The water rise in front of a model planing hull

Abstract

It is known that the water "splashes-up" or rises above the undisturbed surface immediately in front of a planing surface. This rise is greatest in front of a flat planing plate and a number of attempts have been made to reduce the experimental measurements of this phenomenon to some kind of order. Since it was first independently proposed by both Schnitzer and Smiley in 1952, all attempts to correlate the flat plate splash-up have started with the assumption that splash is only a function of the immersed length of the plate and is independent of trim angle at least below about 2o% In part, this was because the three early studies which compared this hypothesis with experimental data omitted those portions of the data which did not support the hypothesis.The present paper concludes that this forty year old hypothesis is fallacious and that the water rise in front of any prismatic planing surface is best approximated by k sin2z where d is the vertical water rise at the water/keel intersection; b is the beam; l is the submerged length of the keel; z is the trim angle; k is a constant determined from experiment, approximated by; k=ze -263, where fi is the deadrise angle in radians.It might be thought that this is a slight contribution, of little practical import, but for one thing. Starting in the 195o's most towing tank experimenters in the United States abandoned the difficult measurement of model draft and obtained only the "actually wetted length" from underwater photographs. But theoretical planing force calculations require a knowledge of the relationship between a hull and the undisturbed water plane. Thus if modern experimental data is to be compared with theory, it is necessary to estimate what the undefined splash-up or water rise was during each experiment, in order to estimate the model's true position in space.The paper concludes by criticizing the format of some modern reports of experiments with model planing hulls and suggests that, in addition to the usual graphical presentations, measured data should always be reported numerically. Also, that when relevant data is omitted from a plot, the facts of such omission should be clearly stated. Water rise and splash-upThe fastest boats are planing craft. As the name implies, the dynamic forces developed on the relatively straight (fore and aft) bottom of such a craft lift it up in the water, so that its actual wetted surface area on calm water is only a small fraction of its total plan area. Ideally, the wetted surface area varies inversely as the square of the boat's speed, so that the high speed resistance is roughly independent of speed. The total hydrodynamic resistance of such a craft is the sum of the skin friction on its bottom and a pressure drag term. For the simplest case of a prismatic planing surface, the pressure drag is R sinz, so that the energy input associated with this drag component is uoR sinz. Half this energy is dissipated in the downwards deflection of the water which produces the dynamic force R and the other half appears ...

Continual skipping on water

“…There was some evidence for this type of jet when the stream velocities were higher than in the experiments reported in § 2. In those reported, however, in common with other experiments on planing hulls (Payne 1994), the recirculating jet collapsed and evolved into a foaming wedge such as is seen in figure 2. Thus, a normal force of the form (3.4) seems inappropriate, and we present a more obviously relevant, if crude, alternative in § 4.…”

“…Such a jet is observed in our experiments when the paddle enters the fluid during skipping. In the steady planing state, however, we see that any such jet collapses rapidly to create a turbulent wedge of fluid much like that preceding the bow of a ship (Payne 1994; see figure 2).…”

Numerical study on interference effects and wetted area pattern of asymmetric planing catamarans

“…By neglecting the pile-up of water at the keel line, L k is obtained from the undisturbed water-level intersection with keel line. Such an assumption is, according to Savitsky’s statement for dead-rise planing surfaces, 3 “up to trim angle of approximately 15 deg there appears to be no noticeable pile-up of water at keel line.” In this regard, Payne 53 by analyzing the previous data gives a simple relation to calculate water rise in front of prismatic planing surfaces. In his relation, the increase in wetted length due to such water splash-up is proportional to sin τ and for a prismatic hull with dead-rise angle of 20° (according to suggested exponentially decaying dependency on dead-rise angle) is approximately 2.5 times less than that for flat plate (zero dead-rise angle).…”

Investigation of free surface flow generated by a planing flat plate using smoothed particle hydrodynamics method and FLOW3D simulations

“…In these references, it is mentioned that accurate transient rise measurement is very difficult. In this context, Payne 13 considered the water ''splash-up'' or rise above the undisturbed surface immediately in front of a planing surface. He surveyed the attempts that had been made to reduce the experimental measurements of the flat plate planing.…”

“…15 All of them had concluded that, when the wetted length to beam ratio exceeded (roughly) unity, the increase in wetted length due to splash-up was approximately 30%-40% of the beam. 13 Payne 16 summarized some of these attempts in his book.…”