Page 123 - Theory and Design of Air Cushion Craft

Sidewall water friction drag 107

Using flexible bow/stern seals

1.0 =._.

0.2

Fig. 3.21 Correction coefficient of outer wetted surface area of SES with flexible bow/stern seals.

11 h eq
,h.
• ^^^* «
| > X / * > X
r—i
-r-^ * d f^
T
» L / ts
r
<F= > <
I
I ^ J
-V ^
T
T
(b)

Fig. 3.22 Sketch of SES running attitude at F r = 0(a) and F r = 00(b).

B (3.28)
where 5 S is the width of the sidewalls with rectangular transverse section (m), s / the
length of sidewalls (m), /z c the depth of cushion air water depression, hovering static
(m), /z, the vertical distance between the lower tip of skirts and inner water surface, i.e.
//! = h 2 ~ T }, as shown in Fig. 3.24, hovering static (m), H 2 the vertical distance
between the lower skirt tip and craft baseline (i.e. z b, z s, in Chapter 5) (m), T { the inner
sidewall draft, hovering static, and /z eq the equivalent air gap,

where Q is the cushion flow rate (m'Vs), p 2 the cushion pressure (N/m), p a the air
4
2
density (Ns /m ), } the total length of air leakage at the bow/stern seal (m) and B c the
l
cushion beam (m).