extending forward from the transom. The inventive hullform lends itself to application to a variety of types and sizes of vessels (ships, boats, etc.) and to association with a variety of types and sites of propulsion means. Depending on the inventive embodiment, the vessel&#39;s topside can be “open” or “closed.” 
     As compared with a conventional tumblehome monohull vessel, the tumblehome monohull vessel according to the present invention has superior characteristics, especially in terms of stability, internal volume and sea-keeping. The tumblehome monohull vessel according to the present invention also has superior characteristics as compared with a conventional trimaran vessel, especially in terms of structural weight. In terms of stability and sea-keeping, when the inventively configured vessel heels it advantageously acts to attain additional water plane area and additional righting force. In terms of internal volume, the inventively configured vessel inherently advantageously provides additional space by virtue of its structurally augmentative quality. 
    
    
     Other objects, advantages and features of this invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein like numbers indicate the same or similar components, and wherein: 
     FIG. 1 is a diagrammatic top plan view, partially broken away to show concealed detail, of a representative embodiment of a hullform in accordance with the present invention, wherein the hullform is characterized by a substantially flat hull bottom. 
     FIG. 2 is a diagrammatic top rear perspective view, partially broken a away to show concealed detail, of the inventive hullform embodiment shown in FIG.  1 . 
     FIG. 3 is a diagrammatic side elevation view, partially in section, of the inventive hullform embodiment shown in FIG.  1 . 
     FIG. 4 is a diagrammatic top, side and front perspective view of an inventive hull form embodiment such as shown in FIG.  1 . 
     FIG. 5 is a diagrammatic bottom, side and rear perspective view of an inventive hullform embodiment such as shown in FIG.  1 . 
     FIG. 6 is a diagrammatic, partial (starboard half), rear elevation view of an inventive hullform embodiment which is similar to that shown in FIG. 1, wherein the hullform is characterized by a substantially flat hull bottom. 
     FIG. 7 is a diagrammatic view, similar to the view shown in FIG. 6, of another inventive hullform embodiment which is similar to that shown in FIG. 1, wherein the hullform is characterized by a substantially curved hull bottom. 
     FIG.  8  and FIG. 9 are diagrammatic rear elevation views of different inventive hullform embodiments wherein the hullform is characterized by tumblehome inner side surfaces. 
     FIG.  10  and FIG. 11 are diagrammatic rear elevation views of different inventive hullform embodiments wherein the hullform is characterized by non-tumblehome, vertical inner side surfaces. 
     FIG.  12  through FIG. 15 are diagrammatic rear elevation views of different inventive hullform embodiments wherein the hullform is characterized by non-tumblehome, nonvertical inner side surfaces. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures generally, marine vessel  10  includes a hull  12  which is inventively characterized by a double tumblehome configuration on each of its port (left-hand) and starboard (right-hand) sides. The views of FIG.  1  through FIG. 3 are at least partially “transparent” to better show the inventive configuration. Generally in these figures, unbroken (e.g., dotted or dashed) lines are for geometric illustrative purposes or to represent configurational aspects which would not be seen when viewing a real (“opaque”) hull  12  from the perspective shown; solid (unbroken) lines represent visible details when viewing such hull  12  from the perspective shown. 
     As shown in FIG. 1, from an upper planwise perspective, hull  12  approximately describes a pentagonal outline. Hull  12  can be considered to be approximately divided into two sections—viz., a front (bow-inclusive) section  14  and a back (stern-inclusive) section  16 —by an imaginary vertical plane which passes through the linear demarcation therebetween as indicated by dashed line s in FIG.  1  and FIG.  3 . Peripherally speaking, front section  14  approximately describes a triangle; back section  16  approximately describes a rectangle. The inventive double tumblehome configurations are relegated to back section  16 , extending from stern  15  to the “break” points  20  and  22  on port and starboard sides, respectively, of hull  12 —that is, from a top plan perspective, the location at which the hull  12  side begins to narrow. 
