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1. www.tanhatarin109.javanblog.com

3. Frames of Reference 10th International Towing Tank Committee (ITTC) initiated thepreparation of a dictionary and nomenclature of ship hydrodynamicterms and this work was completed in 1975. The global reference frame proposed by the ITTC is a right-handedrectangular Cartesian system.www.tanhatarin109.javanblog.com

4. For propeller geometry it is convenient to define a local referenceframe having a common axis such that OX and Ox are coincident butOy and Oz rotate relative to the OY and OZ fixed global frame.www.tanhatarin109.javanblog.com

5. The line normal to the shaft axis is called either propellerreference line or directrix.www.tanhatarin109.javanblog.com

6. Generator line: The line formed by intersection of the pitchhelices and the plane containing the shaft axis and propellerreference line.www.tanhatarin109.javanblog.com

7. The aerofoil sections which together comprise the blade of apropeller are defined on the surfaces of cylinders whose axes areconcentric with the shaft axis. www.tanhatarin109.javanblog.com

8. Face: The side of a propeller blade which faces downstreamduring ahead motion is called face or pressure side (when viewedfrom aft of a ship to the bow the seen side of a propeller blade iscalled face or pressure side). www.tanhatarin109.javanblog.com

9. Back: The side of a propeller blade which faces generallydirection of ahead motion is called back or suction side (whenviewed from aft of a ship to the bow the unseen side of apropeller blade is called back or suction side).www.tanhatarin109.javanblog.com

10. Leading Edge: When the propeller rotating the edge piercingwater is called leading edge.www.tanhatarin109.javanblog.com

11. Trailing Edge: When the propeller rotating the edge trailing theleading edge is called trailing edge.www.tanhatarin109.javanblog.com

13. Consider a point P lying on the surface of a cylinder of radius rwhich is at some initial point P0 and moves as to from a helixover the surface of a cylinder. The propeller moves forward as to rotate and this movementcreates a helix. www.tanhatarin109.javanblog.com

14. When the point P has completed one revolution of helix thatmeans the angle of rotation 360 deg. www.tanhatarin109.javanblog.com

15. In the projection one revolution of the helix around the cylindermeasured normal to the OX axis is equal to 2r. The distance moved forward by the helical line during thisrevolution is p and the helix angle is given by: www.tanhatarin109.javanblog.com

16. There are several pitch definitions:www.tanhatarin109.javanblog.com

17. Nose-tail pitch: The straight line connecting the extremities ofthe mean line or nose and tail of a propeller blade is called nose-tail pitch line The section angles of attack are defined to thenose-tail line. www.tanhatarin109.javanblog.com

18. Face pitch: The face pitch line is basically a tangent to sectionspressure side surface and you can draw so many lines to thepressure side. Therefore its definition is not clear. It is rarely usedbut it can be seen in older drawings like Wageningen B series.www.tanhatarin109.javanblog.com

19. Effective or no-lift pitch: It is the pitch line of the sectioncorresponding to aerodynamic no-lift line which results zero lift.www.tanhatarin109.javanblog.com

20. Hydrodynamic pitch: The hydrodynamic pitch angle (i) is thepitch angle at which the incident flow encounters the bladesection. Pitch values at different radii are called radial pitch distribution.www.tanhatarin109.javanblog.com

21. Slip & Slip Ratiowww.tanhatarin109.javanblog.com

22. Skew It is the angle between the mid-chord position of a section andthe directrix (s). The propeller skew angle (sp) is defined as the greatest anglemeasured at the shaft centre line which can be drawn betweenlines passing from the shaft centreline through the mid chordposition of any two sections. www.tanhatarin109.javanblog.com

23. Skew www.tanhatarin109.javanblog.com

24. The skew can be classified into two types: i- Balanced skew: Directrix intersects with the mid-chord line atleast twice. ii- Biased skew: Mid-chord locus crosses the directrix not morethan once normally in the inner sections. www.tanhatarin109.javanblog.com

25. The displacement from the propeller plane to the generator linein the direction of the shaft axis is called rake. The propeller rakeis divided into two components: generator line rake and skewinduced rake. www.tanhatarin109.javanblog.com

26. Propeller Outlines and Areas www.tanhatarin109.javanblog.com

27. There are five different outlines and associated areas of propellerin use. These are: 1. Disc outline (area) (A0) 2. Projected outline (Ap) 3. Developed outline (AD) 4. Expanded outline (AE) 5. Swept outline (AS) www.tanhatarin109.javanblog.com

28. Swept Outline: This outline is swept by the leading and trailingedges when the propeller is rotating. In general, the developed area is greater than the projected areaand slightly less than the expanded area.www.tanhatarin109.javanblog.com

