[Skarg]

I too recommend Ramspeed - and especially the Interplay article with designer's notes and extra rules that did not fit in the game. I have used Ramspeed for naval combat in my TFT campaign (though not as a two-scale crossover to TFT combat) and liked it a lot. It has not only scorpions but catapults, onagers, ramming hulls and ramming oars. It is all about rowed galleys rather than sails, and most damage is done by ramming and boarding.

I've also used Wooden Ship & Iron Men (sometimes combined with Ramspeed), which covers sailing maneuvers.

The first issue of Hexagram also has an article about ships in TFT.

Supposedly an old issue of The Space Gamer does too, which I'd love to see.