This unique heat shrink vent uses windpower to circulate air and help keep the covered boat dry.DR. SHRINKWind Powered Weather-Tight Vent allows airflow underneath the shrink wrap cover by using anemometer cups to spin blades to actively move air even with the slightest breeze.Key Features Can circulate air 24 hoursa day The cups can be rotated to either deliver air or remove it Removable top for easy installation Coverage: 150 Cu.ft/hr with a 10mph wind speed Self Adhesive Size: 4" x 5"