Propellant actuated embedment anchors are available having pullout capacities up to 250K lb in sandy soils and 150K lb in normally consolidated cohesive soils. This paper describes the development of a larger such anchor that provides more than twice the previously available capacity.
Direct embedment anchors are capable of sustaining loads applied in any direction and at any angle, including direct uplift. Thus, a single such anchor can be used with a short, lightweight line for a surface or subsurface mooring, so long as compliant features are provided to accommodate transient motions in order to preclude excessive peaks and snap loading. For example, a high-capacity direct embedment anchor tautly connected to a semi-spar type submerging buoy would perform well as a supply vessel bow mooring.
Recently a nominal 300K lb propellant actuated embedment anchor was built. It is designed to provide capacities of 380K lb to 600K lb in common sediments and corals. The complete anchor weighs 8 tons and is about 7-1/4 ft in diameter and 14 ft long (container compatible). After-installation of the anchor projectile and cable, the launcher section, weighing 4-1/2 tons, is recovered.
Anchor deployment and installation normally require 30 minutes to one hour, while preparation of the launcher and fitting a projectile for deployment require a similar length of time. Testing completed to date indicates that performance is as expected.
Their capacity to resist uplift, rapid installation, lightweight line compatibility, and capability to function in coral as well as sediments make these anchors attractive for supply vessel moorings, tension legs, and construction moorings. Also, they have potential for replacing pin piles for catenary anchor leg moorings and in the bottom-resting pads of single anchor leg moorings.
Propellant actuated embedment anchors are available in various sizes having capacities ranging from a few thousand pounds to over two hundred thousand pounds, as shown in Table 1 (Taylor, et al., 1975, with updated values). Also shown are data for a larger size, discussed in the next section. This paper addresses briefly the attributes of such anchors as they have been developed and used over the last decade, and describes the development of a larger anchor capable of sustaining the higher loads occurring in permanent or semipermanent offshore moorings.
The Civil Engineering Laboratory (CEL) propellant actuated embedment anchor functions as shown in Figure 1: it is lowered to the seafloor, the gun fires upon bottom contact, the fluke is embedded, and the anchor is set by the line pull. Although the gun may be left on the bottom, its value usually justifies the expense of rigging the extra line needed for recovery.
In multiple anchor moorings, when service loads are in a single, known direction, it is desirable to set the anchor with a pull from the same direction as the service load. With scopes greater than two, the keying distance may be as little as one-half of a fluke length.