Catamaran Drone

The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The invention relates generally to unmanned water surface craft. In particular, the invention relates to low-cost catamaran drone vessels to support sundry operations that require a floating platform.

Threats presented by fast attack craft (FAC) and fast inshore attack craft (FIAC) pose challenges for maritime vessels, including combat ships of modern blue-water navies. An inexpensive powered floating platform would be beneficial for simulating such an attack craft.

Conventional unmanned surface vessels yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, various exemplary embodiments provide a drone catamaran having both length and beam for carrying a platform. The catamaran includes a hull, a bridge, a pair of rails, a pair of pontoons, a waterproof package, a seat, and first and second pairs of elbow flanges. The hull is composed of an open plurality of ribs disposed along the length that extend below and across the beam. The bridge supports the platform and comprises a plurality of struts disposed along the length. Each strut extends laterally beyond the beam.

The pair of rails connects to corresponding port and starboard ends of the struts. The pontoons provide buoyancy. Each pontoon affixes to a corresponding rail. The waterproof contains control, guidance and propulsion equipment. The seat supports the package, and comprises a plurality of slats distributed along the length. The first pair of flanges affixes to the bridge and in particular the struts. The second pair of flanges supports the seat. The struts, ribs, rails, flanges and slats are composed non-corrosive metal. Other various embodiments alternatively or additionally provide for a ballast canister disposed along the ribs below the seat.

In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

The disclosure generally employs quantity units with the following abbreviations: length in meters (m) or feet (ft), mass in grams (g) or pounds-mass (lb), time in seconds (s), angles in degrees (°) and force in newtons (N) or pounds-force (lb). Supplemental measures can be derived from these, such as density in grams-per-cubic-centimeters (g/cm), moment of inertia in kilogram-square-meters (kg-m) and the like.

Historically, the U.S. Navy has used traditional hull vessels as target assets for testing purposes. Traditional in this case refers to a watertight hull design that penetrates from above the waterline to some depth (draft) below the waterline. These vessels may be modified to accept a remote control kit (human operated) or an autonomy kit (algorithmically controlled). The autonomy kits are typically owned by private companies and the cost of these kits is high. Moreover, the traditional vessels can be expensive to repair or replace when severely damaged.

The primary issue with these vehicles is cost, many of which cost over $200 k each. Under the naval doctrine for sailors to “train as they fight”, testing defense against a FAC/FIAC swarm requires five to ten of these vehicles for each live-fire event. In other words, the cost to adequately train Navy crews against this threat is prohibitively high.

Alternatively, a commercial off-the-shelf (CoTS) traditional boat design for test and evaluation restricts the U.S. Navy to an external supply chain, which introduce shortages and delays during production expansion. The exemplary design is readily scalable and can be manufactured by any competent machine shop, and then is simply bolted together. No welding is required in the structure itself.

show respective elevation and isometric viewsof an exemplary first catamaranwith low draft, as depicted from the bow looking aft. A central hullincludes a platform that comprise upper and lower pairs of elbow flangesconnected to each other by underslung ribsdistributed along the length that extend across the beam (between port and starboard), and slatsacross the lower flanges. The ribsare separate and open, such that the volume under the upper flangesis flooded.

A waterproof operations package(shown as a metal box) is supported on the slatsthat form a seat. The packageincludes the control and propulsion systems for the catamaran, as well as communication and/or autonomous guidance equipment. An electric three-bladed propulsive impelleris suspended underneath the packageand within the ribs. The impellercan be powered by an internal motor controlled by the package, both for thrust generation and direction. The packagecan be configured for autonomous operation or alternatively remote control via radio receiver. Alternative appropriate propulsion mechanisms can be used to substitute the impeller. At least one rudder (not shown) can optionally be installed but otherwise unnecessary.

