Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Radial flow devices
Patent
1986-06-12
1990-05-01
Garrett, Robert E.
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Radial flow devices
416243, B63H 126
Patent
active
049214047
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to propellors for watercraft. The term "propellors" shall also include marine screws and like propulsion units.
(2) Prior Art
Conventional propellors have two or more blades fitted to a hub and set at a pitch angle selected as most appropriate for the intended application. The propellors produce a divergent cone of thrust which reduces their efficiency, as the thrust is dissipated in the surrounding water and they also produce a "cocktail" or "roostertail" spray above the waterline, especially at higher speeds, indicating that potential thrust energy has been wasted. The divergent coning effect has been partially eliminated by producing shrouded or ringed propellors but these generate increased turbulence and suffer increased drag. Finally, the known propellors produce very little, if any, reverse thrust which can be used to reverse or brake the vessel to which the propellors are fitted.
Various types of propellors have been proposed. For example, U.S. Pat. No. 2,087,243 (Caldwell) discloses a propellor of convergent radial height along the propellor, where the forward portion of each blade is forwardly inclined and the rearward portion is rearwardly inclined and where the line of junction of the blade with the hub is "a regular spiral of a given pitch, the peripheral pitch of the blade being greater than that of the junction line". United Kingdom Patent No. 8568 of 1909 (Marks) discloses a propellor where the peripheral pitch of the blade increases along the propellor and the radial height of the blade increases in height along the propellor.
Even these propellors have not proved satisfactory in overcoming the problems with the known propellors discussed above.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide a propellor which generates greater thrust than a conventional propellor of similar dimensions.
It is a preferred object to provide a propellor which can generate a large braking effect e.g. upto 50% reverse thrust.
It is a further preferred object to provide a propellor which creates less turbulence, the propellor producing a convergent cone of thrust.
It is a still further preferred object to provide a propellor which can provide a higher vessel speed for a given propellor speed.
Other preferred objects of the present invention will become apparent from the following description.
In one aspect the present invention resides in a propeller for watercraft including:
a hub connectable to a drive shaft; and
a plurality of blades attached to the hub, each blade having a leading portion, a central portion and a trailing portion, wherein:
the line of junction between at least the central and trailing portions of the blades with the hub is of increasing pitch along the hub.
Preferably the leading portion of each blade is forwardly inclined relative to the hub, and the trailing portion of each blade is rearwardly inclined relative to the hub. Preferably the central intermediate portion of the blade, approximately 70.degree.-110.degree. from the leading portion, extends substantially radially to the hub.
Preferably the peripheral pitch of the blades increases along the propellor more preferably from the central or intermediate portion to the trailing portion of the blades.
Preferably the radial height of the blades increases from the leading portion to the central or intermediate portion, where the radial height is a maximum, and the radial height of the blades then decreases to the trailing portion.
Preferably, in side view, the leading portion of each blade has a configuration of an aerofoil and the trailing portion has a configuration of an aerofoil to generate low pressure areas in the water through which the propellor is passing.
Preferably each blade extends around the hub for 180.degree. to 270.degree., more preferably approximately 220.degree..
BRIEF DESCRIPTION OF THE DRAWINGS
To enable the invention to be fully understood, a preferred embodiment will now be described with referenc
REFERENCES:
patent: 1019437 (1912-03-01), Draper
patent: 1358430 (1920-11-01), Faehrmann
patent: 1455591 (1923-05-01), Lawson
patent: 1543261 (1925-06-01), Hickmann
patent: 2087243 (1937-07-01), Caldwell
patent: 2667936 (1954-02-01), Clark
patent: 3635590 (1972-01-01), Phillips
patent: 4632636 (1986-12-01), Smith
Garrett Robert E.
Pitko Joseph M.
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