US2161074A - Propeller - Google Patents

Description

June 6, 1939.

G. R. M ERTENS PROPELLER Filed Dec. 1, 1936 ORNW 5 m 6 m mwnm MW mb 0 G Y. B

AL! 1 ATT Patented June 6, 1939 UNITED STATES PATENT oFFicE PROPELLER Gabriel K. Mertens, Darby, Pa. Application December 1, 1936, Serial No. 113,547

1 Claim.

My invention relates to a screw propeller adapted for use on power propelled boats. The invention consists in a continuous screw propeller having a graduated pitch of its blades from the 5 front towards the rear of the boat or vessel and having a blade which decreases in diameter from the front to the rear part of the blade.

I-Ieretofore vessels have experienced considerable vibration from the use of a screw type of propeller. This vibration is brought about by the unbalanced propeller, for one reason; and second, the churning of water from one side to the other.

By my invention I have been able to eliminate l5 vibration and increase the speed of the boat for the same power input. As a corollary by decreasing the power, I have been able to secure the same speed in a boat of the same size under like conditions where my new and improved go screw propeller is used.

Objects of my invention are to provide a screw propeller which in proportion to its size is possessed of large capacity. The propeller will not be damaged or broken by engaging objects in the 5 water, and the propeller will take firm hold of the water at all times and consequently will not subject the driving engines to sudden shocks and strains.

My invention comprises a continuous screw which (first) decreases from front to rear in a direct geometric ratio, and (second) this continuous screw blade decreases in diameter from the front to the rear so as to outline a truncated cone, as will be further explained in detail, and (third) the blade in crosssection is concave on one side and convex on the other side.

It also should be noted that my new propeller does not require a great depth of immersion so that a vessel equipped with my improved propeller can move in comparatively shallow Waters.

Further, where the ordinary propeller blade might be raised out of the water due to the pitching and the tossing of the vessel and then come down with a sharp blow, this would not occur with my propeller, particularly since the blade is properly balanced.

My invention provides little or no vibration to the shaft and has a slight tendency to throw waves on eitherside of the course of the vessel.

It is also to be observed that the structure of the blade eliminates danger of the blade being broken by contact with logs or other solid objects which infest the waters. The uniform action of 55, the worm type of propeller against the water diconvolution minishes the jarring of the engines and vibration in ships, which vibration is at present objectionable. This vibration is in a large measure caused by the lack of a continuous form of action of the propellers against the water.

With the above and related objects in view, my invention consists in the following details of construction and combination of parts, as will be more fully understood from the following description, when read in conjunction with the accompanying drawing, in which:

Fig. 1 is a side elevational view of my invention as applied to a vessel.

Fig. 2 is a view from the line 2-2 of Fig. 1.

Fig. 3 is a schematic side elevational view of the relative position of the convolutions of the propeller.

Fig. 4 is a sectional view of the upper portion of the front convolution taken on the line 4-4 of Fig. 2.

Referring now in greater detail to the drawing, I show my invention embodied on a boat, vessel, or ship, generally designated as A. My invention is mounted upon a rotatable shaft H], which is suitably mounted on a bearing, or bearings. The shaft is suitably connected to a source of power (not shown) whereby the shaft is rotated.

My improved propeller, of the continuous screw type and of a spiral construction, is composed of a plurality of convolutions I2, [4, l6, i8, 20 and 22 receding in appropriate proportions from the front to the back and decreasing in diameter outwardly from the front to the back. The first [2 of a maximum diameter, designated as L is nearest the source of power, and as the convolution moves a distance D through 360, the diameter of the helix or convolution decreases. A second helix 14 of maximum diameter is a continuation of the helix I2 and is a definite geometric proportion smaller than the first helix I2, and the helix I4 makes one complete turn for a distance designated as D see Fig. 3.

At this point, it is to be observed and carefully noted that the distance D through which the helix l4 passes, is less than the distance D through which the helix I2 passes. This is illustrated diagrammatically in Fig. 3.

