Permanent Anchor Mooring
There are three basic types of permanent anchor moorings; dead weight, mushroom, and helix . These
moorings are used instead of temporary anchors because they have considerably more holding power,
cause less damage to the marine environment, and are convenient. They are also commonly used to hold
dock floats in place.
Example: US Virgin Islands, a vast number of public moorings are set out in popular areas where boats can moor.
This is to avoid the massive damage that would be caused by many vessels anchoring in close proximity.
Dead weight moorings are the simplest kind of mooring. They are generally made as a large concrete
block with a rode attached which resists movement with sheer weight; and, to a small degree, by settling
into the substrate. The advantages are that such moorings are simple and cheap. A dead weight mooring
that drags in a storm still holds well in its new position. Such moorings are better suited to rocky bottoms
where other mooring systems do not hold well. The disadvantages are that they are heavy, bulky, and
Mushroom moorings are the most conventional moorings for mud and silt substrate. They are shaped
like an upside down mushroom which can bury itself in these materials quite readily. The advantage is that
it has up to ten times the holding power to weight ratio as compared to a dead weight mooring. The
disadvantage is that they're more expensive than dead weight moorings, don't hold well on rocky or pebbly
substrates, and they take time to settle in before reaching full holding capacity.
Pyramid mooring anchors are designed to rapidly penetrate the sea floor due to their sharp pointed
sides and compact size. They have be tested and are said to have a range of 3 to 10 times it's dry weight
in holding power. The holding power increases as the anchor penetrates the sea floor. This is due to their
unique pyramid shape and large surface area which increases the suction effect the deeper it sets.
Helix moorings are a modern method. The screw in mooring is a shaft with wide blades spiraling around it
so that it can be screwed into the substrate. The advantages are an extreme high holding power to weight
ratio. An additional consideration is size. Helix moorings create a small footprint in the sea bed floor. In
addition, once in place, they do not drag or move as dead weight or mushroom moorings tend to do. The
advantages are minimized mass, high holding power to weight ratio, and less wear to the gear.
Helix Mooring Benefits: Holding power pull test
Vineyard Haven, Pull Test Results
Mooring Type Bottom Condition Breakout Force
350-lb. Mushroom 5 ft. deep in mud 2,000 lb.
500-lb. Mushroom in sand bottom 1,700 lb.
3,000-lb. Concrete USCG block set in mud 2,100 lb.
6,000 lb. cement block on sand bottom 3,200 lb.
8/10 Helix soft clay mud 20,800+ lb.
We use 8-10-12 helixes -- which provide even greater holding strength