The most direct method of transferring the patterns to sheet material is by the use of CNC cutting equipment. This is pictured below. Here a CNC Plasma machine is cutting the pattern directly from a computer file. This is accurate and fast but costly. CNC files are available on request.

A less expensive way is to use the paper patterns supplied by Metalsailboats.com. simply scribe around the perimeter of each pattern and center punch the bend lines used for the break forming process.

In the picture below a pattern is being cut in a vertical band saw. It is a good idea to reference the direction of each piece, marking left and right, top and bottom and number them to keep the patterns in a workable order.

Forming the patterns

Since these developments are not simple sections of a radius, a press break is used to form the pieces. The tooling used in the press break is fairly standard, consisting of a short length of bottom "V" die and a short rounded top punch.

In the sketch of a sample pattern below, notice that the bend lines are askew and cross in random directions. Additionally, the distances vary between the bend lines. This is typical of Bezier curved formed surfaces. Remember, it is not a constant radius where all the bend lines are parallel to each other and the same distances apart for any given bend line.

When all the patterns are cut and marked, the forming is next. A press break requires accurate setup, it is advisable to have all the patterns ready for the break operation.

In the press break, twenty or more hits are required to form the pre-defined shape of each pattern for a hull skin section. Accurate hits are important, and error in the bend angle even a quarter degree for each will multiply itself, and the piece will end up being 5 degrees over or under the desired mark.

To determine if this distortion occurred see the above drawing and note the diagonal dimensions given on the pattern. It references the finished corner-to-corner length of each formed hull section. If you make your twenty hits as required and you end up with this dimension, your press break bend angle is correct.

If this reference dimension is not reached, the bend angle should be adjusted accordingly, sacrificing a few pieces to get the proper bend angle. The picture below shows the press break operation.

FULL SIZE
WORKING EXAMPLE
OF A TRUE ROUND
BEZIER SURFACE

Figure #7A thru Figure #7D illustrates the construction method, of the bezier true round section, using full size patterns of the hull at the transom.

Figure #7A shows the sections being tack welded together, on a workbench. Remember that the sections in this mock-up have no longitudinal framework to guide the fit as they do when applying to framework. Therefore diagonal dimensions are used to verify the shape along the hull, similar to the method used in the bending process

From the computer model, diagonal dimensions can be obtained for any section or groups of sections at any location along the hull. Using this method to form the mock-up establishes the true shape of the design.

Figure #7bshows the hull surface being roughed in by an aluminum hard grinding wheel. It is used for initial fairing between adjoining sections. Later, finish sanding is used to refine the surface of the hull

Figure 7c shows the curve (edge thickness of the plating) along the girth. The transom plating would join the hull plating here. It can be easily seen from its shape that the curve is a free-formed curve - not the arc of a circle.

Figure #7d shows the curve along the length of the hull, which consist of six sections of preformed plating. The change occurring along the length is less dramatic then the curve along the girth, but still can be seen in this picture.

To Sum It Up ...

A non-developable Clofted surface is converted into an arbitrary number of smaller developable surfaces. These developable surfaces are pre-engineered to fit a specific location on the hull, using full size flat patterns. The patterns provide forming line and reference dimensions markers to verify the bend angle and accuracy of the finished formed skin section.

The hull plating is simplified by shaping in a cold forming press break, using a consistent and predictable method of fabrication.

The curved sections of this hull fit together easily, with minimal adjustment into the framework.

The pre-engineered design and fabrication method enables an average person to build a true round bottom hull using the same skills as required in hard chine construction.

The result is the unmistakable beauty of a round hull - the uninterrupted graceful line curving to meet the water.