Abstract:
A method of making a bathtub providing safe egress by reducing slide forces extended on a user&#39;s feet upon a slippery bathtub floor, wherein the formed bathtub has a limited rectangular footprint, and an optimized floor space is formed with a substantially planar base with a length and width that define the limited rectangular footprint and a front wall, a back wall, a first side wall and a second side wall integral with and extending substantially vertically upwards from the substantially planar base. Each of the front, back, first side wall and second side wall have minimal wall thicknesses to define the optimized floor space and the front wall has a substantially planar inwardly, cantilevered upper apron deck in a substantially parallel relation to the substantially planar base.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of application Ser. No. 14/724,380 filed May 28, 2015. The &#39;380 application is a continuation-in-part of application Ser. No. 14/718,662, filed May 21, 2015 (“the &#39;662 application”), which &#39;662 application is a continuation-in-part of application Ser. No. 14/688,413 filed Apr. 16, 2015, (“the &#39;413 application”). The &#39;380, &#39;662 and &#39;413 applications are incorporated by reference herein, and Applicants claim priority in part under 35 USC§120 therefrom. This application also claims the benefit of provisional patent application No. 62/111,453 filed Feb. 3, 2015 (“the &#39;453 application”) under 35 USC§119(e). The &#39;453 application is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to providing safe egress from wet bathtub floors and to maximizing internal bathtub/shower stall space within predetermined confines of typical residential bathroom space dimensions. 
       BACKGROUND OF THE INVENTION 
       [0003]    Safety studies indicate over 234,000 bathroom injuries each year, of which 81 percent occurred because of falls in the bathroom. See Bakalar, “Watch Your Step While Washing Up”, New York Times, Aug. 15, 2011, citing CDC Centers for Disease Control and Prevention, “Nonfatal Bathroom Injuries Among Persons Aged &gt;15 Years, United States, 2008”, Morbidity and Mortality Weekly Report (MMWR), 60 (22); 729-733, Jun. 10, 2011. Of these injuries, more than one third happen while bathing or showing. The Center for Disease Controls (CDC) estimates that 9.8 percent of all bathroom injuries specifically occur when getting out of a bathtub, which equals at least 22,932 injuries. 
         [0004]    Applicants believe that injuries while getting out of a bathtub occur because of the wide straddling of the bather&#39;s legs when exiting a bathtub. The horizontal component force Fs that arises from this prior art arrangement is 0.306 W or almost 31% of the weight of the person. This horizontal component must be resisted by the frictional force between the ball of the anchor foot and the tub (or a tub mat). Several items affect the local coefficient of friction between foot and tub, or foot and mat and mat to tub. Water, and especially soapy water, is a good lubricant and dramatically reduces the coefficient of friction. If the widely straddled anchor foot slips, the bather&#39;s weight is subject to horizontal sideways force and prone to dangerous falls while attempting to exit the bathtub. 
         [0005]    In addition to the aforementioned safety issues, when viewed in crossection from an end, conventional prior art bathtubs have limited interior bathing space by virtue of the fact that the upper apron deck provided for sliding glass doors is usually three or more inches in top width, which narrows considerably the interior bathing or showering space or volume within the conventional bathtub. Additionally, for symmetry purposes, a similar opposite wall abutting top edge is also typically three or more inches in top width, thereby further limiting the space or volume within the bathtub. While bathtubs are generally four to six feet in length, typical residential bathrooms generally have a limited rectangular footprint area of 60 inches by 30 or 32 inches within which to locate a bathtub and shower installation. So losing 1, 2, 3 or 4 inches in width results in a significant reduction in the overall internal space or volume within a typical bathtub. 
         [0006]    Among known prior art patents includes U.S. Pat. No. 2,431,475 of Gruen, which discloses the elimination of a front bathtub apron wall and the creation of an apron effect, by providing a front wall having an upper edge wall fanning outward, both inside the tub and outwards from the front of the tub, to prevent water from splashing out of the bathtub. 
         [0007]    US Patent Application 2011/0167728 of Alelov discloses an “Expandable Side Enclosure for Bathtubs/Showers”, to provide a solution to prevent arm movement restrictions caused to bathers in bathtubs and/or showers due to the lack of free body and limb movement in baths with standard enclosures. While Alelov provides outwardly extended bay-type windows in the sliding glass doors, which are at standing arm height, to provide more movement of the arms during a shower. However, Alelov does not increase the internal volume of the bathtub itself. 
