Aluminum Boat Design Process...
the technical Stuff

In aluminum boat design Bézier curves are used routinely in both traditional hand drafted or computer aided methods. In computer graphics however, Bézier curves are calculated mathematically to connect separate control points to form smooth free-formed curves or surfaces. The advantage of using Bézier curves in computer aided drafting is that they need only a few points to define a large variety of shapes.

Those who have engineering experience, know that Bézier Curve is the common name used for "free-formed curve." Mathematically they are derived from B-Spline, C-Spline, and Nurb curves. B-Splines and Nurb curves are similar in that the curve itself does not go through any of the interior control points. In C-Splines the curve goes through all control points. All of these curves and splines are useful in boat design.

There are four curves used to define the hull along its length as shown in Detail A. The top is the Sheer line: the next down is the upper longitudinal line; followed by the lower longitudinal line; the last line is the fairbody line. All of these lines are C-Curves. This means that the curve goes through its control points. These lines define true Bézier Curves

The upper and lower longitudinal lines in this aluminum boat design are placed at predetermined locations in the hulls longitudinal framing system. They are located at the point of tangency where a smooth transition takes place between the upper developable surface and the true round section of the hull. This is also true of the transition between the true round section and the lower developable surface. Between the upper and lower longitudinal curved lines are seven B-curves used to control the shape of hull between the developable surfaces.

Picking any one of the B-curves for reference, see (Detail A1,) notice they have three (3) control points each. The top and bottom points are locked to longitudinal curve on which they lie, while also controlling the shape of the longitudinal curve itself. The middle control point of the B-curve is placed to maintain a tangency between the upper and lower developable surfaces.

These seven Type 2, B-curves used in this aluminum boat design to support a C-lofted surface, between the upper and lower developable surfaces. With the C-lofted surface being non-developable, a series of developable sub-surfaces are superimposed or layered over it.

To create developable sub-surfaces, magnets are used, which are required to lie on their assigned C-lofted surface. By placing the magnet entities, the designer defines the size and location of the developable sub-surfaces.

With the magnet point entities in place snake curve entities, which also required to lie on their assigned surface, can be created using the magnets as support. Two adjacent snake curves provide support for the developable sub-surfaces.

A total of thirty-five snakes are used, dividing up the length of the surface at the turn of the chine into thirty-four developable sub surfaces.

Detail-B shows a developable surface, (in blue), overlayed over the host C-lofted surface.

In Detail-C below we can see all the entities. The type 2 B-spline curves which support the C-lofted surface, the magnets assigned to the C-lofted surface, the snake curve entities, and the developable sub-surface.

All the sub-surfaces are then developed to create a flat pattern, to be cut from sheet material. After which the metal patterns are formed in a press break back to a three dimensional hull plating section. They fit seamless to the hull framework. Resulting in a true round hull.

From Bezier Aluminum Boat Design back to Radius Chine