That is going to depend on a couple of things, the size of your boat, and what depth of water you will be anchoring in. You will also want to consider the distance from your mount to the water level. Some boats the bow mount will be mounted higher above the water line. Calculate the distance from your mounting point down to the water line and add a foot for sea floor penetration. This will be the depth of water you will aim to use this system. For an easier rule of thumb, take 2’ off each pole size, that will be close to the depth of water you can use that size anchor in. For example, 8’ Poles are generally good in 6’ of water.