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About This Tool
This tool calculates the catenary curve required for a tarp or tent seam to ensure it remains taut when pitched. A straight cut will sag under tension, but a catenary cut removes this excess material and "pre-tensions" the seam.
The tool also compares the true catenary to a simpler parabolic approximation. For shallow cuts used in tarps and tents, the difference is essentially imperceivable, but for deeper cuts or modelling hanging ropes, the catenary is more accurate.
Input Parameters:
You can use any units e.g. meters, inches.
- Seam Length (Span): The final, straight-line length of the seam / ridgeline.
- Cut Depth (Sag): The maximum depth of the curve you want to cut. This determines how much "belly" is removed.
- Steps: The number of coordinate points to calculate (higher = smoother curve for plotting).
Example: A very general rule of thumb is 1/4 inch for every foot of length (~2 cm per metre). Not much is required.
Download 1:1 Scale SVG Template
Generate a 1:1 scale SVG file of the catenary curve. Ensure the units below match the units you used for the inputs above. This file is ideal for printing or for use with a vinyl/laser cutter to create a physical template.
Coordinate Data
Use these coordinates to plot the curve on your fabric. The centre of the ridgeline corresponds to X=0, with the Y-value representing the sag.
