US2276163A - Watercraft - Google Patents

Description

March 10, 1942. R. N. coouuez WATER CRAFT Filed Feb. 11, 1941 Patented Mar. 10, 1942 UNITED STATES PATENT OFFICE I WATERCRAFT Richard Newell Coolidge, Nashville, Tenn.

Application February 11, 1941, Serial No. 378,455

6 Claims.

This invention relates to improvements in water craft, and more particularly to steering apparatus for use with screw propelled vessels. It is the general object of the invention to improve the efficiency of such craft by proper dilent fiow, and with substantial uniformity re-. gardless of the angle of helm.

It is generally recognized that the action of a marine propeller consists essentially of the stern-ward projection of a column of water which is called the propeller race, the change of momentum per unit of time of this water being equal to the propeller thrust which, during steady motion, is balanced by resistance of the vessel. It is also appreciated that among the more important losses of energy which occur are the deflection of the propeller race from the proper direction and the setting up in the race and adjacent water of turbulent fiow.

Serious loss of energy is also caused on the occurrence of the phenomenon known as cavitation, which arises when there is interference with the natural flow of water to the screw, resulting in excessive slip, reduction in thrust, and consequent very greatly reduced efficiency. The diminution of pressure accompanying the acceleration of water ahead of the screw may under certain circumstances be sufficient to bring about these conditions.

In its preferred form, the invention contemplates the association with the screw of dual rudders which are conjointly turned in steering, each rudder being so shaped as to conform generally to at least a substantial part of the path described by the propeller tips, and so as to afford generally constant clearance with the tips under different angles of helm. The rudders, preferably of the balanced type, are further shaped so as to converge toward and diverge away from the propeller sufiiciently to compensate for the lateral contraction of the accelerating race ahead of the propeller in either direction of movement of the vessel, to the extent necessary to prevent serious or disturbing energy loss by cavitation.

Specifically it is proposed to form the opposed faces of the rudders so that the intermediate part of each rudder adjacent the propellerdefines a portion of a surface of revolution of which the axis of generation is substantially coincident with the rudder axis, and of which thegeneratrix is a circular are substantially concentric with the circle described by the propeller tips and of somewhat greater radius, the opposed rudder faces diverging forward and aft from such intermediate parts. Thus regardless of the direction of movement of the vessel, a sufiicient volume of water flows between the leading ends of the rudders to enable the propeller race to acquire the necessary momentum at the propeller, and the area between the rudders in the plane of the propeller,

remains substantially constant when the rudders are concurrently turned in steering.

Further objects and features will be apparent from the following description, taken in connection with the accompanying drawing, in which- Figure 1 is a plan view of a screw propelled vessel illustrating steering apparatus constructed in accordance with the principles of the invention;

Figure 2 is a partial side elevation of the structure shown in Figure 1;

Figure 3 is a rear elevation of Figure 2;

Figure 4 is a rear elevation corresponding to Figure 3, but illustrating a modified form of the invention applicable to twin screw propelled vessels;

Figure 5 is a horizontal section of a preferred form of rudder element; and

Figures 6, '7, and 8 are vertical sections taken substantially on the lines 6-45, 'l!, and 8-8, respectively, of Figure 5.

In order to facilitate an understanding of the invention, reference will be made to the several embodiments thereof illustrated in the accompanying drawing and specific language will be employed. It will nevertheless be understood that various further modifications of the devices illustrated herein, such as would fall within the province of those skilled in the art to con struct, are contemplated as part of thepresent invention.

The invention is particularly effective when applied to shallow draft vessels, and is so illustrated in the drawing. Thus, referring to Figure 2 of the drawing, it will be observed that the hull It is provided with a bottom which rises at the stern, as indicated at I l, to accommodate the propeller IS, the propeller shaft being indicated at Ill. The propulsion system forms no part of the instant invention, except in combination with the steering system hereinafter described. and may therefore be modified as desired.

The steering system consists essentially of spaced rudders l6 and I1, disposed at opposite sides of the propeller I3 and in contiguous relation therewith. The rudders are illustrated as balanced, and extend both forwardly and rearwardly from the respective pivotal axes thereof, as defined by the usual rudder stems l8 and [9, the latter being rigid with the rudders.

