Low-drag hydrodynamic surfaces

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system, and at least one strut having an upper end and a lower end, the upper end attached to the at least one hull and the lower end attached to a fully-submerged dynamically-lifting hydrofoil, the hydrofoil comprising a substantially continuous upper surface, a substantially continuous lower surface, a leading edge, a trailing edge, a wetted nose section on the lower surface that extends from the leading edge rearward to a spanwise lower discontinuity for causing a lower boundary layer to separate from the lower surface for forming a lower cavity rearward extending along the lower surface, wherein the nose section comprises an upper surface discontinuity for causing an upper water boundary layer to separate from the upper surface of the hydrofoil for forming an upper cavity rearward extending along the upper surface, at least one gas source, a gas releaser on each surface of the hydrofoil behind each discontinuity for forming the cavities that extend rearward, and a gas flow restrictor communicating with each gas flow releaser for ensuring that each cavity closes ahead of the trailing edge.

A body comprising a low-drag surface-piercing elongated body having opposite sides and a symmetrical and essentially-continuous surface on each side, a leading edge, a trailing edge, an upper body region, a lower body region, an upper discontinuity for separating a water boundary layer near the leading edge in the upper region for forming a rearward-extending air-filled upper cavity on each side that is open to the atmosphere, a lower discontinuity for separating a water boundary layer near the leading edge in the lower region for forming a closed rearward-extending air-filled lower cavity that covers a majority of the surface in the lower region on each side, at least one generally horizontal fence for isolating the lower and upper regions, an air supply connected to the lower cavities, and an airflow restrictor for limiting airflow rate into the lower cavities for ensuring that the lower cavities close ahead of the trailing edge.

A hull comprising an elongated low-drag hull having opposite sides, a propulsion system connected to the hull, a symmetrical and essentially-continuous side surface on each of the opposite sides, a leading edge, a trailing edge, a bottom surface, at least one source of pressurized air, multiple vertically-extending discontinuities lying between the leading edge and the trailing edge on each side surface for separating a water boundary layer and forming rearward-extending cavities open to the atmosphere, wherein at least a portion of the hull lies above the water surface, and further comprising at least one pressurized thin air cavity formed on the bottom surface for reducing frictional drag.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system connected to the hull, at least one strut having an upper end attached to the hull and having a lower end, a fully-submerged dynamically-lifting hydrofoil attached to the lower end, the hydrofoil comprising an essentially continuous upper surface on a top of the hydrofoil and an essentially continuous lower surface on a bottom of the hydrofoil, wherein the upper and lower surfaces have a common leading edge and a common trailing edge, wherein the leading edge is swept at least 45 degrees forward or aft, at least one propulsion drive shaft connected to the propulsion system and located within the at least one strut, at least one essentially horizontal drive shaft connected to at least one propeller attached to at least one end of the at least one horizontal drive shaft.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system connected to the hull, and at least one strut having an upper end attached to the hull and having a lower end, a fully-submerged dynamically-lifting hydrofoil attached to the lower end, the hydrofoil comprising an essentially continuous upper surface on a top of the hydrofoil and an essentially continuous lower surface on a bottom of the hydrofoil, wherein the hydrofoil surfaces have a common leading edge and a common trailing edge, wherein the leading edge of the hydrofoil is swept forward or aft at least 45 degrees, and wherein the propulsion system comprises at least one propulsion drive shaft connected to at least one propeller.

Apparatus for reducing drag comprising an essentially continuous underwater surface, a trailing edge of the surface, at least one discontinuity on the surface angled to water flow along the surface for separating a water boundary layer from the surface, at least one gas source, a gas releaser behind the discontinuity for forming a cavity that extends rearward on the surface from the discontinuity, a gas flow limiter connected to the gas releaser for limiting gas flow into the cavity for ensuring that the cavity closes ahead of a trailing edge of the surface without gas being artificially withdrawn from the cavity, wherein the surface is shaped in a desired cavity termination region for a minimum of a cavity contact angle, wherein at least a portion of the surface that lies behind the desired cavity termination region is shaped for increasing the cavity contact angle in case the cavity extends beyond the desired termination region.