         [0008]    U.S. Pat. No. 1,811,896 of Ross discloses a circular topped truncated conical water basin/bowl/tub with an inwardly inverted anti-splash lip/flange. However, Ross cannot be installed in a typical rectangular bathtub footprint in a residential bathroom. 
         [0009]    U.S. Design Pat. No. D619,685 of Hoernig discloses a shower and tub with a “flip up out of the way” apron deck, to expand the interior space of the bathtub. However, Hoernig requires moving parts and hinges, which are complicated and detrimental in a high humidity bathtub environment. 
         [0010]    U.S. Design Pat. No. Des. 335,701 of Zaccui discloses a bathtub which increases interior space by having bulging outwardly extending side walls. 
         [0011]    However, the bulging sides of Zaccui &#39;701 prevents its installation within a standard bathtub area. 
         [0012]    U.S. Pat. No. 7,490,371 B2 of Torres describes a shower receptor base pan formed from a one piece mold, but where the sheet molding compound (SMC) is placed in a two piece mold, and formed and cured. 
         [0013]    U.S. Pat. No. 5,303,519 , of Mustee describes using a two piece mold to form bathroom shower walls with undercuts to form side wall mounting groove recesses. 
         [0014]    These known prior art devices do not maximize internal bathtub/shower stall space within the predetermined confines of typical residential bathroom space dimensions. The use of a small depth apron deck, such as a thin front bathtub wall with straight edges, or optionally with an inwardly extending only cantilevered top apron edge in the present invention for an expanded space bathtub, where the rear wall has no apron edge, would be discouraged, if not clearly taught away from the prior art patents. 
         [0015]    Therefore, the use of a bathtub with both a narrow apron deck, such as an inwardly extending apron deck of about 2-3 inches in depth, on a front wall having a top width of about one inch to about two and one half inches in width, together with an expanded footprint and volume for the bathtub, as in Applicants&#39; present invention, in conjunction with the spatial confines of a rectangular bathtub installation area of a residential bathroom, is not only not suggested, but would be discouraged or taught away by the designs known from the conventional arts. 
       OBJECTS OF THE INVENTION 
       [0016]    An object of the present invention is to provide a bathtub which provides safe egress for the bather. 
         [0017]    It is also an object of the present invention to minimize falls from bathtubs by providing a structural front wall which minimizes wide straddling of the bathtub front wall by a bather exiting from the wet bathtub. 
         [0018]    Another object is to provide a bathtub that fits within standard tub dimensions but has a larger internal floor area and larger volume within. Most bathtubs are used for taking showers but are dimensioned for tub use. The inventive bathtub better accommodates its shower use while still affording the choice of use as a soaking tub. The larger interior floor area of the bathtub simulates the feel of a larger shower by being less confining. 
         [0019]    In a preferred embodiment the apron deck is cantilevered from the front vertical surface of the front wall inward and then rejoins the thin front wall at near the top of the rear vertical surface of the front wall, thereby realizing a tub that does not suffer a reduction in the interior floor space by the front deck width. The floor area covered by a projection of the front deck is usable space for visual appearance, as well as actual space for feet while standing and taking a shower. In this preferred embodiment, the inwardly cantilevered apron deck has an undercut, which preferably requires the use of a secondary mold of a two piece mold for forming. 
         [0020]    In a non-preferred optional embodiment, the front deck width still is maintained to accommodate sliding door tracks thereon, however, to support sliding glass doors. The side decks and back deck are just the thickness of the tub material. In this alternate embodiment, the front deck is maintained with a width of up to a maximum of 3.5 inches, or preferably between one inch and two and one half inches, according to a width required to accommodate siding door tracks. In one embodiment the apron deck is on top of a wall having the same width, except for an increase of one quarter inch on the bottom. 
       SUMMARY OF THE INVENTION 
       [0021]    The substantially vertical walls and thinness of the front wall of the bathtub of the present invention minimize injuries from falls by providing safe egress from the bathtub, by virtue of the fact that the user has a very small straddling angle measured by the angle of the anchor foot planted in the bathtub, as compared to an imaginary vertical line, when lifting the leading foot over the edge of the bathtub. 
