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National Advisory Committee for Aeronautics, Technical Notes - The Planing Characteristics of a Surface having a Basic Angle of Dead Rise of 20° and Horizontal Chine Flare

In order to extend the range of available planing—surface data, the
hydrodynamic characteristics have been obtained for a planing surface
having a basic angle of dead rise of 20° at the keel and horizontal
chine flare. This surface is representative of those used on present—
day flying boats. The wetted lengths, resistances, center-of-pressure
locations, and drafts were determined at speed coefficients (Froude
numbers) ranging from approximately 3.0 to 25.0, with the bulk of the
data obtained at Froude numbers in excess of 7.0. Beam loadings were
varied from 0.85 to 87.33. KEel-wetted—length-—beam ratios were extended
to 7.0 in all cases where excessive loads and spray conditions were not
encountered.

The data obtained indicate that, during high-speed steady—state
planing, the planing characteristics are independent of speed and load
for a given trim and depend,only on lift coefficient. The difference
between the chine wetted length and keel wetted length is constant for
a given trim angle and the variation of this difference with trim is
shown to be in reasonable agreement with theory. The ratio of center-
of-pressure location forward of the step to the mean wetted length, for
practical applications, can be considered a constant equal to 0.67 up
to 18° of trim. A slight decrease in this ratio occurs with further
increase in trim.angle. -The draft data indicate a pile-up of water at
the keel during steady—state planing. Although negligible at low trims,
this pile—up was significant at trims of 12° and higher. The drag data
show that friction drag at trims of 18° and higher is negligible and
that the resistances for those trims may be assumed equal to the load
times the tangent of the trim angle.

Present developments in water-based aircraft show an immediate need
for information on the principal planing characteristics of prismatic
surfaces at higher trims and loads than are covered by the range of
steady-state.experimental dataanW available (refs. 1 to 8). In addi—
tion to this information, the effects of chine flare used on seaplane
hulls to control spray and increase the efficiency of surfaces having
high angles of dead rise need to be studied.