Powerboat

Abstract

A powerboat comprising a hull, a plurality of dynamically adjustable hydrofoils positioned below the waterline towards the rear of the hull, and a control system, wherein the cross sectional area of the hull below the waterline decreases towards the rear of the hull, and the control system is configured to adjust the hydrofoils in operation of the powerboat to control the running trim of the powerboat. The powerboat can operate efficiently at over a wide range of Froude numbers, in particular both low (displacement mode) speeds and high (planing mode) speeds.

Claims

1. A powerboat comprising: a hull; a plurality of dynamically adjustable hydrofoils positioned below the water line towards the rear of the hull; and a control system; wherein the cross-sectional area of the hull below the waterline decreases towards the rear of the hull; and the control system is configured to adjust the hydrofoils in operation of the powerboat to control the running trim of the powerboat; and wherein the hydrofoils are configured to support between 0% and 50% of the weight of the powerboat at its top speed.

2. The powerboat according to claim 1, wherein the hydrofoils are at least one of retractable and movable to a position above the waterline.

3. The powerboat according to claim 2, wherein the hydrofoils are retractable into a recess in the hull.

4. The powerboat according to claim 1, wherein the hydrofoils further comprise a trailing edge flap.

5. The powerboat according to claim 1, further comprising a fixed hydrofoil.

6. The powerboat according to claim 5, wherein the centerline of the fixed hydrofoil is substantially aligned with the centerline of the powerboat.

7. The powerboat according to claim 1 wherein the hydrofoils are positioned aft of the powerboat drive.

8. The powerboat according to claim 1 wherein the hydrofoils are positioned forwards of the powerboat drive.

9. The powerboat according to claim 1 wherein the hydrofoils are positioned both forwards of and aft of the powerboat drive.

10. The powerboat according to claim 1 wherein the hydrofoils are configured to support between 10% and 40% of the weight of the powerboat at top speed.

11. The powerboat according to claim 1 wherein the hydrofoils are configured to support between 15% and 25% of the weight of the powerboat at top speed.

12. The powerboat according to claim 1 wherein the control system is configured to automatically adjust the hydrofoils to at least one of: control the running trim of the powerboat; control at least one of roll and pitch motions of the boat; and reduce and minimize hydrodynamic drag on the hull.

13. The powerboat according to claim 1 wherein the immersed area of the transom at rest is less than 40% of the maximum hull cross-sectional area.

14. The powerboat according to claim 1 wherein the controller comprises a speed sensor and/or attitude sensor.

15. The powerboat according to claim 1 wherein the hydrofoils are positioned in the rear 30% of the length of the hull.

16. The powerboat according to claim 1 wherein each hydrofoil is connected to the hull by one or more struts.

17. The powerboat according to claim 1 wherein a strut connecting the hydrofoil to the hull is used as a rudder.

18. The powerboat according to claim 1 wherein all portions of the bow which are below the design waterline are in line with, or aft of, all portions of the bow which are above the design waterline.

19. The powerboat according to claim 1 wherein the stem of the powerboat is substantially vertical.

20. The powerboat according to claim 1 wherein the longitudinal position of maximum width of the hull is at 70% or less of the distance from bow to stern.

21. The powerboat according to claim 1 wherein a transition from V-shaped hull underwater cross section at the bow to rounded underwater hull cross section occurs by 50% of the distance from bow to stern.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The present invention will now be described by way of example only with reference to the following drawings:

(2) FIG. 1 shows typical displacement, semi-displacement, and planing hulls.

(3) FIG. 2 shows a typical displacement hull form.

(4) FIGS. 3a and 3b show other examples of typical displacement hull forms.

(5) FIG. 4 shows typical curves of areas for displacement, semi-displacement, and planing hull forms.

(6) FIG. 5 shows the pressure distribution on a displacement hull form.

(7) FIG. 6 shows examples of typical semi-displacement hull forms.

(8) FIG. 7 shows an example of a typical planing hull form.

(9) FIG. 8 shows a Fast Displacement Hull Form.

(10) FIG. 9 compares resistance of the present invention with a conventional powerboat.

(11) FIG. 10 is a lines plan of a powerboat according to an embodiment of the present invention.

(12) FIGS. 11a to 11e show configurations of hydrofoils in accordance with embodiments of the invention.

(13) FIGS. 12a, 12b, and 12c show hydrofoils dispositions in conjunction with different propulsion systems in accordance with embodiments of the invention.

