From the rules:
"This game is designed to provide simple and easy to use rules for fighting small scale naval battles featuring around half a dozen ships per side. The rules are written with 1/600th scale ships in mind, but it would be possible to use other sized miniatures...Death on the Seas is historically set in the 5th Century BC, during the Persian Wars, but the rules feature statistics for ships from both earlier and later periods.
Several of the core mechanics for this game have their origins in the 5.56mm game and will therefore be familiar to anyone who has read those rules."
From the Wargames Journal website (blurb by the creator)
"...a fast play set of [free] rules that can be used with just about any scale of ancient ships (the target was 1/600th scale) and are based on a premise of one model equals one ship."