Stern Unit For Marine Craft

Abstract

A stern unit of marine craft that comprises a casing for housing a shaft, a propeller, and at least one rudder actuated by hydraulic pistons is described. The casing is open at the bottom, with its bottom surface having a parabolic shape in cross-section. The casing has an inlet section near to the hull that diverges rearwardly toward an outlet section. The casing provides a housing to the shaft, propeller, rudders, with a gap located above the trace line of the boat bottom where air is sucked above the water surface line such that an air film extends along the bottom surface of the casing towards the outlet section. The stem unit reduces frictional resistance and supplies additional thrust by providing cavitation between the propeller and the rudders.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the stem unit provided in marine craft whereby power generated by the engine and the transmission mechanism is linearly transmitted to the propeller by means of a shaft.

2. Discussion of Related Art

Generally, in the stem section of the marine craft, lubrication oil, felt gaskets against oil leakage, balls for the bearing of the shaft, spider balls for directing the power (sometimes called a universal joint for directing the power), and fastening elements such as bellows, bolts and clamps that provide the inter-connection of these components, gear assemblies and joints are employed.

General information relevant to the invention can be found in U.S. Pat. Nos. 6,193,573; 6,045,420; 5,957,078; 5,439,403; 5,171,175; 5,506,255; 5,074,813; 5,036,781; 4,941,423; 4,746,314; 4,553,945; 4,443,202; 3,942,464; 3,793,980; 3,742,895; 3,336,891 and 3,336,752 and each of these United States Patents is hereby incorporated by reference. Each of these patents, however, suffers from disadvantages, including one or more of the following.

In U.S. Pat. No. 5,066,255, as a document known from the state of art, a drive arrangement in which a drive shaft extends from an inboard engine through the stem wall to a propeller arranged in a tunnel-shaped water flow guide structure extending backwardly from the bottom edge of the stern wall, is described. This structure is movable upwards and downwards as well as to the left and to the right. However the number of the components providing these movements is quite high and furthermore balls, spider, felt (including felt gaskets), gear wheels and lubrication oil are used. Consequently the frequency of break-down and damage increases due to the mechanical wearing-down of the components.

Another disadvantage is that surface drive systems (including Arneson drive systems) utilize propellers with large surface areas that create substantial loads on the engine while initially getting under way, when the boat is not yet on plane and the propeller is fully submerged.

SUMMARY OF THE INVENTION

The object of the present invention is the realization of the stem unit in marine craft, whereby power generated by the engine and the transmission mechanism is linearly transmitted to the propeller by means of a shaft.

Another object of the invention is to create a ventilated propeller, using an air-lubricated fixed casing, that exhibits most of the advantages of a surface drive at high (planing) speeds and reduces the disadvantages of such a surface drive at low (non- planing) speeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The stem unit for marine craft, realized in order to attain the object of the present invention, has been illustrated in the attached drawings; wherein:

FIG. 1 depicts a cross sectional view of the stem unit,

FIG. 2 depicts a plan view of the stern unit, and

FIG. 3 depicts longitudinal and transverse cross-sectional views of the stem unit.

DETAILED DESCRIPTION OF THE EMBODIMENT

The components shown in the figures are individually enumerated as follows:

• 1. Stem unit
• 2. Casing
• 3. Shaft
• 4. Shaft housing
• 5. Water lubricated bearings
• 6. Propeller
• 7. Rudders
• 8. Rudder stand
• 9. Transmission element
• 10. Steering assembly comprising hydraulic cylinder and piston
• 11. Flange
• 12. Rear bottom edge of the hull
• 13. Water surface line
• 14. Inner surface of casing
• 15. Air film
• 16. Gap

The stem unit (1) provides the movement and while having way, the guidance and direction of the marine craft.

The stem unit (1) comprises a casing (2), a shaft (3), a shaft housing (4), water lubricated bearings (5), propeller (6), one or more rudders (7), a rudder-stand (8) and a steering assembly comprising hydraulic cylinder and piston (10). The stem unit (1) contains a parabolic and inclined (sometimes called “a fish-back”) shaped casing (2) serving as a tunnel and a propeller (6) near the outlet of the easing (2).

The propeller (6) is connected to the inboard engine mounted in the marine craft in a straight line, by means of the transmission mechanism using a shaft (3), borne in the shaft bearing (4) and water bearings (5) without using any spiders and balls or any type of universal joint. The rudder is activated by means of a steering assembly comprising hydraulic cylinder and piston and is disposed in front of the propeller (when viewed from the rear of the steering assembly) which enables the marine craft to be guided. An alternative description using the forward direction of the boat as a reference would be that the rudder is behind the propeller.

The casing (2) that protects the propeller and is used to guide the water, consists of two sections that are open at the bottom, namely; an inlet and an outlet section. The inlet section is a narrow section where the stem unit (1) is connected to the transom of the hull (12). The stern unit (1) is fixed to the rear wall of the hull (12) by means of a flange (11) over the inlet section; whereas the outlet section, being an extension of the inlet section, has a fish-back shaped curved structure that expands towards the end portion. The bottom surface of the casing (2) has a parabolic transverse cross-sectional shape at the outlet section (FIG. 1). However at the inlet section, which is nearest to the rear of the marine craft (12), the bottom surface of the casing has an inclined structure. During the planing motion of the marine craft, the water stream passing below the marine craft first strikes this inclined structure which is at the bottom surface of the casing (2). The leading edge of this inclined structure is positioned at a slightly higher level than the level of the water stream. The suction action of the propeller fills the area between the level of the water stream and the bottom surface of the casing with water. However, because of the slightly higher position of the leading edge of the inclined structure, air is also suctioned in, creating a film between the water and the bottom surface of the casing. This air film, preferably a thin air film, reduces friction between the casing (2) and the water. However, the water passing through the propeller is free of air, allowing the propeller to thrust efficiently. In a preferred embodiment of the invention, the water which strikes the propeller blades is free of air, yet the tips of the propeller blades penetrate into the air film between the bottom surface of the casing and the water. The blade tips them pull down some of this air with them as they rotate back into the water. More preferably, this air then creates a film around the propeller blades just as has occurred between the bottom surface of the casing and the water. Most preferably, the result is the significant elimination of friction that would normally be caused by the direct contact of casing and blades with the water. In this most preferred embodiment more of the available power of the engine can go toward thrusting the boat forward rather than being lost to friction. Furthermore, a steering assembly comprising hydraulic cylinder and piston (10) is supported at the upper side of the casing (2) to enable the rudder(s) (7) to move and the rudder stand (8) is provided at the down stream end of the casing (2). In this preferred embodiment, the inner surface of the casing (14), the air film (15), the gap (16), the trace line of the boat bottom, and the direction of the flow are shown in FIG. 1.

