Abstract:
A flow-powered platform carries envirosensors, under tether (or remote-transmission) control from one shore, driven by at least one active waterfoil (ideally remotely interchangeable), with surfaces curved horizontally across the flow. Preferably: there are plural foils; the platform is a single unitary body, best a planar flat shallow panel (deterring aft submersion) or volume-enclosing hull; the foil mounts beside, parallelling, the body, depending from and below it, and, if dual, at opposite sides; the foil has at least one force-enhancing flap, tether-adjustably extending longitudinally to trim an effective overall foil surface, and with laterally extending length roughly 0.05 to 0.4 times the waterfoil length, or 3 to 90 cm, best 60 to 250 cm; and the foil has greatest curvature radius, along a longitudinal surface, roughly 2 to 10 m, or forming a lateral excursion from 0.1 to 0.2 times the foil length, or 2½ to 25 cm.

Description:
[0001]     This patent document claims priority from U.S. provisional patent application 60/635,119, filed Dec. 11, 2004 and wholly incorporated herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention is generally in the broad field of hydrology. This science treats the occurrence, circulation, distribution and properties of the waters of the earth, and their interaction with the environment. This field encompasses hydrography and water-quality measurements.  
         [0003]     Accordingly this field is not to be confused with the wholly distinct and remote arts of oceanographic seismology—i.e., marine seismic studies, exploration, and surveys. Most of seismology, in particular, is directed largely to offshore petroleum discovery rather than to the natural environmental phenomena of water.  
         [0004]     These fields heretofore involve different resources, knowledge bases, and people. The field of the present invention is also of course distinct from the field of aerodynamics.  
         [0005]     More specifically, the invention is in the very narrow and rather new field of carrying hydrological or other environmental sensors across a directionally flowing body of water, i.e. a river or other stream, and back—using horizontally curved hydrofoils. These foils act against the downstream movement of the water to actively generate horizontal hydrodynamic force (analogous to the vertical lift force of a curved wing, as is familiar in aerodynamics) to move the device across the water.  
         [0006]     Throughout this document the terms “active” and “passive” refer to the critical presence or absence, respectively, of hydrodynamic forces generated by interaction of foil camber (and to a lesser extent the curvature of the so-called “chord” side of a foil) with the flowing water of a stream. Thus planar vanes are passive, entirely lacking the capability to develop such forces, and indeed are not in the above-stated field of the invention. Note that this usage departs from other meanings of “active”, which relate to use of e.g. artificially powered force generators and watercraft.  
       RELATED DOCUMENTS  
       [0007]     Based upon both private and professional searching, no relevant prior art is known in the above-indicated field of the invention. The sole exceptions to this statement are the well-known but essentially primitive practices introduced at the beginning of the “BACKGROUND” section, below.  
         [0008]     Accordingly the only documents that can be helpfully introduced here are in very distinctly different fields, namely sportfishing, and swiftwater rescue, and towing of seismic sensors and the like behind oceangoing boats and ships. In the first of these categories are U.S. Pat. No. 4,763,437 of Cuda, and U.S. Pat. No. 3,760,762 of Spongberg.  
         [0009]     In the second, rescue category is published Canadian patent application (currently fragmentary) 2,439,871 of Miller—opened to public inspection in March 2005. In the third, towed-seismic-devices category and even more remote are U.S. Pat. No. 4,484,534 of Thillaye du Boullay, U.S. Pat. No. 4,729,333 of Kirby; U.S. Pat. Nos. 6,532,189, 6,226,225 and publication 2002/0064091 all of Barker, U.S. Pat. Nos. 6,234,102 and 6,267,070 both of Russell; U.S. Pat. No. 4,033,278 of Waters, and U.S. Pat. No. 4,574,723 of Chiles. For convenience one additional patent will be grouped with these, U.S. Pat. No. 3,753,415 of Burtis—relating to a self-compensating stabilizer for boats.  
         [0010]     All of those related documents are wholly incorporated by reference into this present document.  
       BACKGROUND  
       [0011]     Current practice in the field—Currently, hydrological instruments are moved across streams by various means, including: 
        wading;     a manned boat;     an unmanned, powered boat;     an unmanned boat tethered to both shores (for example by a cableway)—the cable being moved clothesline-style across the stream; and     an unmanned boat tethered to a bridge crossing the water. 
 
 As will be understood, these methods are all either extremely cumbersome and slow, or very expensive—or both. 
       
 
         [0017]     Wading is sometimes dangerous, where the stream is too deep or the bottom too irregular, and in some cases is quite impossible. Riding in a boat across the stream makes the data acquisition inordinately expensive and also requires the additional time and inconvenience of transporting a full-size boat to the data-gathering site, launching the boat, and removing it from the water for transportation from the site.  
         [0018]     Moreover deploying such a boat often significantly disturbs some of the natural parameters to be measured. Data from manned boats is noisy, because of the roll of the boat and the fact that instrumentation is usually deployed from the side—meaning that the sensor depth in the water changes with the roll of the boat.  
         [0019]     In principle it is possible to manufacture or modify a manned boat with a centrally positioned instrument well or bay, to minimize variation of sensor depth with roll. A boat customized in this way, however, may be inordinately expensive.  
         [0020]     Furthermore, commitment to use of such a custom boat in turn requires that the entire, special boat must be transported from measurement site to measurement site—i.e., it is no longer possible to rent an ordinary boat for a day or two in one part of the country, then travel to another part of the country and there rent another ordinary boat, etc. Use of a custom boat in turn calls for a boat trailer or heavy-duty automobile-roof rack, plus considerable exertion and time for launching and recovering the boat. In general the acquisition of data at each site becomes quite a project.  
         [0021]     Use of unmanned, powered craft is generally better in terms of time and expense, and possibly also in leaving the natural phenomena in their natural condition. Nevertheless it still calls for dealing with fuel or batteries, or both—as well as costly maintenance of an engine or motor, fire hazards and so forth.  
