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Anchor generally refers to ship anchor, which is the main part of mooring equipment.An ironclad means of stopping a ship, to be attached to the ship with chains, and the anchor thrown to the bottom, so that the ship can be brought to rest.
An old anchor was a large stone, or a basket full of stones, called an anchorage.The anchorage stone is tied up to the sunken water and moored by its weight.Later there were claw-stones anchors, which were attached to the sides of the stones to anchor the ship by weight and strength.There were records about metal anchors in the southern dynasty of China.Ancient Chinese sailing ships used a four-legged iron anchor, which is still used in sampans and small boats.
There are many kinds of anchors, and the drilling platform often USES large grasping anchors, as shown in figure 1.The main characteristic of this anchor is that its holding force can be guaranteed only when the tension is horizontal.Experiments show that the anchor shaft turn up 6 ° holding power began to decline, the anchor on the handle to turn 12 ° holding power dropped significantly.Therefore, when anchoring, the lower end of the chain must be tangent to the sea floor, otherwise there is a risk of anchor.To take advantage of this feature, the anchor is pulled upward to lift the anchor handle. The anchor loses grip and finally breaks through the soil.
The choice of anchor should consider easy operation, convenient storage and economic application, but the most important is the anchor's grasp.The holding power of an anchor is, on the one hand, unknown because of the type of anchor and, on the other hand, related to the subsea soil.
With the advance of ocean development to deep water, new requirements for anchoring are put forward.In deep water, a long chain is required if the lower end of the chain is still required to be tangent to the seafloor to ensure the anchor's grip.Therefore, an anchor capable of bearing vertical force, such as a cement block or anchor pile, should be studied.When pile cannot be driven on the rock bottom, the anchor pile can be drilled into.Some anchors are designed according to specific seabed, and they have poor working performance when they are used in the case that they do not meet the design requirements.Although there is a formula for calculating the grasping force of various anchors under different seabed conditions in FIG. 1, the actual grasping force of anchors shall be determined by field tests.
There are mainly four kinds of cast or forged steel for modern anchor.
Cat anchor: the fluke and stem are usually integral and have a bar perpendicular to the fluke plane.A rod anchor is usually a double claw, but a single claw.When used, one claw is deep in the soil and has great grasp power.The main types of anchor are naval anchor, single-claw anchor foshan anchor, Japanese anchor and so on.
Instead of pole anchor: the anchor claw and anchor can rotate at a certain Angle.When used, both anchor claws are used in the soil at the same time.Hall anchor and its modified type of schbeck anchor are the most representative of the stockless anchor.
Full size anchor: the anchor claws are wide and can be rotated at certain Angle.It is suitable for sandy or soft water bottom due to its large area and strong holding force.The main types of large holding anchors are danforth anchor, Mars claw anchor and speedboat anchor.
Special anchor: it is different from other anchors in shape, such as mushroom anchor, whose head is like fungus or umbrella, deep in the soil, strong grasp and difficult to move.