To set out on a sea expedition, a good ship is naturally indispensable; however, during Japan's Warring States period, there simply weren't any good ships—Japan at this time didn't even have a proper shipyard, and shipbuilding was all handled by relatively large water thief (pirate) groups. Ordinary people had no way to purchase a ship from them.
Fortunately, Da was a retired water thief—formerly a somewhat famous and experienced one at that—so he still had a few old connections. After getting Harano's approval, he personally took action and purchased a second-hand customs ship for seven hundred and fifty kan plus a thirty-kan commission fee.
As for the so-called customs ship, it refers to a type of medium or small vessel that was widely active in Japan's coastal waters from the Muromachi Era to the Edo Era. Because water thieves often used it to set up checkpoints, crack down on smuggling, and patrol territorial seas, it was called the "customs ship."