29. Calculation of AEwww.tanhatarin109.javanblog.com

30. Propeller drawing methodswww.tanhatarin109.javanblog.com

31. Propeller drawing methodswww.tanhatarin109.javanblog.com

32. Propeller section definitionwww.tanhatarin109.javanblog.com

33. Propeller series www.tanhatarin109.javanblog.com

34. Model ship & propeller tests 1- Resistance Test 2. Open water tests 3. Self propulsion tests 4. Cavitation tests 5. Others (wake surveys, hull pressure tests, noise measurements,etc.)www.tanhatarin109.javanblog.com

35. 1- Resistance Test In the resistance test the ship model is towed by the carriage andthe total longitudinal force acting on the model is measured forvarious speeds. The breadth and depth of the towing tankessentially governs the size of the model that can be used. Toddsoriginal criterion that the immersed cross-section of the vesselshould not exceed 1 per cent of the tanks cross sectional areawas placed in doubt after the famous Lucy Ashton experiment.This showed that to avoid boundary interference from the tankwalls and bottom this proportion should be reduced to the orderof 0.4 per cent. www.tanhatarin109.javanblog.com

36. The model, constructed from paraffin wax, wood or glass- reinforced plastic, requires to be manufactured to a high degree of finish and turbulence simulators placed at the bow of the model in order to stimulate the transition from a laminar into a turbulent boundary layer over the hull. The model is positioned under the carriage and towed in such a way that it is free to heave and pitch, and ballasted to the required draught and trim.www.tanhatarin109.javanblog.com

37. In general there are two kinds of resistance tests: the naked hull and the appended resistance test. If appendagesare present local turbulence tripping is applied in order to preventthe occurrence of uncontrolled laminar flow over theappendages. Also the propeller should be replaced by astreamlined cone to prevent flow separation in this area.www.tanhatarin109.javanblog.com

41. 2. Open water tests Open water tests of propellers can be performed either in acavitation tunnel or in a towing tank. Although the test procedureapplied to obtain open water characteristics of a propeller in acavitation tunnel is different from those in a towing tank, thesecharacteristics are the same used in the analysis of the PropulsionTests and the estimation of the required power. www.tanhatarin109.javanblog.com

45. 2.1 Open water test in Towing tank In a towing the model propeller is run without any hull ahead ofit, as shown in the figure.www.tanhatarin109.javanblog.com

47. The drive shaft housing should not be too close to the modelpropeller blades. A distance of not less than 1.5 D to 2.0 D isrecommended, where D is the propeller diameter. The drive shaftshould be arranged parallel to the calm water surface and thecarriage rails. A typical set up is shown in the above figure. The propeller immersion has to be selected such that air drawingfrom the water surface is avoided at any test condition. As aguideline, an immersion of the propeller shaft of at least 1.5 D isrecommended.www.tanhatarin109.javanblog.com

48. The test procedure is as follows: 1. The propeller advances through undisturbed water with aknown forward speed, V, which is the speed of the towingcarriage. Values of thrust, T and torque, Q are taken from thedynamometer, and rate of rotation, n is recorded using atachometer. 2. Usually measurements are taken during series of runs for T &Q at varying J numbers so that n is kept constant and V is variedfrom zero speed (i.e. J=0) to a high value ( J=1). 3. The results are analised and coefficients are derived as similarto those in cavitation tunnel.www.tanhatarin109.javanblog.com

49. 3. Self propulsion tests Self propulsion tests are carried out to estimate ship power atvarious speeds and to derive propulsion factors, w, t, R. The hull model is equipped with an electric motor mountedinside the hull and respective devices (dynamometer) fittedinboard to enable the measurement of thrust, torque and rate ofrevolutions of the model propeller(s). Appendages, such asrudders, single brackets or A-brackets, propeller shafts, shaftprotection tubes, short bossings or bossings, extracted stabilisersand openings in the hull such as for bow thrusters, should be inthe same condition as for the resistance experiment.www.tanhatarin109.javanblog.com

50. 3. Self propulsion testswww.tanhatarin109.javanblog.com

51. The size of the propeller/propulsion unit model for propulsiontests is determined automatically by the size of the ship modeland its scale ratio; this in turn means that the size of the modelpropeller, or say a stock propeller, is also to be taken intoconsideration when the scale for a ship model is selected. During a self propulsion test, an external tow force in propulsionexperiments should be applied along the same line of action asthe tow force in the resistance experiment. This external force comes from the skin friction correction suchthat the skin friction coefficient of the model CFm is greaterthan skin friction coefficient of the ship, CFs. www.tanhatarin109.javanblog.com

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