     As especially shown in FIG.  1  and FIG. 4, front section  14  has a front port tumblehome surface  24  and a front starboard tumblehome surface  26  which (typically according to the present invention) are at least substantially planar and which converge in bow  17  at the hull&#39;s front tip  28 . The front tumblehome surfaces  24  and  26  are disposed at equal but opposite angles with respect to an imaginary vertical plane which axially longitudinally bisects hull  12 , such planar bisector passing through the linear demarcation indicated by dashed line (centerline) c in FIG.  1  and FIG.  3 . Front tumblehome surfaces  24  and  26  are shown to gradually increase in vertical breadth (height-width) toward tip  28 . According to other inventive embodiments, such as shown by front tumblehome surfaces  24   a  and  26   a , the front tumblehome surfaces maintain a constant vertical breadth. 
     Particularly with reference to FIG.  1  and FIG. 2, back section  16  has a port outer tumblehome surface  30 , a starboard outer tumblehome surface  32 , a port inner tumblehome surface  34 , a starboard inner tumblehome surface  36 , a port connective surface  38 , a starboard connective surface  40 , a stern  15  rectilinear transom surface  42  and an undersurface  44 . According to typical inventive embodiments, back section  16  surfaces  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  are, at least to a substantial degree, geometrically planar (flat). The inner tumblehome surfaces and the connective surfaces define a pair of tunnels or channels. Port inner tumblehome surface  34  and port connective surface  38  together describe channel  98 . Starboard inner tumblehome surface  36  and starboard connective surface  40  together describe channel  99 . 
     Certain back section  16  surfaces join each other along certain edges and corners. Port outer tumblehome surface  30  and port connective surface  38  adjoin at port lower outer tumblehome edge  46 . Starboard outer tumblehome surface  32  and starboard connective surface  40  adjoin at starboard lower outer tumblehome edge  48 . Port inner tumblehome surface  34  and port connective surface  38  adjoin at port tumblehome corner  50 . Starboard inner tumblehome surface  36  and starboard connective surface  40  adjoin at starboard tumblehome corner  52 . Transom surface  42  and under surface  44  adjoin at lower transom edge  54 . Port inner tumblehome surface  34  and under surface  44  adjoin at port lower inner tumblehome edge  57 . Starboard inner tumblehome surface  36  and under surface  44  adjoin at starboard lower inner tumblehome edge  59 . 
     Transom  42  also has upper transom edge  56 . As shown in FIG.  4  and FIG. 5, hull  12  is characterized by being “closed” on its top side, and includes above surface  58 . Transom surface  42  and above surface  58  adjoin at upper transom edge  56 . Port outer tumblehome surface  30  and above surface  58  adjoin at port upper tumblehome edge  62 . Starboard outer tumblehome surface  32  and above surface  58  adjoin at starboard upper tumblehome edge  64 . According to many inventive embodiments, hull  12  is characterized by being “open” on its top side. Regardless of whether hull  12  has a closed or open configuration when viewed from above, the essential features of the present invention can be effectuated. 
     Furthermore, the present invention can be practiced in association with practically any kind of propulsion means. For instance, depicted in FIG.  4  and FIG. 5 near stern  15  are two contrarotating tractor pod propulsors  80  which are characterized by reduced cavitation. Each propulsor  80  includes a contrarotating tractor propeller and an azimuthing pod. 
     As best illustrated in FIG. 3, FIG.  6  and FIG. 7, port and starboard corners  50  and  52  each approximately define a horizontal line which is roughly midway between the horizontal plane approximately defined by above surface  58  (or, the horizontal plane in which upper tumblehome edges  62  and  64  coplanarly lie) and the horizontal plane approximately defined by under surface  44 . However, this type of approximate intermediacy of corners  50  and  52  is not necessary according to inventive practice; in terms of vertical distances between horizontally defined planes, corners  50  and  52  can be nearer (or much nearer) to upper tumblehome edges  62  and  64 , or can be nearer (or much nearer) to lower inner tumblehome edges  57  and  59 . 
