Page 211 - Theory and Design of Air Cushion Craft

194 Trim and water surface deformation under the cushion

a/b=0.l

Fig. 5.5 Deformation of water surface of ACV at Fr- 0.57 on centreline for different alb.
(a) y/B=0

-0.5 -0.3 -0.1 o '"0.5 xll c
Fr,=0.578
0=0
calculation
0 0 0 °
4 ooo test data for HD-2
(b)y/B = ±0.497 2 p wgzlp c

-0.5 -0.3 -0.1 ,0.3 0.5 xll c

o o o o o o o

Fig. 5.6 Comparison of water surface deformation of craft HD-2 between calculation and test results, (a) at
centreline; (b) in cushion but in close proximity to cushion peripheral boundary.

ACV over shallow water

In shallow water, tanh kH [53] can be considered as a small value, i.e. tanh kH = kH
and cosh kH = 0. Then, when IIH > 10, the analytical expressions (5.2) can be sim-
plified as

^ G da (5.4)