12 Three ways to model a chine hull
There are three ways of producing surface discontinuities (or chines) in a hull:
1) Compacted control points
Only a single surface, useful for blending a chine into a round bilge. More complicated fairing, more difficult to adjust spline stiffness. Non-optimum control point distribution for different areas of surface.
2) Using Bonded Edges
Surfaces move together can be advantage or disadvantage
3) Trimmed surfaces
For a complete list of steps to produce a chined hull using any of the above three methods, see Tutorial 5.
12.1. Step-by-step: Chine hull using linear surfaces
Perhaps the simplest way to make a chine hull is to make the transverse flexibility of the surface linear (order 2). This will make the surface piecewise linear, with straight lines joining the control points. You can still maintain a smooth hull in the longitudinal direction by using a flexibility of 3 or more in the longitudinal direction.
12.1.1. Create a new design and add a default surface
Select New from the File menu. If you have an existing design open, you will have to close it first.
To add a surface select Surfaces | Add Surface | Default. This will add the default surface, which will be fine for this example.
In the Perspective window, you should have something like this (turn on the Net to show all the control points, and turn on the Half display so that you see just one side – use the commands in the Display menu):
12.1.2. Change the surface flexibility
Note that the ends of the default surface you have just added are curved. We will now change the surface's transverse flexibility so that it is linear.
Select Surfaces | Properties | Default:
you can then set the transverse flexibility to 2 (linear):
click OK and notice that the ends of the surface have now changed so that they are straight lines:
12.1.3. Fairing the Profile
The next stage is to fair the profile. To do this change to the Profile view:
We will add some shear to the hull by lifting the forward control point a little. Remember that there is only one control point here, so it can be selected just by clicking the mouse on it and dragging it to its final position:
Now move the forefoot up a bit. Remember, there are two points here so select them both by dragging a box over them:
First we will close the bow, by dragging all the forward control points onto the centreline: If you hold the shift key down whilst dragging them, they will only move in the vertical or horizontal direction. This helps to just move them into the centreline without moving them longitudinally:
Now close the transom a little. Remember that there are two points here so drag a box over the control points to select them both and move them into the centreline a little:
Review the design in the Perspective window, try turning on the rendering to get a better idea of the shape (Display | Render | Smooth Shading). Note, to get the best shading, ensure that the outside arrow is pointing outwards. Turn on the outside arrows in the Display menu, and click on the arrow's tip to flip its direction:
12.1.5. Fairing the section
In the Body Plan window you can fair the sections more accurately. Change to the Body plan view and don’t forget to turn off the Net so that you can only see the control points for the current column. Also turn off the rendering to speed up the program:
To better visualise the shape, we shall add some sections. This is done in the Data | Grid Spacing dialog:
Click the Add button and type 11 stations. Then click on the Space button and select "Evenly along the length of the model". When you click OK, the station positions will have been automatically
In the Body Plan Window, when you click on one of the control point column indicators in the inset window, the current control point column will change and the closest section to this column will be displayed. Click on the indicator for the middle control point column
If you wish to have a single chine hull, simply move the chine control point to the desired location.
Then do the same thing for the aft control point row. First click on the left hand control point column indicator to get the aft control point column, then move the middle control point to get the desired deadrise:
Also review the design in the Perspective window (you can turn off the Grid from the Display menu to see the shape more clearly):
12.1.6. Adding more chines
You may want to add more chines to the design. To do this go back to the Body Plan view and select the middle control point column by using the control point indicator in the inset window:
Then fair the control point positions for each of the columns to get the desired shape. You may also want to refine the design in the Profile view, especially to get the forefoot correct. Here is the final design in the Perspective view:
12.1.7. Controlling the longitudinal shape
The longitudinal shape can be manipulated in the Plan and Profile views. You can also add more control point rows so that you have more control over the shape.
