Friday, March 6, 2015

A little yellow submarine

A little yellow submarine – Thursday 5thMarch 2015 – At sea heading towards Raoul Island

We might have departed a day late, but we are now on our way to Raoul Island! Along the way we undertook a few tests of deploying and retrieving Sentry. Some dolphins got very interested in this process and came for a visit.
Dolphins come to visit the ship
While in transit, it seems like the ideal opportunity to talk about our key piece of research equipment for the voyage – Sentry, an autonomous underwater vehicle, otherwise known as an AUV. As I mentioned in the first blog, Sentry is owned and operated by Woods Hole Oceanographic Institution (WHOI), a US based institution, and Sentry’s job is to travel to just above the sea floor and collect data related to the geology, structure and water column of (in our case) submarine volcanoes. At first this seems like a simple task, but after talking to some of the team you quickly gain an appreciation for just how complex and truly amazing Sentry is.
Sentry is worth somewhere in the range of $8 million dollars...and we are sending her to the bottom of the ocean and on top of hydrothermally active submarine volcanoes! It probably doesn’t need to be said that when dropping this sort of money into the ocean, you want to be certain that it is going to come back!! This means that Sentry needs to be able handle the high pressures associated with this depth and that it can later be retrieved from the sea surface.
Sentry out for a test deployment at Devonport Naval Base
Retrieving Sentry is no easy task. A large group of people working in sync is required to retrieve Sentry from the water. A group in a boat will first attach a line to Sentry and when this has been done a crane operator will lower the crane so that a heavier line, or strop, can be attached to the crane (pictured).  The crane then lifts Sentry from the water and once close enough, three additional tag lines will be attached by personnel on the ship to help stabilise Sentry as it is lowered onto the deck where it is secured into place in its custom-built cradle.
The retrieval process
 As an AUV, Sentry is unmanned and works essentially by itself. Basically, it gets sent down to the bottom of the ocean, does its data collection job, then when it gets runs out of battery it comes to the surface where its batteries will be recharged for the next deployment. We will be sending Sentrydown for 18 hours per dive, then recharging the batteries for 16 hours (puts my smart phone to shame). Once it is back, data can be retrieved from Sentry. In fact, Sentry’s battery pack has about 13,000 times more power than a high-end smart phone.
When we reach Raoul Island the HMNZS Wellington will be unloading Department of Conservation (DoC) workers and their huge amount of supplies.  Meanwhile, we will have a quick look around the Caldera (the crater at the summit of the island). Once this is complete, we will be heading to Macauley Caldera where we will deploy Sentry for our first dive. In the next blog I will talk about our visit to Raoul Island.

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