Davis Rocker Stopper. Help dampen the rocking motion of boats as anchor. Tie 18 apart, making a string of them, with a 5-10 lb weight attached at the bottom of the string. One string for each side of the boat. Four units per side are what it takes on most boats to 36'. Use 3/8 line. Lightweight and molded of high impact, virtually indestructible styrene. Unaffected by salt water and cannot affect the sides of your boat. 14 diameter. Number of Rocker Stopper Units Needed on Each Side of the Boat (Sail or Power): Up to 26': 3. 27'-36': 4. 37'-42': 5. 43'-50': 8.