Module 8 Final 3

8

MODULE

WEEK 13

RUDDER AND PROPELLER

RUDDE R  Rudders are a means of directional control of ship  Rudders are fitted at aft end because:

RUDDE R a. Driven benefit of increased water velocity induced by the propelleresp. at low speed.

RUDDE R

b. To create where the maximum distance from the ships neutral point where lateral force does not cause ship to deviate from a constant direction. Neutral point is forward of midship.

RUDDE Neutral point isR the point in the length of the ship at which an applied force (lateral) DOES NOT cause the ship to deviate from a constant direction. Generally, neural point is forward of midship. Hence rudder is most effective when located aft, and it gives maximum turning effect.

RUDDE R of rudder is  Size and shape consist by:  Shape and type of stern  Area of rudder deemed necessary  Capacity of steering gear  Service condition of ship

RUDDE RATIO ROF THE

THE DEPTH TO WIDTH OF A THE RUDDER IS KNOWN AS THE ASPECT RATIO AND ITS VALUE IS GENERALLY 2. HIGH ASPECT RATIO IS USED IN LARGE VESSELS, WHERE DEPTH IS NOT A CONSTRAINT. HIGHER ASPECT RATIO REDUCES THE ASTERN TORQUE CONSIDERABLY.

RUDDE R  THE ASPECT RATIO = (DEPTH OF THE RUDDER/WIDTH OF RUDDER)

RUDDE R ON THE RUDDER  THE FORCE DEPEND ON: 1. AREA OF THE RUDDER 2. THE FORM OF RUDDER 3. THE SPEED OF THE SHIP 4. THE ANGLE OF HELM

RUDDE R  

FORCE ACTING ON THE RUDDER, F=k A

RUDDE R  

M = (0.195+ 0.305 sin)L

THREE TYPES OF RUDDERS 01

UN BALANCE D RUDDER

02

03

BALANCED

SEMI BALANCED RUDDER

RUDDER

RUDDE Types of rudder – the main purpose of balancing R rudder is to achieve the reduction in the torque required of the steering gear. Balanced – a portion of the blade area is disposed symmetrically through the rudder height and forward of stock. Unbalance - Blade is entirely aft of stock Semi- balanced area forward of stock does not extend to the full height of the blade aft of the stock – upper portion may be considered unbalanced and the lower portion, balanced.

OLD FASHIONED/ UNBALANCED RUDDER

 Full area aft of the axis.  Fitted with upper, mid and lower arms rested on gudgeons.  At the bearing pintle fitted with hard steel disc and locking nut.  The ordinary pintle arranged with bush and locking nut and locking pintle at the top part of the rudder secured by locking nut.  Turn on pintles and have a small portion of their lateral area forward of the turning axis (less than 20%).  Commonly fitted on twin screw vessels where most of it hinged on the body post by pintles and gudgeons.

SEMI-BALANCED RUDDER

Which are very common today. Have less than 20% of the lateral area forward of the axis . Modern ships use this design of rudder.

BALANCED RUDDER

Axle fitted at its turning axis with large area forward of the axis (25% to 30%). Upper and lower bearing are fitted in the rudder. The bearing consists of a stainless steel bush in the rudder and a stainless steel line on the axle. The stainless steel bush is spirally grooved to permit lubricant. Other materials are in use, such as gun metal for liner and lignum vitae or tufnol for the bush.

RUDDER HOW DOES A RUDDER HELP IN TURNING SHIP?

THEORY OF STEERING

THEORY OF STEERING

LATERAL FORCE

THEORY OF STEERING TRANSVERSE Bodily motion

THEORY OF STEERING Pivot point

THEORY OF STEERING Pivot point

THEORY OF STEERING Pivot point

THEORY OF STEERING

THEORY OF STEERING

THEORY OF STEERING Velocity Decrease Pressure Increase

Velocity Increase Pressure Decrease

THEORY OF STEERING Velocity Decrease Pressure Increase

Force (f)

Velocity Increase Pressure Decrease

THEORY OF STEERING

Lift force

Center of effort

Drag force

Force (F)

THEORY OF STEERING

THEORY OF STEERING d

Torque = Fxd

THEORY OF STEERING

PROPELLER

PROPELLER  A marine propeller is propulsion device which converts the power transmitted from the engine into a thrust force to propel the vessel.