         [0022]    As a result, in a preferred embodiment with a cantilevered front apron deck, only a small percentage, such as ten percent, of the bather&#39;s weight, is subject to slippery horizontal sliding forces. In another embodiment with an apron deck on top of a front wall with straight surfaces, another small percentage, such as fourteen percent, of the bather&#39;s weight is subject to slippery, horizontal sliding forces. This compares to a much larger percentage of weight, such as thirty percent, of the weight of a bather straddling the front wall of the bathtub when the anchor foot planted in the bathtub is far away from the front wall, resulting in a much larger straddling angle, causing substantial horizontal sliding forces of the bather&#39;s feet on the slippery bathtub floor, and /or slippery floor outside the bathtub. 
         [0023]    The safety egress bathtub encompasses a method of providing and using a safe egress bathtub including the steps of: 
         [0024]    a) providing the bathtub with substantially vertical back and front walls, first and second end walls, and a bottom wall, all of these walls being of rigid material, wherein the entry and egress of a bather user is accomplished by stepping over the front wall; 
         [0025]    b) providing the front wall with a thin or cantilevered top horizontal apron deck extending from an outer surface of the front wall toward the back wall, wherein the top horizontal apron deck has sufficient width to support sliding shower wall tracks thereon; 
         [0026]    c) the bottom floor wall extends to a rear, vertical surface of the front wall with the top apron deck adjacent the rear, vertical surface of the front wall; 
         [0027]    d) the user places a first leg on the bottom wall of the bathtub adjacent the vertical front wall of the bathtub, the foot of the leg being generally pointed toward the front wall; and 
         [0028]    e) the user places a second leg over the front wall for stepping out of the bathtub, wherein the first leg makes with the vertical front wall an angle sufficiently small so as to reduce a horizontal component of force on the foot of the user&#39;s first leg, for reducing the incidence of slippage on a wet surface of the bathtub bottom floor. 
         [0029]    Additionally, the bathtub of the present invention has with a limited rectangular footprint and an optimized floor space, including: 
         [0030]    a substantially planar base with a length and width that define the limited rectangular footprint; 
         [0031]    a front wall, a back wall, a first side wall and a second side wall integral with and extending substantially vertically upwards from the substantially planar base; 
         [0032]    wherein each of the front, back, first side wall and second side wall have minimal wall thicknesses to define the optimized floor space, and 
         [0033]    wherein the front wall has a substantially planar cantilevered upper apron deck that extends inwardly from an outer substantially vertical front wall surface for a fixed amount to an inner substantially vertical rear wall surface in a substantially parallel relation to the substantially planar base. 
         [0034]    The bathtub&#39;s front wall is arranged in opposing relation to the back wall and the first side wall is arranged in opposing relation to the second side wall such that all of the walls are integrally joined to define the inner bathtub volume therebetween. 
         [0035]    The bathtub&#39;s minimal wall thickness is a minimum thickness to which the walls can be manufactured and maintain structural integrity, wherein the minimal thickness to which the wall can be manufactured is dependent on a material composition of the walls. 
         [0036]    The bathtub&#39;s substantially planar upper apron deck extends inwardly between and integrally connected to upper portions of the first side wall and the second side wall, in a substantially parallel relation to substantially planar base. 
         [0037]    While dimensions may vary, preferably the limited rectangular footprint of the base of the bathtub is approximately 1419 square inches. 
         [0038]    The bathtub has a distance between an inner surface of the front and back walls and a distance between an inner surface of the first and second side walls, measured at an upper surface of the substantially planar base and a lower inner surface of the substantially planar upper apron deck, respectively, and a minimal distance between the upper surface of the substantially planar base and the substantially planar upper apron deck, define an inner air volume of the bathtub. 
         [0039]    While dimensions may vary, preferably the interior air volume is approximately 20,845 cubic inches. 
         [0040]    Preferably the bathtub&#39;s thickness of the substantially planar upper apron deck is less than or equal to the thickness of the front wall, and wherein the thickness of the substantially planar upper apron deck is a minimum thickness to which the upper apron deck can be manufactured and maintain structural integrity. 
         [0041]    One wall of the first side wall and the second side wall extends vertically at an angle that is greater than 90° between a plane of the base and a plane of the one of the first side wall and the second side wall. 
         [0042]    Preferably, the inner corners formed by vertical ends of the first and second side walls of the bathtub, with vertical ends of the front and back walls, are substantially rounded, but having an arc of about one half inch. 
         [0043]    Also preferably, the inner corners between lower ends of the first and second side walls and the front and back walls and, an inner surface of the substantially planar base are substantially rounded, but having an arc of about one half inch. 
