This is what I saw on the TWRA web site
Tennessee law requires that all mechanically powered vessels (including documented vessels) and all sailboats which are principally used in Tennessee must be registered. Mechanical propulsion includes electric trolling motors but does not include boats powered only by oars or paddles. Boats which require registration must be properly registered before using them upon any public water of Tennessee. Currently registered boats from other states may use Tennessee waters for a period not to exceed 60 consecutive days. Exception: Sailboats brought into Tennessee by persons from states that do not require numbering of sailboats are exempt from registration provided that Tennessee is not the state of principal use and that the vessel will not be used on Tennessee waters over 60 consecutive days.