French OBS on deck
On the 12th of November 2013 we depart La Reunion just in time. The local pilot leaves the Meteor 15 minutes after we have gone out from between the mole heads. We start for the recovery of the remaining ocean bottom seismometers.
The first and second OBS are of French make and since they are apparently more vulnerable than the German ones I will personally collect all of them. In total, we will collect 9 OBS of French type; all others are “ordinary” ones of make KUM Lobster.
In the early morning of the 13th, at 0430, the collection of the first French OBS does not cause any problems. Around 2300 during the following night it is then the turn of the second one. Naturally, it is raining, and shortly before the retrieval attempt onto the starboard deck the OBS moves hard port, thus I have to reverse slightly and then swerve forwards. Besides the rain we experience northeastern winds of strength Bft. 4 and a southsoutheastern swell of 3 meters heights and periods of 8-9 seconds – all of which does not simplify our task. The OBS now appears at port side and I have to move the vessel again in order to bring the OBS to starboard while causing as little rolling as possible and utilizing the wind. This leads to a wind direction from starboard. However, on top of the unexpected wandering of the OBS from starboard to port side, for the collection procedure a port side wind is required. Of course, this is not the fault of the OBS, but rather mine, I should have paid more attention.
In the morning of the 15th of November another French OBS is scheduled for recovery, after Heike, the chief mate, retrieved a KUM type instrument in the early afternoon of the previous day. This time, the OBS labelled ‘RR31’ surfaces at starboard around 30-50m athwardships of stern. Since the wind direction is orthogonal to starboard, of course the vessel has to be turned, whereby it carries off the OBS. But finally, the OBS reaches the Meteor almost directly at its gate and can be collected without problems. The following two OBS are again KUM instruments succeeded by another French OBS which is expected in the evening around 2030. Just as scheduled, it surfaces shortly after 2100, but quite far away at starboard aftwards. The wind is blowing quite intensely with Bft. 5 from starboard and thus Meteor drifts after turning and under influence of the wind from backboard with partly more than 2 knots towards the OBS. Also this instrument can be collected successfully without further problems onto deck at 2143.
The weather conditions regarding winds will develop favorably, i.e. we expect a decrease of wind strengths, but the swell will remain at 2 to 2.5m. This does not affect our profiling but poses challenges during recovery of the OBS, causing rolling episodes of the vessel and eventually slopping of the soups out of our plates.
Recovery of a German OBS ("KUM Lobster")