System and Methods to Provide Lift to a Vessel

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 63/637,787, filed Apr. 23, 2024, the disclosure of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to structures, uses and methods of increasing the lift of hydrofoils and aerofoils by accelerating fluid by constriction within a chamber.

BACKGROUND

Foils in the form of hydrofoils and aerofoils provide lift to vessels traveling in the air and on water. For aerofoils, this lift provides the means for airplanes to fly. For hydrofoils, this lift raises marine vessels upwards from the water, reducing sinkage, and thereby drag forces. Pairs of hydrofoils are further useful in dampening vessel motion caused by wave action. However, conventional hydrofoils on large marine vessels such as cruise ships and naval vessels can be massive, and are typically attached at a single pivot point, placing considerable constraints on materials and methods of use.

SUMMARY

According to some embodiments, a lift unit is disclosed for providing lift to a vessel moving through a fluid, wherein the lift unit includes a passageway configured to allow the fluid to flow within as the vessel moves through the fluid, the passageway including a tapered chamber having a mouth with an inflow area at a fore end, configured for inflow of the fluid into the fore end through the mouth as the vessel moves through the fluid and an aft end opposite the fore end, the tapered chamber narrowing from the fore end toward the aft end, and a constricted chamber having a fore end and an aft end, the fore end of the constricted chamber connected to the aft end of the tapered chamber, the aft end of the constricted chamber having an exit for outflow of the fluid, the exit having an outflow area which is less than the inflow area.

The lift unit further includes a foil situated within the constricted chamber, the foil having an axle about which the foil is configured to rotate, the axle having a outboard-side end and a inboard-side end, the axle being attached to the lift unit at the outboard-side end and at the inboard-side end. The lift unit further includes a drive mechanism disposed in a drive mechanism compartment, the drive mechanism compartment fluidically isolated from the constricted chamber, the drive mechanism connected to the foil and configured to rotate the foil about the axle so as to control the lift as the fluid flows through the constricted chamber.

According to some embodiments, the constricted chamber and the tapering chamber may overlap. The lift unit may be retractable into the hull of the vessel. The foil may be a hydrofoil or a flat plate, and the fluid may be water. The drive mechanism may be housed in a compartment separate from the hydrofoil. The compartment may be watertight. The watertight compartment may be configured to hold oil. The drive mechanism may be rotatably connected to the axle. The drive mechanism may be coupled to a rod which connects at an end of the foil forward or aft of the axle, the drive mechanism configured to move the rod in a linear direction so that the foil rotates about the axle.

According to some embodiments, a system is disclosed for providing lift to a vessel having a hull moving through a fluid. The system includes one or more lift units, as described above, configured to be disposed on the hull of the vessel, and one or more motion sensors, disposed on the vessel, configured to monitor pitch, roll, and heave motions of the vessel. The system further includes a motion control command unit (MCCU) configured to receive signals from the one or more motion sensors, the MCCU configured with a processor and instructions for control of the one or more lift units, based, at least in part, on the signals received from the one or more motion sensors.

According to some embodiments, at least one of the lift units may be retractable into the hull of the vessel. The one or more lift units may include a port lift unit and a starboard lift unit symmetrically disposed with respect to each other on the hull of the vessel. The one or more lift units may include two fore lift units positioned on opposing sides at a forward location on the hull, two midship lift units positioned on opposing sides close to the midship location on the hull, and two aft lift units positioned on opposing sides at an aft location on the hull.

According to another embodiment, the total number of lift units on the vessel can be three, and can include a single lift unit at either an extreme forward location or an extreme aft location on the hull, close to the center line of the ship and two lift units positioned on opposing sides at close to midship on the hull.

According to some embodiments, a method is disclosed of providing lift to a vessel having a hull moving through a fluid. The method includes configuring the vessel with a system for providing lift, as described above, monitoring pitch, roll, and heave motions of the vessel with the one or more motion sensors, transmitting signals related to pitch, roll, and heave motions of the vessel to the motion control command unit from the motion sensors, receiving the transmitted signals from the motion sensors by the motion control command unit, and based, at least in part, on the signals received from the one or more motion sensors, controlling the lift units.

