boat anchor chain weight
Anchor rode guide: boat size anchor rode length (ft.) weight (lbs.) chain (dia.-inch) nylon (dia.-inch) length (ft.) 20 - 25 2,500 3/16 7/16 90 26 - 30 5,000 1/4 7/16 135 31 - 35 10,000 5/16 1/2 190 36 - 40 15,000 3/8 9/16 225 41 - 45 20,000 7/16 5/8 240 46 - 50 30,000 1/2 11/16 315. Basically the anchor just needs t be able to dig in and the blades big enough to have enough area resistance to hold the weight of the boat against the current/wind. the chain.. that is what holds the anchor shaft part down. when this lifts, it then pulls the blades out simply you could in effect have the anchor , no chain then slide a huge. The load on your chain is a combination of the weight of your boat, her windage, the shear of your boat (how much she moves around at anchor), and the momentary wind, scope, current, and a few other factors which are constantly changing. it's a complex calculation, and unlikely to be accurate given the range of variables across all conditions. 
boat anchor chain weight Anchor chains are usually marked in 10m stages, so a practical approach is to round the calculations to the nearest 10m of chain. with 10m boat length added, this gives an easy to use table (below). it seems extraordinary that for all the articles on anchoring and discussions on scope there is so little consideration of how to allow for wind. The anchor rode (or "cable") that connects the anchor to the vessel is made up of chain, sometime with rope ("warp"). large ships will use only chain rode, whereas, to save weight, smaller boats will use a rope/chain combination..
