When the vessel is expected to remain at anchorage for a long period then this may cause the anchor or its chain to get fouled or to be dragged, which could potentially lead to collision or grounding.
1 Anchor/Chain fouled
There may be a possibility of a knot forming in the chain and this will strongly impact the picking up of anchor at departure. To avoid this, consideration should be given to alternating the anchors by heaving up anchor and re-anchoring after a set period of time.
Heaving up the anchor
Careful monitoring of the anchor cable load and lead is important as there will not be any pre-warning of windlass damage if the system is overstressed (unless a cable tension monitor is fitted). Any damage may not be evident until the windlass is next used to heave up the anchor.
Recommendations
- Minimise the tension in the chain and keep the chain as vertical as possible.
- In windy weather conditions or strong current, the rudder and engine must be fine-tuned to prevent too high tension in the chain and overload of the windlass motor. This will also prevent dragging of anchor and breaking out the anchor. The heaving up speed is typically nine metres/ min so speed over ground should be less than this ie 0.3 knots.
- Close communication between bridge and anchor party on deck is essential.
- The anchor party should know the vessel’s windlass capacity to heave up maximum free-hanging shackles.
- Vessel to prevent the overloading of high-pressure windlasses which can result in their catastrophic failure, the ‘heaving in’ should be stopped as soon as any significant tensioning is observed, or difficulty is experienced.
2 Dragging anchor
During extended anchorages, weather conditions may deteriorate, therefore weather forecasts and conditions should be continuously monitored, along with the ships and anchor’s position.
In case the vessel is dragging anchor, keep the ship’s head into the wind and ease the tension on the cable by using the main engine and rudder while heaving up the anchor.
Shifting anchorage or drifting offshore or paying out more cable could be considered depending on the prevailing circumstances. If the weather conditions are likely to deteriorate, it is imperative to heave up and proceed to an open, safe area well in time.
If the vessel is in shallow water and the fully operational windlass is unable to heave up the cable, then the fouling of the anchor should be considered. The vessel can consider steaming around the anchor position or lower and heave the anchor again until it is finally free. In such situations, if there is a suitable work boat available then consideration should be given to using this to help clear the fouled cable.
3 indicators the ship is dragging anchor
- The bow cannot stand against the wind.
- The ship’s side against the wind has not changed.
- There are extraordinarily large vibrations coming from the anchor chains.