Page 106 - Practical Ship Design

74 Chapter 3

Table 3.1
Optimisation of main dimensions
~
Capital cost Operational cost
Hull Machinery
Increase L Most expensive way to Reduces power and cost Reduces fuel consumption
increase displacement: and cost
increases cost
Increase B Increases cost (but less Increases power and cost Increases
proportionately than L).
Facilitates increase in D
by improving stability

Increase D and T Cheapest dimensions to Reduces power and cost Reduces
increase: reduces cost

Increase block Cheapest way to increase Increases power. Above a Increases
coefficient displacement and certain relationship of F,
deadweight to C, can cause rapid
increase in power

3.3.7 Draflhreadth relationship T = f(B)

This is again a secondary relationship, resulting in this case from either of the
following combinations of relationships:
T =f(D> or T=f(D)
and D =AB) and D =f(L) and B =f(L)

3.3.8 Optimisation of main dimensions
Table 3.1 summarises the principal effects on building and operational costs
respectively of alterations in the main dimensions.

3.4 BLOCK COEFFICIENT
3.4.1 General

The last factor required to complete the equation linking dimensions and displace-
ment is the block coefficient. A first principles approach to the determination of the
optimum block coefficient for a ship would involve a trade-off calculation in
which the increment in building cost resulting from the increased dimensions
required for a fine block coefficient is compared with the saving in operational cost