Page 76 - statbility for masters and mates

64 Ship Stability for Masters and Mates
The midships coef®cient (Cm)
The midships coef®cient to any draft is the ratio of the transverse area of the midships Section (Am) to a rectangle having the same breadth and depths.
Fig. 9.3
In Figure 9.3 the shaded portion represents the area of the midships section to the waterline WL, enclosed in a rectangle having the same breadth and depth.
or
Midships coefficient Cm Midships area Am Area of rectangle
Midships area Am B d
Midships area Am B d Cm
The prismatic coef®cient (Cp)
The prismatic coef®cient of a ship at any draft is the ratio of the volume of displacement at that draft to the volume of a prism having the same length as the ship and the same cross-sectional area as the ship's midships area. The prismatic coef®cient is used mostly by ship-model researchers.
In Figure 9.4 the shaded portion represents the volume of the ship's displacement at the draft concerned, enclosed in a prism having the same length as the ship and a cross-sectional area equal to the ship's midships area (Am).
Prismatic coefficient Cp Volume of ship Volume of prism
Volume of ship L Am