GB1600994A - Ship propellor ducts - Google Patents

Description

(54) IMPROVEMENTS RELATING TO SHIP PROPELLER DUCTS (71) We, LIPS B.V., a Limited Liability Company organised and existing under the laws of the Kingdom of the Netherlands, of Lipsstraat 52, Drunen, The Netherlands, do hereby declare this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a duct for a ship's propeller, and in particular to a stationary duct for a marine propeller. Such a duct is sometimes referred to as a propeller nozzle, sometimes referred to as a Kort nozzle.

Basically the invention pertains to the principle of improving or increasing the thrust of a marine propeller by surrounding the rotating propeller with a stationary annular body or duct attached to the hull of a ship, this duct having a foil shape in any axial section. Due to the action of the annular body or duct, the inflow of water to the propeller in general is accelerated. The annular body produces thereby a positive extra thrust force to the ship.

Propulsion devices of this kind are well known and used for ships which have to produce high thrust at low ship speeds, such as tugboats or trawlers. The annular body or duct also offers a means of increasing the efficiency of heavily loaded propellers at moderate ship speeds. However, the advantage of the thrust action of the conventional duct is reduced at increased higher ship speeds. At maximum speed of the ship generally the thrust action of the duct is strongly reduced. Hence the frictional losses of the duct, which are associated with the higher water flow velocities along the duct body, cause a loss in speed of the ship. The present invention aims to provide a propeller duct wherein the disadvantage of the frictional losses are at least partially avoided.

According to the present invention, there is provided a duct for a ship's propeller, the duct being provided with means for attachment at the top and bottom thereof to the hull of the ship, the duct having a foil shape in axial section in any plane intersecting the axis of the duct, which section varies continuously around the circumference of the duct, reaching a first maximum sectional length and/or sectional thickness at the top and a second maximum sectional length and/or sectional thickness at the bottom thereof, the sectional length and/or thickness reducing continuously to a minimum sectional length and/or a minimum sectional thickness in the regions of high water velocities, that is the regions between a horizontal median axial plane and the bottom of the duct.Thus, the shape of the duct is adapted to the wake of the ship in order to reduce frictional losses by presenting the smallest contact area where the water velocity is highest.

As a duct, according to the present invention, exposes a reduced surface in the reglon of high water entrance velocities, the frictional losses at full speed of the ship will be minimised. Another advantage is that a duct according to the invention, having its maximum length at top and bottom, thus offers ample means for strong attachment to the hull of the ship.

A further advantage of the duct, according to the invention, is that the mass distribution favourably influences the natural frequency of the duct, so that resonance vibrations caused by the propeller blades cycling can be avoided.

An embodiment of the invention will be described with reference to the accompanying drawings. Figure 1 of the drawings designates, as an example, the inflow velocity distribution of a ship at the entrance of the propeller duct, the variation of water velocities being caused by the ship's wake.

The circle 1 indicates the inner diameter of the duct. The circle 2 indicates the propeller boss with the axis of rotation 3, while 4 is the sole-piece of the vessel. A multitude of lines 5 show the inflow velocity distribution, the number 1.0 0.95 0.9 .... 0.2 indicating the relation between the maximum (or undisturbed) flow velocity, represented by 1.0 and occurring in the regions at 4 o'clock and 8 o'clock in Figure 1, and the disturbed flow velocity occurring at points around the circumference.

Figure 2 shows a longitudinal section through the propeller duct 6 surrounding a rotating propeller consisting of blades 7 extending radially from a propeller boss 2.

The propeller is mounted for rotation in the stern 8 of a ship. Reference numeral 9 shows the dimensions of the longest axial section of the duct where the duct is attached to the hull by means of a head-box 4a. As can be seen from Figure 1 the water velocities here are low. Reference numeral 10 shows the dimensions of the shortest axial section at a point where, as can be seen from Figure 1, the water velocities are high. In order to reduce the contact area of the duct with the water at this region the sectional thickness may be reduced as well as, or as an alternative to, the reduction in sectional length. Reference numeral 11 indicates the dimensions of the bottom section of the duct and the attachment to the sole-piece 4. The sectional dimensions of the duct are gradually decreased from the top and bottom of the duct to both sides, without discontinuities in length or thickness.

WHAT WE CLAIM IS: 1. A duct for a ship's propeller, the duct being provided with means for attachment at the top and bottom thereof to the hull of the ship, the duct having a foil shape in axial section in any plane intersecting the axis of the duct, which section varies continuously around the circumference reaching a first maximum sectional length and/or sectional thickness at the top and a second maximum sectional length and/or sectional thickness at the bottom thereof the sectional length and/or thickness reducing continuously to a minimum sectional length and/or a minimum sectional thickness in the regions of high water velocities, that is the regions between a horizontal median axis plane and the bottom of the duct.

2. A propeller-duct substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. the duct. The circle 2 indicates the propeller boss with the axis of rotation 3, while 4 is the sole-piece of the vessel. A multitude of lines 5 show the inflow velocity distribution, the number 1.0 0.95 0.9 .... 0.2 indicating the relation between the maximum (or undisturbed) flow velocity, represented by 1.0 and occurring in the regions at 4 o'clock and 8 o'clock in Figure 1, and the disturbed flow velocity occurring at points around the circumference. Figure 2 shows a longitudinal section through the propeller duct 6 surrounding a rotating propeller consisting of blades 7 extending radially from a propeller boss 2. The propeller is mounted for rotation in the stern 8 of a ship. Reference numeral 9 shows the dimensions of the longest axial section of the duct where the duct is attached to the hull by means of a head-box 4a. As can be seen from Figure 1 the water velocities here are low. Reference numeral 10 shows the dimensions of the shortest axial section at a point where, as can be seen from Figure 1, the water velocities are high. In order to reduce the contact area of the duct with the water at this region the sectional thickness may be reduced as well as, or as an alternative to, the reduction in sectional length. Reference numeral 11 indicates the dimensions of the bottom section of the duct and the attachment to the sole-piece 4. The sectional dimensions of the duct are gradually decreased from the top and bottom of the duct to both sides, without discontinuities in length or thickness. WHAT WE CLAIM IS:

1. A duct for a ship's propeller, the duct being provided with means for attachment at the top and bottom thereof to the hull of the ship, the duct having a foil shape in axial section in any plane intersecting the axis of the duct, which section varies continuously around the circumference reaching a first maximum sectional length and/or sectional thickness at the top and a second maximum sectional length and/or sectional thickness at the bottom thereof the sectional length and/or thickness reducing continuously to a minimum sectional length and/or a minimum sectional thickness in the regions of high water velocities, that is the regions between a horizontal median axis plane and the bottom of the duct.

2. A propeller-duct substantially as described with reference to the accompanying drawings.