Marine propulsion – Screw propeller – Having means to control flow around propeller
Patent
1985-07-03
1987-05-19
Peters, Jr., Joseph F.
Marine propulsion
Screw propeller
Having means to control flow around propeller
440 67, B63H 128
Patent
active
046664114
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a thrust augmenter for propeller driven vessels which utilises a wake generator.
Propulsion of objects such as ships is achieved by jetting a stream of fluid to the rear. The force involved in the momentum change is conveyed to the vehicle generating it to effect its propulsion. The jet stream is normally effected by a propeller which accelerates fluid approaching it due to the forward motion of the vessel. As speed increases so the change in momentum is reduced.
Some water reaching the propeller is in the wake of the vessel and hence it is travelling in the direction of movement of the vessel at some proportion of its forward speed. The change in momentum effected by the propeller of the water in the wake of the vessel is then increased so improving the efficiency of propulsion and this improvement is known as a "wake factor". Increasing the wake of a hull however causes high velocities on its stern to produce a rearwards force which negates in part the gain from the wake augmentation of the propeller. As a result the velocities and pressures of water reaching the propeller are not uniform over its circular orbit.
It is an object of the present invention to provide a thrust augmenter by generating a more uniform wake just forward of the propeller for fast moving vessels.
In one form the invention resides in a thrust augmenter for a propeller fluid drive comprising a substantially cylindrical hollow body having an open rear face which is substantially circular or partially circular and is located closely adjacent and ahead of the propeller wherein the outside diameter of the rear face is larger than the propeller.
If a wake is generated by the construction of a hollow body of almost circular cross-section just forward of the propeller with the spacing between the propeller and the rearward extremity of this wake generator being a fraction of the propeller diameter, the wake water reaching the propeller can be moving forward at almost the same speed of the vessel and the velocity of water arriving at the propeller is evenly distributed over its orbit.
According to a preferred feature of the invention the forward end of the body is streamlined to reduce fluid drag as a result of its forward motion.
According to a preferred feature of the invention the forward end of the body is formed with at least one opening to provide for limited fluid flow between the interior and exterior of the body.
According to a preferred feature of the previous feature said openings have closures movable in relation to the openings to vary the degree of opening.
According to a preferred feature the thrust augmenter is mounted to a keel or keel like structure from which the propeller extends rearwardly said thrust augmenter comprising one or more portions fixed to the keel or keel like structure.
According to a preferred feature of the previous feature the forward end of the body is formed with openings to each side of the keel or keel like structure and associated with hinged gates associated with a drive means capable of varying the degree of opening of said gates said gates being openable outwards and being inclined to the hull to reduce forward form drag.
According to a preferred feature of the invention said drive means comprises a fluid activated cylinder mounted to the keel and having its piston connected to the gates by a shaft.
If the gates at the forward end of the wake generator are partially opened water will arrive at the propeller with reduced but evenly distributed velocity at the propeller. At slow forward speeds the gates would be more open than at higher speeds when approach velocities to the propeller need to be reduced.
According to a further preferred feature at least a portion of the inner wall of the body has a diameter of significantly less than the outside diameter the body and the outer end of said inner wall diverges outwardly to define a flared entrance to the body at said rear face.
In the case of propeller reversal for backing or stopping the vessel the closures or gates at the
REFERENCES:
patent: 803671 (1905-11-01), Curtis
patent: 2030375 (1936-02-01), Kort
patent: 2275618 (1942-04-01), Edwards
patent: 3710748 (1973-01-01), Baer et al.
patent: 4106425 (1978-08-01), Gruber
patent: 4309172 (1982-01-01), Narita et al.
Peters Jr. Joseph F.
Salmon Paul E.
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