The Roman ships in question had one sail and lots of men rowing. Torching an old sail is easier than torching wood.
Model Length: 24-1/2" (623mm) Scale: 1/30
provided by Hobby World of Montreal
A typical Roman war ship of the first Century B.C. this Bireme was driven by two rows of oars. Out riggers stabilized the ship and the whales protected the hull from the protruding bows of enemy ships. While fast under oar, this type of vessel capsized easily under too much sail. This ship was built with plank on bulkhead construction.
"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.