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A four-point anchoring system is used primarily by research and diving support vessels to maintain station during underwater operations. Think of a spider in the middle of a window opening, with one strand of a web at each corner. Like the spider, the ship can use her four hydraulic anchor winches to pull along the anchor lines to shift her position forward, backward and to either side. This means that, with a bit of creative anchor handling, she can position herself perfectly for the activity at hand.
Give helm and engine orders to turn the vessel's bow—or front—into the current or wind at slow speed upon arrival at the designated location. If the wind is pushing the vessel so that the current has no effect, aim the bow into the wind. If the current is having a greater effect on the vessel's handling than the wind, aim her bow into the current.
Order the helmsman to move the vessel to the point designated for deployment of the first bow anchor in the anchor spread—the spread of the four anchors—at slow speed and. When that point is reached, reduce speed to bare steerageway You will be holding your own against the movement of the sea. Order the anchor operator lower the anchor and order the deck crew to attach the anchor buoy at the appropriate time to buoy the anchor cable to the surface, marking the anchor location. After your anchor operator has deployed the first anchor, the deck crew will keep an arm raised and aimed in the direction that the anchor line is deploying.
Allow the vessel to drop back slightly; order the anchor operator to continue to deploy anchor cable until ordered to secure. Give helm and engine orders to back the vessel to the location for the second bow anchor. When the second bow anchor location is achieved, order the helmsman to turn into the seas at slow speed and order the anchor operator secure the anchor windlass for the first bow anchor. Order the anchor operator to lower the second bow anchor and tell the deck crew to attach the anchor buoy to the anchor cable to mark the second location.
Order the anchor operator slack both bow anchor cables and give helm and engine orders to move the vessel astern (backwards), toward the third (port stern) anchor position. Have the anchor operator continue to slack the bow cables and, when in position, order the anchor operator to secure the bow windlasses and move to the stern windlasses. Order the anchor operator and deck crew to deploy the third anchor and anchor buoy using the same method as the bow anchors. Order the anchor operator slack the anchor cable for the third anchor, give helm and engine orders to back to the fourth position. Order the deck crew and anchor operator deploy the fourth anchor and anchor buoy.
Move the vessel forward to the final working position by giving helm and engine orders, using "ahead slow" speed. Order the anchor operator and deck crew to take up the slack in the bow anchors, keeping watch on and indicating the direction of the bow anchor rodes, to prevent fouling the vessel's. propellers. Have the anchor operator deploy additional anchor rode astern to compensate for the forward movement.
Once all anchors are deployed, test the set of the anchors by ordering the engines astern, at bare steerageway, slightly faster than the ocean's natural speed. Give orders to test the stern anchors by pulling ahead at bare steerageway. Once the vessel is in position, held by the four-anchor spread, the position can be "fine-tuned" using the windlasses only, to haul the vessel along the anchor rodes. Once the vessel is in her final position, order the anchor operator and deck crew to secure all anchors.
A four-point anchor spread should be planned by the person responsible for the project for which the vessel is hired, not by the vessel's master.
Anchoring is a dangerous evolution aboard ship. All appropriate precautions should be observed.
- A four-point anchor spread should be planned by the person responsible for the project for which the vessel is hired, not by the vessel's master.
- Anchoring is a dangerous evolution aboard ship. All appropriate precautions should be observed.
Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.