Chaser equilibrium

To control the anchor, the chaser collar must always be on the anchor head. The tension in the anchor cable must be equal or larger than 1.5 times the weight of the anchor. If not, the anchor slides through the chaser and the orientation is not controlled (fig. 3-54).

Equilibrium forces determine if chaser is in contact with the anchor. Near bottom, the vertical load at the chaser from the anchor line Flv is small. The chaser remains only in contact with the anchor if the bollard pull Fph is larger than the horizontal line load Flh which in turn must be larger than the anchor weight W (if not the anchor will slide down). The angle of the pendant line must be larger than 45° (fig. 3-55).

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Recommendation: Bollard pull must always be equal or larger than the line tension, i.e. use a minimum bollard pull of 20 to 30 tons for a 12 to 15 ton anchor. Use a minimum pendant line length of 1.4 to 1.5 times the water depth in shallow water (100m) and 1.3 to 1.4 times the depth in deeper water (fig. 3-56).

pendant line force

anchor line tension

anchor weight

fig. 3-54

fig. 3-56

Deployment for permanent moorings

The simplest deployment procedure for the Stevpris anchor is to lower the anchor to the seabed using the mooring line. When the anchor is nearly on the seabed, the AHV should start moving slowly forward to ensure that the anchor lands correctly on the seabed (fig. 3-57).

Another option for the deployment of the Stevpris anchor is to connect a temporary installation bridle (wire rope) to the anchor. The bridle is connected to the padeyes situated at the back of the shank of the anchor. The AHV then lowers the anchor overboard while paying out the mooring line and the bridle simultaneously (fig. 3-58).

To recover a Stevpris anchor after it has been installed, the AHV should take the mooring line and pull it in the opposite direction that the anchor was installed in, generally away from the centre of the mooring. The AHV should recover the mooring line till a length of approximately 1.5 times the water depth is still overboard.

When only 1.5 times the water depth of mooring line is left overboard, the AHV should block the winch and keep a constant tension on the mooring line equal to the pre-load tension. Once the anchor starts to move in the soil, a lower tension in the mooring line can be used (fig. 3-59).

fig. 3-57

temporary bridle

mooring line

fig. 3-58

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fig. 3-59