What is rudder and how it turns the ship? | Construction and Working

What is a rudder? It is the fin at the rear of a ship used for directing the ship?? Actually rudder is a primary control device used to steer a ship, boat, submarine or hovercraft. In simple terms it creates resistance in the water on one side or another and causes the ship to turn.

A rudder makes the boat/ship to rotate and are hollow to provide some buoyancy. To minimize any risk due to corrosion, the inner surface is applied with a protective coating and a drain plug provided to allow drainage of the water. Many of the rudders which are found on present-day ships are semi-balanced, i.e. they have a small proportion of their lateral area forward of the turning axis (less than 20 per cent). A rudder with 20 to 40% of the area before the rudder stock is considered balanced, Most modern rudders are half-balanced design. Which means a part of the force acting on the rear wheel of the water is counteracted by the force acting on the other half of rudder; Therefore, the design can be lighter and smaller. Then rudder is supported by a bearing pintle or a lower bearing according to the design.

There are two main types of rudder based on their design:

Fully fabricated Rudder:

A side plate and the strips of horizontal & vertical reinforcement is welded on the plate. Another plate, often referred to as a "top plate", is weld then only to all internal structure from the outside. Other cables entering the desert tray Welding can be achieved by sealing the plate shown in the solution slot.

Rudder with a cast Frame:

Rudders frames were welded with the side wall. Grooves in the bore of the lever, can take the shape of the solder tube with the plug hole from the bottom and the side plates and the end of the fold. To avoid corrosion in the region, where the wheels can sometimes be inert foamed plastic. On the water under the stairs in the upper surface of the top pole once tested per 2.45 m wheel.

The Rudder consists of five main parts:

1. Rudder Flap (Mentioned and explained above)
2. Rudder stock
3. Rudders bearings
4. Rudder pintles
5. Rudder trunk

Rudder Stock

Rudder stock is the vertical member at the forward edge of a rudder, hinged at the stern post and attached to the helm or steering gear. A rudder stock can be casted or forge. Diameter bending moment is preserve in every moment. Its lower end is connected to the screw bolt horizontally or vertically with respect to the wheel arrangement, which is adapted to withstand torque output. This clutch allows the navigation ease for inspection and service rolls.

Rudder Bearing

To support the weight of the spindle in the internal part of the lower part of the spindle space bearings are provided. Some types of bearings is in segment others in the housing and supported by various kinds of weight bearing Resistances blades. The waterproof steering bearings can be installed on the top edge of the cover of the steering wheel.

Rudder Pintles

A pintle is a pin or bolt, usually inserted into a gudgeon, which is used as part of a pivot or hinge. Pintles have a taper on the radius, and a bearing length which exceeds the diameter.

A gudgeon is a circular fastener, often made of metal, which is bonded to a surface. It allows you to rotate an accessory. It is generally used with an axis of rotation, which is a pivot point in the piston bore. As such is a smooth bearing pin.

Rudder Trunk

Rudder reserves carried in the trunk of the rudder, which closed at its lower end typically does not install the case, a stuffing box, but in the upper part of the trunk when the supply of the trunk intact. This log is kept sufficiently short so that the bearing does not support a minimum length, and is constructed from welded box-shaped with the crossbar forming the bottom of its end plates. The effect of the inside of the helmet in an emergency, a small opening with a cover can be closed so that these initiations are provided on one side of the inspection.

# Various books, study material and other online sources has been refereed prior to writing this article but no part is copied or produced  from any of the source but explained same thing in better detailed way.

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Author Amit                                                                            

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Propeller Types, Working, Checks and repair | Step by Step Explanation

Propeller can be defined as: A mechanical device formed by two or more blades that spin around a shaft and produces a propelling force by converting rotational motion into thrust. The ship propulsion system along with the main engine, Thrust block, Shaft, Stern Tube and propeller works on the third principle of Newtons law. Thrust is generated by the propeller which in turn pushes the ship in the Forward direction.

