A human propelled watercraft having a pair of flexible fins supported by a mast extending into the water each adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of said watercraft. Pedals are provided for applying input force whereby as input force is applied, the flexible fins can twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along the arcuate path. Each of the fins preferably is composed of a layer of stiff and durable material that is wrapped around the mast. The two layers of material touch at the trailing edge and they are free to slide relative to each other. Preferably, each of the fins is provided with adjustable tensioning at the tip of the mast.

A human propelled watercraft having a pair of flexible fins supported by a mast extending into the water each adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of said watercraft. Pedals are provided for applying input force whereby as input force is applied, the flexible fins can twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along the arcuate path. Each of the fins preferably is composed of a layer of stiff and durable material that is wrapped around the mast. The two layers of material touch at the trailing edge and they are free to slide relative to each other. Preferably, each of the fins is provided with adjustable tensioning at the tip of the mast.

A propellable aquatic board includes a main body that is at least partially buoyant. The propellable aquatic board also includes a flexible member secured to the main body by a fastener. The flexible member extends away from the main body in a longitudinal direction. The flexible member is configured to selectively deflect to propel the aquatic board through water.

A propellable aquatic board includes a main body that is at least partially buoyant. The propellable aquatic board also includes a flexible member secured to the main body by a fastener. The flexible member extends away from the main body in a longitudinal direction. The flexible member is configured to selectively deflect to propel the aquatic board through water.

An underwater robotic device includes a housing unit, a control unit and a propelling unit. The housing unit includes a base seat and an upper cover in liquid-tight engagement with the base seat. The control unit is disposed within the housing unit and includes a circuit module and a center-of-gravity transferring module which is electronically connected with the circuit module. The center-of-gravity transferring module has a movable weight member and a transfer driving mechanism which drives movement of the weight member so as to vary a position of a center of gravity of the underwater robotic device and to control downward and upward moving directions of the underwater robotic device in the water. The propelling unit is connected with the housing unit and is electronically connected with the control unit to produce a propelling force to move the underwater robotic device forward in the water.

An underwater robotic device includes a housing unit, a control unit and a propelling unit. The housing unit includes a base seat and an upper cover in liquid-tight engagement with the base seat. The control unit is disposed within the housing unit and includes a circuit module and a center-of-gravity transferring module which is electronically connected with the circuit module. The center-of-gravity transferring module has a movable weight member and a transfer driving mechanism which drives movement of the weight member so as to vary a position of a center of gravity of the underwater robotic device and to control downward and upward moving directions of the underwater robotic device in the water. The propelling unit is connected with the housing unit and is electronically connected with the control unit to produce a propelling force to move the underwater robotic device forward in the water.

A system for controlling movements of a marine surface vessel includes a hull, a bow and a stern. A control unit being controls movements of one or more fins, which control movements of the vessel, in dependence on signals from a position input device, and on signals from a position detecting device. The fin(s) is connected to a respective actuator via a rotation shaft adapted to protrude from the vessel hull, wherein the rotation shaft defines a rotational axis of the fin. Each fin comprises a fin base adapted to be at a first distance from the hull, and a fin tip adapted to be at a second distance from the hull, which second distance is larger than the first distance, wherein a leading edge of the fin, and a trailing edge of the fin extend on opposite sides of the fin, from the fin base to the fin tip.

A system for controlling movements of a marine surface vessel includes a hull, a bow and a stern. A control unit being controls movements of one or more fins, which control movements of the vessel, in dependence on signals from a position input device, and on signals from a position detecting device. The fin(s) is connected to a respective actuator via a rotation shaft adapted to protrude from the vessel hull, wherein the rotation shaft defines a rotational axis of the fin. Each fin comprises a fin base adapted to be at a first distance from the hull, and a fin tip adapted to be at a second distance from the hull, which second distance is larger than the first distance, wherein a leading edge of the fin, and a trailing edge of the fin extend on opposite sides of the fin, from the fin base to the fin tip.

A watercraft propulsion system includes a shaft slidably disposed through an opening formed in a hull, a pull-up cable coupled to the shaft at a predetermined location of the shaft for pulling the shaft upward, a pull-down cable coupled to the shaft at the predetermined location of the shaft for pulling the shaft downward, a fluke disposed beneath a bottom of the watercraft, the fluke having a front portion and a horizontal plate behind the front portion, the front portion being solely and removably attached to a lower end of the shaft, wherein when the shaft is pulled downward by the pull-down cable, the horizontal plate tilts upward, and when the shaft is pulled upward by the pull-up cable, the horizontal plate tilts downward.

A watercraft propulsion system includes a shaft slidably disposed through an opening formed in a hull, a pull-up cable coupled to the shaft at a predetermined location of the shaft for pulling the shaft upward, a pull-down cable coupled to the shaft at the predetermined location of the shaft for pulling the shaft downward, a fluke disposed beneath a bottom of the watercraft, the fluke having a front portion and a horizontal plate behind the front portion, the front portion being solely and removably attached to a lower end of the shaft, wherein when the shaft is pulled downward by the pull-down cable, the horizontal plate tilts upward, and when the shaft is pulled upward by the pull-up cable, the horizontal plate tilts downward.