Copied from the Dept. of Motor Vehicles website:
 
What Boats to Register in Rhode Island
In Rhode Island, the DEM requires boat registration on all motorized boats, sail boats, and personal watercraft.

What Not to Register

  • Non-motorized canoes.
  • Non-motorized kayaks.
  • A rowboat less than 12 ft long.

Exemptions

  • Lifeboats.
  • Boats used only for racing.
  • Any boat registered in another state and not kept in Rhode Island for more than 90 days.

Courtesy of Jim Cole