There can be Two,Three or One propeller fitted on the ship depending on the ships requirement for speed, cost, maintenance and maneuverability.

Material and construction

Ships propellers are made up of corrosion resistance material (Nikalium) having different elements in following proportion:

Copper                   -      80.2 %
Aluminum              -      9.3  %
Nickel                     -      4.3  %
Iron                         -      4.0  %
Manganese              -      1.2  %

Types of Propeller:

The type of propellant used must be chosen early in the design process of the ship as the type of propellant, even have a strong influence on the design of the ship. Most ship screws are fixed pitch fixed-propeller types. But there are various types of propeller that one can use:

1. Fixed pitch propeller
2. Detatchable blade propeller
3. Controllable pitch propeller
4. Voith Scneider propeller
5. Azipod type propeller
6. Kort nozzle propeller

Fixed pitch propeller: A fixed propeller is propeller with simpler models and used on merchant ships. These types of non-traditional feast Propeller is made from individual casting. They usually have an efficiency advantage, cost, and simplicity compared to other types of propellers.

Fixed Pitch Propeller

Controllable pitch propeller: Propeller type in which the propeller thrust direction is controlled by changing the pitch of the propeller is known as CPP. It is used to control the speed and direction of the boat/ Ship without changing the speed or direction of the main shaft of the ship's propulsion.

Advantages:

1. Where the operating conditions vary widely and maximum thrust is desired throughout these operating conditions, such as tug, trawler and offshore supply boat applications.
2. Where shaft reversing capabilities are not readily provided by main engine (e.g. gas turbines).
3. Where extensive low speed maneuvering is required for a diesel powered vessel.
4. Where the ship will operate in ice-covered   water. The unidirectional rotation of CPP subjects the Blades to less ice damage.
5. When an improved maneuverability and a minimum ship stopping distance are desired. An infinitely variable thrust capability in either direction and a more rapid response to thrust reversal commands improve ship maneuverability and reduce the ship’s head reach.
6. Where a constant shaft rpm is an advantage over wide range of operating powers.

Disadvantages :

1. It is a complex system hence reduced reliability compared to fixed pitch.
2. With oil in propeller boss, possibility of pollution of sea with oil.
3. Increased maintenance on the propeller and extra maintenance because of additional equipments involved.
4. Chances of propeller blades getting stuck at some particular pitch angle and thus giving no choice to vary the magnitude of the thrust.

Working of CPP

The pitch of the CPP blades is controlled hydraulically through a system consisting of a pump, piston, crosshead, and blade crank rings. The piston, crosshead, and crank rings are located in the propeller hub. High pressure hydraulic oil, acting on either side of the piston, moves the piston axially within the propeller hub.

The piston is attached to a piston rod that connects to the crosshead that moves axially with the piston. Sliding blocks fit in machined slots on the crosshead and these sliding blocks fit over eccentrically-located pins mounted on the crank pin rings. As the crosshead moves forward and backwards within the hub, the sliding blocks move in an arc that also moves the eccentric pin and rotates the crank pin rings to which the CPP

Checks on propeller in Dry Dock

1. Physical damage to blades, specially on tips
2.Erosion/corrosion damage
3.Pitting due to cavitation
4. Local cracks or tears

Repairs on propellers in Dry dock

1.Straightening of blades by weights and levers while heating
2.Welding- Requires inert gas shielded arc and preheating for abou 1 hr at 120 degree C.
3.All slag,s to be removed between two consecutive welds.
4.Old repairs to be ground out before new repairs.
5.Propeller may be downsized by cutting portions from the edges on all blades as per class approval.

6.Cracks in the key to check and repair
7.To check for cracks on the boss and repair if required
8.Propeller surface to be polished
9.If required  Silicon coating to be applied after polishing the blade

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Author Amit                                                                            Article Requested By: javed iqbal

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