Screw or spiral anchors offer a permanent and efficient mooring system and are cost-competitive to anchors of equivalent holding capacity.
Efficiency of a Screw/Spiral Anchor
Screw anchors are very efficient, suffer no loss of efficiency through buoyancy, and, weighing approx 100 kgs each, are able to withstand tension loads up to several hundred times their own weight. In comparison, a concrete block used as a mooring loses approx 50% of it’s holding power due to buoyancy e.g. applying Safety Factors, to achieve the same holding capacity as a MoorTech/N-Viro screw anchor, a 40 tonne block of concrete would be required.
MoorTech/N-Viro screw anchors are unique in that they are made up of two components – shaft and anchor plate:
- Anchor shafts are available in 89 and 114 diameter steel tube, with larger diameters (up to 165 mm) for special applications.
- Anchor plates are available in gauges from 12 mm up to 20 mm thickness and in diameter from 400 mm up to 1200 mm; they are bolted to the anchor shaft prior to installation.
The ability to interchange anchor plates to suit differing seabed conditions makes the anchors unique and ensures optimum holding capacity is achieved by each anchor during installation.
MoorTech/N-Viro anchors also work on uneven terrain where others fail; both concrete blocks and drag-type anchors can be completely ineffective where uneven/steep-sided seabed terrain occurs.
Passive Earth Plates are used in some instances for swing moorings to provide additional resistance for the anchor head at the seabed.
All MoorTech/N-Viro anchor components are manufactured in accordance with all applicable AS/NZ Standards , including AS2159 Piling Code and designed to provide a life expectancy in excess of 25 years. With cathodic protection, design life criteria in excess of 50 years has been met.