Description
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
A propeller is a rotating fan-like structure that is used to propel the ship by using the power generated and transmitted by the main engine of the ship.
The transmitted power is converted from rotational motion to generate a thrust which imparts momentum to the water, resulting in a force that acts on the ship and pushes it forward(Bertetta et al., 2012).
Propeller design is a highly complex procedure, involving many influencing factors. Tuningthepropellergeometrytowardsefficiencyalsochangesitscharacteristicswithregardtovibration,inboard noise and cavitation behaviour, which will most likely occur when the propeller is inoperation.The propeller experiences varying inflow conditions while travelling through thecircumferential wake. This causes a varying load on the propeller blade during one revolutionand results in a local pressure drop around the blade(Bertetta et al., 2012).Depending on the operating conditions,e.g., submergence of the propeller shaft or rotational speed, the pressure sags below the vapourpressureandcavitation,i.e.,vapourpocketsintheliquid,canbeobservedatthepropeller.Whenagainenteringhigh-pressureregions,thecavitiescollapseextremelyrapidlyandmaycausenoiseand vibration, which are transferred to the ship’s hull, and cause erosion on the propeller or therudder. Cavitation and propeller-induced pressure pulses are the most evident propeller effectscontradictory to efficiency. Consequently, the only solution is to find a trade-off blade geometrythat is adapted to the flow and therefore only valid for a certain ship and the specific operatingconditions(Bertetta et al., 2012).
A ship propels on the basis of Bernoulli’s principle and Newton’s third law. A pressure difference is created on the forward and aft side of the blade and water is accelerated behind the blades.
The thrust from the propeller is transmitted to move the ship through a transmission system which consists of a rotational motion generated by the main engine crankshaft, intermediate shaft and its bearings, stern tube shaft and its bearing and finally by the propeller itself (Bertetta et al., 2012).
A ship can be fitted with one, two and rarely three propellers depending upon the speed and manoeuvring requirements of the vessel.
1.2 STATEMENT OF THE PROBLEM
The National Marine Manufacturers Association has found that approximately 100 million individuals go boating each year. That means there are millions of boats on the water across the globe. As a result, propellers have made a major splash within this industry, with the types of propellers continually expanding as boat technology improves.
Understanding boat propeller design can help solve performance problems that occur when a boat is being driven under power. The wrong prop may be wrong in a number of different ways including blade shape or size.
Your propeller blade shape or size may suffer from cavitation, ventilation or slippage – your boat may be burning too much fuel or lacking acceleration or top speed. It is important to study the effect of propeller shape and size on the performance of a boat.
1.3 AIM AND OBJECTIVES OF THE STUDY
The main aim of this work is to investigate the effects of propeller shape and size on the performance of outboard motors.
The objectives of the study are:
- To study how the shape and size of a propeller affect the performance of outboard motors.
- To study the operation of a propeller in an outboard motors.
1.4 SCOPE OF THE STUDY
The propeller is the means of propulsion whose rotation is driven by the engine. The thrust created by the movement of the blades in the water generates the speed of the boat. The decisive factor in reaching the manufacturer-recommended speed is the propeller pitch. This is the distance travelled by the propeller to complete one full rotation about its axis. The scope of this work covers investigating how shape and size of a propeller affect the performance of outboard motors.
1.5 SIGNIFICANCE OF THE STUDY
This study will serve as a means of understanding factors that determines the efficient performance of outboard motors.
The study will also serve as a means of studying the operation of a propeller of outboard motors.
This study will serve as a means of knowing the constructional details of an outboard motors’ propeller.
