6 Propeller performance characteristics
6.9 Propeller ventilation
Propeller ventilation can have a significant influence on the performance characteristics of a propeller. Koushan (Reference 45) has investigated these effects in relation to a non-ducted thruster. He showed that in a ventilated condition even when the propeller is well submerged the loss of thrust can be as much as 40 per cent. In the cor- responding condition of partial-submergence this loss may rise to as high as 90 per cent. Moreover, the mech- anism of ventilation can take many forms; for example, it may be a direct drawing of air from the water surface or, alternatively, it might be that the air uses some other path such as down the surface of A or P brackets or some other appendage and then passes to the propeller.
Scale effects are particularly influential in assess- ing the propeller characteristics and, in particular, the influence of the Weber (We), Depth Froude (Fnp) and Ventilation (σv) number need to be considered. In this context these numbers are defined as:
We=nD√
(ρD/S) Fnp=πnD/√ (gh) σv=2gh/(VR2)
where Sis the air–water surface tension his the propeller shaft immersion VRis the propeller section inflow velocity uncorrected for induction effects and normally referred to the 0.7Rradial location.
The remaining symbolsρ,g,nandDhave their usual meaning.
In the case of the Weber number, because surface ten- sion is a significant parameter in model testing, it has
Propeller performance characteristics 133
Figure 6.24 Typical fluctuation in bearing forces and moments for a propeller working in a wake field
Figure 6.25 Cavitation pattern on the blades of a model propeller operating in a wake field (Reproduced partly from Reference 39)
Ch06-H8150.tex 15/5/2007 22: 5 page 134
134 Marine propellers and propulsion
a significant influence on the measured results. Shiba (Reference 46) based on a large set of model measure- ments concluded that if the Weber number is greater than 180 then its effect is probably insignificant. Below that critical number, however, it was concluded that less or delayed ventilation might be observed at model scale when compared to full scale.
When the propeller breaks the surface or is close to the free surface and generates a system of local waves and then the Froude depth number assumes importance.
In the case of the ventilation number, this is essentially a cavitation number as discussed in Chapter 9 in which the normal static vapour pressure is replaced with ambi- ent pressure. From a little algebraic manipulation of the relationships defined above, it can be seen that if the advance coefficient of a particular test is defined and then one of either the Froude depth number of the ven- tilation number is satisfied then the other coefficient will also be satisfied.
References and further reading
1. Vasamarov, K.G., Minchev, A.D. A propeller hydro- dynamic scale effect. BSHC Report No. PD-83- 108, 1983.
2. Voitkounski, Y.I. (ed.)Ship Theory Handbook. 1, Sudostroeme, Leningrad, 1985.
3. Troost, L. Open water test series with modern propeller forms.Trans. NECIES,54, 1938.
4. Troost, L. Open water test series with modern pro- peller forms. II. Three bladed propellers. Trans.
NECIES, 1940.
5. Troost, L. Open water test series with modern propeller forms. III. Two bladed and five bladed propellers – extension of the three and four bladed B-series.Trans. NECIES,67, 1951.
6. Lammeren, W.P.A. van, Manen, J.D. van, Oost- erveld, M.W.C. The Wageningen B-screw series.
Trans. SNAME, 1969.
7. Oosterveld, M.W.C., Ossannen, P. van. Fur- ther computer-analysed data of the Wageningen B-screw series.ISP,22, July 1975.
8. Yazaki, A Design diagrams of modern four, five, six and seven-bladed propellers developed in Japan.4th Naval Hydrodynamics Symp., National Academy of Sciences, Washington, 1962.
9. Gawn, R.W.L. Effect of pitch and blade width on propeller performance.Trans. RINA, 1952.
10. Blount, D.L., Hubble, E.N. Sizing for segmental section commercially available propellers for small craft.Propellers 1981 Conference, Trans. SNAME, 1981.
11. Gawn, R.W.L., Burrill, L.C. Effect of cavitation on the performance of a series of 16 in. model propellers.Trans. RINA, 1957.
12. Emerson, A., Sinclair, L. Propeller design and model experiments.Trans. NECIES, 1978.
13. Lingren, H. Model tests with a family of three and five bladed propellers. SSPA Paper No. 47, Göteborg, 1961.
14. Newton, R.N., Rader, H.P. Performance data of propellers for high speed craft.Trans. RINA,103, 1961.
15. Burrill, L.C., Emerson, A. Propeller cavitation:
some observations from the 16 in. propeller tests in the New King’s College cavitation tunnel.Trans.
NECIES,79, 1963.
16. Burrill, L.C., Emerson A. Propeller cavitation:
further tests on 16 in. propeller models in the King’s College cavitation tunnel.Trans. NECIES, 1978.
17. Manen, J.E. van, Oosterveld, M.W.C. Model Tests on Contra-Rotating Propellers. Publication No.
317, NSMB Wageningen, 1969.
