A Novel Becker Rudder for Ocean Vessels

Since 1961 Messrs. Willi Becker Ingenieurburo, Hamburg, are engaged in the manufacture of BECKER rudders, i.e. profile rudders with articulated flap, and up to now approx. 120C rudders with a weight of abt. 20 t each and a driving power up to 10.000 HP were delivered Besides a continuous development of the BECKER rudder construction with regard to economic production-engineering methods and high-grade material, a steady adaptability to the changing needs of the market was required. In the course of this development work now it has introduced for BECKER spade rudders a novel construction for the rudder support at the ship’s hull.
It is generally known that the fluid-mechanical favourable spade rudders are supported in such a way, that the bending moment is increasing to full height up to the rudder bearing in the trunk and has to be absorbed by the rudder stock itself, which results in very strong rudder stock constructions. Consequently the application of spade rudders is limited due to the quite large diameter to be provided for rudder stock and rudder bearing in the trunk, which terminates with a ship size of approx. 10.000 dwt.
The separation of the double-axle state of stress, which is done for semi-spade rudders, results in hydrodynamic unfavourable and asymmetrical properties due to the upper fixed post and the slitting effect caused above the lower movable balance surface in the area of high pressure differences. Due to the rotational flow of the propeller the torque gets very strong asymmetrical which brings about the requirement for comparatively large rudder engines for operation of the semi-spade rudder.
The view of the a fore mentioned disadvantages in rudder support it suggests itself to find a special shaping of the rudder trunk to absorb part of the bending moment directly by the rudder which otherwise first is led over the rudder stock into the rudder bearing in the trunk, and only then into the ship’s hull. This is to enable a stress discharge of the rudder stock which consequently results in a more simple constructive connection of the now smaller rudder stock with the rudder on the one hand and operation with smaller rudder engines on the other.
This novel rudder support has a rudder trunk which is designed as a cantilever with a double bearing for supporting the rudder body and the rudder stock. The exposed lower part of the rudder stock is fixed to the rudder body over a cone connection.
From the shown sketch the principal construction of this rudder support can be seen.
For the double bearing at the lower trunk end as well as for the link and rudder hinge all material of those parts which are moving against each other is made of stainless chromium nickel steel and plastic material.

Besides the constructive preference this kind of bearing has following advantages:
1) no lubricating problems since all bearing points get in touch with water, 2) high wear-resistance of the bearing bushes, 3) low frictional coefficient — consequently smooth operation of bearings.
The rudder body is made of steel plates in shipbuilding quality as welded construction. The necessary casing blocks for the double bearing and for the cone connection of rudder stock and ship’s hull are made of a high-quality cast steel.
The measurement of the double bearing for the rudder trunk and rudder stock is ascertained by means of an extensive electronic data processing programme in an optimum way so that standards of the international classification societies are kept.
In case of a damage of the BECKER rudder either the fully mechanic link of the flap can be set out of operation or the flap is taken off. Although this will cause a diminished manoeuvrability, it will not be less than the efficiency of a conventional profile rudder. The advantages to be achieved with this novel BECKER rudder means a considerable extension of the application range of BECKER rudders as spade rudders in view of realizable rudder sizes. This is made by separation of the double-axle state of stress, providing that the bending moment is absorbed by the rudder trunk which is housed in the rudder body and introduced into the ship’s hull. The torque for rudder operation is transmitted over the long rudder stock. Consequently there are applicable more slender rudder profiles with unchanged size of rudder area which means a lower resistance of speed. In addition, the connection of rudder body and rudder stock gets more favourable as well with regard to the production process as more simple with regard to assembly. Because of the constructional smaller rudder bearing in the trunk there are to be saved investment and installation costs.
The accumulation of the qualitative favourable constructional effects of this novel BECKER rudder, as listed before, are causing advantages which are summarized in the following:
1. Increased Manoeuvrability:
1.1. On course:
By means of the lift increasing profile camber effect of the two-part profile rudder there are required smaller rudder deflections compared with one-part rudders or sectional semi-spade rudders because of the higher lift gradient. Even with the same profile, in this way the appendage resistance of the ship is reduced and consequently in many cases also the fuel demand for the main engine.

Because of the high performance, as a rule, a two-part BECKER flap rudder will require a smaller rudder area for equivalent manoeuvrability of the ship to be equipped. This results in a reduction of the appendage resistance of the ship which also means to save fuel.
1.2. On estuary trading:
In many cases it is achieved a thrust deviation of approx. 50% of the propeller current by means o f the BECKER rudder, provided max. rudder angles (up to 45 degrees) for the main rudder body are set.
In this way, by means of the ship’s main propulsion system it can be steered very well and efficiently, even with low advance speed descending to Vg = O, that means, the so-called pinwheeling.
2. Reduction of the weight of rudder installations:
2.1. The high-performance effect of the BECKER rudder means that frequently up to approx. 20% of the rudder area can be saved with the same manoeuvrability of the ship and consequently lighter rudders may be used.
2.2. Since for BECKER rudders the arrangement of the rotary axis of rudder stock is free of otherwise necessary provisions, such as construction of the ship-tight rudder horn, the well-balanced rudder allows:
— a smaller, lighter and cheaper rudder engine,
— a more slender, lighter and cheaper rudder stock.