an improved boat trailer guide - on comprising bracket means that adjustably attaches to a conventional boat trailer and holds a substantially vertical shaft means with telescopically extendable foamed plastic rollers thereon . such a device allows the roller to float upwards as the boat trailer is backed into the water , thus remaining visible and capable of assisting in the loading and unloading of a boat . optionally , the top of the floating , telescopically extendable , roller is equipped with a tail light lamp for assisting in loading and unloading after dark .