         [0022]     Establishing a guide cable across a stream may be prohibitively expensive, particularly for a one-time survey. A bridge cannot always be luckily found along a segment of stream whose hydrology is of interest.  
         [0023]     Typical hydrological sensors are for measurement of current (i.e., speed of water flow), temperature, dissolved oxygen, chlorophyll, turbidity, rhodamine, global position (local or global), bathymetry (water depth) and bottom classification; and the instrumentation packet may also include video cameras and microphones. Thus in industry the “environmental sensors” most typically are water-quality sensors.  
         [0024]     Features not previously associated with this field—In the above-mentioned fields of lure-placement and swiftwater-rescue, simple planar vanes are used as elementary, passive water-flow deflectors to steer devices across a river or other stream—for support of a fishing lure, or a flood victim. The planar vertical vanes of these devices accordingly generate relatively low levels of horizontal force.  
         [0025]     These devices may be adequate for the purposes of their own inventors, working in their own respective fields of invention. In fact, in sportfishing it may actually be advantageous to move a lure support into position rather gently and slowly, so as not to disturb the quarry. In swiftwater emergency work the amounts of force available are typically excessive, and a major problem may be to modulate those high forces sufficiently to develop stable control of the rescue pad; hence in that environment a passive vertical vane may be ideal.  
         [0026]     I have found, however, that such planar deflectors usually are extremely difficult to control, in a delicate way that fine tunes the position and speed of the attached watercraft. The planar deflector stalls (loses horizontal force suddenly, without warning)—making good control a matter of muscle power, extraordinary coordination, and athletic reflexes on the part of the operator.  
         [0027]     Such requirements in fact are quite evident in the videos offered by the Waterkite company on its website. In the context of swiftwater rescue, such athletic demands may be relatively acceptable; whereas in scientific data acquisition such demands are relatively undesirable.  
         [0028]     Even in the field of swiftwater rescue, however, a planar vane may be undesirable. Such a vane provides horizontal force over only a relatively narrow range of angles of attack. It is probably this that makes the vane stall, and thus the attached craft harder to control.  
         [0029]     In addition, a planar deflector can generate insufficient force for use in the field of the present invention. Stream crossing distances may be quite long, on the order of 30 to 100 meters, and this calls for horizontal force that is rather high.  
         [0030]     Moreover, platform speed is important. While a fisherman may be out for the day and intending largely to enjoy the place and the activity, a professional hydrologist needs to make measurements, get the job done at each site, and move along.  
         [0031]     Moreover the validity of many measurements made at a single site may depend upon their usefulness in deriving secondary parameters from calculated combinations of the values that are directly measured—and such calculated combinations may be meaningless if the data are not all acquired in substantially the same time frame. Ideally in this field the instrumentation is moved across the water surface at a rate that is controlled and rather slow, yet businesslike; in short, the speed should be, so to speak, “just right”—and once again this calls for a level of control that is essentially unattainable using a planar vane.  
         [0032]     Of course time is of the essence in emergency rescues; however, once again in swiftwater work a major problem is that everything is happening  too  quickly, all at once, in an uncontrollable blur—rather than too slowly. Such events create their own timetables, and obtaining adequate speed or force at the rescue pad is not the primary problem.  
         [0033]     Thus essential considerations of speed and time are applicable in the field of the present invention. They most typically fail to come into play at all in those other fields.  
         [0034]     In the sportfishing field another factor is the configuration of the lure support. Cuda and Spongberg use volume-enclosing dual hulls. It will be appreciated that such geometry has inherent appeal—in slow-moving flows these buoyant shapes are typically stable and fit well into the placid, pacific environment so that fish are not frightened away. Cuda goes so far as to ornament his upper hulls with serrated fishlike fins.  
         [0035]     In my own extensive trial-and-error testing, however, I have found that under certain flow conditions dual-hull configurations are very troublesome for hydrology. Particularly in fast-moving currents the aft portions of these devices are often awash, submerged and actually participating in the generation of turbulence. This behavior is adverse to the support of sensitive or delicate instrumentation, and thus to the acquisition of reliable scientific data.  
         [0036]     Once again the essence of good transport for hydrology is good control, enabling operation of a cross-stream speed that is optimized. The speed should be low enough that the  amount  of data collected is ample—to make the standard deviation in the data small. In other words, a rather slow speed across the stream increases the quality of the data.  
         [0037]     Thus the speed should be moderate and rather consistent, but not so slow as to invalidate the assumption that the measurements belong to a common time frame—or so slow as to interfere with an expeditious work schedule for the personnel. Such control heretofore has not been available in an economical, efficient system.  
         [0038]     Cuda provides four small, generally horizontal vanes near the corners of his two-hull catamaran-like structure. According to his discussion these vanes produce force that is actually vertical, in generally the same direction as in aircraft.  
         [0039]     These vanes, however, evidently are simply passive, essentially planar shapes, not active foils. Although they generate some vertical force based upon angle of attack, they apparently do so without vertical curvature or active (as defined earlier) hydrodynamic behavior.  
         [0040]     In this way, Cuda asserts, his overall structure can be made to plane in the water, slightly raising the hulls out of the water to reduce drag. As will later be seen, however, the overall result is a relatively complex shape that would be needlessly elaborate for purposes of the present invention.  
         [0041]     Several of the other prior patents enumerated above, in the towed-devices field, involve horizontally, i.e. laterally, cambered foils rather than essentially planar vanes. Some of these foils are hydrodynamically active, in the sense that their camber can be optimized and tuned to provide a very high level of control and uniformity of operation, particularly stable operation at a moderate speed. Indeed one generally accepted definition of “foil” is “an object designed to optimize lift in a fluid flow”.  