According to some embodiments, controlling the one or more lift units may include controlling the attack angles of the foils disposed in the lift units. Controlling the attack angles provides control of the drag and lift of the vessel. Controlling the attack angles may result in a reduction in vessel motions selected from the group consisting of pitch, roll, heave, and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates how positive lift can raise a vessel upwards out of the water, thus reducing drag from the hull of the vessel.

FIG. 2 illustrates how roll of a vessel can be counteracted by independently controlling lift in positive and negative directions on lift units symmetrically disposed on opposite sides of the vessel.

FIG. 3A shows a conventional retractable hydrofoil in an extended state and illustrates how it is supported by means of a single load-bearing pivot axis.

FIG. 3B shows the conventional retractable hydrofoil of FIG. 3A in a retracted state and illustrates how it is folded back into a vessel by means of a single load-bearing pivot axis.

FIG. 4A shows a vector analysis of how a fluid flowing with a velocity v provides a flow force F_s, which acts on a flat-plate type foil placed at an attack angle α with respect to F_s to give it a normal force F_n, which is the sum of a lift force L and a drag force D.

FIG. 4B shows a vector analysis for a wing-type foil.

FIG. 5 embodies a foil confined in a constricted flow field within a passageway, the passageway having a tapered chamber leading into a constricted chamber. Such a constricted flow field provides an increase in lift proportional to the square of the ratio of the input area through which the fluid enters the tapered chamber divided by the output area through which the fluid flows within a constricted chamber.

FIG. 6 shows a foil with a length l_c and a width w, which has a lift proportional to l_c×w.

FIG. 7 shows a foil with a length l_f and a width w, which has a lift proportional to l_f×w.

FIG. 8 embodies a foil confined in a constricted flow field within a passageway, the passageway differing from the passageway in FIG. 5 in that the tapered chamber and the constricted chamber substantially overlap, so that the constricted flow field decreases in area up to the point at which the fluid exits the passageway.

FIG. 9A provides an embodiment of a system for providing lift and stability control to a vessel according to the instant disclosure. The system includes one or more sensors and one or more retractable lift units disposed on the hull of a vessel, each unit having a foil, with the attack angle α of each foil independently controllable by a motion control command unit based on signals received from the sensors. In this figure the lift units are shown in an extended state, projecting outward from the hull.

FIG. 9B shows the system of FIG. 9A with the lift units retracted into the hull.

FIG. 10 provides a cross-sectional view of a port-side retractable lift unit, viewed inward towards the hull of the vessel of FIG. 9A. The plane of cross-section is shown as a dashed line labeled 10 in FIG. 9A.

FIG. 11A provides a cross-sectional view of the port-side retractable lift unit of FIG. 9A, viewed from aft to fore of the vessel of FIG. 9A. The plane of cross-section is shown as a dashed line labeled 11A in FIG. 9A. The retractable lift unit is shown in an extended configuration. A locking mechanism of the lift unit is shown within a dashed circle.

FIG. 11B provides an exploded view of the locking mechanism of the lift unit of 11A.

FIG. 12 provides a cross-sectional view of the port-side retractable lift unit of FIGS. 10, 11A, and 11B, viewed from aft to fore of the vessel as shown in FIG. 9B. The retractable lift unit is shown in a retracted configuration. The plane of cross-section is shown as a dashed line labeled 12 in FIG. 9B.

FIG. 13 provides a cross-sectional view of an alternative configuration of a port-side retractable lift unit, viewed inward towards the hull of the vessel of FIG. 9A, for which the attack angle of the foil is controlled by a linearly movable rod connected to the foil at a point distal to the rotational axis of the foil.

FIG. 14 provides a cross-sectional view of the port-side retractable lift unit of FIG. 13, viewed from aft to fore of the vessel of FIG. 9A. The retractable lift unit is shown in an extended configuration.

FIG. 15 provides a cross-sectional view of the port-side retractable lift unit of FIGS. 11A, 11B, and 13, viewed from aft to fore of the vessel of FIG. 9B. The retractable lift unit is shown in a retracted configuration.

DETAILED DESCRIPTION

Definitions. As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires:

The “port” side of a vessel is the left side of the vessel when the vessel is facing forward.

The “starboard” side of a vessel is the right side of the vessel when the vessel is facing forward.

“Fore” refers to the front of a forward-facing vessel.

“Aft” refers to the rear of a forward-facing vessel.

