A Typical Shell Pattern

BEZIER SHELL PATTERNS EXPLAINED:

• The number "21" indicates that this pattern is the 21st from the bow.
  
• The word "Sheer" at the top of the pattern indicates that this edge is the located at the Sheer Line, while "Chine Long", at the bottom, indicates the chine longitudinal.
  
• On this particular pattern there are approximately 20 horizontal lines which represent the three (3) degree bend lines. A press break will be used to form this pattern to the curve of the hull along it's girth.
  
• The "Cross Lines" associated with the numbers 21.937 inches and 21.477 inches are reference dimensions aiding the forming process by providing the corner to corner finished dimension after all the horizontal lines have be bent at three (3) degree angles.
  
• The curve line (marked Frame #7) running vertically and curved near the center of the pattern locates the intersection of shell plating with transverse Frame #7. All shell patterns with this type of line will be aligned to it's corresponding transverse frame. After these patterns are formed notice that it has become straight making it possible to line up with it's transverse frame.
  
• Boot Strip Lines (really marked on the other side of the pattern) indicate the painted boot stripe. The lower line of the boot strip is 1/2" above the design water line.
  
• Notice the small half circles along the vertical edges of the pattern. They indicate the location on the shell plating where it crosses a longitudinal frame. They also provide a place to tack weld the shell plating to the longitudinal frames.
  

HOW TO
TRANSFER SHELL PATTERNS TO MATERIAL:

Above are four full size pattern printed a sheet 60" x 22". Cut out these patterns for transfer to sheet aluminum.

A typical arrangement of the paper patterns on a sheet of aluminum 48" x 96". Cut the 48" x 96" sheet into equal sections to reduce the size of the material for easier handling.

Weight are used to hold the patterns in place while marking the perimeter. A magic marker works well here even though it leaves a line of varying thickness. Saw cutting off all traces of the magic marker line will bring you back to the outside of the pattern.

Here the pattern is being cut in a vertical band saw.

Place the paper pattern back on to of the aluminum and reattach with tape.

How to Test Bend

The real beauty of the Bezier Curve Method is that only one bend angle is used for all the shell patterns. Once the bend angle has been set and verified all the sections are formed without ever readjusting the ram (height setting) of the brake.

Since these developments are not simple sections of a radius, a press break is used to form them. The tooling required is a standard 90 degree "V" bottom die and a rounded top punch similar to the tooling shown below.

Setting up the press break for an accurate bend angle is very important. Anywhere from 5 to over 20 bends are required to form the pre-defined shape of each shell section. Any error in the initial setup of the single bend angle of even a quarter degree will cause the piece to be over or under rolled.

For example: If the bend angle was over by 1/4 degree and there are twenty hits the finished pattern would be over-under rolled by 5 degrees. - 1/4 degrees x 20 bends = 5 degrees

Scrap material about the same width as the average shell section is used to set a single initial bend angle. In this case three (3) degrees. Use a protractor or other angle measuring tool. In setting the bend angle always use a new space of the test piece to set a single bend angle. Do not make a new test bend over or near a failed test degree. Use a new section of the scrap material.

With the single bend angle set to 3 degrees take one of the test bend pieces below:

The test bend section is a radius of a circle or a constant radius curve. It bend line are all parellel and equal in distance. This is a perfect test piece to setup the press break. It has 23 bend lines at 3 degree angles. Therefore it is a 70 degree section of a full circle.

With the press break setup as above, bend ALL 23 lines in a single run. To check, measure across the chord and you should have a length of 11 1/2". If you are over are under this mark the depth of the press breaks needs to be adjusted. Adjust the press break up or down and run another sample. Repeat until 11 1/2" is reached.

A Bezier curved pattern can now be run through the press break. Verify each piece you bend with the cross reference given on each pattern for your own piece of mind and accuracy.

Forming the Bezier Sections

The above left picture show all the shell patterns ready to be formed. While the above right picture shows only patterns that align with transverse frames. Note the plywood formers. They are are an additional tool to verify the shape in the bending process. I will be bending these patterns first to make a visual check on the actual framing of the boat before bending the remainder.

Below is a single hull shell section overlayed by its paper pattern. It is ready to be formed.

Pictured below is a pattern being formed in the press break. Note the die used is a standard 1/2" wide 90 degree Vee Bottom. The top is a standard punch die with a rounded tip.

A Look at
The Formed Patterns

• Top Left shows the shell pattern after bending. The paper pattern is still attached but well worn due to the press break operation.
  
• In the Top Right picture the plywood former has been added to check the bending process.
  
• The Bottom Left and Right illustrate the use of the diagonial reference dimensions used to verify the bending process.
  

Initial Fairing - Before Plating

Kinks are in fact bends in the material. The number of kinks required and their distances apart varies with the shape and length of the surface. The closer the kinks are together the smoother the surface to the touch and eye. Kinks a distance apart from each other are felt by the touch and seen by the eye.

FOR MORE DETAILED INFORMATION OF THE FAIRING - ClICK HERE:

Sections of the formed shell surfaces where the kinks are close together will only require finishing with a stainless steel wire rotary powered brush.

Sections where the kinks are further apart require a little sanding of the high pointa using one of the sanding or blending wheel below before finishing with a stainless steel rotary power wire brush.

FOR MORE INFORMATION ON FABRICATION OF TRUE ROUND BEZIER SURFACES - CLICK HERE