# Straight Edges for Developed Surfaces - Method for Designing

Discussion in 'Boat Design' started by DCockey, Nov 19, 2010.

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### DCockeySenior Member

A curve which is the shortest path between two points on a developed surface will be a straight line when the surface and curve are unrolled. The reverse is also true. A straight line on a flat panel will be the shortest path between the ends of the line if the panel is rolled into a developable surface.

To design a panel which is a developed surface so that it will have a straight edge when unrolled, ensure that the the shape of the edge is the shortest path between the end points of the edge. This can be done in Rhino using the ShortPath command to determine the curve which is the shortest path. I don't know about other software.

Why care about a straight edge on a panel? It simplifies cutting the panel and may enable more efficient use of material, assuming it doesn't adversely affect the 3d shape.

Does anyone know of a reference to this relationship between straight lines on flat panels and the shortest path between the corresponding end points on a developed surface? I derived it myself but am sure it's already "known" in geometry. However I haven't found it in the references I've searched nor by an internet search.

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### GilbertSenior Member

Search for Kilgore's method.

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### DCockeySenior Member

Kilgore's method is for how to find the ruling lines to create a developable surface. That's not what I'm talking about.

What I'm talking about is how to find the shape of the curve which cuts across the ruling lines that will be a straight line when the surface is unrolled. Fundamentally a different problem.

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### Perm StressSenior Member

Order Bolger "light scooner" plans. it is designed exactly same way -better part of side panels have straight edges. Basic principle- side frames have the same angle to Base line, and (for the straight part of side panels) chine and deck lines are straight and perpendicular to the frames in bodyplan view.

As to methods of design -my guess it will by "cut and try" or "cheat the software" case. You will have to develop a panel, check where the edges are not straight and make adjustments to hull shape to correct this.

Also check any info you could find on "sharpie" design and build methods.

In general, straight-edge side panels are used, when boats are built from pre-patterned sides and frames/bulkheads to whatever final shape is coming out, instead of building "to the lines drawing".

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