Rim-driven propulsion pod arrangement

#This invention relates to propulsion pods having rim-driven blade sets for propelling marine vessels.

#Conventional propulsion pods with rim-driven blade sets for marine vessels are subject to vibrations produced by turbulence in the water passing through the pod which may be excessive and may be transmitted to a vessel being propelled and also may be subject to wear of the parts supporting the rotating blade sets.

#The Veronesi et al. U.S. Pat. No. 5,252,875 discloses a propulsion pod containing a permanent magnet motor driving a rotating blade set and having a rotor rim surrounding the blade set embedded in the surrounding structure so that it is out of the flow path of water through the pod and providing circulation of water through the space between the rotor and the stator from the high pressure side of the rotor to the low pressure side. That arrangement also provides stationary vanes following the rotating blade set to minimize swirling of the water driven by the blade set and also minimize cavitation and enhance efficiency.

#Further objects and advantages of the invention will be apparent from a reading of the following description in conjunction with the accompanying drawings, in which:

#FIG. 1 is a schematic view in longitudinal section illustrating a representative embodiment of a rim-driven propulsion pod arrangement in accordance with the invention;

#FIG. 2 is a fragmentary view illustrating a path for flow of cooling water between the rotor and the stator in the pod housing;

#In the typical embodiment of a rim-driven propulsion pod arrangement 10 shown in FIG. 1, a pod 12 has a housing 14 supported by a strut 16 from an adjacent vessel 18 which is to be propelled by the propulsion unit. The pod 12 contains a rotor assembly 20 rotatably supported by a rotor support assembly 22 which is centrally mounted within a central duct 24 in the housing 14 by an array of support members 26 shaped in the form of vanes or blades to guide water emerging from the rotor assembly 20.

#The rotor assembly 20 includes a hub 28 containing a plurality of radial bearings 30 rotatably supporting the hub on a central support shaft 32 of the support assembly and an angularly distributed array of blades 34 mounted on the hub and designed and shaped to propel water rearwardly through the housing in an efficient manner during rotation of the rotor assembly. The stationary blades 26 and the rotating blades 34 are designed as a set to cancel the swirl in the water driven by the rotating blades to eject water from the propulsion unit with maximum efficiency while minimizing cavitation and induced structural vibration by recovering pressure that is normally lost on the inside surface of the housing of a rim-driven propulsion unit.

#The factors considered in the design of the fixed and rotating blades to be optimized as a matched set are efficiency, cavitation and hull-induced vibration as well as the length and diameter of the propulsion pod and its weight and structural integrity. A configuration in which the rotating blade row 34 is located upstream of the stationary blades 26 is preferred because of the necessity of positioning the motor at the location of maximum duct thickness, typically about the duct quarter chord which positions the rotating blades forward of the stationary blades to minimize the duct length and pod weight. Preferably, to help maximize efficiency, only two blade rows are used. The forward, rotating blade row 34 converts rotational energy or torque into thrust, resulting in swirling of the downstream flow which is a hydrodynamic loss manifested by reduced efficiency. To increase the efficiency the downstream, stationary blade row 26 is designed to remove the swirl which has been imparted by the rotating blade row resulting in a discharge of water from the pod which is essentially entirely in the axial direction.