Propeller arrangement for a marine propulsion unit

Details Propeller arrangement for a marine propulsion unit Propeller arrangement for a marine propulsion unit

1994-09-14

1995-06-13

Avila, Stephen P.

Marine propulsion

Screw propeller

Propeller arrangement

440 89, 416 93A, B63H 510

Patent

active

054237017

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a propeller arrangement for a marine propulsion unit, comprising first and second concentrically supported propeller shafts for rotation in opposite directions, each shaft carrying a propeller hub having a first sleeve member secured to the shaft for rotation therewith, a second sleeve member provided with propeller blades, and a bushing of elastic material disposed between said sleeve members.
Hitherto, propeller arrangements of this type when used in conjunction with marine propulsion units having so-called stern-drive, for example of the Aquamatic.COPYRGT. type, have had their exhaust passages from the engine discharge via a cavitation plate positioned above the propellers. Discharge of exhaust gases via the cavitation plate is also used in single propeller drive systems, though with such drive systems it is also common to direct the exhaust gases through exhaust passages in the propeller hub. In such a case, the construction of the hub, as well as its sealing to the drive unit, is somewhat more complicated, though this is offset by the advantage that the exhaust gases from the hub fill out the central cavitation void behind the hub centre which is created during high-speed cruising. This allows the stern cone on the propeller hub to be dispensed with. In addition, a somewhat higher propeller efficiency can be attained, at least in the higher speed range.
However, no-one has yet applied the method of exhausting gases through the propeller hub known for single propellers to a double propeller drive system, since it has generally been considered that any possible advantages would be outweighed by the disadvantages associated with increased costs due to the more complicated construction of the double propeller drive, etc.
It is therefore a general object of the present invention to provide a propeller arrangement of the type mentioned in the introduction, which provides an increase in efficiency at least in the higher speed range when compared to conventional double propeller systems, though which is not prohibitively expensive.
This object is achieved in accordance with the present invention by means of the propeller hubs being provided with at least one axial passage for the discharge of exhaust gases from an internal combustion engine forming a part of the propulsion unit.
It has been shown that exhaust gas discharge via the propeller hubs in a double propeller system provides an increase in the total efficiency of the propeller arrangement which is greater than what could be expected in view of that which is achieved with single propeller systems, and that this result can be achieved using a relatively uncomplicated construction.
In known single propellers with exhaust gas discharge through the hub, the exhaust passage is arranged between the outer hub sleeve which carries the propeller blades and the inner sleeve member. Such an arrangement can lead to problems with the front propeller due to the relatively large diameter of the tubular shaft. Depending on the material of the hub, there is a risk that the hub sleeve casting be too thin when employing presently specified sizes of exhaust passages and radius of the propeller blade intersection surface.
In a preferred embodiment of the invention, the exhaust passage is arranged in an inner sleeve member. The inner sleeve member includes an inner sleeve that is shaped with inwardly directed grooves and splines for engagement with corresponding grooves and splines on the propeller shaft, as well as an outer sleeve which is concentric with, and spaced from, the inner sleeve, the spacing forming an exhaust passage which is divided into several axial channels by wall elements which unite the outer and inner sleeves.
By arranging the exhaust passage in the sleeve member radially inwardly with respect to the rubber bushing, the outer sleeve which carries the propeller blades can be sized and cast with sufficient wall thickness. At the same time, the rubber bushing retains its large diameter and optimal adhesion surface area for

REFERENCES:
patent: 2058361 (1936-10-01), Sherwood
patent: 4023353 (1977-05-01), Hall
patent: 4540369 (1985-09-01), Caires
patent: 4793773 (1988-12-01), Kinouchi et al.

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