The method of reducing drag on an essentially continuous underwater surface comprising providing a surface discontinuity on the surface that is angled to water flow along the surface, separating a water boundary layer from the surface, providing at least one gas source, releasing gas behind the discontinuity, forming a cavity, extending the cavity rearward from the discontinuity, limiting gas flow rate into the cavity, ensuring that the cavity closes ahead of a trailing edge of the surface without gas being artificially withdrawn from the cavity, wherein providing the discontinuity comprises providing and angling the plate about 90 degrees to the surface.

The method of closing a gas cavity comprising providing a moving underwater surface, providing gas to the surface, forming a gas cavity on the surface, providing a cross section of the surface transverse to water flow over the surface, providing a desired cavity closure in a cavity closure region, providing a series of substantially symmetrical saw-tooth shapes on the surface in a cross section of the cavity closure region for directing splash sideward and rearward, and for reducing disturbances and drag at the cavity closure due to splash, wherein the saw-tooth shapes comprise contiguous v-shapes or u-shapes.

The method for reducing drag on a hydrofoil comprising providing a hydrofoil, providing an essentially continuous upper surface on a top of the hydrofoil, providing an essentially continuous lower surface on a bottom of the hydrofoil, joining the surfaces at a common leading edge and at a common trailing edge, providing a discontinuity, extending the discontinuity at least partially in a spanwise direction on at least one of the surfaces near the leading edge, separating a water boundary layer from the at least one of the surfaces, providing at least one gas source, releasing gas behind the discontinuity, forming a gas cavity, extending the gas cavity rearward from the discontinuity, limiting gas flow rate into the cavity, closing the cavity ahead of the trailing edge, shaping the at least one of the surfaces in a desired cavity termination region for a minimum cavity contact angle, providing at least a portion of the at least one of the surfaces that lies behind the desired cavity termination region with a shape for increasing the cavity contact angle in case the cavity extends beyond the desired termination region.

The method of reducing drag on a hydrofoil comprising providing an essentially continuous upper surface on a top of the hydrofoil, providing an essentially continuous lower surface on a bottom of the hydrofoil, providing the surfaces with a common leading edge and a common trailing edge, providing a spanwise discontinuity in each surface near the leading edge, causing local boundary layer, separating water flow from the surfaces, providing the lower surface with a spanwise nose section wherein the nose section provides the leading edge and provides the discontinuity on the upper surface of the hydrofoil, and providing a aft edge of the nose section which provides the discontinuity on the lower surface, providing at least one gas source, releasing gas behind the discontinuity on each surface forming cavities on the surfaces, extending the cavities rearward from the discontinuities, limiting gas flow rate into at least one cavity to ensure that it closes ahead of the trailing edge.

The method of supplying gas into a gas cavity on a hydrofoil surface, comprising providing a lifting hydrofoil, providing a gas cavity on the hydrofoil, providing a gas source, flowing gas from the gas source through a spanwise duct in a strut that is attached to a hydrofoil, through at least one opening in the hydrofoil in a strut attachment region into a spanwise duct in the hydrofoil, and through at least one other opening in the hydrofoil into the cavity.