A bridgecomprises lateral box strutsthat extend both port and starboard from the keel beyond the beam's extent. The strutsattach at their ends to a pair of longitudinal rails. The strutsare distributed to openly span along the length. No skin is necessary either between the strutsor the ribs. The upper flangessuspend from the box struts. A float pontoonhangs from each railto provide buoyancy. For a typical configuration, the pontoonscan be approximately eight feet in length and separated by about ten feet, although this can be scaled larger or smaller as designed, such as an order of magnitude in either direction. Such pontoonscan be obtained from CoTS suppliers.

show respective elevation and isometric viewsof an exemplary second catamaranfor high stability. A central hullincludes a platform that comprise upper and lower pairs of elbow flangeconnected to each other by underslung ribsacross the beam, and slatsacross the lower struts, similar to the low draft hull.

The hullincludes a third elbow flangealong the midline keel below the slatsand between the flangesonto which ribsconnect. The flangesupports a ballast canisterto improve roll stability. A set of tabsprovide additional yaw stability when intended for trim, and or thrust vectoring to execute more aggressive maneuvers. In this configuration, the catamaranis about 10 feet wide and about 8 feet long, with a draft of about 5 feet, due to the keel stabilization mechanism. In the embodiments shown, the plurality of strutsand ribsandis three, but this is configuration is exemplary and not limiting.

Similar to the low draft catamaran, the payload packageis supported on the slats. The propulsive impelleris suspended from below the packageand within the ribs. The bridgecomprises box strutswith a pair of railsat the end. The upper flangessuspend from the box struts. Float pontoonshang from the rails.

The bridgecan support a commercially available flat-bottom jon boat bolted thereon. The flanges, ribs, slats, strutsand railsare preferably composed of non-corrosive metal, such as stainless steel or aluminium alloy. The pontoonscan be metal or plastic, depending on function. For subscale surface vehicles, capped polyvinyl-chloride (PVC) pipes can be used to produce the pontoons. The impellercan be pivoted to maneuver the catamaranor, and the number of such impellerscan be increased for increased speed.

Connections between the ribsand the flangesand the slats, as well as strutsand railscan be provided by nuts and bolts, or by riveting, as preferred. Cross-rods can be attached between the ribsand strutsfor additional sheer and twist resistance. The designs for the catamaransandare similar with the primary difference of the respective hullsand.

A 15-foot jon boat was bolted topside onto the bridgeof a prototype example of the catamaranorin order to simulate a FAC/FIAC. A CoTS autonomony kit in the packageand impellerwas integrated onto the hullorto provide motion control. A live-fire 30 mm gun engaged the catamaranorwith the jon boat, demonstrating survivability and usability post-exercise. Typically, the catamaranoror any platform attached onto the bridgewould be unmanned under operation, although personnel can be aboard during water transport, as needed.

The utility of such the exemplary design enables firing ranges to test new weapons and/or train crews without concern over depleting the Navy reserve of traditional high-cost autonomous vessels. Additionally, due to the design of the catamaranor, most of the structure is submerged underwater, thereby protecting the hullorfrom damage; any number of structures can be bolted to the bridgeas the intended target. As an example of cost scale, the proposed structure costs $20 k-$40 k (current dollars), while traditional vehicles cost well over $200 k.

Both exemplary embodiments of the catamaranandas well as similar variations therefrom are comparatively easy to construct. Such low-cost vessel that can use a variety of CoTS bolt-on propulsion mechanism and a CoTS autonomy kit within or extending from the package. As such, cost should be about $20 k-$40 k each, depending on auxiliary equipment and frame scale.

The frame for the bridgeand the hulloris composed of a non-corrosive metal, preferably aluminum, 5052 and 6061. The flanges, ribs, slats, strutsand railsinclude holes drilled along their lengths so as to permit bolting together of the hullor, and the bridge, thereby rendering welding unnecessary. A number of mount points along the frame exist for bolting various components to the catamaranor. Both designs enable a rigid framework using a 500 lbkeel weight for stability that has shown good seaworthiness.