“Midship” refers to the middle region of a vessel.

A first chamber is “fluidically isolated” from a second chamber when fluid entering the second chamber is blocked from entering the first chamber.

A “foil” is a flat or shaped plate configured to provide a lift force on a vessel moving through a fluid.

A “lift force” is a force perpendicular to the motion of the vessel.

A “hydrofoil” is a foil configured to provide a lift force when the fluid flowing is a liquid.

An “aerofoil” is a foil configured to provide a lift force when the fluid flowing is a gas.

“Roll” is side to side tilting motion of a vessel about the roll axis of the vessel, where the roll axis runs horizontally through the length of the ship, from fore to aft, through the vessel's center of mass.

“Pitch” is an up/down rotation of a vessel about the pitch axis of the vessel, where the pitch axis runs horizontally across the ship, from port to starboard, through the vessel's center of mass.

“Heave” is a linear up/down motion of a vessel.

It is known that foils can provide lift forces for vessels moving through a fluid. For aerofoils, such lift forces allow planes to lift off and fly. As indicated in FIG. 1, lift from hydrofoils 130 moving through water can reduce sinkage and thereby reduce drag on a marine vessel. In FIG. 1, the initial level 140 of water on the hull of the vessel decreases to a new level 135 as the vessel is raised out of the in the water by lift force L. Foils can also help to stabilize vessels in the presence of wave motion. Such stabilization is illustrated in FIG. 2, which shows how the action of waves can be counteracted by applying positive lift force (L) on a hydrofoil 130 on one side of a marine vessel and negative lift force (−L) on another hydrofoil 130 symmetrically disposed on an opposing side of the vessel, in order to minimize roll 145.

A conventional hydrofoil configuration 150 is illustrated in FIGS. 3A and 3B. Here, the hydrofoil 130 extends outwards from a hull 170 when operational, and pivots back into the hull 170 about a pivot point 180 when not in use. The pivot point 180 is conventionally a cantilevered, universal joint support. It is noteworthy that in such a configuration, the entire force of the hydrofoil moving through water is placed on the single pivot point 180, placing considerable structural constraints on this universal joint support.

The lift force L and the drag force D on a foil 130 moving through a fluid, the fluid moving with velocity v (distance per unit time) relative to the foil 130 at an attack angle α are illustrated in FIGS. 4A and 4B. Here a is defined as the angle between a chord line 190 of the foil and the direction of the incoming flow of fluid.

A foil can take on a variety of shapes, and a person skilled in the art of foil design would understand that the current disclosure applies equally well to any number of such shapes. As illustrated in FIG. 4A, a foil can be a simple flat plate, and the core features of this disclosure can be understood with reference to such a plate. With respect to the forces on such a plate, the force F_s due to fluid flow against the plate at an attack angle α provides a normal force F_n which is the vector sum of the lift force L and the drag force D. The normal force F_n is given by F_n=F_s cos(90−α)=F_s sin(α) from which it is readily seen that L=F_n cos(α)=F_s sin(α)cos(α) and that D=F_n sin(α)=F_s sin² (α).

FIG. 4B shows a foil 130 having a wing-type shape. General hydrodynamic models of a foil having a modest attack angle α moving through a fluid with density ρ with a velocity v provide a lift force L described by:

L = 1 2 ⁢ ρ ⁢ SC L ⁢ v 2 ,

where S is the surface area of the foil, and C_L is the lift coefficient, a parameter which depends on the attack angle of the foil with the fluid, and on various hydrodynamic parameters including the viscosity of the fluid. The drag force D can be described by an equation with similar form:

D = 1 2 ⁢ ρ ⁢ SC D ⁢ v 2

where C_D is the drag coefficient. Notably, as discussed in more detail below, because both the lift force and the drag force depend as the square of the velocity v, increasing the velocity of fluid by channel constriction allows a dramatic reduction of size of the foil without sacrificing lift, while maintaining a constant ratio of lift to drag.

