A mooring refers to any permanent structure to which a vessel may be secured. A "mooring system" refers to the various components - an anchor, a rode (typically a rope, chain, or cable), a buoy and a pennant. An anchor is used to fix a vessel to a point on the bottom of the seafloor without connecting it to land.

There are four basic types of anchors used in moorings: deadweight anchor, mushroom anchors, pyramid anchors and helix anchors. Below describes the types of anchors and their characteristics.

Deadweight Anchor

Holding Power:  An 8,000-lb. concrete mooring has approximately 4,000 lb. of holding power.

Advantages: Simple design; Good for most bottom types; Holds position even if dragged during storm.

Disadvantages: Heavy and bulky; Requires assistance for installation

Notes: 

• Better suited for rock bottoms.
• Deadweight moorings made from concrete can lose over one-half of their weight when submerged in water.
• Deadweight moorings made from granite can lose over one-third of their weight when submerged in water.
• Fault lines in stone anchors can crack when putting in staples.

Mushroom Anchor

Holding Power:  A 500-lb. mushroom anchor has approximately 1,200 lb. of holding power.

Advantages: High holding power-to-weight ratio.

Disadvantages: Limited success in rocky areas; Prone to spin-out and chain wrap.

Notes:

• Better suited for muddy bottom conditions.
• Weight of mushroom anchors generally would be 10 to 20 lbs per foot of boat in mud bottom.
• Proper installation is important to assure it's buried.

Pyramid Anchor

Holding Power:  A 650-lb. pyramid anchor has approximately 6,500 lb. of holding power.

Advantages:  High holding power-to-weight ratio; Simple design.

Disadvantages: Limited success in rocky areas; Higher Cost.

Notes:

• Better suited for muddy bottom conditions.
• Size and shape help penetrate the bottom more rapidly.
• Weight of pyramid anchors generally would be 10 to 20 lbs per foot of boat in mud bottom.

Helix Anchor

Holding Power: A 10-inch screw Helix anchor has approximately 10,000 lb. of holding power.

Advantages: High holding power-to-weight ratio; Small size; Longevity; More environmentally sensitive.

Disadvantages: Heavy and bulky; Requires specialized installer; Difficult in rock; More difficult to move.

Notes:

• Better suited for softer bottom conditions.
• Don't perform as well in rocky bottoms.
• Type of helix used might differ with condition of bottom.
• Requires diver to set and maintain.