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National Advisory Committee for Aeronautics, Technical Notes - Impact Loads Investigation of Chine Immersed Models Having Concave-Convex Transverse Shape in Straight or Curved Keel Lines

As part of an investigation of hydrodynamic impact loads on chine-
immersed bodies of heavy beam loading, three narrowébeam.models of concave-
convex transverse shape and having, respectively, a straight keel, a curved
bow, and a curved stern were tested. at the Langley impact basin. The tests
were made over a wide range of trim and initial-flight-path angles. Most
of the landing impacts were made at a beamploading coefficient of 18.77
with a few impacts at beam—loading coefficients of 27.59 and 56.15. The
investigation was conducted.primarily in smooth water; hovever, a few
impacts with the curved bow were made in rough water.

The impact-loads data are presented in tables, and the derived coef—
ficients of loads and motions are presented in figures as the variation
with initial-flight-path angle. The experimental effects of transverse
and longitudinal curvatures agree reasonably well with those predicted
by theory. The concave-convex bottom, which was similar to shapes con-
sidered as being of constant-force type, yields slightly higher peak loads
than a narrowaeam.model having conventional vee bottom of equivalent angle
of dead rise, with.the possible exception of certain rough-water-impact
conditions. The effect of stern curvature for the configurations tested
is greater than the effect of how curvature. _The rough-water loads were
found to be much greater than smooth—water loads for similar initial impact
conditions and were in reasonable agreement with loads obtained from theory
when the flight-path angle, velocity, and trim angle relative to the wave
slope were used.

In previous investigations of hydrodynamic impact loads on chine-
immersed bodies of heavy'beam loading, experimental data were obtained
for straight-keel models of flat and vee transverse shapes. These data
were presented in reference 1 for a model having 00 angle of dead rise
(flat bottom) and in reference 2 for the vee—shape model with 50° angle
of dead rise. A theoretical.method for predicting the impact loads on
chine-immersed models having straight keel lines was developed and pre—
sented in reference 5.