….. and now we know why we support geophysical Earth science.
The Boss has reported in …… still alive …… and now heading back to port.
The Boss abides by the adage that you always have to try something at least once.
And geophysicists – which the Boss is – try not to come into close contact with rocks, and in the marine case, the sediment of the seabed.
However – there is always once – and this once is coring, which is being used here to test the repairs affected to the winches at the last vessel refit.
Here is the report on the once, and once only, Boss’ experience of coring – and piston coring to be exact.
So – what is needed?
One corer “bomb” – the heavy bit at the top – attached to which is a steel tube (or more than one if you want really long/deep samples).
Inside this tube is a piston – hence the name. The piston is designed to provide extra “drive” when the end of the barrel hits the seabed, hopefully ensuring the corer barrel goes into the seabed rather than hitting it and falling over.
Here is the complete system lying in its cradle along side the working deck.
Next – rotate the entire corer to the vertical so that it can be attached to a crane and moved to its deployment location under the winch parallelogram.
Quite unwieldy, but this gives an idea of size and this piston corer only has one barrel section attached, often they have multiple.
Drop into the yellow bracket and attach the trigger arm, hanging on the end of which is a weight on a piece of rope that is longer than the total length of the corer and its barrel combined.
When the trigger weight hits the seabed, it causes the trigger arm to lift and release the corer bomb from the hook mechanism on the end of the winch wire.
It is still attached though, by a loop of wire secured within the top of the bomb – you can just see it in the image below, curled inside the round vaned top part.
Then – lower away until just above the seabed – about 100m – and then slow down the winding out of the wire. And ……. then watch the wire tension and wait for the tension to drop sharply – this is when the corer trigger hits the seabed, and releases the entire corer to drop under free fall towards the seabed.
Wait a few minutes and then start hauling in the wire and watch the wire tension go back up and ……… hope the corer comes out ……. and that the vessel is not anchored.
You can see the change in wire tension in the blue line graph in the image below.
Eventually the corer arrives back at the surface and has to be dismantled and put back in its cradle – following a process that is the mirror image of the deployment process.
Here is a better view of the trigger.
And the trigger weight – this went into the seabed too looking at the mud on it.
Here is the core barrel – this also went in up to its “elbows” – well about 50cm by the look of the mud tide mark.
Now sitting in its deployment cradle while the yellow crane is readied to pick it up and put it in its storage cradle.
One hop …. and then rotate to the horizontal.
Remove core barrel and lift onto rack on deck.
Remove end of pipe.
And ……. loads of gloop – stinky gloop at that too. Now to get this out.
How? Well the steel tube actually has a plastic liner and that easily pushes out with the sediment intact inside it.
Geologists then cut the filled liner into 1m lengths and then split them longitudinally for sampling. Some of this was just put in a bag as you can see from the finger prints.
Boss decided that she’ll stick to geophysics.
And here is some of what she has been up to – a lovely map of the seabed topography showing that she has been round and round a bit and perhaps tied herself in a knot.
The Boss has also written a tool that does the processing of the data “on the fly” and “publishes” it to a web site that repeatedly refreshes over time as each new file is recorded and added into the total coverage.
But the primary reason the Boss has been going round in circles is to acquire some gravity data repeatedly over the same place to test the fitness for science of a newly upgraded gravimeter. But first – this requires good navigation – the tracks should all lie on top of each other in a ideal world – the annotation on the axis is effectively in increments of 10m – so in a big ocean – this is quite good repeatability in track keeping – all these tracks should go through the red dot.
The bottom image is the lattice of lines that have been acquired that the Boss is currently analysing the gravity from.
We hope the answer will arrive at some point before she reaches port!