Optimum design of an anchor is influenced by the spe- cific composition of the ocean floor. Basically, we catego- rize the ocean bottoms into three groups:1. Mud, or silt, which varies the most in consistency and offers little resistance to forces.
3. Physical strength.
4. Freedom from fouling, which all anchors do, but some in lesser degrees.
5. Influence developed by the chain’s catenary which absorbs shock loads and lowers the angle of pull at the anchor by its weight.
The anchor is the key to effective anchoring or mooring. It is essential to know what to expect from various anchors. The resistance of an anchor to being dragged through a soil has been considered as occurring in two stages: first, biting into the bottom due to the ploughing effect of the flukes, and secondly, maintaining a continuous resistance to drag after it is planted into the bottom.
Holding power is directly proportional to projected fluke area, and shear strength of the bottom material, and in- versely proportional to penetration-area resistance. In many cases a smaller anchor with favorable fluke area to weight ratio is more dependable than a heavier anchor. Holding Power for the two most widely used anchors are as follows:
1. Stockless Type anchors, in sand, develop a holding power to weight ratio of seven to one. In mud they develop three to one. The angle of penetration in both cases is 45°.
2. Lightweight Type anchors, in sand, develop a holding power to weight ratio of twenty to one, with the angle of penetration being 30°. In mud they develop nine to one with the angle of penetration being 50°.
The depth of penetration in all preceding cases is com- piled from three to seven feet in sand, and from seven- teen to twenty feet in mud. All calculations incorporate a 0° scope angle.
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