Officer’s Log: Vessel on anchorage with poor visibility

While I was on anchorage, in a situation with strong rain, the visibility was less than a mile. For this reason, I decided to inform captain about the situation and I called him to his Office.

Captain came to the bridge and evaluated the situation. Then, testing me, he asked me which was the signal for a vessel on anchorage on a poor visibility situation. That question was a tramp in case you haven’t realized it yet.

I answered without hesitation that we should put a signal that, on intervals on not more than 2 minutes, will sound with one short blast, one long blast and another short blast, but, if we go to the COLREG’s rule 35 (g), we can read:

A vessel at anchor shall at intervals of not more than one minute ring the bell rapidly for about 5 seconds. In a vessel of 100 m or more in length the bell shall be sounded in the forepart of the vessel and immediately after the ringing of the bell the gong shall be sounded rapidly for about 5 seconds in the after part of the vessel. A vessel at anchor may in addition sound three blasts in succession, namely one short, one prolonged and one short blast, to give warning of her position and of the possibility of collision to an approaching vessel.

Lesson learned: Blasts is only if a vessel is approaching, it is not necessary to put them if you are alone, you will only get yourself killed by your crew mates because they cannot sleep. Keep the bell ringing sounding and a sharp lookout on AIS, RADAR and by eyesight and only put blasts when needed.

How to calculate the swinging circle for a ship on anchorage

The idea of this post came to my mind while I was on anchorage as 2/O on board the M/F Al Andalus Express. Who knows, maybe while you are reading it I’m still on anchorage.

On board we had one ECDIS equipment capable of create an anchor watch zone, but this was so simple that you only needed to put the radius of the circle of watch and that is. Seeing this I remembered when, while I was cadet on the M/T Petroport I had to make the calculation of the swinging circle of the ship on paper charts. I still remember that was the 2/O Rubén who taught me how to do this.

This calculation is quite simple but, for doing it properly we will need a some information.

The first date is really easy to get. It is the Length overall of the vessel, which you can get, for example, from the pilot card.

The next one is the rode. This is defined as:

The anchor line, rope or cable connecting the anchor chain to the vessel

It can sound a little tricky, isn’t it? But I can show you a little trick to get it, with only two positions.

  1. You need to note the exact position of the place where you drop the anchor.
  2. You need to note the exact position where, after dropping the anchor, your vessel is considered to be on anchorage.

Once you have those two positions, you can put them in your chart and get the distance between them.

After the rode you need to get the Depth, which is easy to get using the sounder or the charts.

Finally, you’ll need to know your freeboard.

With all that information, and being sure that you have all of them in the proper units, you only need to put them in the next formula:

Swinging circle = L.O.A+\sqrt{Rode^2-(Depth+Freeboard)^2}