(14) FIG. 13 shows a block diagram of the control system components of the powerboat of an embodiment of the present invention.

(15) FIGS. 14a and 14b show a hydrofoil installation arrangement in accordance with an embodiment of the invention.

(16) FIGS. 15a and 15b show alternative arrangements for hydrofoil configurations in accordance with embodiments of the invention.

(17) FIGS. 16a and 16b show various hydrofoil retraction arrangements in accordance with embodiments of the invention.

(18) FIG. 17 illustrates the difference between a hull according to an embodiment of the present invention and a conventional planing hull.

(19) FIG. 18 shows a block diagram of a control system according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(20) A powerboat 1 according to the present invention will now be described with reference to FIGS. 10-18.

(21) As shown in FIGS. 10 and 11, the powerboat 1 of a first embodiment of the invention comprises a hull 2, a plurality of dynamically adjustable hydrofoils 3 positioned towards the rear of the hull 2, below the design waterline, and a control system 14 for the hydrofoils.

(22) The hull 2 is shaped similarly to hulls typically used for operation in a displacement mode. The cross sectional area of the hull 2 reduces from the midship point to the transom (i.e. to the stern), such that the immersed area of the transom at rest is less than 40%, preferably less than 30%, more preferably less than 20%, and most preferably less than 10% of the maximum hull cross sectional area. In other words, the immersed volume of the hull 2 reduces from the midship section to the rear of the hull 2. This form of section distribution gives rise to a curve of areas (line A in FIG. 4) that corresponds to the norms for optimum resistance for a displacement hull. The LCB lies preferably between 45% and 65% of LWL aft of the forward perpendicular, more preferably between 50% and 60% and most preferably approximately 55%, and the prismatic coefficient (C.sub.p) lies preferably in the range of 0.5 to 0.7, more preferably in the range of 0.55 to 0.65. The values of these coefficients of form may be adjusted depending on the length and displacement of the vessel.

(23) The forward sections of the hull 4 are shaped to avoid pounding and slamming when operating in head waves. The forward sections are V-shaped, similarly to a conventional planing hull form, but the V-shaped sections are not present as far towards the rear of the craft as in a conventional planing hull form. In other words, the hull sections between 25% and 65% chord are more rounded than the V-shaped sections typically found at these locations in a conventional planing hull. The hull form can be different from a conventional planing boat, despite its planing performance, because the active foils mean that relative motion of the bow at planing speeds can be controlled with active foils. Thus, the impacts that the hull form will be called upon to mitigate will be less severe than for a conventional planing hull form due to the active attitude control. The plumb (near vertical) stem 5 is employed to maximize waterline length, again a feature that reduces resistance when operating in the displacement mode.

(24) The hull form is not constrained by limits on Displacement/Length ratio, Length/Beam ratio, nor Beam/Draft ratio. The mid ship section shape 6 is configured for minimum resistance, coupled to the need to maintain a V or deep-U shape section to manage the potential wave impacts when travelling at high speed. The main feature of the centerline profile 7 is the plumb stem and the smoothly rising aft buttock lines that terminate at or just below the static waterline. The curvature of the aft buttock lines between midships and the stern 8 may be varied to adjust the volume of displacement and LCB to suit particular vessel configurations and fit out.

(25) The hull of the present invention does not include a bulbous bow. In other words, the bow is shaped such that the whole portion of the bow below the design waterline is in line with, or aft of, the portion immediately above the design waterline.

(26) Conventionally, as set out above, such a hull shape would be unsuitable for operation at a Froude number above 1 (i.e. in a planing mode). However, when this hull 2 is used in combination with the dynamically adjustable hydrofoils 3 (FIGS. 11a and 11b), the trim of the vessel can be controlled to prevent the stern sinking and thus to keep hull resistance down and ensure roll and pitch stability at high speeds.

(27) The number of hydrofoils in the array is not fixed, for example three hydrofoils might be used with a center foil, and two outboard (FIG. 11c). The number of vertical supports for each hydrofoil may vary dependent on structural design (FIGS. 11d & 11e). Where the vertical support is positioned downstream of the propeller then the rudder may be incorporated as a vertical support to the hydrofoil, removing the need for a separate rudder and reducing hydrodynamic resistance.

(28) The powerboat 1 may be powered by an inboard engine and outdrive leg propeller (FIG. 12b) (i.e. stern drive propulsion) or by any other suitable source of propulsion such as shaft drive (FIG. 12a), pod drive (FIG. 12c), an outboard motor, or water jet.