         [0042]     The word “lift” is related to vertical lifting force created by curved airfoils in aircraft, but to a certain extent is applicable, by analogy, to lateral hydrodynamic forces that curved foils create in water. In addition to sensitive control and a moderate cross-flow speed, cambered foils can be tuned and optimized to yield strong horizontal force (“lift”) over a wider range of angles of attack than a planar vane—and this is particularly important where a stream or river to be surveyed is rather wide, e.g. in the general realm of 30 m and more.  
         [0043]     The towed seismic devices, however, are not in the field of the present invention. The corresponding patents fail to suggest any applicability to placement devices in a directionally flowing body of water, or controlled from just one shore.  
         [0044]     Curiously, the Spongberg (fishing) invention may also be in the towed-devices category, since his invention—unlike Cuda&#39;s—is pictured as being manipulated from an adjacent small fishing boat. Spongberg nevertheless as noted above uses only a planar vane, rather than a laterally curved foil.  
         [0045]     Conclusion—Accordingly the prior art has continued to impede achievement of uniformly excellent positioning of hydrological sensors across a directionally flowing water body. Thus important aspects of the technology used in this field remain amenable to useful refinement.  
       SUMMARY OF THE DISCLOSURE  
       [0046]     The present invention introduces just such refinement. In preferred embodiments the invention has several independent aspects or facets, which are advantageously used in conjunction together, although they are capable of practice independently.  
         [0047]     In preferred embodiments of its first major independent facet or aspect, the invention is a platform for displacing an environmental sensor across a stream, or portion of a stream. The platform is powered by water flow of the stream and controlled by tether from just one shore.  
         [0048]     The platform includes a flotation element. It also includes at least one hydrodynamically active waterfoil, attached to or integrated with the flotation element.  
         [0049]     As mentioned above, the term “active” here means that the foil is cambered. The “DETAILED DESCRIPTION” section of this document shows that a hydrodynamically cambered foil shape can be tuned or optimized to develop a strong, steady horizontal hydrodynamic force.  
         [0050]     This force persists at moderate speeds and, in particular, is available over a broad range of angles of attack. A planar vane cannot accomplish this and accordingly for purposes of this document is denominated “passive”.  
         [0051]     The active foil has surfaces curved horizontally, transversely to the stream flow, for interaction with the stream flow to generate substantially horizontal force transverse to the stream flow. This force is for propelling the flotation element across the stream, or stream portion.  
         [0052]     Also included are some means for supporting the environmental sensor from the platform. For purposes of generality and breadth in discussion of the invention, these means will be called simply the “supporting means”.  
         [0053]     In the accompanying claims generally the term “such” is used (instead of “said” or “the”) in the bodies of the claims, when reciting elements of the claimed invention—for referring back to features which are introduced in preamble as part of the context or environment of the claimed invention. The purpose of this convention is to aid in more distinctly and emphatically pointing out which features are elements of the claimed invention, and which are parts of its context—and thereby to more particularly claim the invention.  
         [0054]     Merely by way of example, in the accompanying claims this convention draws attention to the fact that the banks of the stream are not parts of the invention. It likewise draws attention to the fact that the environmental sensor or sensors carried by the invention are no part of the invention—unless elsewhere expressly declared to be part or parts of the invention.  
         [0055]     The invention also includes some means for responding to the tether control, from the one shore, to maneuver the flotation element relative to the stream. These means, again for breadth and generality, will be called simply the “responding means”.  
         [0056]     The foregoing may represent a description or definition of the first aspect or facet of the invention in its broadest or most general form. Even as couched in these broad terms, however, it can be seen that this facet of the invention importantly advances the art.  
         [0057]     In particular, this invention offers the first practical apparatus for conducting a hydrological survey without wading or riding across a stream, or taking the time to install a guide cable, or locating a bridge that is luckily positioned near hydrological features of interest. The invention is minimally intrusive to the phenomena being monitored, and is virtually noiseless, very safe, and extremely economical in use.  
         [0058]     In particular a hydrodynamically active foil makes possible a very prompt, powerful and sure conveyance of the measuring equipment across the stream and back. Most importantly the foil can be shaped to provide horizontal force that is strong and reliable over a wide range of angles of attack, so that the platform is easy to control. The environmental sensor can thus be moved across the stream at a speed that is controlled and rather slow, but fast enough to facilitate a businesslike working environment for the personnel involved.  
         [0059]     Although the first major aspect of the invention thus significantly advances the art, nevertheless to optimize enjoyment of its benefits preferably the invention is practiced in conjunction with certain additional features or characteristics. In particular, preferably the “at least one transversely curved foil” preferably includes at least two transversely curved foils, each interacting with the flow to generate the transverse force.  
         [0060]     If this first, basic preference is observed, then several subpreferences arise, some of which are nested: preferably the flotation element is formed as a single, substantially unitary body. In this event also preferably that body is either a single generally planar flat shallow panel, or a single volume-enclosing hull.  
         [0061]     There are two alternative preferences as to the at least one transversely curved foil. In one such preference, the at least one foil is mounted beside and very generally parallel to the single, substantially unitary body. In this case the “at least one” transversely curved foil includes at least two such foils, mounted respectively at opposite sides of and very generally parallel to the body. In the other such preference the at least one foil depends from, and below, the flotation element.  
         [0062]     In another set of preferences, the platform further includes at least one flap attached to, or formed in, or integrated with the waterfoil. The flap perturbs the interaction with the stream flow, to enhance the substantially horizontal force.  
         [0063]     If the basic preference for including a flap is observed, then other preferences—sometimes nested—come into play. Preferably the flap adjustably extends from the foil longitudinally to lengthen or shorten the effective overall active surface of the foil. Thereby operation of the flap modifies the interaction between the foil and the stream flow.  
         [0064]     Further preferably the platform includes some means for adjusting the flap via the tether control, from the one shore. Preferably the flap adjustably extends laterally from the foil to trim the interaction.  
         [0065]     I prefer that the flap have laterally extending length in the range of roughly 0.05 to 0.4 times the waterfoil length. I prefer that the flap have laterally extending length in the range of approximately 3 to 90 cm (roughly 1 to 40 inches).  
