US3416480A

US3416480A - Ship's stern and propeller arrangement

Info

Publication number: US3416480A
Application number: US613043A
Authority: US
Inventors: Pao C Pien
Original assignee: Navy Usa
Current assignee: US Department of Navy
Priority date: 1967-01-31
Filing date: 1967-01-31
Publication date: 1968-12-17
Anticipated expiration: 1985-12-17
Also published as: GB1207051A; SE345833B; FR1555919A; DE1556512A1

Description

Dec. 17, 1968 P. c. PlEN SHIPS STERN AND PROPELLER ARRANGEMENT Filed Jan. 31, 1 967 2 Sheets-Sheet 1 FIG.

F/GZ.

'INVENTOR PAO CH/ PIE/V Dec. 17, 1968 RIC. PIEN 3,416,480

SHIPS STERN AND PROPELLER ARRANGEMENT Filed Jan. 31, 1967 v 2 Sheets-Sheet 2 INVENTOR P40 CH/ PIE/V ATTORNEY United States Patent 3,416,480 SHIPS STERN AND PROPELLER v ARRANGEMENT Pao C. Pien, Montgomery County, Md., assignor to the United States of America as represented by the Secretary of the Navy Filed Jan. 31, 1967, Ser. No. 613,043 4 Claims. (Cl. 11457) ABSTRACT OF THE DISCLOSURE A ships stern and propeller arrangement having twin laterally spaced and overlapping propellers mounted symmetrically with respect to the central longitudinal plane close to the main hull on shafts extending from stern tube bossings which are smoothly faired into the sterm form or which are carried on short struts attached to the stern. This arrangement utilizes the energy of the water in the viscous wake-belt which normally follows the ship due to skin friction, yet avoids the cavitation and vibration problems normally associated with single-screw ship configurations.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Background of the invention This invention relates generally to ships hull form and screw propeller arrangements and more particularly to twin laterally spaced propellers with overlapping fields. It recognizes the long overlooked fact that the energy of the water normally following the ship may be captured without the attendant problems of cavitation and vibration by using twin propellers properly phased and mounted close to the ships bull in the viscous wake-belt. This viscous wake-belt may be described as the water close to the ships hull which has some forward motion due to skin friction between the water and the moving hull.

The prior art discloses many attempts by experts in this field to increase the propulsion efficiency and at the same time to eliminate the cavitation and the vibration problems, but no significant advances have been made to date. While many have recognized propeller limits of load and cavitation, they have generally solved this problem by using multiple propellers to decrease propeller loading and have placed such propellers away from the hull in the clear undisturbed water to avoid cavitation and vibration problems. These arrangements necessitated the use of long exposed shafts and bearing struts which induced eddy currents and considerable resistance. The inventers of the prior art failed to recognize that they could obtain increased efficiency by mounting the propellers close to the hull and thereby capture the energy in the viscous wake-belt created by skin friction and yet minimize or eliminate cavitation and vibration problems by using two overlapping propellers properly phased.

In particular, Lundborg (Patent No. 384,047) saw advantages in twin propellers, but he mounted them away from the hull in clear water. Browne (Patent No. 162,- 619) also recognizing the need for twin screws to reduce propeller loading, chose concentric counter-rotating propellers for efiiciency, but did not solve the problems of cavitation and vibration.

Summary From the above exemplications it can be seen that the prior art teaches away from the present invention. The instant invention takes advantage of the energy of the water in the viscous wake-belt without the attendant problems of cavitation and hull vibration which had not been previously done in spite of the extensive work of expert ship designers working in this art. Firstly, by placing propellers close to the hull of the ship, these propellers will be working in the viscous wake-belt from which energy can be recovered. Secondly, the use of two propellers overlapped and properly phased eliminates the need for long exposed shafts and struts with their attendant appendage resistance. Thirdly, by overlapping the propellers, the action of one propeller evens out the inflow to the other and thus evens out propeller loading to reduce vibration and cavitation where heretofore, propellers operating the wake-belt, which normally has great velocity variations, created excess vibration and cavitation. Experts in the field did not over many years recognize the unobvious solution to the problem.

The general purpose of this invention is to increase propulsion efficiency, increase speed and endurance of a ship and decrease fuel consumption. To attain these ends, the present invention contemplates placing two propellers in an overlapping, laterally spaced relationship symmetrical with respect to the central longitudinal plane of the ship, and in close proximity to the hull of a single screw type ship. The propeller shafts may be carried by bossings which are smoothly faired into the stern form, or by short struts attached to the stern form having lengths of approximately 30%55% of the propeller diameter. The propellers may rotate in the same plane, in which case they must be phased and counter-rotating, they may be in offset longitudinally spaced closely adjacent planes, or the blades may be raked forward in one propeller and aft in the other propeller in which case they may rotate in either the same or opposite direction.

Accordingly a primary object of this invention is to capture energy existing in the water of the viscous wakebelt normally following the ship.

Another object is to decrease or eliminate cavitation and vibration problems.

Still another object is to eliminate appendage resistance.

