WO2001047770A1

WO2001047770A1 - Partially submerged controllable pitch propeller fitted to a transom contoured thereto

Info

Publication number: WO2001047770A1
Application number: PCT/HR1999/000037
Authority: WO
Inventors: Nenad FLEŠ
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-12-28
Filing date: 1999-12-28
Publication date: 2001-07-05
Anticipated expiration: 2002-06-28
Also published as: AU3068100A

Abstract

Partially submerged disc with variable pitch blades provided for installation to articulated transom consists of hub of sufficient size (14) flanged to main shaft (13) with number of inner flanges (16) actuated by linear movement of joke (11) to transfer rotation via short inserts (19) to propulsor blades (15). All other parts are usually encountered in well-proven CPP and stern tube systems. This kind of integration of the propulsor into slender, displacement type hull results in steady flow within selected bottom segment, ability to control fluctuating forces either by choice of low profile at the blade-entry and blade-exit positions or by choice of blade number with respect to active angular size of the bottom segment and yet, utilizing benefits of low resistance of hull with raunded sections, horizontally oriented thrust, possible installation of propulsor on cut stern to enable contribution of blade drag force to the propulsive thrust, the total efficiency of hull-propulsor is expected to overcome efficiency obtainable by conventional partially submerged propeller installation while, due to mechanical/hydrodinamical configuration capability of new propulsor to overcome power limitation of conventional system is evident.

Description

PARTIALLY SUBMERGED CONTROLLABLE PITCH PROPELLER FITTED TO A TRANSOM CONTOURED THERETO

TECHNICAL FIELD

Propulsion of fast catamarans almost exclusively relies on water jets application with installed power reaching 15000 -20000 kW or more.

Use of water jets on very fast vessels such as monohulls, slender catamarans or surface effect ships, encounter at speeds exceeding 55 knots with cavitation phenomena at the bottom water inlet resulting in air suction from the transom side and flow irregularities with uncontrolled trim variations. This technical problem is to be solved by one innovative solution which could be alternative to water jets at very high speed and installed power. BACKGROUND ART

For the speed range concerned an alternative propulsor is well known partially submerged propeller, usually protruding to some distance behind the transom in a way that lower half of a propeller disc runs, at operating speeds, in flow of the water leaving the vessel's bottom. Usual mechanical execution includes universal shaft with pivoted propeller carrier allowing steering and vertical adjustment of propeller immersion to control absorption and to avoid overload of the engine.

The most powerfull commercial installations of partially submerged propeller reaches abt. 4000 kW per unit. Higher outputs would considerably increase strength, steerability and apsorption control problems. Strength and steerability can be enhanced by fixed-non steerable installation - and absorbtion control can be solved by variable pitch blades. However, number of blades is limited by geometry and engineering possibility of pitch actuating mechanism and by hub strength so that already five blades execution seems to be not solvable. In the other hand, the less the number of blades the higher fluctuating forces at the blade - entry and blade - exit phases are induced, leading to excessive vibration and damages of the ship's hull or propulsor itself.

SUBSTITUTE SHE R L 2 DISCLOSURE OF THE INVENTION

If we arrange active part of the propulsor - this means the blades - at the outer edge of one disc, size and shape of which just coincide with rounded transom of slender catamaran hull the result will be ideal interaction between hull and propulsor, beneficial to both in a way:

1. For propulsion: a) The propulsor is fitted immediately behined the transom, meaning that side and vertical forces are easily transfered to the hull structure, while in the case of conventional partially submerged propeller transverse and vertical forces produce high momets at the points where non - pivoting type propeller carrier is flanged to the transom b) By modeling of catamaran's hull just ahead ot transom i.e. by fitting suitable appendages stable flow can be produced within desired angular range. Selection of the number of blades, in relation to angular range, can be done in a way to avoid interference of the fluctuating forces arising at blade - entry and blade - exit phases. c) Diameter of the disc, which is considerably exceeding conventional CP propeller hub diameter, enables fitting of larger number of blades (8 or more) and this helps in keeping frequency and magnitude of fluctuating forces under control. The blades are supposed to run in homogeneous flow with regular and constant radial wake distribution, promoting use of the wake adopted propeller (at the design point) with high efficiency. d) Propulsor's thrust is directed horizontally, meaning that actual efficiency is abt. 2% higher when compared to conventional partially -submerged propeller with 12° shaft angle. 2. For resistance: a) Large today's catamarans do not utilize any hydrodinamic lifting forces at high speeds alike conventional planing vessels as they actually rely on high slenderness ratio (length/breadth relation) of displacement type hulls, the slenderness being the reason for very low residual resistance (wave resistance). When it comes to decrease of viscous resistance (friction and eddy) wetted area and simplicity of form i.e. regularity of flow are decisive factors. The most suitable form fulfilling length, without any widening or flattening of the bottom, knuckles or variation of hull sections as this irregularities, as a rule, increase wetted area and provoke unsteady flow.

The fact is that installation of water jets or conventional partially submerged propellers requires more- less flat bottom in the aft part. On contrary, installation of patented propulsor requires exclusively rounded (semi circular) sections in the aft part. Bottom plating of the catamaran's hull (1) is slightly protruding over the transom (2) to which reduction gear box (3) with integrated CPP control system is fitted. All parts of gear box are standard and well known, starting from input shaft (4), clutch (5), pair of gears (6), hollow propeller shaft (7) with seals (8), thrust bearing (9), pitch controlling piston (10) with joke (11) and distribution valve (12) with control lever.

