Fluid reaction surfaces (i.e. – impellers) – Articulated – resiliently mounted or self-shifting impeller... – Resilient bias or mount
Patent
1996-07-12
2000-10-03
Verdier, Christopher
Fluid reaction surfaces (i.e., impellers)
Articulated, resiliently mounted or self-shifting impeller...
Resilient bias or mount
416136, 416140, B63H 300, B63H 302
Patent
active
061263990
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to improvements in and/or relating to folding or feathering propellers.
BACKGROUND OF THE INVENTION
Folding or feathering propellers have been used in a number of, particularly, marine applications.
The ordinary folding propeller often used on cruising yachts has the propeller blades fold so as to provide low drag from the propeller when under sail. The disadvantage of such folding propellers (e.g. as disclosed in U.S. Patent Specification No. 4,086,025) is that the blades may not open when in ahead operation and can cause vibration if not perfectly aligned or true to each other. However, the most important detriment from this form of changing profile propeller is that motoring efficiency compared to a fixed blade propeller of the same diameter is about 70%. The same type of folding propeller in astern operation will not open to the maximum diameter due to the thrust on the blades balancing the centrifugal force holding the blades open with the result that seldom is more than 50% of the motoring efficiency achieved as compared to a fixed blade propeller of the same diameter.
In addition, these propellers require significant mass in the tips of the blades to provide the maximum centrifugal force thus constraining optimum blade design and causing vibration problems. In racing yachts this extra mass is a disadvantage.
To address the deficiencies of such folding propellers, a variety of different bladed propellers of a feathering kind have been proposed. Usually these are of two or three blades but can have more. Frequently such feathering propeller blades are fitted with a bevel pinion that engages a central cone gear driven by a shaft. Such arrangements tend to be complex notwithstanding their wide spread acceptance in the boating industry. Moreover, even in the feathered condition, the propeller and its shaft will auto-rotate, thereby increasing drag. An example of such a propeller is marketed under the trade mark "MAX-PROP".TM. available in New Zealand from Marine Power and Service Limited, 50 Cook Street, Auckland 1, New Zealand.
Some feathering propellers are known, such as the propeller disclosed in U.S. Patent Specification 4,058,360, that have blades that, when fully feathered, are constrained by stops that hold the feathered blades in line with the shaft. Other feathering propellers such as the MAX-PROP.TM. cause the blades to turn to and from the pitch position by a bevel gear at the base of each blade engaged with a bevel gear on the propeller shaft. Thus the blades are geared together and only face in the same direction (are feathered) when they are in line with the shaft.
Blades feathered in that position may cause resistance or drag because, in practice, the flow of water is not commonly in line with the shaft. For example, in order for the propeller shaft to penetrate the hull surface and give adequate clearance for the propeller it is commonly angled down at an angle to the horizontal. Inclinations of between 10.degree. and 20.degree. are known.
Also common is a surface of the hull immediately above or adjacent the propeller which curves or slopes upwards. As fluid flowing along a surface tends to flow parallel to the surface, the water flow at or near the propeller is at an angle substantially similar to the angle of the adjacent hull surface. For example, it is known to have a propeller shaft at an angle of 11.degree. to the horizontal but the flow of water parallel to the hull at an angle of 17.degree. to the shaft.
Further problems are encountered with sailing yachts which, when sailing against the wind, have the longitudinal centre line of the craft offset from the direction oftravel by 5.degree. or more. This is caused by slippage.
Yet another example is the sailing of a boat in rough weather where the boat is caused to surge sideways with wave action which causes a flow of water across the line of, and therefore, substantially non-parallel to the propeller shaft.
When the blades in a feathered condition are substantially parallel
REFERENCES:
patent: 0608265 (1898-08-01), Olsen
patent: 1520746 (1924-12-01), Boyce
patent: 1718525 (1929-06-01), Casey
patent: 3099321 (1963-07-01), Watts
patent: 3897170 (1975-07-01), Darvishian
patent: 4058360 (1977-11-01), Hirschberger
patent: 5232345 (1993-08-01), Rocco
Bartley Bryan Allen
Blundell John McKenzie
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