System to enhance directional stability of waterborne vessels

Abstract: This invention provides for a ships rudder capable of being turned to any desired angle which confers the following attributes:- 1. When rotated to the 180° position (Fig 2) the boat can move aft while the rudder still tends to "feather", with no tendency to oversteer and a reduction of stresses. 2. The rudder may extent rearwards aft of the stern or transom in order to improve directional stability and control, coupled with the ability to allow control tabs on its trailing edge, if fitted, to be operated by simple, cheap and direct external means, as in fig 1. 3. The vulnerability resulting from an overhanging rudder can be mitigated by rotating the rudder when not in use by rotating it to stow under the hull. In this position it may also act as a brake and also facilitate rotation of the hull in azimuth ,eg during docking manoeuvers.

Description: A notable element in this application is the proliferation of windvane and electronic automatic steering gears both past and present, a few of which operate via trim tabs on the rudder trailing edge: Typically:- from Germany, Offenlegungsschrift DE-A-26 49 291 (Rosen), and from France, No de publication FR-A-2 105 724 Directional stability, control, safety and convenience may be further improved by a combination of features described below. Historically, a ship or boat's rudder has been constrained by stops from being turned through more than about 35°. It follows therefore, that unwanted hydrodynamic forces are applied when the rudder is required to steer the craft aft. That is to say that when moving forward a boat's rudder has a tendency to "feather" or align itself with the normal fluid flow whereas when moving aft it is constrained by the usual stops and the normal fluid flow over the rudder section, which is often of a teardrop design, becomes inefficient on this account in addition to stressing the rudder and its operating mechanisms more highly. The above mentioned disadvantages are avoided by a vessel as defined in claim 1. This invention provides for a non transom hung boat's rudder to be turned to any desired angle and will involve the temporary retraction of the usual stops if fitted. It may be turned to 180° ± the required steering angle when the boat reverses, or across the boat's centre-line thus inhibiting fore and aft movement of the boat while facilitating sideways movement, eg while docking. The rotation of the rudder stock is achieved by replacing the normal quadrantwith suitable linkages, eg a pulley or large sector of a pulley, a chain drive or a system of levers or gears, or an electric or hydraulic drive. In the case of tiller steered boats, a horizontal pivot atop the stock would allow the tiller to be rotated in the vertical plane during rotation of the rudder to enable the rudder to be reversed and the tiller to settle in itsnormal position. A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Fig 1. Shows a spade rudder which may or may not be partially balanced in the "normal" position, with the boat moving forward in the direction of the arrow. Ancillary windvane is also represented. Fig 2. Shows a boat moving aft but with the rudder reversed, the fluid flow still travelling from its leading towards its trailing edge. Fig 3. Shows the rudder in the nominal 90° athwartships position. Fig 1 shows the boat in forward motion with the rudder (with or without stops which nominally restrict movement to 35-40°) subjected to normal fluid flow, eg from its leading edge towards its trailing edge. The rudder stock is positioned as usual at the leading edge or, in the case of a balanced rudder as shown, nearer the leading edge that the trailing edge. The rudder will thus tend to "feather". The rudder may be turned through a nominal 180° in order to maintain the above flow while the boat is moving a stern as in fig 2, The rudder is tending to "feather" and not oversteer, as is normally the case, resulting in unwanted forces being applied.It is also more efficient since the fluid flow is maintained, especially in thecase of a streamlined teardrop section, from the leading towards the trailing edge. The rudder may be set nominally across the direction of normal flow as in fig 3. This position may be adopted to reduce boat speed when necessary, the effect being slightly similar to the tail parachute on an aircraft. It also facilitates a rotational movement in azimuth of the bow and/or stern of a boat around the keel when desired, as when manoeuvering near a quay under warps or using the "propellor walk" effect when it also inhibits the sometimes unwanted forward or aft movement which tends to accompany the "prop walk". The protection rendered by the 90° selection when the rudder is not in normal use allows the rudder to be positioned, when under way, such that its trailing edge extends aft of the boat's stern or transom. In consequence of there being no vulnerability problem servo, balance, anti-balance and or trim tabs may be employed on the rudder's trailing edge and connected when normally under way to a simple, external and disconnectable linkage (fig 1) directly to a small hand control, any remote control, windvane (fig 1), autopilot or even the ship's normal wheel, by which control may be achieved with a dramatic reduction in rudder torque loads. On balance therefore, a much larger than normal rudder may be safely employed, conferring the further advantage of a considerably increased second moment of area in azimuth of the combined under water foils which, in turn, further augments directional stability.

Claims: A waterborne vessel having a hull, propulsion means and a rudder on a stern portion of the hull, the rudder stock being located forward of the transom wherein the rudder is mounted so as to be capable of being turned through a full circle, characterised in that stops if provided are retractable and allow the rudder to be turned to any desired angle, the rudder stock being positioned nearer the leading edge than the trailing edge of the rudder and the trailing edge being positioned such that it extends aft of the boat's stern or transom while the boat is moving forward. A vessel as claimed in claim 1 in which the rudder is provided with trailing edge tabs connected by an external linkage to a control means.

Inventors: ELMES JOHN, ELMES, JOHN
Applicants: ELMES JOHN, ELMES, JOHN
Application year: 1995
Main classification: B63H25
IPC codes: B63H25