This principle is embodied in FIG. 5, which shows a passageway 210 having a fore end and an aft end, forming part of a lift unit for a vessel, the passageway having a mouth 220 through which fluid can flow as the vessel moves forward. The mouth 220 provides an inlet area A_i through which the fluid enters at the fore end. The passageway 210 tapers from the mouth 220, forming a tapered chamber 225, the tapered chamber 225 connecting to a constricted chamber 235, the constricted chamber 235 terminating at the aft end in an exit 240, the exit providing an outlet area A_o. A foil 230 for providing lift for the vessel as the vessel moves through the fluid is disposed inside the constricted chamber 235. The foil 230 is attached at both ends of an axle 245 to interior attachment points on the constricted chamber 235. The attack angle α of the foil with fluid flowing into the constricted chamber 235 is controlled by means discussed below. Notably, in contrast to the conventional retractable foil of FIGS. 3A and 3B, which are attached at a single pivot point 180, attachment at both ends of the axle 245 eliminates the requirement that the entire force of the hydrofoil moving through water be placed on the single pivot point 180.

According to the embodiment of FIG. 5, as the vessel moves through the fluid, the fluid in turn moves into the passageway 210 at a free stream velocity v_f. The fluid enters through the mouth 220, into the tapered chamber 225, and into the constricted chamber 235. As the fluid passes through the tapered chamber 225 and into the constricted chamber 235, its velocity increases, with the velocity in the constricted chamber 235 being given by v_c. According to this embodiment, because of the conservation of mass, the volume per unit time entering the mouth 220 must equal the volume per unit time leaving the exit 240, meaning that the following equation of continuity must hold:

A i ⁢ v f = A o ⁢ v c

The velocity of the fluid in the constricted chamber can be written as v_c=C_Rv_f, where

C R = A i A o

is the constriction ratio.

Comparing the lift force L_f for a foil subject to free flow velocity and the lift force L_c in the constricted chamber, we obtain:

L f = 1 2 ⁢ ρ ⁢ S f ⁢ C L ⁢ v f 2 and L c = 1 2 ⁢ ρ ⁢ S C ⁢ C L ⁢ C R 2 ⁢ v f 2

• • where S_f and S_c are the respective surface areas of the foil subject to free flow and constricted flow, respectively. Dividing these two equations gives:

L c L f = C R 2 ⁢ S c S f

Based on this equation, it is evident that for a constant area of foil, the increase in lift for a foil subject to constricted flow compared to free flow is by a factor of

C R 2 .

For example, a two-fold reduction in the outflow area compared to the inflow area gives a four-fold increase in lift.

Looked at another way, to obtain a given value of lift (L_c=L_f) the surface area of a foil 230 in the constricted chamber 235 can be reduced by a factor of

C R 2

compared to the surface area of a foil subject to free flow. For example, a two-fold reduction in the outflow area compared to the inflow area allows the surface area of the foil to be reduced 4-fold.

Compare for example a constricted chamber foil 230 in FIG. 6, with a free-flow foil 230 in FIG. 7. The foils in FIG. 6 and FIG. 7 have the same width w, but different lengths, l_c and l_f, respectively. If the area ratio

S c S f = L C L f ,

then constant lift force (L_c=L_f) implies that

C R = l f l c ,

meaning that for a given lift force, a 4-fold reduction of length can be achieved with a constriction ratio of 2.

To summarize, the configuration of FIG. 5 has at least two key advantages over the conventional design of FIG. 3. First, disposing the foil 230 in a region of constricted flow allows a dramatic reduction in size of the foil 230 that scales as the square of the area of the foil 230. Second, attaching the foil 230 at two ends of an axle 245 considerably reduces the structural constraints for a retractable foil.

Shown in FIG. 8 is an embodiment for which the constricted chamber 235 and the tapered chamber 225 are the same chamber. According to this embodiment, as fluid flows from the mouth 220 to the exit 240, the velocity v_c in the constricted chamber 235 increases from v_f at the mouth 220 to v_o at the exit. The same principles apply in FIG. 8 and in FIG. 5, with the lift experienced by the foil 230 in the constricted chamber 235 being greater than the lift that the same foil would experience in the absence of flow constriction.