         [0044]    The bathtub&#39;s one or more first and second side walls extend inwardly from an outer substantially vertical wall surface of the one or more first and second side walls for a fixed amount, in a substantially parallel relation to the substantially planar base. 
         [0045]    Also preferably, when the apron deck is cantilevered, the bathtub&#39;s front wall and rear wall each have a thickness of about one inch. When the apron deck is not cantilevered and extends downward in front and rear surface walls to the planar base, the thickness is preferably about two and a half inches, although it can be reduced to about one inch in thickness. 
         [0046]    Preferably, the bathtub&#39;s front wall and rear wall are tapered, with a top thickness of about one inch and with a bottom thickness of about one and one quarter inch in thickness. 
         [0047]    The bathtub also may optionally have hollow interiors, wherein the front wall is hollow, with an outer front wall of about one quarter inch in thickness and an inner front wall of about one quarter inch in thickness, further with a hollow air space therebetween. 
         [0048]    The bathtub&#39;s rear wall may also optionally have a front rear wall of about one quarter inch in thickness, and a hollow air space of about three quarter inches extending behind the front rear wall up to the surface of the bathroom wall, to accommodate tile and tile grout therebetween. 
         [0049]    The cantilevered slanted inward ledge of the apron deck is preferably made of a separate secondary mold, which is attached to the main primary mold for the body of the bathtub. Then the acrylic or other malleable molding material is poured over the two joined molds and the main primary tub mold is inverted, so that the assembled acrylic bathtub will slide downward out of the main primary tub mold. The smaller secondary inward ledge mold is therefore encased within the portion of the tub corresponding to the inwardly extending cantilevered ledge. In the completed acrylic tub, the encased secondary mold piece is slid out laterally from an open end of the tub, within the actual integrally formed cantilevered inward ledge portion of the bathtub. While the bathtub is preferably made with acrylic, it can be made from any malleable material which conforms to complex curves of an analog mold used to form the bathtub. 
         [0050]    In the alternate embodiment of this invention, the front of the bathtub is increased in thickness and the cantilevered top apron is not used, so that in that situation, a one piece mold can be used for the assembled bathtub. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0051]    The present invention can best be understood in connection with the accompanying drawings. It is noted that the invention is not limited to the precise embodiments shown in the accompanying drawings, in which: 
           [0052]      FIG. 1  is a perspective view of a portion of a bathroom enclosing a prior art bathtub; 
           [0053]      FIG. 1A  is a cross-sectional view of a prior art bathtub with a limited space interior; 
           [0054]      FIG. 2  is a perspective detail in partial crossection of a front corner of the prior art tub showing the front deck width; 
           [0055]      FIG. 3  is perspective view of a portion of a bathroom enclosing the bathtub of this invention; 
           [0056]      FIG. 4  is a perspective view of the bathtub of this invention; 
           [0057]      FIG. 5  is an end view crossection showing the profile of the cantilevered front deck; 
           [0058]      FIG. 5A  is an end view crossection of an alternate embodiment, showing the profile of the cantilevered front deck; 
           [0059]      FIG. 6  is an enlarged cross-section detail of the cantilevered front deck; 
           [0060]      FIG. 7  is a side cross-section view of the bathtub of this invention; 
           [0061]      FIG. 8  is an end view profile of a prior art tub with rounded edges at bottom. An outline of the anchor leg of a person in unsupported egress is shown at a particular instant. Also shown is a vector force diagram at the same instant; 
           [0062]      FIG. 9  is an end view profile of the tub of this invention with an outline of the anchor leg of a person in unsupported egress at a comparable instant to that shown in  FIG. 8 . Also shown is a vector force diagram at the same instant. 
           [0063]      FIG. 10  is a top plan view of an alternate embodiment bathtub of this invention with a thicker front panel (without top cantilever) as shown; 
           [0064]      FIG. 11  is a side crossection view of the alternate embodiment of  FIG. 10 ; 
           [0065]      FIG. 12  is a side exterior elevation view of the alternate embodiment; 
           [0066]      FIG. 13  is an end exterior elevation view of the alternate embodiment and, 
           [0067]      FIG. 14  is an end view profile of the alternate embodiment tub with an outline of the anchor leg of a person in unsupported egress at an instant comparable to that shown in  FIGS. 8 and 9 . A vector force diagram at the same instant is also shown. 
           [0068]      FIG. 15  is a perspective view of the primary mold piece of a two piece mold used to form that bathtub of the present invention with a cantilevered, inwardly extending apron deck with an undercut. 