An overall object of this invention is to increase fuel economy, speed, and endurance.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following detailed description of the preferred embodiment of the invention as illustrated in the accompanying sheets of drawings in which:

Brief description 0 the drawings FIG. 1 is a perspective quartering view of a single screw cruiser type stern form;

FIG. 2 is a perspective quarting-view showing a transom type stern form;

FIG. 3 is a perspective straight-on aft view more clearly showing the single screw form and overlapping propellers close to the hull; and

FIG. 4 is a water line plan view of a vessel moving in water showing diagrammatically the viscous wake-belt.

Description of the preferred embodiment Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 the after portion of a cruiser type stern hull form designated generally as 10. The water-line is generally designated by a dashed line 12 separating the free-board portion 14 from the submerged bottom portion 16 of the hull form. The extreme after end of the stern form of the cruiser type hull is convexly curved as shown generally at 18. FIG. 3 more clearly shows that there is no break in the smooth continuity of the lines and that there is no discrete transom.

At the extreme after end of the hull form 16 below the water line and on the central axis of the hull, there is a rudder 20 supported by a rudder stock (not shown). The space between the skeg or vertical stern frame 26 and the rudder 20 forms a stern aperture 27.

On either side of the central vertical plane of the hull there is a stern tube bossing 29 equally laterally spaced and smoothly faired into the lower hull form of skeg or vertical stern frame 26. Within the aperture 27 and on shafts extending through the stern tube bossings 29 are propellers 25. As shown in FIG. 1, but more clearly in FIG. 3, these propellers are overlapped. Although shown as physically overlapped it is to be understood that only the propeller induced velocity field need be overlapped to provide the advantages of this invention. As can be seen in FIG. 1, when the propellers are rotating, the tips pass in close proximity to the main hull form, where the viscous wake-belt exists. Alternatively, these propellers may be offset longitudinally spaced planes, in which case they rotate in the same direction or in opposite directions. Also, the propellers may be in the same transverse plane and the blades of one raked forwardly and the blades of the other raked aftwardly to avoid blade contact, and then they may rotate in either direction. It is obvious that when the propellers are overlapped and in the same transverse plane and When the blades are not raked, the propellers must be counter-rotating to avoid blade damage.

FIG. 2 shows an alternative embodiment of this invention wherein the stern form is of the transom type having a discrete transom 30, and where the after bottom portion 16 is flatter from beam to beam and cants forwardly and downwardly to the keel line well forward. The keel line is extended horizontally and aftwardly to terminate in a stern tube bossing which is attached to the main hull form by a thin web or skeg 26 or the propeller shafts may be attached to the hull by struts (not shown). Either a single rudder in the central plane or two rudders, one behind each propeller, may be provided. This transom type ships stern form and propeller arrangement provides the same advantages as the preferred embodiment by placing the propellers close to the hull in the viscous wake-belt. The princpal is also equally applicable to submarine type hulls.

Description of operation FIG. 4 shows in diagrammatical form, the evolution of the viscous wake-belt 32 at and below the water line of a ship traveling forwardly through the water. This viscous wake-belt develops because of the skin friction between the hull and the displaced water. When the ship is moving forward, the water adjacent the skin clings and is thereby carried forward with the ship. It can be understood that there is less relative motion between the water in the viscous wake-belt and the ship than there is between the undisturbed clear water and the ship. As a result, considerable energy is imparted to this water and it is the intent of this invention to capture this energy and thereby increase efficiency of the hull and propulsion system. It is also known that the water in the viscous wake-belt has a high velocity variation which in the past often created severe cavitation and hull vibration. The use of two propellers either physically overlapped or having their fields overlapped, etfectvely reduces the pulsations which occur when a propeller blade moved through the velocity gradient existing in the viscous wake-belt because each propeller evens out the inflow to the other. And obviously, the use of two propellers reduces propeller loading and thereby cavitation, which therefor allows more power to be put into the propulsion system.

Various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter defined by the appended claims, as only the preferred embodiments thereof have been disclosed.

What is claimed is:

1. A ships stern and propeller arrangement comprismg:

a rudder;

a stern form having a vertical stern frame spaced from said rudder to form a stern aperture;

a pair of propellers; and

a pair of propeller shafts having the propellers mounted thereon, extending aftward out of said stern form into the stern aperture, said shafts being laterally spaced equidistantly from the longitudinal center plane of the ship so as to dispose said propellers in the ships viscous wake belt, and the spacing and diameter of the propellers being so related as to dispose each propeller in the induced velocity field of the other propeller to achieve a uniform inflow to each propeller.

2. The ships stern and propeller arrangement of claim 1, wherein the spacing of the propellers is from 100% of the propeller diameter.

3. The ships stern and propeller arrangement of claim 1 wherein the propellers rotate in the same plane.

4. The ships stern and propeller arrangement of claim 1, wherein the propellers rotate in longitudinally spaced planes.

References Cited UNITED STATES PATENTS 1,302,982 5/1919 Shonnard --37 1,628,837 5/1927 Gebers 115-37 2,283,291 5/1942 Selden 114-57 2,371,013 3/1945 Wosenitz 11537 FOREIGN PATENTS 11,676 1884 Great Britain.

ANDREW H. FARRELL, Primary Examiner.

US. Cl. X.R.