Page 109 - Theory and Design of Air Cushion Craft

Air cushion wave-making drag 93

1.0
l:c/g=Q b/a=0.5
2: c/g=0.05
3: c/g=0.10

0.6 a: cushion length
b: cushion beam
c: acceleration
0.4 d: water depth

0.2

2 4
2
l/(2Fr )

Fig. 3.9 Variation of cushion wave-making drag on accelerating craft. [21]
2.0
1: c/g=0
2: c/g=0.
3:cA?=0.10

a: cushion length
b: cushion beam
c: acceleration
d: water depth

l/(2Fr)

Fig. 3.10 Variation of cushion wave making drag on accelerating craft. [21]

The principal research work into wave-making drag due to an air cushion travelling
in yaw was carried out by Tatinclaux, who showed that peak drag of a craft in yaw
increased dramatically. MARIC also has practical experience that a craft travelling in
yaw on water is very difficult to pass through hump speed, particularly for an amphibi-
ous ACV. An ACV travelling in yaw in a beam wind condition will probably have diffi-
culty in passing through the hump speed as well as increasing handling difficulties.
Pilots with such problems in open water will usually make a track across or down
wind to accelerate through the hump and then return to the intended course. In more
restricted conditions, a downwind track to a more sheltered area where the craft can
be turned around over the hump may be needed.