This is simply a graph of displacements against maximum-deadweight moments. Figure 4.28
shows a typical curve with the ship’s draft superimposed onto the vertical axis. The deadweightmoment
has been calculated about the keel. Note that this ship’s Lightweight is 370 tonnes.
It is very important to realise that the total deadweight–moment at any displacement must not
under any circumstances exceed the maximum deadweight–moment at this displacement. In
other words the x,y intercept must NOT occur in the shaded area of Fig. 4.28. If it does, then
deficient stability will occur for this ship.
For example when the displacement is 1000 tonnes, then a deadweight–moment of 1200 tm
is acceptable. However, a deadweight-moment of 1480 tm would mean this ship has deficient
stability and is not acceptable. A deadweight–moment value of 1375 tm would be just allowable.