The pair of rudders are connected for conjoint steering movement by any convenient means, the details of which form no part of the instant invention. For example, a worm gear sector may be secured to each rudder stem, these sectors being indicated at 22 and 23 respectively, and a transversely extending shaft 25 may be provided 1 at its opposite end with worms 26 and 21 meshing respectively with the sectors 22 and 23. The shaft 25 may be rotated through bevelled gears 28 and O 29 by the steering shaft 3|, to which is secured the usual wheel 30.

The configuration of the rudders l6 and I! in elevation is not important, although I prefer to form them as shown in Figure 2. The outwardly facing surface of each rudder is preferably flat, defining a plane substantially parallel to the rudder axis; the planes thus defined by the pair of rudders are generally parallel to each other.

The opposed or inner facesof the rudders are shaped as shown more particularly in Figures 5 to 8, inclusive.

Thus the intermediate part of the inner face of rudder [6, indicated at 33 in Figure 5, conforms generally to a surface of revolution of which the axis of generation is coincident with the axis of rotation of the rudder, the generatrix being constituted by an arc of a circle substantially concentric with the circle described by the propeller tips and of somewhat greater radius, the difference in radius being at least sufficient to afford adequate clearance between the rudders and the propeller tips. It will be appreciated that as the rudders are rotated about their respective steering axes, the area enclosed between them in the plane of the propeller will remain substantially constant, and the clearance for the propeller tips will remain constant, the shape of the area being unchanged. As shown in Figure 3, the surface of revolution just described is of substantial extent, measured in a vertical direction, so as to extend both above and below the horizontal plane containing the propeller axis and partially surround the propeller, The extent of this surface of revolution, measured longitudinally of the vessel, is preferably suificient to maintain constant clearance with the propeller when the helm it put over in either direction to its extreme angle.

Alternatively, the intermediate part of the inner face of the rudder may be described as of such contour that generally horizontal sections define circular arcs about the axis of the rudder stem, whereas a transverse generally vertical section through the rudder stem defines a circular are about the propeller axis having a radius greater than the propeller tip radius.

As hereinbefore pointed out, it is extremely important, in order to secure the highest operating efficiency in either direction of motion of the vessel, that the inner faces of the rudders diverge forward and aft of the propeller. With this end in view, and in order to secure optimum flow conditions, the surfaces at the intermediate parts of the rudders are gradually flattened in each direction from the propeller and preferably merge, adjacent the rudder tips 34 and 35, into divergent plane surfaces. The curvature of the inner face of each rudder in vertical planes thus gradually decreases both fore and aft of the rudder stem, as illustrated more particularly in Figures 6, 7, and 8 of the drawing. The area defined between the rudder tips both fore and aft should be sufficient, as hereinbefore indicated, to compensate for contraction of v the propeller race resulting from normal acceleration in the direction of and deceleration away from the propeller. In other words, the divergence of the inner surfaces ofthe rudders away from the propeller in each direction should be at least sufficient to prevent substantial cavitation regardless of the direction in which the vessel is proceeding.

For convenience in illustrating the invention, the propeller shaft is shown in a horizontal position. In the event the invention is applied to craft in which the propeller shaft is inclined, some corresponding modification of the disposition of the rudder surfaces may be desirable in order to attain maximum efliciency. It is intended that all ordinary deviations of the propeller shaft from a true horizontal are comprised within the scope of the term generally horizontal.

In the modified form shown in Figure 4, applicable to Vessels propelled by twin screws, the two outer rudders 40 and 4| may be shaped as hereinbefore described. The rudder 42, intermediate the propellers, is formed on both its surfaces as described hereinbefore with reference to the inner surfaces of rudders l6 and I1. Thus the propeller race is directed toward and awai from each of the propellers 44 and 45 in precisely the same manner as in the embodiment first described, Suitable means, not shown, may be provided for effecting concurrent rotation of all three rudders.

