GB2179312A

GB2179312A - Turnable propeller assembly

Info

Publication number: GB2179312A
Application number: GB08617643A
Authority: GB
Inventors: Juhani Halkola; Pyry Vainio
Original assignee: Hollming Oy
Current assignee: Hollming Oy
Priority date: 1985-08-19
Filing date: 1986-07-18
Publication date: 1987-03-04
Also published as: NL8601957A; NO863284D0; FI75775B; DE3626568A1; CN86105134A; CN1006624B; NO863284L; SE8603445D0; FI75775C; SE466254B; GB8617643D0; GB2179312B; FI853173A0; FI853173L; SE8603445L

Abstract

A turnable propeller assembly (3) which can be turned around a vertical axis for steering a vessel comprises an annular propeller nozzle (7) located so that the axial distance (c) from the leading edge (12) of the nozzle to the middle plane of the propeller (9) is between 0.70 and 0.85 times the length (b) of the propeller nozzle (7). To allow the propeller device (3) in any orientation to be locatable inside a well (14) at the bottom (2) of the vessel (1), when not in use, the propeller nozzle (7) lies close to the turning axis (13) of the propeller device (3) and the diameter (D2) of the well (14) is substantially 1.6 times diameter (d) of the propeller. Alternatively, if the propeller device (3) is to be accommodated in a predetermined relative orientation a diameter (D2) of substantially 1.35 times diameter (d) of the propeller (9) is sufficient. <IMAGE>

Description

SPECIFICATION Turnable propeller assembly The invention concerns apropeller assembly ofthe type in which a propeller on a horizontal shaft is surrounded by an annular ring or nozzle, and driven from a vertical shaft through the intermediary of angle gearing. Such an assembly is mounted so that it can be turned around a vertical axis for steering a vessel, being located beneath, behind, at the bows or to one or other side of the vessel.

Such devices are particularly advantageous in vessels such as tug-boats, which must be easily steerable in confinedspaces.Apropellerforatug-boatshould be rather large in size to be effective at low towing velocities. However, a large propeller assembly protrudes so far beneath the vessel that the vessel cannot be used in shallow waters. Furthermore, a large propeller assembly requires a very big well at the vessel bottom in those assemblies where mounting or detachmenttakes place fro above or where the propeller assembly (for example for use in shallowwaters) can be lifted up into a bottom well.

An annular nozzle or ring around the propeller in such an assembly is a well-known arrangementto increase the thrust of the propeller at low velocities.

The propeller diameter can thereby be possibly be slightly reduced, in its unsurrounded form, but even then the nozzle is a large object, which adds to the problems recited above. Thus, in such assemblies both the propeller and the nozzle around it should be abletoturn in an uninterrupted fashion underthe vessel. When the space required for such turning is unduly large problems arise, particularly when two parallel propeller assemblies are used and theframe workofthevessel is relatively small as e.g. in tug- boats.Use of a ring or nozzle also increases the steering momentforturning the assembly depending on how far the nozzle is located from the vertical axis of the assembly (the farther the nozzle the greaterthe moment required) The invention sets outto provide a propeller assembly in which the aforementioned disadvantages are reduced or eliminated.

The invention consists in a turnable propeller assemblyofthetypecomprisinga propellerona horizontal propeller shaft driven from a vertical drive by angle gearing, the propeller being surrounded by an annular propeller ring or nozzle, and the whole assemblybeingturnableaboutavertical axisfor steering a vessel on which it is mounted; in which the axial distance f02e from the leading edge of the ring or nozzle to the mid-plane ofthe propeller is from 0.70 to 0.85 times the total axial length 6 of the ring or nozzle.

The propeller nozzle isthus located almostentirely in frontofthe propeller i.e. substantially nearer to the turning axis ofthe propeller device. The space needed forthe propeller nozzle is substantially smal- lerthan in conventional arrangements. Such a propeller assemblytypicallyfits in a well formed vessel bottom and of equal size to the well required forthe corresponding propeller without a nozzle. The small space requirement of the assembly also has the advantage that an assembly with a bigger propeller can be fitted to a small vessel to get greaterthrust.

The assemblyofthe invention also possesses the advantagethatthe distance ofthe middle point ofthe nozzle from the vertical turning axis is small. There- fore,the moment needed forturning the assembly is smallerthan in conventional propeller devices. The steering equipment can therefore be of significantly lighter construction with reduced manufacturing costs.

Another advantage ofthe present assembly is that the propeller can easily be demounted when it is placed nearthe rear edge ofthe nozzle. The nozzle can also be more steadily fastened to the frame ofthe propeller device so that the clearance between the nozzle and the propeller can be reduced, with consequent improvement in efficiency.

Preferably, the leading edge ofthe propeller assembly nozzle is substantially at, or near the center line ofthe vertical shaft or of the turning axisofthe propellerassembly. When the propeller nozzle isthus installed,thesteering moment is almostzero intrans- versal flow. In other words, the nozzle is at its optimum point, and the steering equipment need only be of very light construction.

