Page 177 - Theory and Design of Air Cushion Craft

160 Stability

speed. This was found both on model test and full-scale ship trials. This occurred to
the SES type 717C with thinner sidewalls, which rolled violently at hump speed and
even led to unstable yawing and plough-in. For this reason, it is very important to
analyze the stability of craft during take-off.
Figure 4.25 shows experimental results of transverse stability of an SES model run-
ning at different speeds over water obtained by Soviet engineer A. Y. Bogdanov [44]. He
presents the relative stability moment Ml = MllM g, in which Mj denotes the restoring
moment of model at speed of v, M^ denotes the restoring moment of model at zero speed
and Fr D denotes the Froude number based on volumetric displacement of the craft.

750
'e
•
500

250

0.5 1.0 1.5 2.0 2.5 0(°)

Fig. 4.24 Composition of transverse righting moment of SES model 717C. 1: Sidewall moment, v = 44.2 kph;
2: Stern planing seal moment, v = 44.2 kph; 3: Sidewall moment, v = 26.5 kph; 4: Stern planing seal moment,
v = 26.5 kph.

Fig. 4.25 Transverse stability moment of heeled SES at speed.