Creating the Eccentricity Curve

The eccentricity curve defines the ratio between the major and minor axes of the ellipse generated by a waterline cross section of the end surface (see Figure 3:82 below). Thus an eccentricity of 1.0 will generate a circular cross section and hence a circular waterline ending.

Figure 3:82. Eccentricity Curve Definition.

If the radii curve has been estimated from the half siding curve (see Creating the Radii Curve from the Half Siding), then an eccentricity curve will have generated with a uniform value of 1.0.

Generate a new eccentricity curve

1. On the Curve Endings dialog, select the End Surface page.

2. Select the appropriate end and select Eccentricity Curve.

   The Normal option will cause the system to create a curve where the ellipse ratio at each waterline is the result of the radius being applied normal to the profile curve. If this option is not supplied, then the default eccentricity curve is created to provide circular endings.

3. Click on the Create button to generate the curve.

4. Fit a curve using the centripetal option, . This will give a tighter fit between the data points. (Especially if "normal" has been used to generate the curves) The eccentricity curve can be displayed by clicking on the display curve icon, .

5. If the eccentricity curve is acceptable click the accept icon, . Otherwise fair it using the fairing procedure.

The eccentricity curve for both the forward and afterbody is measured from "0".

If the eccentricity is undefined at a waterline height, the algorithm to produce a circular radius normal to the profile curve is used. Thus, by defining the eccentricity only at certain heights, it is possible to create a mixture of circular and elliptical endings (see the example in Waterlines with No Endings).