You have three guidelines for selecting the right chain or rope length for your anchor. The first rule of thumb is that the anchor chain or rope should be no less than 15-feet in length, regardless of the boat size or the design. The second rule is that the anchor chain or rope should feature at least one foot of length for every foot of boat length. Finally, the third rule is for the anchor to have at least one foot of chain per six feet of anchor rope. So, you’ll need around 1000-feet of marine rope for every 17-feet of anchor chain.