     Overall, hull  12  is symmetrical with respect to the imaginary vertical plane bisector therethrough along dashed line c. It is helpful to describe hull  12  in relation to imaginary lines and planes. In addition to (i) a first imaginary vertical plane traversely intersecting said vessel (along dashed line s) and (ii) a second imaginary vertical plane longitudinally intersecting and bisecting said vessel (along dashed line c), hull  12  conceivably defines (iii) an imaginary horizontal plane (imagined to be passing horizontally therethrough, but not indicated in the drawings). 
     Imaginary dotted lines  90  and  92 , shown in FIG.  1  and FIG. 2, indicate where inner tumblehome surfaces  34  and  36  would meet the above surface  54  if inner tumblehome surfaces  34  and  36  were imagined to be extended. The respective imaginary planes passing through inner tumblehome surfaces  34  and  36  intersect, at dotted lines  90  and  92 , respectively, an imaginary horizontal plane passing through above surface  54 . Port and starboard dotted lines  90  and  92  generally connect transom  42  to port and starboard “break” points  20  and  22 , respectively. 
     Reference now being made especially to FIG.  6  and FIG. 7, port outer tumblehome surface  30  (not shown in FIG.  6  and FIG. 7) and starboard outer tumblehome surface  32  are approximately equally and oppositely inclined, in tumblehome fashion, at angle α with respect to the imaginary horizontal plane. Port inner tumblehome surface  34  (not shown in FIG.  6  and FIG. 7) and starboard inner tumblehome surface  36  are approximately equally and oppositely inclined, in tumblehome fashion, at angle β with respect to the imaginary horizontal plane. Although angle α and angle β are shown in the figures to be about equal, it is emphasized that this angular equality is not essential to inventive practice, albeit many inventive embodiments preferably effectuate such angular equality. 
     Angle α is approximately constant (nonvariable, unchanging) throughout the longitudinal expanse of each of outer tumblehome surfaces  30  and  32 . Similarly, angle β is show to be approximately constant (nonvariable, unchanging) throughout the longitudinal expanse of each of inner tumblehome surfaces  34  and  36  but angle β can be variable in accordance with this invention. However, angle φ described by each of connective surface  38  and  40  is shown as nonconstant (variable, changing) but angle φ can be a constant according to this invention. Port connective surface  38  and starboard connective surface  40  are approximately equally and oppositely inclined at angle φ with respect to the imaginary horizontal plane. Angle φ of each of connective surfaces  38  and  40  changes in accordance with longitudinal position (i.e., in accordance with distance from transom  42 ; this angular variability is associated with the parallel orientations of the outer tumblehomes and the oblique orientations of the inner tumblehomes, in relation to longitudinal axis c of hull  12 . 
     Outer tumblehome surfaces  30  and  32  are each approximately parallel with respect to longitudinal axis b and with respect to each other. In contrast, inner tumblehome surfaces  34  and  36  are each nonparallel with respect to longitudinal axis c and with respect to each other. Viewing hull  12  from above, inner tumblehome surfaces  34  and  36  slant approximately equally and oppositely outward, away from longitudinal axis c, as inner tumblehome surfaces  34  and  36  proceed forward from transom  42 ; otherwise expressed, inner tumblehome surfaces  34  and  36  slant approximately equally and oppositely inward, toward longitudinal axis c, as inner tumblehome surfaces  34  and  36  proceed aftward from transom  42  to the transverse plane delineated by dashed line s. 