Deviation from standard execution, if we disregard non existance of intermediate shaft, long propeller shaft and stern tube, starts from large propulsor flange (13) and hub (14) which is of sufficient size to accommodate standard pitch control mechanism serving not only 3 or 4 blades (15) but 8 or more. Inner flange (16) is not connected directly to blade flange (17) as there is short inserted shaft (18) between them. Inserted shaft is enclosed with tube (19), space between being filled with oil from the hub mechanism lubricating system. Hub (14) and outer ring are connected with discs (21). At planing speeds, flow separation take place at the bottom, while transom remains dry. Contour of the transom can be somewhat wider - with bigger radius - than disc of the propulsor for the purpose of avoding flow of water to the blade root representing a mode of absorption control as the effect is comparable with the effect of immersion of conventional partially submerged propeller. Further improvement of propulsive efficiency can be obtained by cutting stern of the each of two hulls at on angle of abt. 60-70° to the centreline in plan view so that resulting force, composed of blade lift and drag components, will act right in desired direction of vessel's motion. In this way, normally useless side force, better to say energy normally lost to overcome drag of the blades, is converted to useful thrust energy. A number of vanes can be fitted along bottom circumference immediately forward of the propulsor to compensate for rotational losses induced by propulsor rotation. In order to reduce mass of the propulsor some parts can be built of epoxy reinforced carbon fibres (discs, inserts and similar)

Compared to water jet partially submerged wheel with C.P. blades fitted to articulated transom is featuring following advantages: 1) Easier integration within hull (transom is effected only, not bottom)

2) Resistance "friendly" - rounded - aft sections compared to more flat bottom needed for water jet inlet integration

3) Higher efficiency, especially if transom is jawed in a way that side force contribute to thrust o 4) Absolute insensitivity to air ingress below bottom, therefore particularly advantageous for SES propulsion

5) Less total installed weight

6) Less space occupied

7) Ability to maintain constant RPM regardless of vessel's speed and load 5 8) Possibility to clean and exchange the blades while afloat, even exchange of complete sheel vessel is slightly trimmed by bow

Compared to water jet partially submerged wheel with C.P. blades fitted to articulated transom is featuring following advantages:

1) Less stressed transom structure 0 2) Less fluctuating forces due to stable inflow conditions and increased number of blades

3) No vertical thrust force component usually provoked by inclined shaft, meaning that effective thrust is abt. 2% higher if compared to 12 deg. inclined shaft

4) It can be excepted that weeled blades running at ^L'high efficiency" part of the disc at relatively low RPM will feature better propulsive efficiency than conventional (small 5 diameter/high RPM) partially submerged propeller blades

5) wheel is not protruding aft of transom as it is the case with conventional surface drive meaning that protective stern overhang will be of smaller dimensions i.e. weight

This kind of propulsor can be, obviously, powered by one diesel engine or one gas turbine per each hull. However, in case, that output available from one engine is not 0 sufficient, two engines can be fitted, in staggered corfiguration due to hull narowness, so that gear box will have two input shafts. Invention is to be exclusively used for the propulsion of very fast catamarans with slender displacement hulls. Width of hulls can be in the range 1 to 4 m or more and length from 20 to 80 m or more.

Installed power per propulsor could be in the range 2000 kW to 20000 kW and more.

Depending on selection of power plant (diesel or turbine) and size of the installation, reduction gear ratio can be selected to suit to expected output speed range from 800 to 200 rpm.

Claims

CLAIMSPatent is requested for new propulsor with variable pitch blades of partially submerged type fitted to articulated transom of the very fast catamaran characterized by the arrangement of blades which are not fitted to conventional hub protruding far behind transom but fitted on the circumference of one disc, size and shape of which coincide with size and shape of transom, being mounted immediately aft of the transom resulting in steady flow within selected bottom segment, ability to control fluctuating forces either by choice of flow profile at the blade-entry and blade-exit positions or by choice of blade number with respect to active angular size of the bottom segment and yet, utilizing benefits of low resistance of hull with rounded sections, horizontally oriented thrust, possible installation of propulsor on cut stern to enable contribution of blade drag force to the propulsive thrust, the total efficiency of hull-propulsor is expected to overcome efficiency obtainable by conventional partially submerged propeller installation while, due to mechanical / hydrodinamical configuration, capability of new propulsor to overcame power limitation of conventional system is evident. AMENDED CLAIMS[received by the International Bureau on 12 ctober 2000 (12.10.00); original claim replaced by new claims 1 and 2 (1 page)]

1. Patent is requested for new propulsor with variable pitch blades of partially submerged type fitted to articulated transom of the very fast catamaran characterized by the arrangement of blades which are not fitted to conventional hub protruding far behind transom but fitted on the circumference of one disc, size and shape of which coincide with size and shape of transom, being mounted immediately aft of the transom resulting in steady flow within selected bottom segment, ability to control fluctuating forces either by choice of flow profile at the blade-entry and blade-exit positions or by choice of blade number with respect to active angular size of the bottom segment and yet, utilizing benefits of low interaction between well spaced adjacent blades and horizontally oπented thrust, the total efficiency of propulsor is expected to overcome efficiency obtainable by conventional partially submerged propeller installation while, due to mechanical / hydrodinamical configuration, capability of new propulsor to overcame power limitation of conventional system is evident.

2. As described under 1 but with propulsors fitted to a transoms of slender catamaran hulls having an (yaw) angle of abt 60-70° to the centreline in plane view, providing that inlet/outlet gear box shafts are similarly declined in horizontal plane, exact declination angle being determined by theory/model experiments in a way to have resulting force of the blade lift and drag components oriented just longitudinally in the desired thrust direction, hence exceeding propulsive efficiency over conventional partially submerged propeller for 10-15%.