           [0069]      FIG. 16  is a close up view of a top portion of the front wall of the primary mold piece of  FIG. 15 , showing a mounting ledge with holes for temporarily attaching a secondary mold piece to the primary mold piece, for making the cantilevered, inwardly extending apron deck of the bathtub, and showing in partial cutaway the long edge of the secondary mold piece, showing the holes. 
           [0070]      FIG. 17  is an exploded perspective view of the secondary mold piece used to form the cantilevered, inwardly extending apron deck, and wherein the secondary mold piece is shown being installed over the mounting ledge of the primary mold piece for the bathtub. 
           [0071]      FIG. 18  is a perspective view of the secondary mold piece for the inward ledge having been installed over the primary mold piece for making the bathtub. 
           [0072]      FIG. 19  is a close up perspective detail view of a portion of the secondary mold piece having been installed over the primary mold piece for making the bathtub. 
           [0073]      FIG. 20  is a diagrammatic perspective partial crossectional view of a portion of the pourable acrylic material having been poured over a fiberglass sheet laid over a portion of the assembled primary and secondary mold pieces of the two piece mold, used to form the bathtub, with the acrylic material shown sectioned within one portion of one half of the mold, so it can be appreciated how the poured acrylic material conforms to the surfaces of the mold. 
           [0074]      FIG. 21  is an inverted side perspective view of the downward release of the assembled acrylic bathtub with the cantilevered, inwardly extending apron deck, down from the inverted primary mold piece, showing the now formed acrylic bathtub being dropping out partially therefrom, and wherein the secondary mold piece is embedded under the newly formed acrylic cantilevered apron deck. 
           [0075]      FIG. 22  is an inverted close-up perspective detail view of a portion of the assembled bathtub, having been dropped by gravity from the inverted primary mold piece, with an arrow indicating the lateral sideways pull out directional movement of the removal of the secondary mold piece from beneath the assembled, inwardly cantilevered apron deck portion of the assembled acrylic bathtub. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0076]    As shown in Prior Art drawing  FIGS. 1 and 2 , the prior art tub  2  in bathroom  1  as shown in  FIG. 1  is meant to represent any commonly available design. Front deck  3 , back deck  4  and side decks  5  are shown.  FIG. 2  is a close-up showing the typical wide dimension  8  of front deck  3  as well as the narrower side decks  5  dimension  7 . 
         [0077]      FIGS. 3-9  pertain to one embodiment of the bathtub of this invention. The length of the bathtub can be from four to six feet, the height which could be from fourteen to eighteen inches, and the width which could be from thirty to thirty-six inches.  FIG. 3  shows tub  15  in bathroom  10  which is of the same dimensions as bathroom  1  in  FIG. 1 , which is typically five feet wide (60 inches), thirty inches in front to back depth, and about fourteen inches in height.  FIG. 4  shows tub  15  in a perspective view with back deck  17  in the forefront and front deck  16  at the far side. It is noted that side decks  18  as well as back deck  17  have wall widths that are equivalent to the thickness or width of the material comprising the side walls, the back wall and the front wall below the front deck. The crossectional views of  FIGS. 5, 5A and 6  show the cantilevered shape of front deck  16  in detail, highlighting that the front deck width does not encumber the interior width of the tub floor. It is further noted that the width dimension  19  is the same as dimension  8  in prior art  FIG. 2 .  FIG. 7  is a length wise crossection showing sloping backrest  20  and slight drain slope  21 , which is preferred. In these  FIGS. 3-9 , large sections are shown as being solid material just for interior dimensional clarity, however they may in fact have enclosed air spaces. This would be especially true of the large wedge shape under back rest  20  and the cantilevered front deck as in  FIG. 6 ; it would depend on the material used and method of construction. 
         [0078]    An expanded space bathtub  15  fits in standard tub dimensions of bathroom  10  having footprint floor area  10   a  and vertically extending bathroom wall surfaces  10   b ,  10   c  and  10   d , and has a larger internal floor area  15   e  of bottom base wall  15   f , and larger air volume  30  within. The bathtub  15  includes thin walls, including four vertically extending walls, including front wall  15   a , rear wall  15   b , left side wall  15   c  with sloping backrest  20  adjacent thereto and separated from left side wall  15   c  by hollow interior area  21   a ′, and right side wall  15   d  having trip lever hole  23 . Vertical walls  15   a ,  15   b ,  15   c  and  15   d  extend vertically upward from rectangular bottom base wall  15   f  having an exterior footprint to fit within the pre-determined rectangular bathtub insertion floor footprint area  10   a  of bathroom  10 . Bottom base wall  15   f  has an interior footprint  15   e , which, with the inside surfaces of vertically extending walls  15   a ,  15   b    15   c  and sloping backrest wall  20  of left side wall  15   c , define the enlarged air volume  30  extending therebetween. 
