California Code, Revenue and Taxation Code - RTC § 6273

(a) A seaplane,

(b) A watercraft specifically designed to operate on a permanently fixed course, the movement of which is restricted to or guided on such permanently fixed course by means of a mechanical device on a fixed track or arm to which the watercraft is attached or by which the watercraft is controlled, or by means of a mechanical device attached to the watercraft itself,

(c) A watercraft of a type designed to be propelled solely by oars or paddles,

(d) A watercraft of eight feet or less in length of a type designed to be propelled by sail.

A motor or other component of a vessel, whether or not detachable, shall be deemed to be part of the vessel when sold therewith.