         [0066]     In addition I prefer that the foil have length in the range of approximately 60 to 250 cm (roughly 2 to 7½ feet)—and also that the foil have curvature, along a most strongly curved segment of a longitudinal surface, characterized by a radius of curvature in the range of approximately 2 to 10 m (roughly  6½ to  33 feet). As will be seen, the shape of a whole foil according to my invention is not usually characterizable by a radius of curvature; usually the shape is complicated and would require an engineering spline technique to describe accurately.  
         [0067]     Nevertheless, specification of the radius of curvature of a most strongly curved segment does provide a thumbnail picture of how severe the shape is. Note that the curvature is of a longitudinal segment, not of either the leading, hairpin-shaped edge of the foil or the usually cusp-like trailing edge.  
         [0068]     Also preferably the foil has curvature, along a longitudinal surface, forming a lateral excursion in the range of approximately 0.1 to 0.2 times the foil length. Specification of such a lateral excursion as a fraction of the foil length simply represents another way of quickly characterizing, with a single number, how severe, or radical, the shape is.  
         [0069]     Yet another preference is that the foil have curvature, along a longitudinal surface, forming a lateral excursion in the range of approximately 2½ to 25 cm (roughly 1 to 10 inches)—here given in absolute measure, rather than a fractional measure. (It will be understood, however, that all dimensions of preferred embodiments—i.e., those of the platform, the foils, and the flaps—vary with the size and weight of the hydrological instrumentation.) Another preference is that the supporting means include some means for supporting plural environmental sensors, rather than only one. Yet another preference is that the platform further includes a single tether, for applying the tether control, and a remote-transmission control system for supplementing the tether control (as, e.g., for operating a flap).  
         [0070]     In preferred embodiments of its second major independent facet or aspect, the invention is a platform for displacing an environmental sensor across a stream or portion thereof, powered by water flow of the stream and controlled by tether from just one shore. The platform includes some means for supporting the environmental sensor in flotation relative to the stream flow.  
         [0071]     Once again for generality and breadth these means will be called simply the “supporting means”. It will be understood that under the patent statute the “supporting means” by definition constitute structure specifically for supporting the environmental sensor in flotation relative to the stream flow; thus no other structure can answer to this recitation, “supporting means”.  
         [0072]     Also included are some means for propelling the environmental sensor, together with the supporting means, across the stream or portion thereof. Here again, these means will be called the “propelling means”, and are by definition uniquely for the purpose stated.  
         [0073]     The propelling means include at least one hydrodynamically active (as defined in this document) waterfoil, attached to or integrated with the flotation element. The waterfoil has surfaces curved transversely to the stream flow, for interaction with the stream flow—to generate substantially horizontal force transverse to the stream flow.  
         [0074]     Additionally included are some means for responding to the tether control, from the one shore, to maneuver the flotation element relative to the stream. As before these means will be called th “responding means”.  
         [0075]     The foregoing may represent a description or definition of the second aspect or facet of the invention in its broadest or most general form. Even as couched in these broad terms, however, it can be seen that this facet of the invention importantly advances the art.  
         [0076]     In particular, this second facet of the invention enjoys, in substance, essentially all of the advantages that have been described above for the first facet. In comparison with all devices and methods in use heretofore, the invention is much faster and safer, far more convenient and practical, and also more economical.  
         [0077]     Further these two main aspects of the invention are particularly appealing to hydrologists and hydrographers because each aspect provides and projects a system that both is and appears very professional. It is businesslike, tidy and efficient.  
         [0078]     Although the second major aspect of the invention thus significantly advances the art, nevertheless to optimize enjoyment of its benefits preferably the invention is practiced in conjunction with certain additional features or characteristics. In particular, preferably the supporting means include some means for supporting a plurality of the environmental sensors in flotation relative to the stream flow, and the propelling means include some means for propelling a plurality of the environmental sensors, together with the supporting means, across the stream or portion of the stream. Thus the invention can serve more than a single sensor.  
         [0079]     It is also preferable that the at least one transversely curved foil include at least two transversely curved foils, each interacting with the flow to generate the transverse force. I also prefer that the flotation element include some means for deterring submersion of an aft end of the flotation element, particularly in relatively high flow—and that these submersion-deterring means include configuration of at least the aft end of the flotation element as a single, generally planar flat shallow panel.  
         [0080]     In this case I also prefer that the at least one transversely curved foil be mounted below and very generally parallel to the flat shallow panel. I further prefer, in one form of this second facet of the invention, that the at least one transversely curved foil include at least two transversely curved foils, mounted respectively at opposite sides and very generally parallel to the flat shallow panel.  
         [0081]     Another preference is that the apparatus also include some means for controllably extending or retracting the at least one curved foil in the fore-aft direction, with respect to the supporting means, for use at faster or slower stream-flow speeds respectively. In this case it is further preferable that the extending or retracting means be operable remotely.  
         [0082]     Another preference is inclusion of some means for controllably extending or retracting a flap from the at least one curved foil, with respect to the supporting means, for use at slower or faster stream-flow speeds respectively. Still another, in this case, is that the extending or retracting means be operable remotely.  
         [0083]     In preferred embodiments of its third major independent facet or aspect, the invention is a platform for displacing an environmental sensor across a stream or portion thereof, powered by water flow of the stream and controlled by tether from just one shore. The platform includes some means—the “supporting means”—for supporting the environmental sensor in flotation relative to the stream flow.  
         [0084]     It also includes some means—“propelling means”—for propelling the environmental sensor, together with the supporting means, across the stream or portion. The propelling means include a plurality of interchangeable hydrodynamically active waterfoils for respective use, selectively, at different speeds of the stream flow.  
         [0085]     Further included are some means—“securing means”—fixed to the supporting means, for releasably securing any of the plurality of foils to the supporting means. A selected one of the foils is attached to the flotation element by the securing means, for use at a corresponding speed of the stream flow.  