         [0079]    The thickness of the vertical walls  15   a ,  15   b ,  15   c ,  15   d  and sloping side backrest  20  is preferably one inch in thickness near the top, up to about one and one quarter inches on the bottom, to provide a slightly sloped surface for easy removal of the tub from a mold. The one inch and one and one quarter inch dimensions need not be solid, so that a wall (not shown) having a thickness of one quarter inch on each side can have a hollow interior of one half inch. A similar hollow area can be provided at the slightly wider bottom width of one and one quarter inches total, combined with the walls and hollow interior. Moreover, for the rear, wall facing wall  15   b , the wall  15   b  can be just one layer of one quarter inch in thickness, with a three quarter inch hollow area behind the one quarter inch wall, up to the bathroom wall surface  25  itself. The one inch thickness at the top  17  of rear wall  15   b  is required to accommodate tiles of up to ⅝ inch in thickness and accompanying grout against the bathroom wall surface  25 . As shown in  FIG. 5A , an optional attachment flange  24  can be attached to rear wall  15   b  for attachment to bathroom wall surface  25 . 
         [0080]    As shown in the crossectional view of  FIG. 7 , the inside bottom footprint  15   e  of bottom base wall  15   f  preferably has a slope  21 , sloping downward from the corner  21   a  defined by sloping backrest  20  and an adjacent edge of interior footprint  15   e  of bottom base wall  15   f , downwards towards water drain hole  22 . 
         [0081]    In the cantilevered apron deck embodiment of  FIGS. 3-9 , the front apron deck  16 &#39;s width of up to a maximum of 3.5 inches is maintained within normal construction requirements to support the sliding glass door tracks, but without the need for limiting interior bathtub volume with thick walls. The cantilevered apron deck  16  can also have a reduced width of about two and one half inches. The side decks  18  and back deck  17  are limited to the thickness of the tub material. In the embodiment of  FIGS. 3-9 , the front apron deck  16  has a width which is maintained to industry standards to support sliding shower wall tracks thereon, but it is cantilevered from the front surface of front wall  15   a  inward and then rejoins the thin inner wall of the front wall  15   a  where its inwardly preferably curved backwards undersurface wall  16   a  meets near the top of the inner surface of front wall  15   a  of bathtub  15 , thereby not reducing the interior floor space  15   e  or the interior air volume  30  by the front deck  16 &#39;s width. The bathtub  15  therefore maximizes internal bathtub/shower stall space within the predetermined confines of typical residential bathroom bathtub and shower space dimensions. 
         [0082]    The bathtub  15  of this invention can be made of steel or plastic resin materials and finished as is common in the industry. 
         [0083]    A comparison of the interior floor space and enclosed air volume (to the top edge of all four vertical walls the tub) has been made to compare a prior art tub and a tub of  FIGS. 3-9  of this invention of the same external dimensions. A prior art front deck of 4″ and a back deck of 3″ with side decks of 2″ in a 60 inch external length by 30 inch tub of 15″ average internal depth was assumed for comparison. The wall thickness of the tub of this invention is assumed to be 1″. Both tubs have the angled backrest and straight vertical walls. The increased floor area and air volume in the tub of this invention is due to the 1″ wall thickness and decks (on 3 edges) vs. the decks of the prior art tub which reduce the internal dimensions. 
         [0084]    The results of the comparison are as follows: 
         [0085]    Interior floor area 
         [0086]    prior art 1120 sq. in. 
         [0087]    this tub 1419 sq. in., a 27% increase. 
         [0088]    Interior air volume 
         [0089]    prior art 16790 cubic in. 
         [0090]    this tub 20845 cubic in., a 24% increase 
         [0091]    Additionally, the above calculations were based upon a prior art bathtub with a front deck of 4″ and a back deck of 3″ with side decks of 2″ in a 60 inch external length by 30 inch tub of 15″ average internal depth for comparison. However, since most prior art tubs have sloping and bottom rounded sides, the numbers of this estimate represent the minimum percentage increases in interior floor area and interior volume. It is estimated that in comparison with other prior art bathtubs, with increased sloping and bottom rounded sides, the savings can be up to approximately 35% increase in interior floor area and interior air volume. 