     Angle φ of each of connective surfaces  38  and  40  varies as a function of longitudinal distance along axis c. This angular variability is attributable to certain inventive configurational characteristics, viz.: (i) the contradistinction between the parallelness of outer tumblehome surfaces  30  and  32  and the nonparallelness of inner tumblehome surfaces  34  and  36 , as best shown in FIG. 1; and, (ii) the approximately horizontal disposition of each of port tumblehome corner  50  and starboard tumblehome corner  52 , as best shown in FIG.  3 . Thus, angle φ of each of connective surfaces  38  and  40  varies as a function of longitudinal distance along axis c. As to each of connective surfaces  38  and  40 , the more forward the longitudinal position therealong, the greater the value of angle φ; conversely, the more aftward the longitudinal position therealong, the lesser the value of angle φ. 
     With reference to FIG.  6  and FIG. 7, hull  12  can be considered to be (or be part of) a twenty station ship, wherein transom  42  represents station  20 . At transom  42 , each of connective surfaces  38  and  40  is sloped at an angle φ TRAN . At station  18  (indicated as “STA  18 ”), which is forward of transom  42 , each of connective surfaces  38  and  40  is sloped at an angle φ STA18  which is greater than angle φ TRAN . At station  16  (indicated as “STA  16 ”), which is forward of station  18 , each of connective surfaces  38  and  40  is sloped at an angle φ STA16  which is greater than angle φ STA18 . At station  14  (indicated as “STA  14 ”), which is forward of station  16 , each of connective surfaces  38  and  40  is sloped at an angle φ STA14  which is greater than angle φ STA16 . This increasing trend of angle φ while proceeding forward continues past “midships” (the transverse midline intermediate bow and stern, or the longitudinal “fifty-yard line”) until connective surfaces  38  and  40  reach break points  20  and  22 , respectively, which are located at approximately station  6  of the twenty station ship. 
     In accordance with the inventive configurational details discussed hereinabove, the overall hull  12  essentially describes three basic components, viz., a port stabilizer  70 , a starboard stabilizer  72  and a main hull  74 . Side stabilizers  70  and  72  are located in back section  16  of hull  12 . Port stabilizer  70  includes port outer tumblehome surface  30 , port connective surface  38 , port transom surface portion  56  and starboard transom surface portion  58 . Starboard stabilizer  72  includes starboard outer tumblehome surface  32  and starboard connective surface  40 . Main hull  74 , which is located both in front section  14  and back section  16  of hull  12 , includes port inner tumblehome surface  34 , starboard inner tumblehome surface  36 , medial transom surface portion  60  and under surface  44 . Under surface  44  is located both in front section and back section  16  of hull  12 . From a bottom (underneath) planwise perspective, the portion of under surface  44  which is in front section  14  approximately describes a triangular outline; the portion of under surface  44  which is in back section  16  approximately describes a regular trapezoidal outline. Above surface  58 , shown in FIG.  4  and FIG. 5, is seen to subsume both the centric main hull  74  and the lateral stabilizers  70  and  72 . 
     As best shown in FIG. 2, FIG.  5  and FIG. 6, lower outer tumblehome edges  46  and  48  are not only approximately parallel to each other but are also approximately even horizontally with substantially flat under surface  44  and with each other. That is, substantially flat under surface  44  (or at least the portion thereof in back section  16 ) generally defines a horizontal plane, and lower outer tumblehome edges  46  and  48  and lower transom edge  54  are approximately coplanar in this horizontal plane. Some inventive embodiments provide for lower outer tumblehome edges  46  and  48  which, though horizontally coplanar with each other, are situated in a vertically different horizontal level from that in which lower transom edge  54  is situated or from that which is described by a substantially flat under surface  44 . As shown in FIG. 7, substantially curved under surface  44  is connected to transom  42  such that lower transom edge  54  approximately is horizontally coplanar with lower outer tumblehome edges  46  and  48 , while under surface  44  curves below this level forward of transom  42 . Regardless of whether under surface  44  is substantially flat or substantially curved, in inventive practice lower outer tumblehome edges  46  and  48  will themselves preferably lie in parallel fashion in approximately the same horizontal plane; however, the disposition of such horizontal plane in relation to lower transom edge  54  or under surface  44  can be coincident or noncoincident, depending on the inventive embodiment. 