A hydrofoil method comprising supplying gas into gas cavities on the upper and lower surfaces of a hydrofoil, by flowing the gas from multiple gas sources through multiple spanwise ducts in at least one strut that is attached to the hydrofoil, through multiple openings in the hydrofoil at strut attachment regions into multiple spanwise ducts in the hydrofoil, and through multiple openings in the hydrofoil into the cavities.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system, at least one strut having an upper end attached to a hull and having a lower end, a fully-submerged dynamically-lifting hydrofoil attached to the lower end, an essentially continuous upper surface on a top of the hydrofoil and an essentially continuous lower surface on a bottom of the hydrofoil, wherein the surfaces have a common leading edge and a common trailing edge, further comprising a spanwise discontinuity on at least one of the surfaces near the leading edge for causing a local water boundary layer to separate, at least one gas source, a gas releaser behind the discontinuity for forming a cavity that extends rearward, a gas flow limiter for limiting a gas flow rate into the cavity for ensuring that the cavity closes ahead of the trailing edge, wherein most of the surface of the hydrofoil on the cavity side lies within the cavity, and wherein the hydrofoil craft further comprises a bow lifter positioned near a front of the craft for stabilizing the craft in at least heave and pitch.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system, at least one strut having an upper end attached to a hull having a lower end, a fully-submerged dynamically-lifting v-hydrofoil in plan view attached to the lower end, the v-hydrofoil having leading edges swept at least 45 degrees, the craft further comprising a bow lifter positioned near a front of the craft for dynamically stabilizing the craft in at least heave and pitch.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system, a dynamically-lifting hydrofoil for helping to lift at least most of a weight of the craft, the lifting hydrofoil comprising an essentially continuous upper surface on a top of the hydrofoil and an essentially continuous lower surface on a bottom of the hydrofoil, wherein the surfaces have a common leading edge and a common trailing edge, further comprising a spanwise discontinuity on at least a portion of at least one surface near the leading edge for causing a local water boundary layer to separate, at least one gas source, a gas releaser behind the discontinuity for forming a cavity that extends rearward, a gas flow limiter for limiting a gas flow rate into the cavity for ensuring that the cavity closes ahead of the trailing edge, an angled upward tip region at each end of the lifting hydrofoil for piercing a water surface and for attaching to the one or more above-water hulls.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system, a dynamically-lifting hydrofoil for helping to lift at least most of the weight of the craft, the hydrofoil comprising an essentially continuous upper surface on a top of the hydrofoil and an essentially continuous lower surface on a bottom of the hydrofoil, wherein the surfaces have a common leading edge and a common trailing edge, a spanwise discontinuity on at least a portion of at least one of the surfaces near the leading edge for causing a local water boundary layer to separate, at least one gas source, a gas releaser behind the discontinuity for forming a cavity that extends rearward, a gas flow limiter connected to the gas releaser for limiting a gas flow rate into the cavity for ensuring that the cavity closes ahead of the trailing edge, a hydrofoil tip on each side of the hydrofoil, a strut attached inboard of a hydrofoil tip on each side for connecting the hydrofoil to the one or more hulls, wherein each strut is angled from vertical, and wherein each strut provides lift for dynamically stabilizing the craft in roll.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system, a dynamically-lifting hydrofoil for helping to lift part of the weight of the craft, the hydrofoil comprising an essentially continuous upper surface on a top of the hydrofoil and an essentially continuous lower surface on a bottom of the hydrofoil, wherein the surfaces have a common leading edge and a common trailing edge, a spanwise discontinuity on at least a portion of at least one of the surfaces near the leading edge for causing a local water boundary layer to separate, at least one gas source, a gas releaser behind the discontinuity for forming a cavity that extends rearward, a gas flow limiter connected to the gas releaser for limiting a gas flow rate into the cavity for ensuring that the cavity closes ahead of the trailing edge, wherein an above-water portion of the craft provides aerodynamic lift and makes use of water proximity for further increasing the aerodynamic lift by using a surface effect.

A hydrofoil craft comprising at least one hull that lies at least mostly above water, a propulsion system, and at least one strut whose upper end is attached to the at least one hull and whose lower end is attached to a fully-submerged hydrofoil, the hydrofoil further comprising a leading edge and a trailing edge, a substantially continuous upper surface and a substantially continuous lower surface, a spanwise discontinuity in the lower surface near the leading edge for causing a local water boundary layer to separate from the surface, at least one gas source, a gas releaser behind the discontinuity for forming a lower cavity that extends rearward beyond the trailing edge on the lower surface, and further comprising a cavity on each side of the at least one strut.