         [0092]    Bathtub  15  of this invention also offers safety improvement over that of the prior art. Safety studies indicate over 234,000 bathroom injuries each year, of which 81 percent occurred because of falls in the bathroom. Of these injuries, more than one third happen while bathing or showing. The Center for Disease Controls (CDC) estimates that 9.8 percent of all bathroom injuries specifically occur when getting out of a bathtub, which equals at least 22,932 injuries. 
         [0093]      FIG. 8  shows a profile of a person  42  exiting a prior art bathtub  40  with rounded walls at the bottom. The “average person”  42  is a composite 50 th  percentile man or woman with a hip joint to floor dimension L of 35 inches. Although the results of the analysis to follow are somewhat dependent on this selected number, let it be said that a taller person would experience slightly less difference in egress from either a prior art tub or the tub  15  of  FIGS. 3-9  of this invention, and vice versa for a shorter person. Note that the rounded side bottom edge forces the anchor foot farther away from the front edge of the tub (toward the middle) to be supported by the flat portion; this is also true of prior art profile shown in  FIG. 1A  with the sloping sides. 
         [0094]    The instant for the static analysis of  FIG. 8  is that corresponding to the hip joint being directly above the front edge of the tub with the ball of the anchor foot carrying the entire weight of the person before the forward foot (not shown) touches the ground. For the purpose of analysis, the anchor leg can be represented by a rigid rod from the hip joint  44  to the ball of the anchor foot. By measuring the angle in  FIG. 8 , it is found that this rod makes a 17 degree angle with the vertical as shown in the vector force diagram to the right. The weight of person  42 , W, is shown vertically. The horizontal component force Fs that arises from this arrangement is 0.306 W or almost 31% of the weight of the person. This horizontal component must be resisted by the frictional force between the ball of the anchor foot and the tub (or a tub mat). Several items affect the local coefficient of friction between foot and tub, or foot and mat and mat to tub. Water, and especially soapy water, is a good lubricant and dramatically reduces the coefficient of friction. If the anchor foot slips, the bather is in trouble! 
         [0095]    If a similar analysis of Applicants&#39; expanded space tub  15  is performed as depicted in  FIG. 9 , the angle of rigid rod and the vertical is only 5.5 degrees because now the anchor foot is so close to the front edge. The horizontal component force Fs that results in this analysis is 0.096 W or only less than 10% of the weight of the person. Thus with the same bather exiting either a prior art tub or a tub  15 , slippage can be avoided in a tub  15  of this invention even if the friction coefficient were ⅓ of that which minimally prevented a spill in a conventional tub. Common sense reinforces the numeric example; the tub  15  side walls are substantially vertical; the bather can have the planted leg being substantially vertical and stable, and this requires only lifting the leading leg up and over the thin apron of 3.5 inches or less. 
         [0096]    A non-preferred alternate embodiment tub  50  of this invention is the subject of  FIGS. 10-14 . This tub is similar to tub  15  of this invention, but uses a front panel of thicker material instead of a top cantilever to provide the top resting surface to receive door tracks (if used). 
         [0097]      FIG. 10  is a top view showing a front panel  52  of about 2.5″ in thickness. It is noted that the 2.5″ thickness can be reduced down from 2.5″ in a range of to a top thickness of about one inch. Other dimensions shown in  FIGS. 10, 11, 12, and 13  include the length which could be from four to six feet, the height which could be from fourteen to eighteen inches, and the width which could be from thirty to thirty-six inches. The side crossection of  FIG. 11  reveals that it is identical in shape to that of  FIG. 7  for tub  15 . 
         [0098]    The side profile of  FIG. 14  showing the front panel  52  in crossection more clearly shows the distinction from tub  15  with it&#39;s cantilever at the top edge (see  FIG. 9 ).  FIG. 14  is an egress analysis of person  42  exiting the alternate embodiment tub  50  as was performed before for the prior art, and for tub  15  of this invention. Again, dimension L of a rod from hip joint  44  to the ball of the foot is 35″. In this case however, the rod makes an angle of 7.97 degrees with the vertical as opposed to 17 degrees for the prior art situation or 5.5 degrees for tub  15 . In tub  50 , person  42 &#39;s foot is forced slightly back (1.5″) from the front surface relative to the position in tub  15  due to the thicker front panel  52 . This geometry results in a side force (Fs) of 14% of the person&#39;s weight, W. While this is not as safe as the case for tub  15 , this is still less than half the side force of the prior art tub (31% of the person&#39;s weight) analysis of  FIG. 8 . 
