Page 163 - Theory and Design of Air Cushion Craft

146 Stability

1. width of keel plate of sidewall, B v;
2. deadrise angle of midships section of sidewalls, a;
3. height of hard chine line amidships, /z k;
4. width of sidewall, B sw;
5. flare angle of sidewall above hard chine, ft;
6. external draft of the sidewall, t 0.
From Fig. 4.10, we have

B^ = 5, + cot a (4.11)
t 0
= (B, + t 0 cot (4.12)
BJB C a)IB c
In general, 5, can be kept as a constant, can be determined by the cushion pressure
t 0
p c, so we can take the parameters a, ft and B^ as variables, the variable range of which
is shown in Table 4.2.
The calculation results are shown in Fig. 4.11. In order to investigate the effect of
BI on stability, we obtain the second set of variables shown in Table 4.3. The basic
parameters were kept the same as for craft type 717, such as principal dimensions,
cushion pressure/length ratio, flow rate coefficient, flare angle of sidewall section
above the hard chine, the gap between the lower edge of the bow/stern seals and the
base-line, fan characteristic, etc., except the parameters a and ft. Then the static trans-
verse stability could be calculated. The results are as shown in Fig. 4.12.
From the figures, it is found that:
1. The static transverse stability of craft at large heeling angles is strongly affected,
but not at small angles.

Table 4.2 The variable range of a, /?, 5 OT
a(°) 40 45 50 55 60
0(m) 55, 60, 65 50, 60, 65 60, 65, 70 60, 65, 70 65,70
B w 0.62 0.54 0.472 0.414 0.362
0.177 0.154 0.135 0.118 0.104
BJB C

Fig. 4.10 Geometrical parameters for sidewalls.