Side-boat tow to test the influence of flaps in a 2-meter planing craft model


  • José R. Marín Faculty of Maritime Engineering, ESPOL. Guayaquil, Ecuador.
  • Daniela A. Benites Naval Engineer, Guayaquil, Ecuador.



planing boat, model test


A small craft is considered in the planing regime when its Froude number is higher than 1.2, and under that condition its weight is mainly supported by hydrodynamic pressure acting on the bottom of the hull. It is also known that installing stern flaps at a certain angle from the bottom line will alter the trim angle and, as a consequence, the resistance exerted by the water. In this work, using the classical work from Savitsky, the resistance on a planing craft is estimated, including the effect of flaps, and then the influence of those appendages on the hydrodynamic behavior of a craft of local design was experimentally verified. The wooden model was 2.0 meters long and was side towed from an outboard powered boat, with a 3.2-m arm, in a small artificial lake. The tests were run between 5 and 12 knots, with uneven intervals due to the outboard control; the model was towed without and with flaps at 5 and 10°. Finally, experimental and empirical results for towing force and trim angle were plotted. In some of the experimental curves the presence of humps may be identified, but less pronounced than with the theoretical results. Experimental resistance values are lower than those obtained from Savistky’s formulation for no flaps; in the case of flaps at 5°, the agreement in trim angle was very good. Finally, the benefit of flaps on the performance of the planing model was corroborated, but it should be emphasized that this improvement is only valid for a certain velocity range.


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BENITES, D. A., Pruebas Experimentales para Determinar la Influencia de Flaps en la Resistencia al Avance de una Lancha Planeadora de 11 metros, Naval Engineer Thesis, Faculty of Maritime Engineering, ESPOL, Guayaquil, Ecuador, 2012.

BROWN, W. AND SAVITSKY, D., Procedures for Hydrodynamic Evaluation of Planing Hulls in Smooth and Rough Water, Marine Technology, SNAME, Vol 13, No.4, 1976.

FALTINSEN, O., Hydrodynamics of High-Speed Marine Vehicles, Cambridge University, 2005.

ITTC, Recommended Procedures and Guidelines – Testing and Extrapolation Methods (Resistance Test for High Speed Marine Vehicles), 7.5-02-05-01, 2002.

SAVITSKY, D., Hydrodynamic Design of Planing Hulls, Marine Technology, SNAME, Vol. I, 1964.

VAN MANEN, Resistance, Ch. 5 in Principles of Naval Architecture Vol II, E. Lewis, Ed., SNAME, 1988.




How to Cite

Marín, J. R., & Benites, D. A. (2012). Side-boat tow to test the influence of flaps in a 2-meter planing craft model. Ciencia Y tecnología De Buques, 6(11), 67–78. Retrieved from



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