Finite Element Analysis (FEA) has been employed with these designs with 5-foot waves at a 5-second period, which represents an intense sea state. Actual vehicle tests at sea state three have been demonstrated. Other materials conducive to the maritime environment could be used as well (stainless steel for example). However, further FEA would need to be worked in order to guarantee no additional structural component would be needed.

A minimum number of distinct components is required to bolt the vehicle together. This is intentional, and contributes to the low-cost and scalability of the design. For the “high stability” design, there are only nine distinct machined pieces of aluminum/components. There are three bolt sizes used over the entire design, with two different thread pitches. The point here is that mass producing these components will drive the cost of the vehicles down considerably, even compared to the unit costs quoted in this disclosure.

Two exemplary designs of the vessel platform exist: a “low draft” catamaranand “high stability” catamaran, both of which comprise of simple materials: aluminum box-beam, angle, and plate bent into shape. A watertight box for the packageis used to house the motor, autonomy kit, and batteries, although other means of enclosing these components is possible.

Either catamaranorcan also be modified to a trimaran design, whereby a large pontoon float is located along the hull centerline and two enclosures, symmetrically flanking that center pontoon, are used for propulsion, control, etc. The catamaransandcan employ any number of bolt-on autonomy kits, such as ArduPilot or PX4. This is intentional. The vessel is specifically designed to be scalable for testing, and as such must be capable of using a wide array of components.

The design for either catamaranoris scalable. If a larger vessel is required, more structural components can be bolted together, the width increased (by increasing the length of the aluminum box-beams) for better stability, the length increased by merely bolting additional components together longitudinally along the keel. Buoyancy can enhanced by adding pontoonsonto the bridge. The bolt-together design also facilitates a reduced storage footprint: the bridgeand hullorreduce to stacks of structural tubing.

A similar observation can be applied for the system mass, which is far less than a traditional rigid hull boat design. From a maintenance perspective, so long as materials are used that can survive in an aqueous medium (whether fresh or sea), the maintenance of these catamaransandis essentially negligible. Buoyancy can also be modified to accept various add-on payloads. The design can use PVC pipes (in various sizes) or CoTS pontoons, further enabling customization of the vessel's draft. Multiple mount points for these buoyancy generators can be used. Any number of physical characteristics-visual or radar/electromagnetic-can be bolted to the structure to emulate various targets desired for testing.

While pontoon boats are certainly not new, the rib vessel design does appear to be novel. Given the U.S. Navy's long-standing practice of target practice and fire exercise, such a cost-saving development represents a long-standing need. The design itself directly influences the cost of the vessel, which has many advantages as previously mentioned, including maintainability, scalability, seaworthiness, and survivability during live-fire test events. However, given the “bolt together” design, even if a component is damaged, that item can be quickly removed and replaced. This differs significantly from a traditional rigid hull boat, which can either sink or require extensive hull repairs that can exceed the value of the boat itself.

Additionally, the vehicle proposed here enables a new target type to be easily assembled and quickly tested: one simply attaches the intended target to this exemplary catamaranor. Attributes, such as test vehicle speed and maneuverability, simply scale with the bolted on propulsion system the operator prefers to install.

The vessel is intrinsically scalable by adding larger pontoons, increasing the vessel width or length, etc, which increases utility for emulating many different types of targets. Frame components can also be longer and wider, or shorter and narrower, depending on availability of such structural components. Additionally, PVC pipe can be used for flotation instead of CoTS pontoons. This can become a consideration in the event that commercially available pontoons become scarce. Also, such an exemplary vessel can be modified into a trimaran design for high-speed operation.

The market for low-cost, autonomous vessels may be possible, for personal, foreign government, and corporate use. Maritime vessels typically are quite costly due to manufacturing techniques, which exemplary embodiments overcome. Bathymetry, surveying and ecological monitoring constitute investigative endeavors in which exemplary embodiments could be utilized.

While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.