According to the embodiment of FIGS. 9A and 9B, one or more lift units 320, 325, 330, 335, 340, 345, each having such a passageway 210 and a foil 230, are attached to the hull 350 of a vessel 310, thereby providing lift and allowing the vessel 310 to dampen motions of the vessel 310 in response to fluid motions which would otherwise cause pitch, roll, or heave motions of the vessel 310. FIG. 9A shows the configuration when the lift units are extended from the hull of the vessel. FIG. 9B shows the lift units retracted into the hull of the vessel. The total number of units in the lift units will depend on the size of the vessel 310 and the extent of the motion which needs to be controlled. For some configurations, the total number of lift units can be 2, 3, 4, 5, or 6. In some embodiments, as in FIGS. 9A and 9B, the lift units are arranged symmetrically in pairs, with each pair having a port-side member and a corresponding starboard-side member. In the embodiment of FIGS. 9A and 9B, six lift units are arranged symmetrically in three pairs, with each pair having a port-side member and a corresponding starboard-side member.

The primary purpose of each lift unit will depend on location. For example, in FIG. 9, forward lift units 320 and 325 are well-suited for controlling pitch. Midships units 330 and 335 are well suited for roll dampening and/or heave compensation. Aft units 340 and 345 can be combined with forward lift units 320 and 325 for more effective pitch control, and/or with midships units 330 and 335 for more effective roll control.

In some configurations, a total of three lift units are attached to the hull of a ship, with two lift units being symmetrically disposed close to the midship location on the vessel, one port-side, and one starboard-side. In this configuration, the remaining lift unit is disposed either in an extreme forward position or in an extreme aft position, close to the center line of the vessel 370. Three lift units positioned in this manner provide the minimum number required to exert effective control over pitch and roll or pitch and heave.

As discussed in more detail below, each lift unit is associated with an actuator to adjust the attack angle α of the foil associated with that lift unit. Each actuator can in turn be independently controlled by a motion control command unit (MCCU) 360. The MCCU 360 is configured to receive signals from one or more motion sensors, the motion sensors being configured to monitor pitch, roll, and heave motions. The MCCU 360 is configured with a processor and instructions for automatic and/or manual control. Under automatic control, the signals received from the motion sensors can be processed by the MCCU 360 and output to each actuator associated with each lift unit in order to control the attack angle α of the associated foil 230, and thereby control the lift and drag forces of that foil 230 as the vessel 310 moves through the fluid. Under manual or semi-automatic control, signals received from the motion sensors provide feedback to an operator who can control in whole or in part the attack angles of the lift units.

Each lift unit can be attached externally to a vessel hull or can be attached internally in a vessel hull recess with a retractable stowage system. One embodiment of such a retractable port-side lift unit of a vessel such as the vessel of FIGS. 9A and 9B is shown in FIGS. 10 through 12. For this rotationally actuated embodiment 410, the attack angle of the foil 230 is controlled by one or more spur gears 435 and a motor 425 coupled to these gears. A linearly actuated embodiment 412 is provided in FIGS. 13 through 15. For this linearly actuated embodiment, the actuator is a linear actuator 460 directly coupled to the foil 230 of the lift unit.

For the rotationally actuated embodiment 410, FIG. 10 provides a cross-sectional view inward towards the hull of the vessel, with the cross-sectional plane indicated by the dashed line 10 in FIG. 9A. FIG. 11A provides a cross-sectional view from aft to fore of the vessel, with the retractable lift unit shown in an extended configuration, with the cross-sectional plane indicated by the dashed line labeled 11A in FIG. 9A. An exploded image of a locking mechanism 405 formed in the extended configuration is shown within a dashed circle in FIG. 11B. FIG. 12 provides a cross-sectional view of the retractable lift unit of the rotationally actuated embodiment 410 viewed from fore to aft of the vessel. Here, the retractable lift unit is shown in a retracted configuration. The cross-sectional plane is indicated by the dashed line labeled 12 in FIG. 9B.

According to the linearly actuated embodiment 412, as provided in FIGS. 13-15, a linear actuator 460 provides a mechanism for controlling the attack angle of the foil 230.

For each of these embodiments, as shown in the cross-sections of FIGS. 10-15, the lift unit 410, 412 includes a flow-through passageway 210, open to fluid, into which fluid flows at a velocity v_f through an inlet 220, the inlet having an inlet area A_i, and exits at a velocity v_c through an outlet 240, the outlet having an outlet area A_o. The passageway includes a tapered chamber 225, which tapers from the mouth of the inlet 220 to a constricted chamber 235, the constricted chamber 235 terminating at the outlet 240. A foil 230 for providing lift as fluid flows past the foil 230 at a velocity v_c is disposed inside the constricted chamber 235. The foil 230 is rotationally attached at two ends of an axle 245.

