1. Observation of anchor chain judgment method
When the anchor position is normal, if the wind, current and waves have little effect, the anchor chain will generally be basically perpendicular to the sea surface. If the wind, current and waves act heavily, the direction of the anchor chain should be opposite to the same direction of the wind, current and waves, and the angle between the anchor chain and the water surface also changes, which means that the difficulty of the anchor chain is different at any time, and usually the anchor chain will be regularly tight and loose. When anchoring, the anchor chain will continue to bear a large force, and it will no longer be tight and loose, and the angle between the anchor chain and the water surface will change little, and the ship will vibrate.
2. method for judging the direction of the bow of the anchored ship
when the anchor position is normal, if the wind, current and waves have little effect, the yaw angle of the bow is very small. If the wind, current and waves are strong, the yaw angle of the bow will increase, and the change of the bow direction basically conforms to the law of sine and cosine functions.
when anchoring, the deflection angle of the bow will be small or even no deflection, and the anchored ship will have a continuous backward speed.
3. judging the position of the anchored ship
when the anchor position is normal, the position of the anchored ship changes little or even does not change when the wind, current and waves are very small. When the action of wind, current and waves is great, the position of the anchored ship changes regularly, basically in a horizontal figure of eight. When anchoring, the position changes basically in a straight line, or the general trend changes in the direction of wind, current and waves, and the position changes in an "S" shape.
4. using COG and SOG judgment method provided by GPS
using COG (heading to the ground) and SOG (speed to the ground) data provided by the anchor ship's GPS (global positioning system) receiver, whether the anchor ship is anchored or not can be judged.
when the anchor position is normal, when the wind, current and waves are small, the COG change will be very small, and the SOG will also be very small or equal to zero, generally not exceeding .1kn. When the wind vagrancy is great, the COG data will change constantly, and it is generally irregular, but the SOG will be different with the severity of the ship's yaw, and the value is also inconsistent.
when anchoring, COG data will be basically stable in a small range, and SOG is also relatively stable.
5. Determination of bearing and distance of the target on the shore
When the anchor position is normal, the bearing and distance of the same target on the shore should change little, because the actual position of the ship is not affected by wind and current. Of course, the distance between the target and the ship is relatively large, and the target in the bow and stern direction cannot be used. It is best to choose the target near the ship's right cross, or choose both targets at the same time.
when anchoring, the orientation of the target measured on the ship will continue to increase or decrease, and the distance between the ship and the target will also continue to increase or decrease.
6. Setting the conventional warning circle judgment method
When the anchor position is normal, the ship position should be in a circular warning circle with the anchor position as the center and the sum of the chain length and the captain as the radius. If the ship position exceeds the warning circle, it is possible to anchor. Usually, the ship's position here refers to the position obtained by the ship's GPS receiver, and the anchor position refers to the GPS ship's position at the moment of anchoring.