20 ft of water how much anchor line?

A common rule of thumb for anchoring is to use a scope of 7:1 in calm conditions, meaning for every foot of water depth, you should have seven feet of anchor line. Therefore, for 20 feet of water, you would need approximately 140 feet of anchor line. In rougher conditions, you might increase the scope to 10:1, requiring 200 feet of line. Always consider the specific conditions and type of anchor being used.