Over the years with RPGs in general, there has been a trend to put out extra supplements strictly for handling the sea. Biremes and Triremes was one of the first; this is one of the latest. Every time one of these books comes out, it is filled with interesting information, but there tend to be many extra rules that most storyguides would be wise to ignore. In Ars Magica, money is of secondary (at best!) importance; this book, as it deals with merchants and ship construction, tends to emphsize money. That is a count against it. There are extra ways to organize long-term expeditions by sea. This gets very complicated. That is a second count against it. Conversely, there is some very interesting material on the types of vessels used during the Middle Ages and some fun bits of nautical lore. If you intend to spend a LOT of time in your campaign on the waves, pick up this book. If you do not, don't bother. It is amusing, but not the most useful of supplements.