Page 122 - Practical Ship Design

Weight-Based Designs 89

0.8D

Fig. 4.3. Midship section compared with an I beam.

4.2.7 A rutional base for approximate structural weight estimation
Following the modulus-dependent thesis, the midship section of a ship may be
compared with the cross section of an I beam as shown in Fig 4.3.
The hull steel-weight per metre = R(A, + A, + A, + A,) (4.4)
where
A, = area of deck plating + deck longitudinals + other longitudinal material
above 0.90 from base
A, = area of bottom plating + bottom longitudinals + other longitudinal
material below 0.1D from the base
A, = area of shell plating and longitudinals + area of longitudinal bulkhead
plating and longitudinal within the middle 0.80
A, = area of transverse material per metre of ship’s length
R = weight per metre per unit area.

The deck modulus of the hull girder is approximately
A,(H,)’ +A,(H,)* +I/ 12A,(0.800)2
z= (4.5)
Hb
If k,.D is substituted for Hd and k,.D for Hb, then

A, + A,(k,lk,)’ +A,( 1/4.33 k,)’ = Z/k,.D

If we approximate and take kd = k, = 0.45, then

A, + A, + A,/3.8 = K(Z/D)

or