Many readers are here because up until now construction of a true round aluminum hull was only for professional builders. They have the special equipment, capitol investment, and secret abilities. Until now true round aluminum boat building was not for the faint of heart.
I am sure that all of you have read books illustrating methods to form a true round metal hull. Every thing written in these books just seem all so vague.
Lets look at some of the methods used by the professional, and leave them to their methods !!!
- Dogs and clamps to force the shell plating to the framework.
- Explosive, stretch, and hydraulic forming.
- Line heating with a torch.
- Rolling equipment.
- Special and expensive forming die.
Bezier Curve Design uses none of the above methods.
TYPES OF METAL HULL SURFACES
There are two basic types of surfaces used in hull design for boats of Steel and Aluminum. They are "developable" and "non-developable surfaces.
A developable surface is any surface that can be formed from a flat sheet of material without deforming. Developable shapes are sections of cylinders, cones, or any other shape formed by pattern development methods know as triangulation, radial line development and parallel line development. In boat building they will lie naturally on framework. They are easily placed in position, since they are designed to only roll in one direction at a time.
A non-developable surface is one that is rolled in two directions at the same time. Rolling a piece of sheet material in two directions deforms the material requiring skill and equipment to produce the desired faired result. An example of a non-developable surface is a potato chip. Another example is a round bottom sailboat hull.
After reviewing various design and fabrication methods for steel and aluminum sailing hulls, something was very apparent. There was little information on construction methods for the individual builders wanting a true round bottom sailboat in steel or aluminum. Until now, the backyard builder with average skills and equipment has been limited to hard chine designs and depending on their skill level the constant radius chine design.
Professional builders are able to construct true round bottom hulls in steel or aluminum. They staff professional workers with years of metalworking, boat building, and surface finishing skills. Their shops contain the equipment, both heavy and light, needed to achieve this kind of construction. It is not, however realistic for the average hands on person to build a steel or aluminum round bottom hull equal in beauty and fairness to those being built by highly skilled professionals.
The Question:
Do you really have the skill and equipment to take on a round bottom design?
The Answer:
Yes
At last, there is another method for the "backyard builder" to achieve the beauty of a true round bottom hull using average skills. The following innovative construction method, Bézier Curved Chine, offers amateur builders the option of constructing a true round bottom design that's as easy to build as a hard chine constructed boat.
What are the differences between Bézier Curve Design and Constant Radius chine
BEZIER CURVE FRAMING METHODS
Bezier Curve Designed boats are longitudinal framed. This means that the transverse frames will support the longitudinal frames, which then support the hull skin. The longitudinal frame method of construction is used because the developable and non-developable surfaces or any combination thereof, meets at the longitudinal framing and provides a fair curve to weld to.
BéZIER CURVED CONSTRUCTION EXAMPLE
The hull illustrated (Fig. #1) is drawn with a Bézier curved surface between two developable surfaces, one above and one below the turn of the chine. Note that the hull surface at the turn of the chine is visible both at rest and underway.
Because the curved surface of the hull is a free-formed surface, there is more freedom in the design process. Bézier curved designs have no need to use the same radius along the length of the hull. It is a free formed curve that changes at every location on the surface to enhance the hull lines, similar to a fiberglass design.
An example for the need of the Bézier curve design method is best seen at the transom. At this location, a much smaller free formed curve is required for a more pleasing hull proportion. Unlike the constant radius design, Bézier curved designed hulls do not require the same radius at the transom as at amidships.
What about skill and tooling needed for construction of a Bézier curved chine? No more than building a hard chine hull. Labor hours increase with this method, but not the skill required. Again, more hours, but not more skill to achieve a hull that is a true round bottom design.
Read on to see how this is possible!
The design example is a combination of developable and undevelopable surfaces use to complete this trued round bottom design.
There are four major surfaces:
- The upper developable surface;
- The non-developable surface at the turn of the chine;
- The lower developable surface; and
- The keel developable surface.
The upper, lower, and keel surfaces are developable and fabricated from flat sheet metal. They will not deform in the plating process. Hull plating for these three developable surfaces are the same as that of hard chine construction. The average skilled person will have no problem plating these areas of the hull surface.
The section of focus is the non-developable free formed area between the upper and lower developable surfaces. This is the section which cannot be formed from flat material and therefore, the most challenging for the average person.
Figure #1 shows the many-stationed sectioned view of the hull, while Figure #1A, a three dimensional view is used to further clarify the hull shape.
The longitudinal lines shown in the body plan and the tree dimensional view indicate the point of change from the developable surface to the non-developable surface and vice versa. There is no interruption of smoothness here because the curves of the joining surfaces are tangent.
To illustrate that the curve is free formed, look at the body plan in Figure #1. The right side of the body plan shows the first half of the hull from the Bow to midpoint. The left side picks up from the midpoint to the transom.
Note the tightness of the curves at the last stations ending with the transom in the non-developable section of the hull. Compare this to the ever increasing fullness of the stations in this section of the hull, as your eye moves forward from the transom along the hull. You can see that the free formed shape of the curve changes. Additionally, note that free formed curve between the developable surfaces is not a simple radius of a circle, as would be required with a constant radius hull design. Bézier curve design is free-formed. A true round bottom boat.
PLATING THE HULL
If you would like to learn more about fabrication of the Shell Plating before its installation on the framework go to: HOW TO FABRICATE THE SHELL PLATING
The picture above shows the plating clamped to the sheer longitudinal and has been tack welded in place. It was located by using the references give on the patterns.
With the sheer tacked in place work the plating from bottom to top or sheer line to chine line. The longitudinal's are aligned with the notches in the shell plate. Clamps are placed on the longitudinal, while another clamp at the top of the picture holds a transverse frame alignment. When happy with the alignment tack the longitudinal.
As you can see the notches are aligning nicely. Move the clamps - Check things over and tack weld the this longitudinal to the shell plating.
Still looking good here. Move clamps and tack weld.
Finally tack weld along the chine longitudinal as shown in the above picture.
The real holding power of plating to framework is on the inside of the hull. Place welds, about 1" long, at the end of the plating where the next plate will be positioned. Where two plates have come together tie the end welds together. This will produce a 2" weld wherever plates join.
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.
About the 12.5 Design