         [0099]      FIGS. 15 to 22  show the method of making the bathtub  15  of  FIGS. 1-9 , with the inwardly extending apron deck ledge  16 , by using a two-piece mold  100 , so that after the acrylic material  101  is poured into the primary mold piece  102  and set, then the primary mold piece  102  is inverted and the completed bathtub  15  falls easily out of the primary mold piece  102  having hollow tub-shaped portion  105 , shown in  FIG. 20 . The two piece mold is necessary because of the undercut of the inwardly cantilevered apron deck  16 . 
         [0100]    For example, the cantilevered slanted inward ledge apron deck  16  has to be made of a separate secondary mold piece  103 , which is attached to the bathtub  15  as shown in the drawing  FIGS. 17-19 . Then the acrylic material  101  is poured over a fiberglass layer laid over the two mold pieces  102 ,  103  as in  FIG. 20  and then the main tub mold piece  102  is inverted as in  FIG. 21 , so that, upon subsequent completion of the mold making of the bathtub  15 , the assembled acrylic bathtub  15  will slide downward out of the primary mold piece  102 . The smaller secondary inward ledge mold  103  for the inwardly, cantilevered apron deck  16  is then encased within the portion of the tub  15  being the inwardly extending ledge apron deck  16 .  FIG. 21  also shows excess acrylic material which is trimmed to form the final bathtub  15 . 
         [0101]    As shown in drawing  FIG. 22 , of the completed white acrylic tub  15 , which is shown inverted after removal as in  FIG. 21 , the encased secondary mold piece  103  is slid out laterally, in the direction of the arrow shown, from within and below the actual integrally formed inward ledge cantilevered apron deck portion  16  of the bathtub  15 . 
         [0102]    It is further noted that  FIG. 22  shows the upside down inverted bathtub  15 , so that the lower right corner of bathtub  15  in  FIG. 22  is actually the upper front apron deck  26 , when the completed bathtub  15  is turned right side up. 
         [0103]      FIGS. 15 and 16  show that the primary mold piece  102  is an analog mirror image of the walls of the bathtub  15 , without the cantilevered apron deck  16 . A stepped ledge  102   a  with cut-out holes  102   b  is provided for protruding nibs (not shown), to anchor and steady the secondary mold piece  103  in place therein, for positioning of the molding of the cantilevered apron deck  16  with an undercut. 
         [0104]      FIGS. 17-19  show the angled secondary mold piece  103  with substantially horizontal top ledge  103   a  and angled undercut slanted surface  103   b , which has a bottom edge, which meets the inside  102   c  of the front wall  102   d  of the primary mold piece  102 . 
         [0105]      FIG. 20  shows the acrylic mold material  101  being poured over the flexible fiberglass sheet covering the assembled two piece mold  102 ,  103 . 
         [0106]      FIG. 21  shows the inverted bathtub  15  being dropped out of the primary mold piece  102 , while the secondary mold piece  103  (shown in phantom) is captured under the cantilevered apron deck  16 , and laterally or otherwise removed as in  FIG. 22  in the direction of the arrow. 
         [0107]    It is further noted that the slanted undersurface of the inwardly extending cantilevered apron deck can assume various configurations. For example, the sloping undercut surface of the apron deck can have variable angles, such as, for example, the undersurface  16   a  descending from a shoulder, at a wide angle. Alternatively, the slanted undersurface can be longer and have less of an inwardly extending angle, such as would be formed by acrylic poured over undercut slanted surface  103   b  of a secondary mold piece, shown in  FIGS. 17-19 . Moreover, the slanted undercut surface can be straight, curved or combinations thereof. 
         [0108]    In the foregoing description, certain terms and visual depictions are used to illustrate the preferred embodiment. However, no unnecessary limitations are to be construed by the terms used or illustrations depicted, beyond what is shown in the prior art, since the terms and illustrations are exemplary only, and are not meant to limit the scope of the present invention. 
         [0109]    It is further known that other modifications may be made to the present invention, without departing the scope of the invention, as noted in the appended Claims.