"The Roman ships in question had one sail and lots of men rowing. Torching an old sail is easier than torching wood."
It ain't necessarily so. A plane, porous surface like a sail allows much of the "heat ray" to pass through and also to dissipate heat away from the dark side via rapid air transport. If you can't get smouldering temperatures on a wood plank, you are unlikely to succeed on a sail.
A similar issue of observation comes up for Noah's flood adherents. Plants do not survive 40 days under water. A simple experiment in a bathtub shows the story has to be false.
No. You need to have some sailing experience to truly understand this one, but cloth out on the open sea becomes dry...drier than kindling...and frays easily.
Roman sails were prime targets for a sun ray. Better materials were only used later in Time.
says the fellow who limits Gods miracles, and God himself