Fluid reaction surfaces (i.e. – impellers) – Working member foldable – pivotable or collapsible to non-use...
Patent
1987-03-10
1988-09-06
Powell, Jr., Everette A.
Fluid reaction surfaces (i.e., impellers)
Working member foldable, pivotable or collapsible to non-use...
416 87, 416212R, B63H 124
Patent
active
047689277
DESCRIPTION:
BRIEF SUMMARY
This invention relates to so-called folding propellers which are screw propellers with foldable blades and are intended for use on sailing boats equipped with an engine for auxiliary propulsion.
Sailing boat propellers where the blades are hinged at the hub and take up a normal position perpendicular or nearly perpendicular to the driving shaft when the ship is propelled by the engine but which are folded up by the water pressure when the ship is using sails alone with the engine stopped, have been known for a long time under the name of folding propellers. The advantage of folding up the propeller blades is that the relatively high resistance of a stopped propeller, or of a propeller driven very slowly around by passing water, is avoided.
The hinged blades of nearly all types of folding propellers are in some way mechanically connected to each other in order to ensure that the positions of the blades are identical as they move from the position at rest to the working position and vice versa. This is very important, because different positions of the blades will bring the propeller out of balance and thus create dangerous vibrating forces. The most common way to ensure the identical movements of the blades is to arrange cog-wheel sectors at the hub end of the blades. The shafts, on which the blades are hinged to the hub, are then arranged in such a way that the cog-wheel sectors are in mesh with each other or with a common cog-rod. A movement of one blade will then cause a similar movement of the other blade or the other blades.
There are however a number of disadvantages connected with this type of folding propeller.
The centrifugal force will move the blades from the position at rest to a position perpendicular to the driving shaft when the engine is started and the hydrodynamic force on the blades will try to pull them either forward or backward depending on the direction of the rotation. A certain position of the blades in the working condition can easily be obtained when the propeller is driving the boat forward, by arranging stops which prevent the blades from moving further forward. A similar arrangement is however not possible when the propeller has to drive the boat astern. The hydrodynamic force will then try to fold up the propeller and the blades will only remain in a position suitable for propulsion if the centrifugal force on a blade is large compared to the hydrodynamic force. Unfortunately, it is not possible from practical reasons to make the blades so heavy that they will remain perpendicular or nearly perpendicular to the driving shaft under all backing conditions and the final position of the blades will therefore be one where the centrifugal forces and the hydrodynamical forces are counterbalancing each other. This position of equilibrium is not well determined because it is strongly affected by the propeller blade geometry and the hydrodynamic working conditions. The virtual diameter of the propeller which is smaller than the maximum diameter because of the inclination of the blades may therefore be too small resulting in a reduced performance of the propeller.
Further, it is not easy to manufacture the cog-wheel sectors at the end of the blades and there are difficulties in making them sufficiently strong. They are therefore exposed to fractures and heavy wear and the blades will then have to be scrapped.
The folding propeller, according to the present invention, is characterised by the stops which only allow the blades to turn about 56 degrees from the position at rest to the working position and by the cog-wheel mechanism which consists of only two teeth per blade placed side by side, one a little offset from the other. Only one face of each tooth is used and for two teeth of one blade it will be the opposite sides.
The centrifugal force will pull the blades out to the working position when the driving shaft rotates. The turning moment of the centrifugal force around the hinge shaft of a blade is, according to simple and well-known physical and geometrical laws, at a maximum when t
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patent: 4364711 (1982-12-01), Brandt et al.
patent: 4427341 (1984-01-01), Eichler
patent: 4565531 (1986-01-01), Kimon
Confol ApS
Powell Jr. Everette A.
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