It will be appreciated that by the arrangement described, the propeller race is so controlled and directed inits movement toward and away from the propellers that losses due to lateral deflection of the race and turbulent fiow may be materially reduced. This is especially true in the case of vessels proceeding in water of shallow draft, where the bottom cooperates to a certain extent with the rudders and with the vessel bottom to confine the propeller race rather closely to a prescribed path affording optimum operating conditions. The flaring inlet and outlet offers little resistance to flow and inhibits the suction or draw of the water to the propeller from the side, thus increasing the tractive effort. The tendency of the vessel to squat when in shallow water is accordingly materially reduced. The steering apparatus herein described is found to give greatly increased response, particularly for small angles of helm, and thus the water channel remains practically constant and is properly directed to the propeller regardless of the sharpness of angle through which the vessel is turned or of the direction in which the vessel is propelled.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In steering apparatus for screw propelled vessels, the combination with a propeller, of balanced rudders, one disposed at each side of said propeller, means supporting said rudders for pivotal and concurrent movement about upstanding axes disposed in a common plane generally perpendicular to the propeller axis, each of said rudders having an intermediate part of the inner face thereof formed as a portion of a surface of revolution of which the generating axis is substantially coincident with the rudder axis, and of which the generatrix is an arc of a circle substantially concentric with the circle described by the propeller tips and of slightly greater radius, the inner faces of the rudders diverging forward and aft from the said intermediate parts thereof to an extent sufficient to permit required acceleration and deceleration of the propeller race without disturbing loss due to cavitation in either forward or reverse direction of movement of the vessel.

2. In steering apparatus for screw propelled vessels, the combination with a propeller, of balanced rudders, one disposed at each side of said propeller, means supporting said rudders for pivotal and concurrent movement about upby the propeller tips and of slightly greater radius, the inner faces of the rudders diverging forward and aft from the saidintermediate parts thereof to an extent sufficient to permit required acceleration and deceleration of the propeller race without disturbing loss due to cavitation in 3 either forward or reverse direction of movement of the vessel, the outer faces of the rudders defining substantially parallel planes.

3. In steering apparatus for screw propelled vessels, the combination with a propeller, of a pair of rudders, one disposed at each side of said propeller, means supporting said rudders for pivotal and concurrent movement about upstanding axes disposed in a common plane generally perpendicular to the propeller axis, each of said rudders having a part of the inner face thereof formed as a portion of a surface of revolution of which the generating axis is substantially coincident with the rudder axis, and of which the generatrix is an arc of a circle substantially concentric with the circle described by the propeller tips and of slightly greater radius.

4. In steering apparatus for screw propelled vessels, the combination with a propeller, of a pair of rudders, one disposed at each side of said propeller, means supporting said rudders for pivotal and concurrent movement about upstanding axes disposed in a common plane generally perpendicular to the propeller axis, each of said rudders having a part of the inner face thereof formed as a portion of a surface of revolution of which the generating axis is substantially coincident with the rudder axis, and of which the generatrix is an arc of a circle substantially concentric with the circle described by the propeller tips and of slightly greater radius, the outer faces of the rudders defining substantially parallel planes.

5. In steering apparatus for screw propelled vessels, the combination with a propeller, of a pair of rudders, one disposed at each side of said propeller, means supporting said rudders for pivotal and concurrent movement about upstanding axes disposed in a common plane generally perpendicular to the propeller axis, each of said rudders having a part of the inner face thereof formed asa portion of a surface of revolution of which the generating axis is substantially coincident with the rudder axis, and. of which the generatrix is an arc of a circle substantially concentric with the circle described by the propeller tips and of slightly greater radius, said surface extending a substantial distance above and below the generally horizontal plane containing the propeller axis.

6. In steering apparatus for screw propelled vessels, the combination with a propeller, of balanced rudders, one disposed at each side of said propeller, means supporting said rudders for pivotal and concurrent movement about upstanding axes disposed in a common plane generally perpendicular to the propeller axis, each of said rudders having an intermediate part of the inner face thereof formed as a portion of a surface of revolution of which the generating axis is substantially coincident with the rudder axis, and of which the generatrix is an arc of a circle substantially concentric with the circle described by the propeller tips and of greater radius, the inner faces of the rudders diverging forward and aft from the said intermediate parts thereof to an extent sufiicient to permit required acceleration and deceleration of the propeller race without disturbing loss due to cavitation in either forward or reverse direction of movement of the vessel, said propeller being unconfined over a substantial part of the lower portion of the path traced out by the propeller tips.

RICHARD NEWELL COOLIDGE.

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