(29) The hydrofoils 3 may be positioned to best suit the vessel's drive train arrangement, e.g. ahead of sterndrive units, ahead or astern of pod propulsion systems, or astern of propellers on fixed shafts.

(30) The planform and cross section (foil shape) of the hydrofoils can be of any conventional form. The shape and construction of the hydrofoils may be simple and robust or complex and sophisticated depending on the time and budget available. For example, the hydrofoils may be made from metal fabrications faired with solid material or clad in an FRP shroud. Typically the foil sections will be based on conventional sections, for example the NACA series. For operation at high Froude numbers the hydrofoil sections must be designed to optimize their behavior if cavitation is likely to occur.

(31) The hydrofoils 3 are dynamically adjustable by means of a control system 14, as shown in FIG. 13. The control system 14 is configured to move the hydrofoils 3 in the water as described in more detail below.

(32) An important characteristic of the hydrofoil arrangement is that it comprises of a plurality of foils lying typically between 1 and 3 chord lengths below the local hull surface. As shown in FIG. 14, the foils are aligned in the transverse direction between horizontal and the local deadrise angle of the hull surface. The foils are attached to vertical supports 15 which penetrate the hull surface. The foils are connected to a system of actuators 16 that adjust the angle of the foils to the horizontal plane, and thereby produce a varying vertical force as directed by the control system. The foils can be adjusted independently of each other so that the array of foils may produce both a time varying vertical force and roll moment. By way of example, the angle of attack of the foils may be adjusted in the following ways, although this is a nonexhaustive list and a person skilled in the art will understand that further modifications are possible within the scope of the inventive concept described:

(33) The foils may be fixed to vertical supports 15 that pass through the hull surface. The axis of rotation 17 is normal to the centerplane and the actuator 16 may be attached inside the hull, above or below the waterline, as shown in FIGS. 14a and 14b.

(34) The foil may be articulated at the lower end of the support strut 18, with the control mechanism 19 passing down the strut, as shown in FIG. 15a.

(35) A flapped hydrofoil may be used, where the main part of the foil is rigidly attached to support strut 21 and the trailing edge flap is controlled by a mechanism that passes down the strut, as shown in FIG. 15b.

(36) The hydrofoils may be retracted when not in use. This has several advantages. First, it allows the drag associated with the hydrofoils to be reduced and/or eliminated when they are not required. Second, it prevents the hydrofoils from being damaged and suffering from marine growth.

(37) The arrangement chosen for a particular application will depend on the competing features of the installation, trading retractability against simplicity of operation. Typically the foils might be retracted into a recess in the hull bottom 22 as shown in FIG. 16a, which may have a closing plate 23, or rotated aft in a slot in the transom to lie above the water when retracted, as shown in FIG. 16b, or rotated laterally to be alongside the hull.

(38) At a predetermined speed, the hydrofoils 3 are deployed by the control system 14. A block diagram of the control system 14 is shown in FIG. 18. The control system may comprise speed and attitude sensors, linked to PID controllers, with appropriate filters such as Kalman filters, and a power supply 27, to provide a control system which responds to the speed and attitude of the boat to deploy and then dynamically adjust the angle of attack of the foils to control the attitude of the boat as desired. As shown in FIG. 13, the control system may also be linked to the steering wheel 26 to provide fly by wire capability in which the foils operate in response also to the steering inputs to control the boat's attitude (e.g. trim and roll) to be within a safe envelope of operation.

(39) As shown in FIG. 18, the control system 14 includes a state machine which is a model of the behavior of the boat. The state machine takes measurements of vessel speed and attitude (roll and pitch) and vessel motions (heave and sway) from the sensors as its inputs. Preferably these are filtered, e.g. by a Kalman filter, to provide stable control in the event that the input measurements are temporarily unavailable or incorrect. The boat state is output from the state machine to the high level controller, which calculates the movements required by the hydrofoils to carry out the necessary control. These are fed to the low level controller, which calculates the valve demands necessary to carry out the actuation demands ordered by the high level controller. The valve demands are then fed to the hardware that controls the movement of the hydrofoils. The hardware may be valves linked to the actuators as described above or may be any other suitable hardware for moving the hydrofoils. The output from the hardware is then fed back to the low level controller in a feedback loop, using a PID controller or other suitable feedback controller.