         [0086]     The waterfoils have surfaces curved transversely to the stream flow, for interaction with the stream flow—to generate substantially horizontal force transverse to the stream flow. Also included in the third facet of the invention are some means (“responding means”) for responding to the tether control, from the one shore, to maneuver the flotation element relative to the stream.  
         [0087]     The foregoing may represent a description or definition of the third aspect or facet of the invention in its broadest or most general form. Even as couched in these broad terms, however, it can be seen that this third facet of the invention importantly advances the art. In particular, beyond the advantages of the first and second aspects of the invention, this apparatus adds a remarkable versatility and flexibility in use.  
         [0088]     Although the third major aspect of the invention thus significantly advances the art, nevertheless to optimize enjoyment of its benefits preferably the invention is practiced in conjunction with certain additional features or characteristics. In particular, preferably the foils for use at higher flow speeds are smaller than the foils for use at lower flow speeds. Also preferably the apparatus further includes some means for selecting, and engaging with the releasably-securing means, any of the foils remotely.  
         [0089]     The foregoing features and benefits of the invention will be more fully appreciated from the following detailed description of preferred embodiments—with reference to the appended drawings, of which:  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0090]      FIG. 1  is a top plan of a first preferred embodiment of the invention, having a central volume-displacing hull-like buoyant body and generally parallel horizontally cambered foils at left and right of (in the drawing seen respectively below and above) that body;  
         [0091]      FIG. 2  is a side elevation of the same embodiment, taken along the line  2 - 2  in  FIG. 1 ;  
         [0092]      FIG. 3  is a front elevation of the same embodiment, taken along the line  3 - 3  in  FIG. 1 ;  
         [0093]      FIG. 4  is another top plan of the  FIG. 1  embodiment as deployed in a stream;  
         [0094]      FIG. 5  is an upper perspective or isometric view of a second preferred embodiment, having a generally planar buoyant board rather than a hollow or volumetric hull, and having one or more foils affixed below the board—the foil being cambered horizontally;  
         [0095]      FIG. 6  is a lower perspective or isometric view of the  FIG. 5  embodiment, particularly having a single shallow foil secured below the board;  
         [0096]      FIG. 7  is an isometric view (taken from below the left-front corner) of an embodiment similar to that of  FIG. 6  but instead having two substantially identical horizontally cambered foils, somewhat taller than the  FIG. 6  foil and mounted below the board generally parallel to each other;  
         [0097]      FIG. 8  is a top plan of the  FIG. 7  embodiment, showing the foils (which are below the board) in the dashed line;  
         [0098]      FIG. 9  is a side view of the same embodiment, taken along the line  9 - 9  in  FIG. 8 ;  
         [0099]      FIG. 10  is an aft view of the same embodiment, taken along the line  10 - 10  in  FIG. 9 ;  
         [0100]      FIG. 11  is a cross-sectional view of a basic foil, or hydrofoil;  
         [0101]      FIG. 12  is a like view of a similar foil but having a plain flap mounted for downward rotation near the aft end of the foil;  
         [0102]      FIG. 13  is an exemplary diagram, with calculations, of a particular foil as calculated and presented by Dr. Kevin D. Jones on a publicly available website: http://www.aa.nps.navy.mil/˜jones/online_tools/panel2/;  
         [0103]      FIG. 14  is a like diagram, together with data, of another foil on another such site, http://www.ae.uiuc.edu/m-selig/ads/coord_database.html;  
         [0104]      FIG. 15  is a perspective or isometric right-side view of a complete, constructed preferred embodiment according to  FIGS. 1 through 3 ; and  
         [0105]      FIG. 16  is a like front view of the same embodiment.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0106]     Preferred embodiments  20  ( FIGS. 1 through 4 , and  15  and  16 ) of my invention carry sensors  30  across a flowing body of water  10  (river or other stream) and back without using any artificially generated propulsive power (as in an electrical motor or combustion engine). The device is operated and controlled by an operator  40 , at only one side  11 ′ of the water body, by means of a tether or tethers  26 .  
         [0107]     The device utilizes the downstream movement  12  of the water to generate the horizontal force necessary to move the device across the water, i.e. between the shores  11 . The tethers  26  are preferably quite light, floatable ropes, to minimize the weight that must be borne by both the operator  40  and the waterborne apparatus  20 .  
         [0108]     My invention allows a single operator  40  on one shore  11 ′ to move the instrumentation  30  across the water and back—without wading, using a towing vessel (or any other vessel), having access to the opposite shore  11 ″, or using artificially generated power. Preferred embodiments include a platform  21 , tethered to a fixture or person  28  on the near shore  11 ′.  
         [0109]     The instrumentation packet  30  is carried in a well  29  in the platform  21 —in this case, in the center of the main hull. The platform has wing- or foil-section members  22 ,  23  mounted vertically, extending downward into the water.  
         [0110]     These members are “actively” (as defined earlier) propelled by the substantially horizontal force  13  of the relative motion  12  of the water, in a direction that moves the platform across the body of water. Under some circumstances the force  13  is not accurately horizontal; but to the extent this force has a very significant vertical component, as noted below that component is an undesired effect which is to be avoided.  
         [0111]     The platform is set in the water adjacent to the near shore  11 ′. The downstream flow  12  across the foil members  22 ,  23  creates the active force  13  away from the near shore.  
         [0112]     The amount of force is adjusted by the angle of attack of each foil section. This is controlled most straightforwardly by varying the orientation in the water of the entire assemblage  20 .  
         [0113]     The operator  40 , in turn, accomplishes this varying of the orientation through varying the tension on the two tethers  26 —in a very intuitive and instinctive way. When the platform reaches the far shore  11 ″, the operator reduces the angle of attack and pulls the platform back across the water by the tethers.  
