EP0033322B1

EP0033322B1 - A rudder arrangement for boats and ships

Info

Publication number: EP0033322B1
Application number: EP80901451A
Authority: EP
Inventors: Odd Braa
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-08-10
Filing date: 1981-03-24
Publication date: 1984-12-12
Also published as: FI63904B; NO792611L; DK160481A; DE3069796D1; EP0033322A1; NO144737B; JPS56501005A; NO144737C; WO1981000389A1; FI63904C; FI802492A

Abstract

A modification on a rudder for boats and ships, comprising a channel disposed rearward of the screw which is rotatable about a substantially vertical axis. The channel has a closed, circular cross-sectional configuration. Two V-shaped notches are provided in the rearward end of the tunnel, the V-tips lying in the central vertical plane through the tunnel, such that on each side of this plane, a curved tongue (17) is formed. In one embodiment, the channel can be arranged in connection with a conventional plateshaped rudder (9), one halfsection of the channel being arranged on each side of the rudder.

Description

The present invention relates to a rudder arrangement for boats and ships according to the preamble of claim 1.
Many boats have poor steering capabilities, especially at slow speeds. This is particularly true for small boats, such as the Norwegian "snekke" (a 16- to 24-foot open fishing boat, pointed at both ends, most often clinker-built), and for other types of boats having a relatively deep bottom, a long keel and driven by an inboard motor, where the propeller turns about the same axis at all times and thus cannot participate in the steering. Such boats have especially poor steering capabilities when reversing. In fact, some boats do not answer the helm at all when reversing at slow speeds. Some other boats can answer the helm when reversing by turning only in the one direction. It is obvious that this deficiency presents great problems in situations in which precise manoever- ing is required, for example, when sailing out of or into a harbor or in other situations where it is necessary to steer the craft while reversing. The problems with such boats can be so great that the owner of the boat simply cannot risk taking his boat out of harbor if the winds and sea are blowing toward land.
The effect of a boat rudder is to deflect the flow of water relative to the longitudinal direction of the boat, whether this flow results from the speed of the boat or from water which has been set in motion by the screw. The propeller flow, however, is far from laminar, and it therefore has a relatively bad effect on the steering of the boat. Therefore, a boat travelling at slow speed will have poorer steering than the same boat travelling at higher speeds. In some cases, the screw will reduce the steering properties of the boat. This is particularly true when reversing, because the laminar flow of water which moves along the hull of the boat will be broken up by the propeller, which has poor screw properties when reversing, the blades of a propeller being constructed first and foremost with forward propulsion in mind. On boats which have poor steering capabilities in reverse, therefore, one must often set the boat in motion backwards and then cut out the propeller before the rudder will have any steering effect.
Several different types of aids have been tried in attempts to improve the steering properties of boats of the above type. Thus, various types of guide plates on both sides of the rudder surface have been tried.
A rudder arrangement of the type defined in the preamble of claim 1 is previously known from DE-C-345 785. This known arrangement is primarily adapted for controlling the speed of and enabling backwards movement of a vessel which cannot be caused to move astern by reversing the rotational direction of its propeller. It comprises a tunnel formed by two tunnel sections which are rotatable both individually and in unison about a substantially vertical axis and which require a complicated control device. The forward portions of the tunnel sections are normally located like a shield outside the propeller blades and adversely interfere with the action of the propeller.
A modification on a rudder is known from NO-A-59 795, in which plates that are parallel with the rudder surface are provided on each side of the rudder, the leading edge of the plates projecting forward of the middle leading edge of the rudder. The primary object of this modification is to balance the rudder, in that one thereby obtains steering surfaces which lie in front of the rudder shaft. A similar modification is known from US-A-3 181 492.
It is known from US-A-2 328 041 to mount arch-shaped guide wings on both sides of a conventional plate rudder in such a manner that the guide wings are disposed radially exterior of the propeller when the rudder is in the neutral position.
However, the modifications of this type known hitherto have not had the desired effect, and at present no effective aid exists for increasing or improving the steering capabilities, especially when reversing, on boats of the type defined above.
The object of the present invention is to provide a rudder arrangement for boats and ships which improves the steering properties of the boat both when reversing and during forward propulsion.
This is obtained according to the invention by providing a rudder arrangement according to the preamble of claim 1, which arrangement further comprises the features set forth in the characterizing clause of claim 1.
Numerous trials have shown that the rudder configuration according to the present invention provides quite superior steering properties, especially when reversing. This is very important, as reversing with boats having a pointed bottom configuration, such as the Norwegian "snekke" fishing boat, has always been problematic. With a rudder having the configuration defined above, such a boat will answer the helm equally well in both directions, while it would normally answer the helm only in the direction of rotation for the propeller. The steering properties of the boat will also be improved in the forward direction, especially when moving forward at very slow speeds.
A practical embodiment of the invention is characterized in that the tongues constitute approximately one-half of the total length of the tunnel in the longitudinal direction. Conveniently, the ratio of the total length of the tunnel to the diameter of the tunnel lies between 3:4 and 3:6.
The invention will be elucidated further in the following with reference to the accompanying drawings, which illustrate two different embodiments of the invention.