Preferably moreoverthe distance between the leading edge ofthe nozzle inserted intheturnable propeller device and its trailing edge (i.e. the length of the propeller nozzle) issubstantiallyhalfoftheprop- ellerdiameter. If, however, the vessel is intended to function mostly at low velocities, the nozzle thrust can be increased by lengthening the nozzle, and in practice the nozzle length can then be up to 0.6 or 0.7 times propeller diameter. Since however the distance from the leading edge ofthe nozzle to the point ofthe propeller blades is 0.70 to 0.85 times the nozzle length,thespace required by the propeller assembly does not increase (over the prior art assembly) in spite ofthe extended nozzle. It is therefore not necessaryto alterthe dimensioning ofthe steering mechanism.By the invention it is therefore possible to insert on to a conventional propellerdevicealon- ger nozzle for special applications, with the main dimensions ofthe defice remaining unchanged.

When the turntable propeller assembly is arranged to be lifted up into dwell at the vessel bottom. the wel I is dimensioned according to an additional feature as follows. The propeller nozzle has bee placed so near the turning axis of the propeller device, that a sufficientwell diameterto accommodate the assembly in any relative orientation, is substantially 1.6 times propeller diameter. This corresponds closely to thedimension of a well intendedforaturnablepropeller assembly without a nozzle. If the propeller device need only be accommodated at one predetermined orientation in thewell,the center line ofthewell can be displaced from the turning axis ofthe propeller assembly and the well diameterneedonlybesub- stantially 1.35 propeller diameter.

The invention will now be described with reference to the accompanying drawings, in which Figure lisa diagrammatic axial section through a turnable propeller assembly with a conventional propeller nozzle, and Figure2 is a diagrammatic axial section generally corresponding to thatof Figure 1,through aturnable propeller assembly with a nozzle according to the present invention.

Figure 1 shows a turnable propeller assembly 3 beneath a well 14in the bottom 2 of a vessel 1 .A vertical shaft 5 drives by an angle gear within housing 6a horizontal propellershaft4,towhich a propeller9 is connected. Around the propeller an annular propeller nozzle 7 is located so that the points 11 ofthe blades 10 ofthe propeller 9 are situated approximate ly atthe middle point of the propeller nozzle 7 as measured between inlet and outlet planes of the nozzle. The moment distance a1 of the steering moment caused by the propeller nozzle is significant and turn ing ofthe propeller nozzle in this Figure 1 arrangement takes up substantical space whereby the dia meterD1 ofthewell 14 must be also quite large.

Because ofthese disadvantages the conventional construction shown in Figure 1 cannot always be used.

Figure 2 shows a propeller assembly according to the invention. In this case the propeller nozzle 7 is so located that the distance cfrom the middle plane of the blades 10 to the front i.e. leading edge 12 ofthe propeller nozzle 7 is from 0.70 to 0.85 times the length b ofthe nozzle. The front i.e. leading edge 12 ofthe propeller nozzle is then situated near the turning axis 13 of the propeller assembly. Maximum thrust ofthe propeller nozzle 7 is achieved when the distance c is about 0.7 x the length b. Ifthe propeller9 is placed any nearerthan this to the front edge ofthe nozzle performance is not essentially improved.Thrust is > /90% ofthe maximum when c is 0.85 x the length b.

Thrust below 90% ofthe maximum is not technically acceptable or economical.

Distancea is in the embodiment of Figure 2 smaller than the analogous distance a in Figure 1. Steering forces necessary are therefore substantially smaller.

The proposal of Figure2 decreases the required dia meterofthe well 14 because the rear (trailing) edge 8 ofthe nozzle 7 is generally in a plane with the end of the propeller hub as shown in the Figure 2. Diameter D2 ofthewell 14in Figure 2 is approximately 1.6 x the diameter dofthe propeller 9.

In measurements carried out in practice the most advantageous length b of the propeller nozlle is about half of the diameter dofthe propeller 9.

In the embodiment of Figure 2 the fastening ofthe propeller nozzle 7 to the frame of the propeller assembly is steadier, so thatthe clearance between the propeller nozzle 7 and the points 11 of the propeller blades can be smallerthan those in the arrangement according to Figure 1.

It is obvious two the man skilled in the art that modifications ofthe invention may be made within the scope ofthe claims presented below.

Claims

1. Aturnable propeller assembly of the type comprising a propeller on a horizontal propeller shaft driven from a vertical drive by angle gearing, the propeller being surrounded by an annular propeller ring or nozzle, and the whole assembly being turnable about a vertical axis for steering a vessel on which it is mounted; in which the axial distance c from the leading edge ofthe ring or nozzle to the mid-planeofthepropellerisfrom O.70to O.85times the total axial length b of the ring or nozzle.

2. Apropellerassemblyasclaimed in claim 1 in which the leading edge ofthe propeller ring or nozzle lies at or near the assembly vertical turning axis.

3. A propeller assembly as claimed in claim 1 or2 in which the distance (b) is substantially half ofthe diameter (d) ofthe propeller.

4. A propeller assembly as claimed in claim 1, or 3 located in association with a housing well at the bottom of a vessel in such a way that the propeller assembly can be lifted upwards into the well when not in use, and which the propeller ring or nozzle lies sufficiently near the vertical turning axis ofthe assemblythatthe diameter (D1) of the well is substantially 1.6 times the diameter (d) ofthe propeller whereby the propeller assembly can be accommo- dated in any relative orientation.

5. A propeller assembly as claimed in claim 1,2 or 3, located in associated with a housing well ofavessel in such awaythatthe propeller assembly can be lifted upwards into the well when not in use, in which the propeller ring or nozzle lies sufficently near the vertical turning axis thatthe diameter (D2) ofthewell is substantially 1.35 times the diameter of the propeller whereby the propeller assembly can be accommodated in a predetermined orientation.