CHARACTERISTICS PROPELLER It consists of a number of identical twisted blades usually 3-5 equally spaced around the hub or boss. The bud or boss is mounted on the propeller shaft. The hub of the propeller is fitted at one end of the propeller shaft by means of a nut.

CHARACTERISTICS PROPELLER

 Propeller is made up of mainly manganese bronze, stainless steel and phosphorus bronze.

The purposed of the propeller  is to convert the power of the main engine into thrust (pushing force).

DIAMETER 

The measurement of two times the distance from the centerline of the hub to the tip of one blade propeller.

Propeller hub

Blade tip

DIAMETER 

"Diameter is determined primarily by hub the rpm at which the propeller Propeller will be turning and the amount of power that will be delivered to the propeller“ Blade tip

-Mercury Marine's manual

PITCH OF THE PROPELLER 

Pitch of the propeller is the apparent distance moved by the propeller on its axis on one rotation of the propeller.

SLIP 

The difference between the distances a propeller should travel and the distance it actually travels in one complete revolution. It is expressed as a percentage.

SLIP Formula: Engine distance = Pitch X RPM X 60 X 24 / 1852. Example:- During 24 hrs of a period ship's propeller shaft was observed to turn 87 RPM. the pitch of the propeller was 3.8 m. the observed ships speed over ground was 10 knts. Calculate the value of the propeller slip during this period. ( A nautical mile equals 1852 m.) Soln: Slip (percent) = Engine distance - ship's distance/ Engine's distance X 100. Engine distance = Pitch X RPM X 60 X 24 / 1852. = (3.8 X 87 X 60 X 24)/1852 =257.054. Ship's distance = 24 X 10 = 240. Therefore slip = (257.054-240)/257.054 x 100 = +6.6%

PROPELLER SPEED  When the vessel is moving ahead the propeller exerts pressure on the water to create the forward motion.

PITCH OF THE PROPELLER Controllable Pitch Propeller (CPP)

PITCH OF THE PROPELLER Controllable Pitch Propeller (CPP)

TYPES OF PROPELLER  Classification Number of Attached:

by Blades

PROPELLER SPEED  When the vessel is moving ahead the propeller exerts pressure on the water to create the forward motion.

Types of Propeller  Classification Number of Attached:

by Blades

3 blade propeller 

*The manufacturing cost is lower than other types *Are normally made up of aluminium alloy. *Gives a good high-speed performance. *The acceleration is better than other types. *Low-speed handling is not much efficient.

4 blade propeller 

*The manufacturing cost is higher than 3 blade propellers. *4 blade propellers are normally made up of stainless steel alloys. *Have better strength and durability. *Gives good low-speed handling and performance. *Has a better holding power in rough seas. *4 blade propeller provides a better fuel economy than all the other type

5 blade propeller 

*Manufacturing cost is higher of all. *Vibration is minimal from all the other types. *5 blade propellers have better holding power in rough seas.



Large container ships are mainly fitted with 5 or 6bladed propellers.

6 blade propeller 

*Manufacturing cost is high *Vibration is minimal from all the other types. *6 blade propellers have better holding power in rough seas. *With six blade propeller, the induced pressure field over the propeller decreases



Large container ships are mainly fitted with 5 or 6bladed propellers.

Propeller cavitation 

A phenomenon called cavitation occurs under certain conditions during the rotation of the propeller wherein cavities (bubbles) are formed in contact with the propeller blades reducing its thrust and thereby, reducing the ship speed.

APPARENT SLIP

 Difference between the speed of the stream and speed of the ship.

TRUE SLIP  Difference between speed at which the water is fed to the propeller and which it is projected at the stern.

TRUE and APPARENT SLIP

SPECIAL TYPE OF PROPELLER

CONTROLLABL E PITCH FIXED PITCH PROPELLER

THREE TYPES OF PROPELLER

FIXED PITCH  Simplest PROPELLER of the propeller designs.

CONTROLLABLE PITCH  Propeller/Variable Pitch Propeller Blades are adjustable

SPECIAL TYPE OF PROPELLER VOITH SCHREIDER PROPELLER

Rotating axis perpendicular to th direction of fluid motion.

SPECIAL TYPE OF PROPELLER KORT NOZZLE PROPELLER

Is a marine propeller fitted with a nonrotating nozzle.

PROPELLER BLADES 2 COMPONENTS/PARTS

FORE AND AFT

ATHWARTSHIP ONE

DEAD IN THE WATER

Ship unable to move

TWIN SCREW (PROPELLER)

Having two propeller