The ratio of taper is that the angle X of the cone shown in Fig. 3 is an angle whose tangent is A,. In other words, the outer edge of convolutions must be in the curved surface of the outline of a truncated cone whose generatrix and medial axis defines an angle whose tangent is The helix [6 is of less diameter than the aforementioned helixes l2 and I l, and the distance, designated as D, along the axis of the shaft traversed by the helix [6 is in proportion to its maximum diameter D The helixes I8, 26 and 22 are constructed in the same pitch ratio and diametrical ratio as the previously mentioned helixes l2, l4 and I6.

Six convolutions of the propeller preferably are used, and they cover five-eighths of the medial axis of the outline of the theoretical truncated cone, and the diameter of the base of the truncated cone is one-half the height of the full cone. In other words, if the base is 20 inches, the height of the cone is 40 inches, and the convolutions of the blades will extend for 25 inches.

A schematic diagram shown in Fig. 3 illustrates that the decrease in diameter of each helix is directly proportioned to the distance the helix travels as measured along the axis of the shaft. Hence, since the ratio of diameter is a direct proportion of the length as measured along the axis, the tip of each blade will lie in the same straight line.

Expressed in another manner, the contour or outline produced by the revolution of the propeller is a truncated cone. The longitudinal distance decreases along the shaft from one convolution of the blade to the next convolution.

In other words, the pitch, which is the amount of advance of a screw-thread in a single turn, decreases from front to rear for each convolution. This decrease in pitch is in accordance with the definite arithmetical ratio aforementioned.

F'or the sake of emphasis as to the efficiency produced with my invention, I shall assume for the purposes of illustration that the vessel is stationary while its propeller is revolved. Considering the forward convolution l2 and the water acted upon by that convolution, the revolving of the convolution would be to drive the body of water rearwardly in a straight line extending diagonally away from the axis of the propeller; this is the resultant effect of the centrifugal force of the revolving inclined or camlike surface of the blade. This movement is likewise theoretically true of each separate body of water acted upon by each separate part of the blade. The convolution also gradually releases dead water or water which is not effective.

Hence, if the vessel be stationary, the water is forced rearwardly by a screw in a series of frustoconical sheets-the apex of each being in the axis of the propeller shaft and the cone base extending rearwardly; and some dead water is also forced rearwardly through each convolution.

It is to be observed that there would be no effect on the water reaching the next succeeding convolution since the next succeeding convolution is of a smaller diameter, so that the particular body of water being driven back by its predecessor blade does not interfere with that particular body of water. However, each blade is sufiiciently far out radially as to act upon a fresh portion or portions of water which have not been broken up by the precedent portions of the blade, and the blade or convolution also acts on a part of the dead water. Under such circumstances, a maximum driving effect is obtained.

In the above discussion, the assumption was made that the vessel was remaining stationary while the propeller was revolving, but the principle is equally the same if the vessel is considered as being in motion. The successive bodies of water are passing simultaneously and constantly from every successive portion of the blade (without interference from any other part of the blade) while the vessel and the propeller are themselves likewise advancing forwardly.

Further, since the vessel is going ahead, the rearward parts of the blade are constantly being brought into position where they are acting upon waters which may already be broken up by the forward portions of the blade and which ordinarily'cause a suction or drag on the blade.

There is no requirement for placing the propeller blade in a tapering tunnel.

I prefer to form the entire worm propeller in one integral casting, as is shown in the drawing, but the worm may, of course, be formed in separate sections securely united together. The worm propeller outside from its other improved advantages is of an outline presenting great strength and durability.

Although my invention has been described in considerable detaiL such description is intended as illustrative rather than limiting, since the invention may be variously embodied, and the scope of the invention is claimed.

I claim as my invention:

An integral boat screw propeller comprising a central shaft, a continuous blade comprising a plurality of complete convolutions surrounding said shaft, said convolutions decreasing in pitch from the front to the rear in a direct arithmetical progression, the diameter of each convolution of the propeller decreasing in diameter l.

by a direct arithmetical progression from the front to the rear, the convolutions arranged to have their edges within the outline of a cone whose pitch extends for -.a distance of fiveeighths of the length of the medial axis of said cone, and the outline of a truncated cone whose medial axis forms an angle with the generatrix of the truncated cone so that the tangent of the angle is approximately 0.25.

GABRIEL R. MERTENS.

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