True Round
Metal Boat Building

 Bezier Chine Design:

Existing books on True Round steel and aluminum metal boat building methods are vague and obscure, often referring to metal boat building methods that require artistic skills such as Line Heating, English Wheeling, and well placed hammering methods with nondescript names such as :  'Cupping',  'Compounding', 'Cramping', and other undefinable terms. 

While 'Line Heating' and 'English Wheeling' are viable methods for professionals.  These skills are beyond the average metal boat builder.  Therefore, ultimately metal boat building books suggest that steel and aluminum true round hull forms are not worth the time and effort, unless you have the proceeding raw arcane and artistic like skills.

The steel and aluminum True Round boat Building method that I am about to introduce, 'Bezier Chine Design and Construction', was developed by  It is a high-tech computer design method that blends well with the proven time-honored metal fabrication layout method know as 'Approximate Development'

What is Approximate Development

The build used to illustrate 'Bezier Chine Design and Construction' is a small, curvy, classic tumblehome design. If this curvy aluminum fabricated boat can be built using Bezier Chine Design and Construction then any other 'Bezier' true round hull shape would certainly be a breeze.

It is a design and construction method that pre-engineered the entire boat structure. All components, including the shell plating of the hull are predefined and can be formed to fit seamlessly together.  There are no vague and obscure or artistic techniques involved in construction.

The development of 'Bezier Chine Design and Construction' is a result of my career in Architectural Metal Fabrication, CNC Programming, Sheetmetal pattern Development, and my studies at the 'Westlawn Institute of Marine Technology.

'Bezier Chine Design and Construction' takes the arcane and artistic skills out of plating a True Round metal hull. Those skills are replaced with time honored sheet- metal fabrication methods use every day in the Metal Fabrication Industry!

Although I have built several plywood and hard chined steel designs, I had no experience building a true round metal hull. I have no arcane or artistic like skills. What I do have is a complete understanding of the theory of 'Approximate' Sheetmetal development. The Bezier 12.5 was my first aluminum true round build.

Most notable 'Bezier Construction’ is simple, consistent, and predictable.

    Click the below links for full details.

Hull Components

Hull Construction

Images of the Result

Hull Configerations

If you have come to this point on the subject of Steel and Aluminum boat building you are aware that boat hull are nothing but complex sheet-metal fabrications.  You are also aware that boat hull surfaces fall into two catagorys with the following interchange words:

Elementary - (Developable) - (Hard Chine)

Warped - (Compound) - (True Round)

What you probably are not aware of is the Bezier designs can be a combination of both.  Lets look at the combinations.

Single Surface

Bezier single surface designs use a single warped surface to define the entire hull.  The True Round surface runs from the sheer-line to the fairbody line at bottom center of the hull.

You can look at a Bezier Single Surface design as be akin to any true round fiberglass sailboat hull design, including tradition wine glass hull forms.

The below three drawings show a Single Surface Bezier design.  From the Section and Profile 'Lines' drawing you can see that the hull is design with a single 'Warped' or 'True Round' surface.

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Double Surface

Bezier Double Surface hull designs combine both an Elementary and Warped surfaces into a hull design.  The design below is the prototype and 'Proof of Concept' build for 'Bezier Design and Construction'.  It is the double surface version of the preceeding Single surface hull.

Here the top panel is a True Round surface that begins at the sheer-line, continues around the turn of the bilge and end seamlessly and tangent to the theoretical chine line and can be seen in both the Section and Profiles drawings below.

A developable surface, then picks up seamlessly and tangent from that theoretical chine line to the centerline at the bottom of the hull.

The thought process in the double surface design was to reduce the time required to apply the shell plating to the framework.  That thought, however, can be a matter of opinion.

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Triple Surface

Bezier Designs can combine two Elementary surfaces and one Warped surface to define a hull. 

Here the top surface is an ‘Elementary’ surface that defines the freeboard of the hull. It begins at the sheer-line and ends seamlessly and tangent to a ’Warped’ surface that defines the center surface of the hull, which in turn ends tangent to a 'Elementary' surface that defines the bottom panel of the hull.

In the 'Section' drawing, below, I have labled the free-form curves at Frames Three, Seven, and Eleven  with an approximate radius to demenstrate why this surface is indeed True Round.  The drawing shows how the hull changes radius along the length of the hull, therefore True Round.

Note: The middle True Round surface could be a redesigned with a ‘Single Constant radius’ to becoming a ‘Radius Chine Design’, however with the design criteria for a 'Radius Chine' design a totally different hull form would emerge.  See the page on 'Radius Chine'.

'Radius Chine Design'

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By Shell Plate Expansion:

For 'Builders' who prefer a more traditional approach 'Bezier Chine Design and Construction' can develop Full Size flat shell plate expansion patterns defining the perimeter of the surface and the forming Strain Lines that guide the operator of an 'English Wheel' or other metal streaching machinery in the forming operation.

These flat patterns provided the operator with a visual reference of where the curvature is and how deep it is.


'Shell Plate Expansion'

Floating the Longitudinals:

'Floating the Longitudinals' is an intergral part of the 'Bezier Chine Construction' since some design incorporate developable srfaces.

'Floating the Longitudinals' is a fabrication technique used to plate the the Hard Chinned portions of a Bezier hull design.  This plating method cancels the 'Hungary Horse' look that is often seen in so many Single and Double hard chined finished hulls.

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'Floating the Longintudinals'

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Bezier 12.5

Bezier 28

Bezier 35

Bezier 34