Boat Anchoring and Assessing Bottom Conditions
Anchors work by developing enough resistance in the seabed to withstand the environmental forces such as wind and waves.
So it makes sense that before you choose the right anchor for your boat, you must first take into account the expected bottom conditions where you boat.
Fine-grained sand is relatively easy for anchors to penetrate and offers consistently high holding power and repeatable results. Most anchors will hold the greatest tension in hard sand. Best in the sand are lightweight Danforth-style anchors.
Mud has low sheer strength, and requires anchor designs with a broader shank-fluke angle and greater fluke area. This allows the anchor to penetrate deeply to where the mud has greater sheer strength, and also presents more surface area in the direction of pull. Mud is frequently only a thin layer over some other material, so anchors that can penetrate through the mud to the underlying material will hold better. Fortress anchors have superior holding power in mud, because they can be converted to a broad fluke angle.
Rock and coral:
Holding power is more dependent on where you happen to drop the hook, than on the type of anchor you have. Plow-shaped or grapnel-type anchors, with high structural strength to sustain the high point loads generally work the best.
Shale, clay and grassy bottoms:
These are the toughest bottoms for all anchor designs. The weight of the anchor, more than its design, may be the most important factor in penetration and holding power. CQR and Delta anchors are thought to be good due to their ability to penetrate the vegetation. However, these conditions have a high probability of false setting, due to the anchor catching on roots and protrusions, rather than something solid.
Despite claims to the contrary, no single anchor design is best in all conditions. Boaters voyaging to areas where there is a specific type of bottom must carry an anchor(s) suitable for that bottom.
For all but very small boats, it is recommended that all boats carry at least two anchors so that you’ll have another if one anchor is lost. Also, different anchor types work best for different conditions, and two anchors allow you to anchor bow and stern in tight anchorages.