lecture 1 propulsor

UNIVERSITAS HASANUDDIN FAKULTAS TEKNIK

SHIP PROPULSION (Propulsor)Lecturer: Dr. Andi Haris Muhammad


IntroductionIn the last chapter of this module we shall look into some special propeller and some other type of marine propulsion as well.Also, in the chapter of this module we have seen that a good marine propeller can achieve 75-80 percent of ideal efficiency.

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Types of Propulsors Propellers Fixed Pitch (fig. a) Controllable (Reversible) Pitch (fig. b) Ducted (fig. c) Thrusters (fig. d) Contra-rotating (fig. e) Super Cavitating (fig. f) Super piercing (fig. g) Jet Water jet (fig. h) Other type of marine Propulsors Voith-Schneider (fig. i) etc20 May 2012 Propulsors 3


Types of Propulsors

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Propeller geometry Propellers Blades (attached to the hub) Edge of the blade (Leading and Trailing edge) Surface of the blade (back and face) Blade section Chord line Angle of attack Camber line Pitch angle etcPropulsors 5

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Sketch of a propeller

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Propeller Geometry

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Definitions of Pitch and Slip

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Systematic propeller series

The propulsive performance of a screw propeller is dependent on: Geometry, Rotation rate Forward speed through the water.An important method of designing a propeller is to determine its main features from the results of open-water experiments carried out with model propellers.20 May 2012 Propulsors 9


Propeller Basics

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Definitions (cont.)

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Parameter Studies For preliminary design studies the open water diagram can be use straightway The Open water diagram are given as a function of J. For B-series open water diagram have been converted to two other types: Bp1-1/J and Bp2-1/J

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Propeller Coefficients Thrust Coefficient (KT)

KT = KQ = J=

T r n2 D 4 Q rn2 D5

Torque Coefficient (KQ)

Advance Coefficient (J)

VA nD

Open-water Propeller Efficiency (h0)

h0 = TVA = J KT 2p nQ 2p KQ

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Typical Chart

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Propeller Selection Method

Inputs: Design speed. Diameter constraints. EHP at design speed. Type and number of propellers (skew angle, blades, etc.). Wake fraction (w) and thrust deduction (t). Approach Select number of blades based on frequency of excitation (similar designs). Select area ratio based on cavitations limitations: The minimum area ratio allowed by cavitations or strength will have the best efficiency. In general, larger diameter is better. In general, lower RPM is better. If machinery sets RPM, then seek the optimum diameter. If stern aperture sets the diameter, seek the optimum RPM.20 May 2012 Propulsors 16


Controllable Pitch Propellers (CPP) Controllable pitch vs. self pitching propellers. C.P. has slightly less efficiency than fixed pitch. Can better match engine characteristics at different speeds. Ship maneuverability is also increased. Very attractive in warships where cruising endurance speed is often less than half the full speed. Need for CRP since gas turbines run in one direction only.

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CRP Operational Profile

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Ducts and Nozzles Concept Kort nozzle (1934) Shrouding or ducting surrounding propeller Recovers energy lost of the tips of blades Directs incoming water into propeller disc, increasing efficiency Can be designed to protect propeller against damage and shield noise Improves vibration excitation Several designs: Duct in front of propeller Asymmetrical duct Nozzle fixed to ship Nozzle fixed to propeller 20 May 2012 Propulsors Combinations

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Nozzle ConfigurationsRegular duct

Asymmetrical (vertically and circumferentially) duct

Wake distributor

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Contra rotating Propellers

Constraints on diameter caused by ship draft and hull form lead to inefficient propellers Two propellers on same shaft share loading and can thus the propeller diameter can be reduced Propellers rotating in same direction are called Tandem Propellers rotating opposite directions are Contra rotating Opposite direction allows after prop to recover rotational energy imparted to water by forward prop One shaft turns inside outer shaft Improved efficiency but higher drag and cost Should be avoided at higher rotational speeds because of effects from forward propeller cavitations on after propeller.20 May 2012 Propulsors 21


Vertical Axis Propellers

Essentially a horizontal disc rotating about a vertical axis. By controlling the angle of the blades. A thrust can be produced in any desired direction vertical axis propeller are fitted in tugs or other cases where low speed maneuverability is desired. Gears set limitation on power.

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Water Jets and Pump Jets Water jet uses ducts to bring water into ship, impart acceleration using an impeller, and discharge resultant jet of water through the stern. Same momentum theory applies. Useful at high speeds (hydrofoils, planing boats) and where sufficient draft is a problem. Propulsive coefficients lower due to energy lost in discharge. Maximum PCs from 0.50 to 0.55, although recent progress claims higher numbers. Lost volume in hull due to impeller and ducting. Lower appendage drag due to no shafts, struts, or propellers. Pump jets use impellers mounted outside the hull and enclosed in large duct or shroud ring.20 May 2012 Propulsors 23


Propeller Efficiencies Comparison

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SummaryA description of the most important design features of marine propulsions was given. It was shown how test results of systematic propeller series can be used in the design of propellers. A propeller can now be designed in a preliminary way using the results of systematic tests with the B-series propellers. A critical judgement of several design parameters of screw propellers can be made. In a global way the geometry of a marine screw propeller was discussed.


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lecture 1 propulsor

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