The sea is rarely stationary and if a ship stops it will drift with the wind, tides and currents. To stop that happening the ship needs to drop anchor and even then the ship will swing on the anchor according to the effect of wind and tidal currents on the hull.
In the case of HELIOS RAY we are seeing her drifting, repositioning and drifting some more. This is very likely because the Captain does not want to drop anchor. There could be a number of reasons for this - there could be submarine cables nearby (nothing to do with submarines!) which the anchor could snag, it may be too deep or the seabed may be simply unsuitable for anchoring but I would guess she is in an area with lots of seaweed. When you raise the anchor, the anchor chain is washed with high pressure water to clean off mud and anything else that may have attached itself to the chain but seaweed can be the devil to remove and it must be removed. Even a small amount of rotting seaweed stinks to high heaven after a day or two and it just gets worse. Cleaning rotting seaweed off an anchor chain is a job you will only do once and vow never to do again. There is an awful lot of anchor chain onboard and working with anchor chains is a high risk activity. Even the cleanest anchor lockers can become pretty ripe. Sometimes its unavoidable but if you can possibly avoid picking up seaweed, you will.
BTW although we use the term dropping anchor there is nothing reckless in this manoeuvre and it is more of a controlled lowering for the most part. It is the anchor chain lying on the seabed that stops the ship moving rather than the anchor itself.
