Selection Guide Anchor size recommendations are for boats of average windage and proportions, 30 knots of wind, average bottom conditions, and moderate protection from open seas. For storm conditions, we recommend using an anchor one or two sizes larger. Fortress Model Boat Length (ft) (m) Weight lb (kg) Replaces Steel Fluke Anchors (lb) Holding Power 32° Hard Sand Holding 45° Soft Mud Holding 32° Soft Mud Holding Support Hardware Proof Coil Chain Nylon Rope Shackle Size Use three-strand nylon rope and a minimum of 6 ft (2 m) of chain for every 25 ft (8 m) of water depth. Be sure to use enough chain and rope for a minimum 5:1 scope.