         [0114]     As will shortly become clear to those skilled in this field, many other control mechanisms and techniques (not shown) can be added to or substituted for (or combinations of these), the simple approach just described. The overall choices within the scope of my invention, including the basic approach already set forth, can include, for example and without limitation: 
    1. control system—
        a. two tether lines  26 ;     b. two lines  26  plus rudder/flap control;     c. bar with single reel set (reel in middle, lines running outward to end of pole and through eyes to platform  21 );     d. single line with radio-controlled bridle reel(s) on platform;     e. handheld reels;     f. reels attached to the shore  11  or structure on the shore, or in the water;     g. automated reels (constant tension);     h. separate rudder(s), flap(s) or foil(s) for steering;     i. other tether eye locations  27  on platform  21  to change angle of attack;     j. radio or other remote control of rudders, flaps or reels;     k. radio or other remote control of location of tether fixtures on platform;     l. combination of remote control and tether;     m. adjustable foils for different flow rates; and     n. interchangeable foils for different flow rates;    
        2. hulls—
        a. main hull  21  with foil outriggers  22 ,  23 ;     b. hull  121  ( FIGS. 5 and 6 ) with single or multiple foil shapes  122 ,  222  ( FIGS. 7 through 10 ) for active horizontal force or control;     c. planing or displacement hulls;     d. hulls themselves have foil-like plan section;     e. invertible foil-shaped hulls for lift in both directions of flow; and     f. detachable foil sections for lift in both directions. Other principles and variations (some included in the above listing) are discussed next.    
       
 
         [0137]     Through extensive trial-and-error testing I have learned that in higher flows, neither foil-shaped hulls nor volume-displacing hollow hulls work at all well. In relatively rapid flows (most typically above 1½ m/sec, 5 ft./sec) the rear is submerged due to hydrodynamic forces.  
         [0138]     The above-discussed trimaran with two active foil hulls, although thoroughly satisfactory in low-speed flows, in particular suffers from this drawback. In high-speed flows, both foils tend to immerse aft. This makes them less effective and also very undesirably changes the inclination of the instrument package—as some sensors should be pointing in specific directions e.g. straight downward.  
         [0139]     This difficulty is greatly mitigated by a planing surface that keeps the assembly horizontal in transverse and longitudinal senses. Such a solution will be discussed shortly.  
         [0140]     On the other hand, foils are effective at higher angles of attack than planar vanes. Foils also provide smoother control because they don&#39;t stall as readily as vanes.  
         [0141]     Therefore a much better solution for relatively rapid flows is a single planing hull  121  ( FIGS. 5 through 10 ) with flat bottom aft, and with one or more foil-shaped appendages  122  ( FIG. 6 ),  222  ( FIGS. 7 through 10 ). Even the relatively higher flows under discussion here are almost always much lower than flow rates in the swift water-rescue field.  
         [0142]     With such a single planing hull  121 ,  221 , I provide tethers  126 ,  226  to attachment points  127 ,  227  generally as described earlier. As noted in the above listing, the two tethers  26 ,  126  etc. advantageously can be replaced by a single tether supplemented by a remote-transmission control system—radio-, infrared-, acoustic-controlled or the like.  
         [0143]     In such single-tether arrangements the tether simply prevents the assembly from floating off downstream, while the remote-control system maintains desired attitude of the assembly to the flow direction, so as to provide optimum horizontal active force at each point in the traverse. This convenient variability is particularly desirable because the flow rate, depth and other conditions vary as the assembly moves to different points in the stream crossing. It will be clear to those of ordinary skill in this field, however, that the attitude control can instead be provided by a second tether.  
         [0144]     Nevertheless my embodiment first described above—a catamaran or trimaran with volume-displacing hull  21  ( FIGS. 1 through 4 )—is entirely adequate for lower flow rates. As mentioned in the listing above, interchangeable or adjustable foils are very useful for adapting the overall assembly to different flow rates.  
         [0145]     Throughout the present document it is to be understood that the apparatus  20  etc., with its foils, is essentially stationary. Thus the speed of water relative to the foils is almost always approximately equal to the speeds of the water down the streambed.  
         [0146]     Below are ranges of dimensions which are typical of hydrological sensor platforms, according to the invention, that I have built and have found satisfactory. It will be clear that these values are merely representative or exemplary, not intended to limit the scope of my invention:  
                                                                                               parameter (cm)            structural   overall length   overall width   depth            feature   range   typical   range   typical   range   typical               overall   60-300   120    45-180   60-90   —   —       apparatus       foil   60-240   90-120   2.5-25     5-10   7.5-50   5-10                  
 
 As noted earlier, dimensions of preferred embodiments—including those of the platform, the foils, and the flaps—vary in dependence upon the size and weight of the hydrological instruments to be carried. 
 
         [0147]     As suggested above, two or even multiple foils can be mounted to a single platform. If the foils are spaced apart adequately, the amount of force generated can be accordingly a multiple of that provided by a single foil—and the stream-crossing distance thus increased very markedly, as for example even to 100 m and beyond.  
         [0148]     For such a multifoil configuration, individual adjustment of attack angle for each foil can be quite important to optimizing the overall force for the entire assembly. Accordingly corresponding multichannel remote control is advisable.  
         [0149]     In the tri- or catamaran embodiments, and also in some downward-depending-foil geometries, for some applications a significant improvement can be achieved by using only one foil  22 ,  222 —on the far side of the assembly  20 . Accordingly  FIGS. 1 through 4 , and  7  through  10 , are to be also understood as representing such an asymmetrical monofoil format.  
         [0150]     This configuration reduces flow interference around the instrumental transducers. Any flow disturbance around the instruments may bias, in particular, the measurement of velocity.  
         [0151]     Some hydrological instrument packages also include devices that transmit acoustic probe beams and detect the beams reflected from natural features, for analysis. In these cases it is critical to place the foils far enough from the propagating acoustic beams.  
