A pretty old set of rules produced by Fantasy Games Unlimited, the set can be played with either miniature galleys or a series of cutout counters for a variety of different vessels.  There is also a large map showing a couple of basic oared vessels for staging man-to-man combat during boarding actions.  The map and one of the counters can be seen in the photo above.

For what it covers, the rules offer a fair amount of information and appear to be usable for all oared naval actions from ancient to encounters during the Renaissance.  The rules were likely meant for historical gaming but appear to offer enough detail to allow their use in RPGs.

One thing to make note of is that a clear overlay is provided with the rules for determining such things as turn radius for ships so if purchasing the set used which I assume is the only way to get it these days, make sure the overlay is included.