Page 176 - Practical Ship Design

142 Chapter 5

2 7 .A
.

Ship I - Small % of erection

Ship II - Large % of erection

Fig. 5.2. Ships with small and large percentages of erections. With the exception of the dotted parts,
Ships I and I1 are identical, but D and the proportion of the erection volume to total volume are
obviously widely different.

5.3 FIXING THE DIMENSIONS OF A PASSENGER SHIP

5.3.1 Main hull and superstructure
In the 1976 paper it was suggested that the next step should be the division of the
total volume into a main hull volume and a superstructure volume and that this
should be done by assuming that the superstructure volume was a certain percentage
of the total volume.
However, as Fig. 5.2 shows, a very small change in the design of a ship can
make a very major change in this percentage. To overcome this difficulty it is
suggested that the percentage should be derived from a suitable basis ship. If
suitable data is not available a reasonable first approximation might assume that
the superstructure will provide 25% of the total volume. A ship of this sort will
have a relatively high uppermost continuous deck and the minimum of erections.
With the volume of the main hull known, the dimensions can be derived in the way
outlined in 35.1.
With the main dimensions and the volume of the superstructure known a
preliminary profile can be drawn, but in the course of doing this it will usually be
desirable to modify the depth D to provide a double bottom, holds and tween decks
all of suitable heights. This modification should take the form of reducing the
depth and adding the volume thus subtracted from the main hull to the super-
structure to maintain the total volume. The ship will consequently change from
Type 1 towards Type 11.

5.3.2 Modern passenger ship design

The trend in recent passenger ship design of extending all the superstructure decks
from near the bow to the extreme stern, with little of the step back terracing which