Anchoring

Anchoring is integral to many UCT operations both on land and offshore. Often, there is no one anchor choice that is the best for any application. Many anchors and anchor types will work acceptably if used correctly and with a little creativity. This section discusses the various anchor types, their limitations, and their strengths to allow the UCTs to solve most of the anchoring problems typical of nearshore operations.

Anchors are classified as:

• Drag embedment

• Deadweight

• Direct embedment

Drag embedment anchors rely on dragging to embed the anchor to achieve holding capacity. Deadweight anchors rely on weight to counteract uplift loading and to develop capacity through friction or adhesion with the seabed. Direct embedment anchors are anchors embedded deeply into the seafloor by various means and they rely on the strength of the overlying soil to develop capacity.

2.8.1 Drag Embedment Anchors

2.8.1.1 Anchor Selection. Common types of drag embedment anchors are shown in Figure 2-40. They include:

• Hooking anchors like the Northill and grapnel

• Lightweight (Danforth, LWT, Fortress)

• Navmoor 100 pound

• Stockless anchors

The seafloor conditions where these anchors work best are listed in Table 2-18. Approximate holding capacity to weight ratios (efficiency) are listed in Table 2-19.

Sharp-fluked anchors like the CQR, Lightweights, Northill, and Navmoor are suitable for hard sand and clay seafloors. Broader fluked anchors like the Bruce, Stato, and Stockless anchors have difficulty biting into and penetrating harder soils; thus, they are better suited to less dense sands and clays.

Bruce, CQR, Stato, and Navmoor anchors are stable and do not tend to roll out of the seafloor when they are dragged. Deep burying anchors with pointed flukes and small crowns (lightweight types), and Stockless anchors can roll out of the seafloor when they are overloaded and may not re-engage with further pull.

Lightweight anchors are built from steel and aluminum. The capacities of similar size steel and aluminum anchors are roughly equal, even though the aluminum anchors

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cause the shanks have a tendency to bend when loading direction changes.

The small Navmoor and Stato anchors are unlike most small anchors, because they are configured just like the much larger fleet mooring size anchors. They are included here because they are available, provide similar performance in most seafloors, and are less likely to be damaged (bent flukes or shank) during use than streamlined small boat anchors.

Hooking anchors are effective in coral and rock seafloors. The Navmoor 100 has also worked effectively in rock. It is designed like its full-size counterparts and is capable of tolerating very high loads on the fluke tips. Lightweight anchors cannot tolerate loads on the fluke tops, thus they are not recommended for rocky conditions.

Table 2-18 Where Common Anchors Are Effective

Anchor

Sand/Clay

Mud

Gravel

Coral/Rock

Weeds

Bruce

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