Figure 1 shows a first embodiment of a rudder according to the invention, mounted on a small boat, in perspective, and
Figure 2 shows the same embodiment seen directly from above.
Figure 3 shows a second embodiment of the rudder according to the invention, in perspective, and
Figures 4 and 5 show the embodiment of Figure 3 seen straight from the back and directly from above, respectively.

In accordance with the embodiment illustrated in Figure 1, a circular, tunnel- or channel- shaped rudder 1 is provided between the stern 2 of the boat and a lower rudder support 3. The rearwardly-projecting support 3 is the most common construction on small boats, but one also finds types of boats in which this support is not present, in which case the rudder is supported solely by the rudder post 4. The boat illustrated in this example is driven by a three-blade screw with reversible directions of rotation. The rudder shaft 4 is attached to the channel 1 forward of the middle of the total length L of the channel. Two V-shaped notches have been cut into the tunnel at its rearward end, the tip of each V lying in the central vertical plane through the channel 1. In this manner, respective arch- shaped tongues 7, 8 are formed on each side of said plane, the total length a of the tongues in the longitudinal direction of the channel being approximately equal to one-half the total length L of the channel.
Figure 3 shows an embodiment which is well suited for rebuilding the rudder of a boat which is already equipped with a conventional plate rudder 9, placed between the stern 2 of the boat and the lower support 3. In this example, also, the boat is driven by a three-blade screw 5 with reversible directions of rotation. The rudder is rotated by means of a rudder shaft 4, which is placed a distance behind the leading edge of the rudder plate 9 in order to obtain a certain balancing effect. Attached to both flat sides of the rudder 9 are arched guide plates 11 and 12. The curvature of the plates is in accordance with a circular line in the crosswise direction of the boat, such that the two plates 11, 12 together form a circular-shaped channel. The lateral marginal edges 13 of the plates 11, 12 (Figure 5) are parallel with one another and with the rudder surface on the plate rudder 9. The plates 11 and 12 are attached at their upper and lower edges 14 and 15 to the respective upper and lower edges of the rudder surface. The forward edge 16 on the plates 11, 12 is disposed somewhat astern of the rudder shaft 4. The plates 11, 12 have a curved rearward edge 16, such that the outer marginal edges 13 of the plate project somewhat astern of the plate parts, which are attached to the rudder at 14 and 15. In this way, tongues or overhangs 17 are formed.
The diameter of the channel which is formed by the two plates 11 and 12 is larger than the screw diameter of the propeller 5. In regard to the dimensions of the plates 11 and 12, the length a of the overhang 17 is approximately equal to the remaining length b of the total length L (see Figure 5), i.e., the length a of the overhang 17 is approximately equal to one-half of the total length of the plates 11 or 12. The ratio of the length L (= a + b) to the diameter lies between 3:4 and 3:6.
A rudder modification in accordance with the exemplified embodiments was tested on a small fishing boat which had extremely poor steering properties, especially when reversing. At slow speeds, this "snekke" boat did not answer the helm at all in one direction during a reversing operation. The boat's berth was situated such that the sea and wind often blew toward land, and it often happened that the owner could not take his boat out for the sole reason that it was not sufficiently manoeverable, as it was impossible to steer the boat in reverse. After the modification according to the invention was installed, the owner claimed that the boat was as easy to steer as an automobile, and that it answered the helm when driven in reverse both at slow speeds and at full speed. In addition, the turn radius during forward propulsion had also become substantially smaller.
Another effect of the modification according to the invention is that it also prevents or greatly reduces the downward drag on the stern end of boats of this type. This is a common phenomenon, and it reduces speed or increases fuel consumption rather significantly. In order to prevent this, some boats have a hull built with an expensive support plane or support-fins in the region of the screw. Such hull modifications can be rendered unnecessary with the use of the invention, and the price of the hull correspondingly reduced.

Claims

1. A rudder arrangement for boats and ships, comprising a tunnel (1; 11, 12) of substantially circular cross-section which is disposed rearwardly and coaxially of the propeller and which is rotatable about a substantially vertical axis (4), the walls of said tunnel at the rearward end thereof being provided with two V-shaped notches with the respective apices of the notches lying on a central vertical plane extending through the tunnel so as to form an arched tongue (7, 8; 17) on both sides of said plane, characterized in that the front edge of said tunnel (1; 11, 12) is spaced from the propeller plane so as not to intersect said plane in any rudder position, and in that the two arched tongues (7, 8; 17) are immovable relative to one another.

2. A rudder arrangement according to claim 1, characterized in that the tongues (7, 8; 17) constitute approximately one-half of the total length L of the tunnel (1; 11, 12) in the longitudinal direction.

3. A rudder arrangement according to claims 1 or 2, characterized in that the ratio of the total length L of the tunnel (1; 11, 12) to the diameter of the tunnel lies between 3:4 and 3:6.