In some embodiments the tapered chamber 225 and the constricted chamber 235 substantially overlap. In some embodiments, the tapered chamber 225 and the constricted chamber 235 are the same chamber, according to a geometry like that in FIG. 8.

Because the foil 230 is confined to a constricted flow chamber having a flow velocity v_c, it can provide a lift that is comparable to a much larger foil in the flow region having a flow velocity v_f due to the motion of the vessel 310. Because the foil 230 is rotationally attached at two ends, rather than at a single end as in a conventional foil, it has fewer structural constraints.

Each of these embodiments also features a foil actuator compartment 420, which in the rotationally actuated embodiment 410 includes a motor 425, and in the linearly actuated embodiment 412 includes a linear actuator 460. For the linearly actuated embodiment 412, the linear actuator 460 passes from the foil actuator compartment 420 directly to the constricted chamber 235, where it contacts an end of the foil 230 away from the axle 245 of the foil 230.

As provided in FIGS. 10-12, the rotationally actuated embodiment 410 includes a gear compartment 430. In this embodiment, the motor 425 is rotationally coupled to one or more spur gears 435 in the gear compartment 430. The one or more spur gears 435 are in turn rotationally coupled to the foil 230 by the foil axle 245, so that actuation by the motor 425 causes rotation of the spur gears 435, in turn causing rotation of the foil 230, thereby changing the attack angle α. As is seen most clearly in FIGS. 11A and 12, the gear compartment 430 projects outward from the lift unit, away from the hull of the vessel 310. For embodiments where the fluid is water, the foil actuator compartment 420 and the gear compartment 430 may be sealed from ingress of water by water-tight bushings 440. In some such embodiments, the gear compartment 430 and/or the foil actuator compartment 420 may be filled with oil. In such embodiments, equalizer bellows 445 may be used to equalize the pressure between the gear and/or foil actuator compartments 430, 420 and the flow-through passageway.

As provided in FIGS. 13-15, according to the linearly actuated embodiment 412, the attack angle of the foil is controlled by a linear actuator 460 which is connected to the foil at a point distal to the rotational axis 245 of the foil 230. FIG. 13 provides a cross-sectional view of the linearly actuated embodiment of a port-side retractable lift unit, viewed inward towards the hull of the vessel 310 of FIGS. 9A and 9B.

FIG. 14 provides a cross-sectional view of the port-side retractable lift unit of FIG. 13, viewed from aft to fore of the vessel 310 of FIG. 9A. The retractable lift unit is shown in an extended configuration.

FIG. 15 provides a cross-sectional view of the port-side retractable lift unit of FIGS. 13 and 14, viewed from aft to fore of the vessel 310 of FIG. 9B. The retractable lift unit is shown in a retracted configuration.

For both the rotationally actuated embodiment of FIGS. 10-12, and the linearly actuated embodiment of FIGS. 13-15, in the retracted state (FIGS. 12 and 15), the lift unit is housed in a hull recess 450 of a vessel 310. A water-tight set of pistons 455, is configured to receive signals from the MCC 360. In response to such signals, each piston is configured to push the lift unit 410 outward from the hull of the vessel 310, thereby allowing water to flow into the flow-through passageway 210, where it impacts the foil 230, which can then provide lift to the vessel 310.

The lift units are individually controlled with respect to extension/retraction and with respect to foil attack angle by signals received from the MCCU 360. In some embodiments, the lift unit extension/retraction and the foil attack angle are controlled automatically by the processing unit of the MCCU 360. According to other embodiments, the lift unit extension/retraction and foil attack angle are controlled manually by controls on the MCCU 360. In some embodiments, the lift unit is controlled by a combination of manual and automatic controls.

If the vessel 310 moves at a right angle directly into a wave, the vessel 310 will tend to pitch, and this pitch can be counterbalanced by the MCCU 360 adjusting the attack angles of foils to the fore and aft of the vessel 310. Similarly, the attack angles of port and starboard foils may be adjusted by the MCCU 360 to minimize roll.

What has been described and illustrated herein is an example along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the subject matter, which is intended to be defined by the following claims—and their equivalents—in which all terms are meant in their broadest reasonable sense unless otherwise indicated.