What is a good rule for determining the appropriate anchor line length?

Using a ratio of 7-10 times the depth of the water is a reliable guideline for determining the appropriate length of anchor line. This practice ensures that the anchor has sufficient scope, which is the distance from the tip of the anchor to the point where the line meets the water's surface. The more scope there is, the better the anchor can hold the vessel, especially in windy or rough conditions.

By using a longer anchor line, you allow the anchor to set properly in the seabed, which is crucial for holding power. It creates a sloped angle that helps prevent the anchor from pulling out of the ground due to the forces acting on the boat. The 7-10 times depth ratio takes into consideration both the water conditions and the overall stability needed for safely anchoring a vessel.