     Side stabilizers  70  and  72 , which are each generally characterized by an upwardly inward slope, according to many inventive embodiments constitute only about five to ten percent of the hull  12  (e.g., ship) displacement. However, side stabilizers  70  and  72  provide a significant increase in water plane area and righting moment as soon as hull  12  (e.g., ship) rolls, thus providing for enhanced stability. 
     In addition, the static water plane moment of inertia is greatly increased by stabilizers  70  and  72 , thus providing stability that enables a reduced transom width, e.g., a reduced width of medial transom surface portion  60  of main hull  74 . Stabilizers  70  and  72  “hide” the main hull  74  knuckle associated with the reduced transom width of the main hull. The reduced main hull transom width results in less volume above the “designed water line” (“DWL”) at the stern (e.g., stern  15 ) of the vessel (e.g., hull  12 ). Excessive volume in this region of the vessel is thought to contribute to undesirable sea keeping. As distinguished from the inventive tumblehome design, conventional tumblehome designs are deficient in terms of their ability to provide a restoring moment. When stern quartering waves lift up the stern of a conventional tumblehome vessel, the conventional tumblehome vessel&#39;s bow has little ability to provide a restoring moment; that is, the conventional tumblehome vessel&#39;s bow digs in and the hull broaches as a result. 
     According to typical embodiments of the present invention, the outsides of the main hull and the outsides of the stabilizers are at about the same tumblehome slope in order to facilitate the blending of the stabilizers with the main hull at the two (port and starboard) lengthwise commensurate junctional locations (e.g., break points  20  and  22  shown in FIG.  1  and FIG. 2) in back of or behind the bow. For instance, outer tumblehome surfaces  30  and  32  generally are sloped at angle α. At least in the vicinity of break points  20  and  22 , front port tumblehome surface  24  and front starboard tumblehome surface  26  are each also sloped approximately at angle α. As illustrated in FIG. 6 or FIG. 7 considered in conjunction with FIG. 1 or FIG. 2, break points  20  and  22  roughly correspond to station  6  of a twenty-station ship. 
     In inventive practice, there will be some small additional hull weight associated with the side stabilizers (e.g., stabilizers  50  and  52 ); however, this additional weight is much less than that associated with conventional trimaran side hulls (outriggers). The bending moment associated with conventional trimaran-type outriggers is avoided by the present invention. 
     As exemplified by above surface  58  of hull  12  in FIG.  4  and FIG. 5, the width at the top deck of an inventive vessel is significantly increased in comparison with conventional vessels. This inventive increase in width will promote and increase arrangement flexibility and load capacity. Furthermore, this inventive width increase will provide additional damage stability, and will provide stability at large heel angles. 
     Now referring to FIG.  8  through FIG. 15, some inventive embodiments provide inner surfaces  34  and  36  which are: (i) tumblehome surfaces (such as shown in FIG.  8  and FIG.  9 ); or, (ii) non-tumblehome, vertical surfaces (such as shown in FIG.  10  and FIG.  11 ); or, non-tumblehome, non-vertical surfaces (such as shown in FIG.  12  through FIG.  15 ). In each of FIG.  8  through FIG. 15, hull  12  has: a port tumblehome outer surface  30 ; a starboard tumblehome outer surface  32 ; a port inner surface  34  which (depending on the figure) is either a tumblehome surface or a non-tumblehome surface; a starboard inner surface  36  which (depending on the figure) is either a tumblehome surface or a non-tumblehome surface; a port connective surface  38 ; a starboard connective surface  40 ; a stern  15  rectilinear transom surface  42 ; and, a curved undersurface  44 . Not only inner surfaces  34  and  36 , but also tumblehome outer surfaces  30  and  32 , are variously slanted in FIG.  8  through FIG.  15 . 
