How much anchor line should you use in 20 feet of water?

A general rule for anchoring is to use a scope of 7:1 in calm conditions, which means for 20 feet of water, you should use about 140 feet of anchor line. In adverse weather or rough conditions, you might want to increase the scope to 10:1, requiring 200 feet of line. Always consider factors like current, wind, and the type of anchor being used when determining the appropriate amount of anchor line.