How to draw a gentle curve

A large boat roof is a challenge. I wanted a gently curved profile but struggled to draw this on a sheet of plastic.

It's too large for compases and I needed something larger than a dustbin lid (remember them, before wheelie bins) and nothing suitable was to hand.

Mt dad suggested I try the roof from a G gauge tram loco kit. He was right, it's pretty much spot on. Close enough for my freelance model anyway.

This made me think - if I took a piece of brass trip and feed it through my rolling bars, templates for any curviture would be easy to make.

I'll remember that next time.