There are many anchor types and to understand how each works we first need to understand the Anatomy of an anchor
Here are the parts of a typical anchor.
The shank is the stem of the anchor in which direction is pulled to set (bury) the anchor. Weak shanks will bend when the boat pulls from another direction.
The crown connects the various parts of the modern anchor. Also know as the hinge in the case of the CQR
The stock turns the anchor into an attitude that enables the flukes to dig into the sea bed. Fortress, Danforth and Fisherman anchors are examples of anchors with a stock to help guide the points into the seabed.
Many Modern anchors have roll bars to help the Anchor dig in.
The tripping ring is used for the optional tripping line: by pulling the tripping line, the anchor will break out.
The flukes will be buried into the seabed. The very tip of a fluke is sometimes called the bill.
The fisherman is a traditional design and is often see on the bow of old Sailing Ships like HMS Victory. The design is a non-burying type, and grabs rocks with one arm penetrating the seabed and the other standing proud. It has a good reputation for use in rock, kelp, and grass, but is unlikely to be any more effective than a good modern design and its holding power to weight ratio is among the worst of all anchor types.
The primary weakness of the design is its ability to foul the cable over changing tides. Once fouled the anchor is likely to drag. It is difficult to bring aboard without scarring the topsides, and does not stow in a hawse pipe or over an anchor roller.
The Bruce anchor was designed by Peter Bruce in the 1970’s. The Bruce is known generically as a “claw” and sometimes “Scoop”.
The flukes wings angle up which makes them differ from the Plough anchor where the fluke wings angle down.
Claw types have difficulty penetrating weedy bottoms and grass. They offer a fairly low holding power to weight ratio and generally have to be over-sized to compete with other types. On the other hand they perform relatively well with low rode scopes and set fairly reliably.
Modern Claw types have proven much better in holding and setting than the original Bruce. Innovations like the roll bar and re designed flukes help the anchors set and hold. The flukes are U shaped, V shaped or Curved upwards back toward the pull. They often have pointed ballasted tips.
Examples of the Bruce/Claw type anchor;
Claw from Lewmar, Rocna, Manson Supreme, Spade, Mantus, Quickline Ultra
Danforth & Fortress
The fluke style anchor uses a stock at the crown to which two large flat surfaces are attached. The stock is hinged so the flukes can orient toward the bottom (and on some designs may be adjusted for an optimal angle depending on the bottom type.) The design is a burying variety, and once well set can develop an amazing amount of resistance. Its light weight and compact flat design make it easy to retrieve and relatively easy to store; some anchor rollers and hawse pipes can accommodate a fluke-style anchor. A few high-performance designs are available, such as the Fortress, which are lighter in weight for a given area and in tests have shown better than average results.
The fluke anchor has difficulty penetrating kelp and weed-covered bottoms, as well as rocky and particularly hard sand or clay bottoms. If there is much current or the vessel is moving while dropping the anchor it may “kite” or “skate” over the bottom due to the large fluke area acting as a sail or wing. Once set, the anchor tends to break out and reset when the direction of force changes dramatically, such as with the changing tide, and on some occasions it might not reset but instead drag.
Examples of the Fluke anchor type; Fortress Danforth Navy
A traditional design, the grapnel style is simple to design and build. The design is a non-burying variety, with one or more tines digging in and the remainder above the seabed. In coral it is often able to set quickly by hooking into the structure, but may be more difficult to retrieve. A grapnel is often quite light, and used aboard smaller boats where its weight makes it relatively easy to bring aboard.
Grapnels rarely have enough fluke area to develop much hold in sand, clay, or mud. It is not unknown for the anchor to foul on its own rode, or to foul the tines with refuse from the bottom, preventing it from digging in. It is quite possible for this anchor to find such a good hook that, without a trip line, it is impossible to retrieve.
Examples of the Grapnel type anchor; Folding Grapnel anchor
“Mushroom” anchors get their name from, as you might imagine, their rounded, mushroom shape. Mushroom anchors are used extensively for moorings, and can weigh several thousand pounds for this use.
The shape works best in soft bottoms, where it can create a suction that can be difficult to break. Decent for very small boats to use as a lunch hook, but not practical for larger boats.