Kobaya-bune (小早船), or simply, kobaya , is a term for a type of military-style traditional Japanese vessel that was fast and maneuverable. The size of the boats labeled kobaya, which translates literally to “small, fast,” seem to vary widely. I have seen boats called kobaya that had as few as 6 oars, and larger ones that had 24 or more oars, but my access to details on these warcraft is limited.
The largest warships were called atakebune. They were big, slow, lumbering craft with a castle-like structure atop. The mid-sized warships were called sekibune, and sometimes called hayabune, or fast boats, ostensibly because they were faster than atakebune. War boats smaller than this seem to have all been classed as kobaya.
During the Tokugawa period (A.K.A. Edo period), which began in 1603, daimyo were forbidden to have atakebune. During the time of relative peace, the smaller warships, most commonly sekibune, were turned into gozabune (御座船), highly ornate and brightly painted vessels used by daimyo and their clans for ceremonial and other official purposes.