18. Bjarne, E. Systematic studies of control-rotating propellers for merchant ships, IMAS Conference, Trans.I.Mar.E, 1973.
19. Boswell, R.J. Design, Cavitation Performance, and Open Water Performance of a Series of Research Skewed Propellers. NSRDC Report No. 3339, March 1971.
20. Gutsche, F. Untersuchung von Schiffsschrauben in Schräger Anstromung. Schiffbanforschung, 3, 1964.
21. Taniguchi, K., Tanibayashi, H., Chiba, N. Inves- tigation into the Propeller Cavitation in Oblique Flow. Mitsubishi Technical Bulletin No. 45, March 1969.
22. Bednarzik, R. Untersuchungen über die Belaslungs- schwankungen am Einzelflügel schräg angeströmter Propeller.Schiffbanforschung,8, 1969.
23. Meyne, K., Nolte, A. Experimentalle Untersuchun- gen der hydrodynamischen Kräfte und Momente an einem Flügel eines Schiffspropellers bei schräger Anströmung.Schiff und Hafen,5, 1969.
24. Peck, J.G., Moore, D.H. Inclined-shaft propeller performance characteristics.Trans. IESS. Sname, Spring Meeting, 1973.
25. Oosterveld, M.W.C. Wake Adapted Ducted Pro- pellers. NSMB Wageningen Publication No. 345.
June 1970.
26. Oosterveld, M.W.C. Ducted propeller characteris- tics. RINA Symp. on Ducted Propellers, London 1973.
27. Gutsche, F.A., Schroeder, G. Freifahruersuche an Propellern mit festen und verstellbaren Flügeln
‘voraus’ und ‘zuruck’. Schiffbauforschung, 2(4), 1963.
28. Chu, C., Chan, Z.L., She, Y.S., Yuan, V.Z. The 3-bladed JD–CPP series.4th Lips Propeller Symp., October 1979.
29. Yazaki, A. Model Tests on Four Bladed Controllable Pitch Propellers. Ship Research Institute, Tokyo, Paper 1, March 1964.
30. Hansen, E.O. Thrust and Blade Spindle Torque Measurements of Five Controllable Pitch Propeller
Propeller performance characteristics 135 Designs for MS0421. NSRDC Report No. 2325,
April 1967.
31. Miller, M.L. Spindle Torque Test on Four CPP Pro- peller Blade Designs for MS0421. DTMB Report No. 1837, July 1964.
32. Conn, J.F.C. Backing of propellers. Trans. IESS, 1923.
33. Nordstrom, H.F. Screw Propeller Characteristics.
SSPA Publication No. 9, Göteborg, 1948.
34. Strom-Tejsen, J., Porter, R.R. Prediction of controllable-pitch propeller performance in off- design conditions. Third Ship Control System Symp., Paper VII B-1, Bath, UK, 1972.
35. Nagamatsu, T., Sasajima, T. Effect of Propeller Suction on Wake.J. Soc. Nav. Arch. Jpn,137, 1975.
36. Leathard, F.I. Analysis of the Performance of Marine Propellers, with Particular Reference to Controllable Pitch Propellers. M.Sc. Thesis, New- castle University, 1974.
37. Keh-Sik, Min. Numerical and Experimental Methods for the Prediction of Field Point Velocities around Propeller Blades. MIT, Department Ocean Engineering Report No. 78–12, June 1978.
38. Kerwin, J.E., Chang-Sup Lee. Prediction of steady and unsteady marine propeller performance by numerical lifting-surface theory. Trans. SNAME, Paper No. 8, Annual Meeting, 1978.
39. Oossanen, P. van.Calculation of Performance and Cavitation Characteristics of Propellers Includ- ing Effects of Non-Uniform Flow and Viscosity.
MARIN Publication no. 457, 1970.
40. Kuiper,The Wageningen Propeller Series. MARIN, May 1992.
41. Bazilevski, Y.S. On the Propeller Blade Turbu- lization in Model Tests. Laventiev Lectures, St Petersburg, pp. 201–206, 2001.
42. Boorsma, A. Improving Full Scale Ship Powering Predictions by Application of Propeller Leading Edge Roughness. M.Sc. Thesis, Delft, December 2000.
43. Ball, W. and Carlton, J.S. Podded propulsor shaft loads from free-running model experiments in calm-water and waves.Int. J. Maritime Eng.,148 (Part A4).Trans. RINA, 2006.
44. Holtrop, J. Extrapolation of Propulsion Tests for Ships with Appendages and Complex Propulsors.
Mar. Technol.,38, 2001.
45. Koushan, K. Dynamics of ventilated propeller blade loading on thrusters. WTMC Conf. Trans.
I.Mar.EST, London, 2006.
46. Shiba, H. Air Drawing of Marine Propellers.Trans- portation Technical Research Institute, Report No. 9, Japan, August 1953.