It’s such a pity. Douglas Hunter has all of the ingredients to cook up an enveloping and heretofore untold story. The premise is delicious: The story of how Henry Hudson’s New York Harbor-discovering adventure was really a maniacal farce involving the essential hijacking of an East India Company ship and its incompatible (half English, half Dutch, fully unable to communicate with each other) crew. For months the officers back in Amsterdam assume he’s doing what he should be: probing the northeast arctic maritime frontier for a miraculous route to China (p.s. no such thing). Instead Hudson is bopping up and down the eastern seaboard of the (now) United States in flagrant insubordination, eventually tripping upon the harbor at New York and the river that bears his name.

This sounds wickedly intriguing. The Jacobean era–Hudson’s voyage was in 1609–is a fascinating one and also one with which I have some facility and a good dose of interest. Mr. Hunter must have been furiously excited to write this book; it has all of the heart-pounding tidbits a historian could wish for. Intrigue. Discovery. A story that hasn’t really been told before.

And yet something goes wrong with the delivery. Mr. Hunter’s second passion, along with history, is sailing and maritime lore. This is an excellent pastime to inform the details of the story. But so often, instead playing a supporting role, it becomes the foreground focus that we lose track of what it is exactly that Henry Hudson is doing. Points of the compass, shoals, fathoms and soundings come up more than the lay reader would expect or desire.

The specifics interrupt the flow enough that it is difficult to become attached to the story. Every so often it drops enticingly into narrative–a tale of a ill-begotten raid on a native village or the homey mention of the crew’s cat running to and fro across the ship–but then it’s as if Mr. Hunter gets distracted and suddenly once again we’re hearing about the politics of previous voyages or the minutiae of the ship’s armaments.

It’s not that asides are detrimental. Herodotus showed us that they can be beautiful. But “Half Moon” is a book composed of asides.

This is not entirely Mr. Hunter’s fault. The scarcity of surviving primary material is almost shocking. Nothing is known of Henry Hudson’s personal life. He appeared on the historical map in 1607, as if sprung fully grown from Zeus’ head. We don’t really have much in the way of logs for the voyage, other than some fragments written by crew member Robert Juet. Much of the documentation of any relevant previous voyages is lost, too.

Without Mr. Hunter’s sailing asides, a relatively unreasonable amount of speculations (an uncomfortable number of sentences end in question marks), and healthy seasonings of surrounding European politics and other (mostly failed) colonization attempts, there wouldn’t be a book here. And that, in a nutshell, is the problem.

Distilled to half its length, the story would hold the interest of the average history aficionado. As it exists today, it requires a keen interest in the times and the equipment of the sea.