     As shown in FIG.  8  and FIG. 9, port inner surface  34  and starboard inner surface  36  are each slanted in tumblehome fashion, similarly as illustrated in prior figures; however, the hullforms  12  shown in FIG.  8  and FIG. 9 are configurationally distinguishable therefrom and from each other. FIG.  10  through FIG. 15 depict various tumblehome modes of outer surfaces  30  and  32 , and various non-tumblehome modes of inner surfaces  34  and  36 . As shown in FIG.  10  and FIG. 11, non-tumblehome port inner surface  34  and non-tumblehome starboard inner surface  36  are each approximately vertical. As shown in FIG.  11  through FIG. 15, non-tumblehome port inner surface  34  and non-tumblehome starboard inner surface  36  are each non-vertical. 
     A possible advantage of providing a tumblehome port inner surface  34  and a tumblehome starboard inner surface  36 , as distinguished from non-tumblehome inner surfaces  34  and  36 , is that it facilitates the port and starboard fairings located in the vicinity of port and starboard break points  20  and  22 , respectively, which are the port and starboard forward ends of the port and starboard “furrows,” respectively. Nevertheless, it is to be emphasized that inventive practice does not dictate that inner surfaces  34  and  36  be tumblehome surfaces. Many inventive embodiments provide inner surfaces  34  and  36  which are not tumblehome surfaces. 
     According to this invention, inner surfaces  34  and  36  can be slanted practically any which way. Similarly, port and starboard front surfaces  24  and  26  can be slanted practically any which way. Connective surfaces  38  and  40  can be slanted practically any which way, so long as connective surfaces  38  and  40  are slanted in appropriately connective fashion. Outer surfaces  30  and  32  can be slanted practically any which way, so long as outer surfaces  30  and  32  are slanted in tumblehome fashion. 
     Furthermore, inner surfaces  34  and  36 , and/or connective surfaces  38  and  40 , and/or front surfaces  24  and  26 , and/or front tip  28 , and/or under surface  44 , and/or stern  42  (e.g., transom surface  42 ) can be flat, curved, straight, rounded or some combination thereof. According to typical inventive practice, the tumblehome outside surfaces  30  and  32  will be at least substantially characterized by linearity or flatness, but can to some degree be characterized by curvilinearity or curvature. Moreover, the hull&#39;s top side can be “closed,” “open” or some combination thereof. In addition, in terms of shapes and orientations, inventive principles do not necessarily require either similarity or dissimilarity, vis-a-vis&#39; each other, between and among: inner surfaces  34  and  36 ; front surfaces  24  and  26 ; tip  28 ; tumblehome outer surfaces  30  and  32 ; stern (transom)  42 ; and, under surface  44 . 
     In accordance with the present invention, there is practically a limitless diversity of possible combinations of the vertical angles described by the port and starboard tumblehome outer surfaces (e.g., angles α, the port and starboard inner surfaces (e.g., angles β), the port and starboard connective surfaces (e.g., angles φ), and the port and starboard front surfaces  24  and  26 . According to inventive principles, port and starboard outer surfaces are tumblehome surfaces; port and starboard inner surfaces can be tumblehome or non-tumblehome surfaces; further, port and starboard front surfaces  24  and  26  can be tumblehome or non-tumblehome surfaces. 
     Regardless of the specific shapes and angularities and the overall configuration of the inventive hullform, An important aspect of the present invention is that the port and starboard configurations are such as to afford a kind of stability analogous to that associated with a conventional trimaran vessel, as well as a kind of tumblehome hull shape analogous to that associated with a conventional tumblehome hull. In accordance with the present invention, the port and starboard configurations, correspondingly associated with the port and starboard tumblehome outer surfaces, afford trimaran-like stability without resorting to outriggers that protrude from the hull; the additional stability allows for a tumblehome-type hull form. 
     Other embodiments of this invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Various omissions, modifications and changes to the principles described may be made by one skilled in the art without departing from the true scope and spirit of the invention which is indicated by the following claims.