I think it would work, from wiki,
A test of the Archimedes heat ray was carried out in 1973 by the Greek scientist Ioannis Sakkas. The experiment took place at the Skaramagas naval base outside Athens. On this occasion 70 mirrors were used, each with a copper coating and a size of around five by three feet (1.5 by 1 m). The mirrors were pointed at a plywood mock-up of a Roman warship at a distance of around 160 feet (50 m). When the mirrors were focused accurately, the ship burst into flames within a few seconds. The plywood ship had a coating of tar paint, which may have aided combustion.[31
wonderful. i think it would be hard to focus when the "roman ship" is far away, and there may be dispersion of the light by particles in air.
As said they did this on Mythbusters, and with the Greek technology it was impossible, with parabolic silvered/modern mirrors and the optimal set up, something the Greeks didn't have, then it was difficult, possible but impractical in a war setting.
Just to show a link to compliment the OP.
I don't think it was feasible.
Unless a ship was stationary all the time, I can't see how this would work. And Greek fire would be far more effective anyway, a sort of ancient Napalm. Or jelly like "naptha"/oil based product.
Sounds like wartime propaganda to me.
Myth busters is good but not exhaustive, just one fluke success would be enough to terrify
an unknowing people.
True combined with flinging naptha at them, they may have got the wrong end of the stick and believed the fires came from some ray of light being focussed on the vessel. All speculation but I doubt you could do it with copper mirrors under most circumstances, unless as you say it was a fluke.
Mind you the Greeks beat off the entire Persian task force at Platea with nothing but their reflective shields, at least according to the arch myth monger Herodotus and his histories, they used their bright shields to blind the Persians, so you can see where the myths come from.
Although he was right about one thing ~196 Greeks (forget exact figures) did in fact die in the initial battles they uncovered a grave that attests to this. But it was a bit more complicated than Herodotus made out.
I think it would be possible. Once I had an astronomy class where we set stuff on fire using a telescope with a 10 inch primary mirror.
Was the person running at 0-20 knots intermittently with the object that was set on fire?
no, but it only took less than a second to light a piece of paper on fire.
That's paper not wood, and even with paper if it was moving it would be harder to set it on fire. I think it's a myth personally.
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