         [0152]     Some instrument packages have three or four such transmitted probe beams that point obliquely downward and outward. Therefore the taller (or deeper) the foils, the wider the overall assembly must be to avoid intersection of the beams and foils.  
         [0153]     Foil selection or design—The preferred embodiments of my invention employ wing-shaped foil sections which provide horizontal “active” force, as specifically defined and explained above, which is called “lift” (by analogy, as previously mentioned, with aircraft). This active force is generated by interaction of the foil surfaces with water flow of the stream, and moves the vessel strongly across the stream.  
         [0154]     Most air- and hydrofoil shapes are not symmetrical; instead they have one rather strongly curved, convex so-called “camber” face  351  ( FIG. 11 ),  51  ( FIGS. 1 through 3 ),  151  ( FIG. 6 ),  251  ( FIGS. 7 through 9 ). Such foils also have an opposite, less strongly curved—but still sometimes convex—“chord” face  352  ( FIG. 11 ). The latter in some cases is almost straight, but in many other foil surfaces  52 ,  152 ,  252  actually is concave.  
         [0155]     It is in the interplay between these two different surfaces  351 ,  352  and the water flow against and around them that “active” forces develop. They are key to understanding my invention.  
         [0156]     I am not expert in aeronautical engineering or science, which is a different field from that of the present invention. I have learned, however, that development of these active forces in water is rather similar to that in air—allowing for the extremely great differences in density, viscosity, speed and of course compressibility between the two fluids.  
         [0157]     Hence it is practical, in designing or selecting foil shapes for my horizontal active force generation in water, to begin with foil shapes that have originated in the distinct field of aerodynamics. It is extremely beneficial to know this fact, because many such aerodynamic shapes are known and analyzed in formats that are available not only publicly but also gratis.  
         [0158]     Publicly available design data—In fact as will be seen there are actually catalogs of foil shapes with lift and drag coefficients (see following subsection). These are available online, i.e. through the Internet, as well as in conventional books and technical periodicals.  
         [0159]     I have been pleasantly surprised to learn that it is not necessary to have a theoretical or deep understanding of the active properties of foils. Rather, in my own experience, only a certain amount of thoughtful experimentation with some of the disclosed shapes is sufficient to develop an adequate feeling for optimum selection—and sometimes modification. This kind of technique is well within the capabilities of a person of ordinary skill in this field.  
         [0160]     I have explored use of a few different shapes; I try to maximize the lift and minimize drag for given speed and length. Values in the catalogs as developed theoretically are a fair approximation of actual values.  
         [0161]     Many such foils are in databases developed by universities. Here are two such websites that are currently operating: 
        http://www.aa.nps.navy.mil/˜jones/online_tools/panel2/     http://www.ae.uiuc.edu/m-selig/ads/coord_database.html 
 
 Additionally, a catalog of NACA foils (NACA is the precursor to NASA) is presented by Abbott and Von Doenhoff, Theory of Wing Sections (McGraw-Hill 1949). 
       
 
         [0164]     Actually after some empirical experience it is possible to simply make up foil shapes. The sites I use are just tools to find some that are particularly useful.  
         [0165]     The above-mentioned “jones” site, very generously provided by Professor Kevin Jones, is a computational site that calculates flows for many foil shapes. These are not unique calculations. Following is Jones&#39;s own description of the assumptions he makes to do his calculations: 
        “Potential Flow: The study of how a gas or fluid flows is called Fluid Dynamics. The Navier-Stokes equations, derived independently by Navier in France in 1827, and by Stokes in England in 1845, describe this motion, but except for a handful of fairly simple problems, the equations cannot be solved exactly. Instead, the equations must be solved approximately using numerical methods, and this we refer to as Computational Fluid Dynamics (CFD).     “Unfortunately, even with the vast power available with today&#39;s computers, for problems of interest the full Navier-Stokes equations are still too expensive to solve numerically. Consequently, based on the problem of interest, various assumptions are usually made that allow us to simplify the governing equations by dropping terms that we think will be negligible. For example, if we&#39;re interested in computing the flow about a high aspect-ratio (aspect ratio is the wing-span divided by the chord or width), nonswept wing at a constant attitude and speed, we make the assumptions that the flow is two-dimensional (2D) (i.e., there is no flow in the span-wise direction) and steady-state (the solution does not vary in time). Also, if we assume that the wing is not traveling too fast, say less than about ⅓ the speed of sound, then we can assume that the air is incompressible, meaning that the air density has a constant value. Additionally, we may also make the assumption that the flow is inviscid, although this assumption may come back to bite us, as we&#39;ll see later.     “OK, so these are the assumptions we&#39;ve made; the flow is steady, 2D, incompressible and inviscid. If we also state that the flow is irrotational (we&#39;ll get into what this means later), then we have a potential flow. I won&#39;t get into all the details of what this means, but basically it means it&#39;s a lossless system. This means that our code should predict zero drag for our wing, and we can use this to check the accuracy of our code.”       
 
         [0169]     I present in this document a foil solution ( FIG. 18 ) that was generated by the Kevin Jones “panel solver”. It is just a sample that demonstrates what result I get by using his website: it is a picture of the foil cross-section, with certain parameters displayed below, from which I can judge the foil suitability from a buoyancy/mechanical standpoint, and knowing a lift coefficient at a given angle of attack.  
         [0170]     The other site mentioned above, the UIUC site, is a catalog of foil shapes. These are foil shapes developed by governments, corporations and individuals over the last sixty years.  
         [0171]     Some of these are of special historical interest—and, among these, certain shapes are particularly inefficient or weak. Others are just particular engineers&#39; ideas of what foil shapes might be useful.  
         [0172]     I present one of these UIUC shapes, too, in this document ( FIG. 19 ). There is an infinite number of such shapes, since anyone can generate them. There&#39;s nothing magic about these; until fully analyzed and evaluated, they are just shapes.  
