Day 7 - A windy sunday
6th february 2022
Throw back to BathyBot's immersion the 3rd of february
We are going through a few difficult days and this Sunday is a very windy day. Launching operations are impossible with winds of force 9 on the Beaufort scale (75 to 88 km/h).
We take advantage of this moment to share with you the backstage of BathyBot's immersion, the underwater robot of MIO - INSU - OSU (CNRS).
On the picture, we see BathyBot going down to the water in its BathyDock. The launching is done from the rear deck just like the other instruments. So far, nothing too different. Only, our dear little robot is one of the lightest devices that have been sent to the site. His weight in the BathyDock is a few hundred kilos, unlike the infrastructure of the Scientific Junction Box, which is several tons. Okay, but what difference does it make? It's important to know that all objects destined for the bottom are sent with a target landing point. The launch is considered successful when the device arrives within 10m of its target point. Remember, the Scientific Junction Box had landed 3m from its target, which is a very good score! Well, when it comes to the launching of a lighter device, this precision becomes more complex.
Another element complicates the task of the teams. As you can see, the launching cable is made of textile, which makes it much more sensitive to current and boat movement than a rigid steel cable - and even more so when it's carrying a light object. However, a steel cable, while more durable, would be much more dangerous in case of a break, as it could damage a bottom instrument by crushing on it. The choice of a flexible cable is therefore a compromise.
The sailors do everything possible to succeed in these long and delicate operations...
A long work
So how do they manage to position the object accurately?
The team on the rear deck communicates with the control point of the wheelhouse. In the photo, we see Eva, the multi-skilled officer in charge of the positioning of the boat, and, next to her, the BathyBot scientific team concerned with the follow-up of the operation. Their eyes are on the control screens that show the position of the BathyDock underwater and the trajectory of the vessel. An important detail in the picture is that the Pourquoi pas ? can't anchor in this area because of the depth of 2500m under the ship. The vessel therefore has two choices: either to drift and catch up with its position, or to be constantly sailing. And during the launching operations, it's the second option: the ship's engine remains running to be able to adjust and maintain the object's sending point.
Many attempts to steer
That evening, the textile cable, with an impressive length of 2400m, was subjected to the West-Ligure current. This is a constant current known to the area, but it's quite strong, which slows down the operation. The work started at 5:30 pm and ended at 8:30 pm, it took 3 hours to release the BathyDock!
On her screen Eva uses the data from the BUC, it's a tracking system placed on the cable 15m above the BathyDock. The BUC emits a signal that allows her to have an idea of the location of the object under water.
To send the object to the target point it tries to match the BUC signal with the coordinates of the target point. However, the BUC does not emit a continuous signal: the location is only reported every 10 seconds. Maneuvering to send an object in the current on a point located at 2400m depth is far from being easy !
Crédit photo : Nicolas Fromont - @nicolasfromontphoto
Signal on screen
This is what the wheelhouse team sees when communicating with the rear deck team. The black line that looks like a tangled loop is the tracking of the ship; the small circle a little to the left is the target point to aim at during the launch; and the green dots are the history of the signals emitted by the BUC, where the object is located.
The screen displays 7:12 pm, they still have 1 hour 15 of handling and there are already so many different green points, it gives an idea of the path of the object under water... Aiming at a point with an object suspended from a soft cable of 2.4 kilometers is a real challenge!
In spite of these difficult conditions, BathyDock succeeded in landing at 10m from its target point, congratulations to the mobilized teams! Thanks to them BathyBot is in place!
Crédit photo : Nicolas Fromont - @nicolasfromontphoto