Most modern lightweight anchors are designed to work with the pull on the shank being no more than a few degrees above the horizontal. This includes Danforths, Fortresses, Ploughs, Deltas, and their variants. I believe that Robert Ogg, designer of the Danforth anchor, specified 8 degrees as ideal. The sine of 8 degrees = .139. To achieve the required angle with an unweighted line, the line must be (DEPTH/.139) long or about 7.2 times the depth of the water plus the height of the bow of the boat This is where the famous 7:1 scope requirement comes from. Any weight placed near the shank lowers this requirement. For an all chain rode a kellet near the anchor increases the anchor's holding power and permits a reduction in scope. For a nylon rode a length of chain placed next to the shank of a lightweight anchor satisfies two requirements. It lessens the slope of the line and protects the vulnerable nylon from abrasion. However, a kellet can be placed anywhere along the anchor rode. The best position for the kellet depends on what you want to do. To keep the anchor shank as flat as possible, the weight should be attached to the lower end of the rode near the anchor. For best rode elasticity, the weight should be positioned at one water depth from the upper end of the rode. Maximum elasticity is achieved when the rode hangs straight down from the bow to a weight resting on the bottom, then goes horizontally to the anchor. In light winds this is the shape that an all chain rode naturally takes. The much discussed chain catenary is a maritime myth unless the wind is so strong that the chain is lifted entirely off the bottom. Hanging the weight halfway along the rode, the way most books suggest, is a compromise between the two requirements. Personally I fudge on the use of a sliding kellet. For my last boat, a Willard Horizon, my primary anchor rode consisted of 150 ft. of 1/2" 8 strand nylon Brait with 30' of 3/8 chain at the anchor. Nylon was chosen for the bulk of the main rode both because I am a believer in rode elasticity and because we had no electric windlass on board. Also as a former competitive sailor, I abhorred extra weight. Better to carry a couple of cases of beer than an extra 100' of chain. For my permanent mooring in a fairly exposed area, I used a 300 lb. mushroom with 1/2" chain. Shackled to the midpoint of the chain was a 50 lb. elevator test weight, basically a 6" iron cube with an attached shackle. This kellet kept the boat in a relatively stable position despite current and tide shifts. In 15 years of cruising this boat from Maine to Florida we never dragged after properly setting the anchor. The boat, on anchor, survived one direct hit by a hurricane and one near miss. The only damage suffered during storm anchoring was being impacted by drifting boats that had torn loose. Larry Z