         [0173]     Flaps—I want to use a flap  428  ( FIG. 12 ) because any given foil is most efficient at a certain range of speeds. As I  perturb  the foil shape with a flap, the range of effective speeds changes—with out  the need for actually revising the basic shape  422 ,  451  of the foil itself.  
         [0174]     For purposes of my invention, the primary use of a flap is to change the effective foil shape, i.e. camber. Extending the chord length of the foil is secondary and probably much more difficult.  
         [0175]     Very generally, low speeds need more curvature and a longer chord (the distance from the leading edge to the trailing edge of the foil). Making the chord length of the basic foil adjustable is mechanically complex, and I probably would not try to do that in one of my own production platforms.  
         [0176]     Deflecting a flap, however, is instead very simple, and easily done with any one of a great varieties of elementary mechanisms. As suggested earlier, control of flaps—if not manually preset on shore—can be effectuated through additional tether controls, radio, etc.  
         [0177]     Control of the amount of active force can thus be provided using another control line or any of these remote-control technologies for flaps on the foils, to  change the effective camber . This enables development of active horizontal drive force over a wide range of flows—and in particular, as noted earlier, a wide range of angles of attack. This makes the foil and attached platform easier to control.  
         [0178]     Once again, control of cross-stream speed is critical to surface water hydrology. The foil and flap design should proceed with the specific objective of moving the instruments across the water surface at a controlled, slow speed, yet one that expedites the data-collecting work to be done.  
         [0179]     At low flows, the foil and flap considered together amount to a strongly cambered foil ( FIG. 12 ). Active cross-stream force and drag are optimized for low flow.  
         [0180]     At high flows, the operator (or an automatic system) fold the flap back toward or even within the contour of the foil itself, so that the foil and flap as a unit are made to flatten out. This optimizes the active-force vs. drag for this flow situation, very much as if the flap were absent and the configuration were that of a simple foil ( FIG. 11 ).  
         [0181]     The flap  428  is oriented at the aft end of the foil, analogously to a rudder on a sailboat. Typically the flap has a vertical shaft, like a rudderpost, about which it rotates; however, a cardan hinge or other rotational provision may be substituted.  
         [0182]     Advantageously the flap is spring-loaded so that it is normally in the low-speed position ( FIG. 11 ). At higher speed, the operator (or automatic mechanism) pulls on the third tether, which is connected to a rudder arm on the vertical shaft (or the like) that enables the flap to rotate. This action straightens the flap into the “airfoil” shape which is more suited to higher speed.  
         [0183]     The stronger forces—at low flow rates—thus provided by flaps have significant beneficial effects. Among these benefits, if suitably exploited, are potentially greater speed across the stream (and possibly back as well), but also more-sensitive control and better stability, and combinations of these.  
         [0184]     For some special environments it is also possible to tune the spring on the flap, so that the flap straightens itself out when the flow is high enough to, essentially, push the flap aside. The flap can also be made to rotate, and translate aft in addition to rotating. Such a mechanism, however, is susceptible to overcomplexity—or tends to catch flotsam, or both.  
         [0185]     A first step in introducing these beneficial effects, for purposes of my invention, is to add a flap with rudder post or other hinge member to the end of the foil. Either the foil can be cut into two parts, or the end of the foil can be faired (smoothed, for less flow resistance) and a separate foil section provided as the flap.  
         [0186]     It is helpful to search aeronautical texts for typical flap chord lengths, and experiment with different angles of attack for the flap at low flow speeds. If this does not give enough lift at low speed, a longer-chord flap can be substituted.  
         [0187]     It should be possible to find a combination of flap length and angle that extends the usefulness of the foil down to 0.2 m/s. Then, if the active horizontal force remains inadequate at low speeds, a linkage can be provided that allows the flap to translate aft and inward (toward the operator) to create more lift at low speeds.  
         [0188]     In this way, controllable active-force surfaces (flaps) can be provided to develop appropriate force at a variety of flow speeds. I see an analogy to aircraft operation: more flap angle (or possibly larger area) for landing and takeoff corresponds to my low-flow operation.  
         [0189]     On the other hand, little flap (low angle or small area) for aircraft cruising corresponds to my high-speed operation. This is quite important because of the wide range of flow speeds we encounter.  
         [0190]     Quantitative considerations—Following is the method I use for designing the foils and flaps. I have chosen 40 cm as the maximum foil depth because the system must work in very shallow water. I want the system to work in flows from 0.2 to 3 m/s.  
         [0191]     Next I choose a foil section that provides good horizontal active force at the necessary top speed. For this purpose, by “good” force I mean enough to pull at least 30 m (and preferably up to 100 m and more) of tethers across a stream.  
         [0192]     I use Professor Kevin Jones&#39;s foil generator to maximize force coefficient (in his analyses this is called the “lift” coefficient). I know that I need relatively little buoyancy, so I want a fairly flat foil (in Jones&#39;s analyses often called a “wing”). This may also help keep drag down at flows above 2 m/s.  
         [0193]     The foil must be easy to machine or cast, e.g. not too thin at the trailing edge. I can judge this too from the Jones site.  
         [0194]     Then I download the coordinates from the UIUC site and calculate buoyancy. If I plan to use  two  foils, each 40 cm deep by 1 m long, then each of the foils must support half of the system—with the main hull(s) slightly immersed.  
         [0195]     An ideal foil length is 1 m because my platforms are ideally shorter than 1.2 m. Platforms of this size can be readily transported in ordinary automobiles or other vehicles commonly used by hydrologists.  
         [0196]     My experience has shown that I may not have enough active horizontal force at low speeds. Therefore after I find the ideal combination of active force (“lift”), drag, and buoyancy for high speed, I try the design at low speed. If I can pull the tethers over 30 m, I consider the design satisfactory and complete.  
         [0197]     It will be understood that the foregoing disclosure is intended to be merely exemplary, and not to limit the scope of the invention—which is to be determined by reference to the appended claims.