(40) The control system 14 dynamically adjusts the angle of attack of the hydrofoils 3 in accordance with the boat speed to increase lift to the stern as the speed increases, which controls the trim of the boat 1. The speed at which the foils are deployed and the angle of attack of the hydrofoils for optimum performance will be predetermined for each speed and loading condition.

(41) The trim of the boat 1 may be adjusted by adjusting the hydrofoils 3 in order to maintain the boat 1 at an optimum trim. This optimum trim will usually be associated with minimum resistance but may be adjusted to improve ride comfort or visibility if required. The predetermined initial deployment speed may be set by the preconfigured control system 14 or may be set manually by the helmsman.

(42) When deployed at high speed, the hydrofoils 3 effectively replace the trim controlling effect of the missing part of the hull 2 towards the aft end of the boat 1 compared with a conventional high speed (planing) boat (FIG. 17). That is, the lift force that is provided by the rear part of the hull in a conventional high speed (planing) boat is instead provided by the hydrofoils 3. The hydrofoils also provide the stability conventionally derived from the hard chine and deep-V hull shape. The hydrofoils provide this damping effect even when in a fixed position, but because they may be individually controlled the angle of attack of the foils may be adjusted in antiphase to create a roll moment whilst maintaining the desired vertical force. With suitable software in the hydrofoil controller, this effect may be tuned to simulate the behavior of the hard chine hull shape, or to provide more effective active roll stabilization. At high speed, i.e. in planing mode, a significant fraction of the boat weight may be supported on the foils, the remainder being substantially supported by buoyancy and hydrodynamic lift on the hull 2. Thus the boat of the invention does not operate as a typical hydrofoiling craft in which the hydrofoils are designed to take the whole weight of the craft, but instead the foils 3 provide lift to support the aft portion of the boat and the fore portion is supported by the hull shape.

(43) The proportion of the boat weight supported by the hydrofoils will depend on the speed of the boat. At low speed, the foils will support no substantial weight, and may even be fully retracted. As the speed rises, the foils will be adjusted to provide a vertical force that adjusts the boats running trim to an optimal value. Depending on the proportions (length/beam ratio, displacement/length ratio) of the vessel, at top speed the hydrofoils will support between 0% and 50%, preferably between 10% and 40%, more preferably 15%-25%, and most preferably 20% of the boat's weight. These values are the proportion of the boat's weight carried in flat water. However, these values will change transiently due to the fluctuating loads on the hydrofoils induced by the vessel's passage through the waves.

(44) As described above, the adjustment of the hydrofoils 3 may take place automatically based on predetermined data. However, the control system 14 may also allow manual adjustment of trim prompted by a user input.

(45) The control system 14 may also be configured to optimize characteristics other than resistance, such as comfort or safety. For example, the hydrofoils 3 may be automatically adjusted to control roll and pitch movements of the hull 2 at any speed using hull state data from an Inertial Navigation Unit (INU) 25. It may also be integrated with control of the steering of the boat 26 to maintain it within a safe operating envelope of roll and turn rate regardless of the operator inputs (FIG. 13).

(46) The powerboat of the present invention has the advantage that it can be optimized to operate efficiently at a wide range of speeds. Typically powerboats of the present invention will be between 8-25 meters length. Typically such a vessel of 10 meters length may have a speed range of 8-45 knots, and a vessel of 25 meters length may have a speed range of 12-70 knots. Powered watercraft that are designed to operate at the upper end of this range, such as high performance powerboats, typically have the disadvantage that in order to be safe at their maximum speed, they have hulls with very high resistance at low speeds. Likewise, watercraft that are designed to operate at the lower end of this speed range are not suitable for use at high speeds. Thus, the present invention provides a watercraft which can operate efficiently across the whole speed range or can be optimized for comfort or stability across the whole speed range.

(47) A further advantage of the arrangement of the present invention is that the dynamically adjustable hydrofoils 3 may be used to control the roll and pitch motions of the boat, as well as to control trim. The control system may have user selected modes that modify the handling and feel of how the boat dynamically responds to the sea state. For example a sports mode or a comfort mode may be selected which vary the active roll and trim response of the boat to the control system inputs.

(48) This invention is particularly useful for power craft which are battery/thermal engine hybrids. Such a hybrid propulsion system uses batteries and electric motor for low speed operation and a thermal engine for high speed operation. To ensure maximum battery duration and minimize battery weight the hull resistance at lower speeds must be as low as possible.