The torque and the thrust obtained from the inboard engine and the transmission mechanism are linearly transmitted to the shaft (3) by using an elastic transmission element (9).

In this case, the force and movement obtained from the inboard engine and the transmission mechanism, are linearly transmitted to the propeller (6) mounted at the end of the shaft (3) without any energy loss. The shaft (3) is placed in the casing (2), between the water bearings (5) preferably made of rubber, that surround the shaft (3) and which are placed in the tube formed shaft housing (4) in the casing (2) so that preferably one is provided at the front and one at the back side.

Water taken in for cooling the engine is transmitted to the shaft housing (4) wherein the shaft (3) is placed between the water bearings (5), by means of a pump and a valve, in order to form a thin layer of water between the shaft (3) and the water bearings (5) and the shaft housing (4). Formation of such a layer of water, cools the shaft (3) and minimizes the friction between the shaft (3) and the water bearings (5).

Preferably two rudders (7) which are activated by means of a steering assembly comprising a hydraulic cylinder and piston (10) placed above the casing (2), are located in back (when viewed from the front of the boat) of the propeller (6).

In a preferred embodiment, the rudders (7) are placed in the rudder stands (8) located above the casing (2), in such a manner that a certain distance is kept between them. Using the axis of the rudder stands (8), the rudders (7) may be moved. By means of the rudders (7) which are simultaneously oriented to the same direction by the steering assembly comprising hydraulic cylinder and piston (10), the direction of water stream is changed which also changes the direction of the boat. In other preferred embodiments, one or more rudders may be used depending on the deflection created by the rudder(s) and how much rudder surface area is needed to turn the boat.

In the stern unit (1) according to the present invention, the components used in other conventional stem units, such as lubrication, felts (including felt gaskets) against oil leakage, balls used in shaft bearings (3), spider balls used to direct the power and in association with these, the supplementary fastening elements such as the bellows, bolts and clamps, gear assemblies and joints, are not used.

In addition to the linear transmission of the engine power to the propeller (6) and water without any loss of energy, the number of operating components is minimized, thus reducing the potential of break-down and damage to a minimum level. Furthermore, intervals between successive maintenance are longer due to the fact that the number of components is less and no mechanical wearing is observed; and as no balls are used in the stem unit (1), it operates with less noise and without any vibrations, as compared to other stem units.

FIG. 1 shows a preferred embodiment of the stem unit for a marine craft (1) comprising a shaft (3) which transmits the torque produced by the inboard engine linearly, a propeller (6) activated by and located at the front end of the the shaft, at least one rudder (7) located in front of the propeller guiding the marine craft, which are activated by means of a steering assembly comprising hydraulic cylinder and piston (10). In a more preferred embodiment the propeller is ventilated where some part of the blades pierce the air film between the bottom surface of the casing and the water and pull some of this air down creating a second air film that coats the blades and reduces friction. This preferred embodiment has an advantage over a typical ventilated propeller, like a surface drive (including an Arneson surface drive), because only the very tip (or end) of the propeller blades contact the air layer under the casing to achieve the ventilation of the blade, and preferably, the entire blade. This is in contrast to a typical surface drive where typically a full half of the propeller disc is above the waterline, thus the ratio of blade area to void area in the propeller disc has to be very high so that enough thrust can be generated; for example, when the marine craft is just getting under way and is not yet on plane and the entire propeller is submerged, turning such a “dense” propeller puts a high load on the engine and acceleration is slow. Thus, the preferred invention works well during the entire speed range and the stop-and-go conditions typically associated with real-world marine craft usage, and a wider variety of propeller shapes and sizes can be used with good result.

Claims

1. A method of reducing water friction on a non-surface drive propeller casing comprising: coupling a movable parabolic and inclined casing having a lower surface to a boat hull over a linear drive propeller, and adjusting the movable parabolic and inclined casing such that an air film is formed between the lower surface and the water when the boat is moving wherein the water friction is reduced.

2. The method of claim 1 wherein the movable and inclined casing transversely expands rearwardly from the boat hull.

3. The method of claim 1 further comprising adjusting the movable parabolic and inclined casing over the linear drive propeller using a hydraulic piston system.

4. A method of ventilating a non-surface drive propeller comprising: coupling a movable parabolic and inclined casing having a lower surface to a boat hull over a linear non-surface drive propeller having blades and blade ends, adjusting the movable parabolic and inclined casing such that an air film is formed between the lower surface and the water when the boat is moving and ventilating the non-surface drive propeller using the blade ends to draw air into the propeller.

5. The method of ventilating a non-surface drive propeller of claim 4, wherein adjusting the movable parabolic and inclined casing further comprises the step of moving the casing using a hydraulic piston system.