Moorings, moorings, moorings.

Seeing as the main purpose of this cruise is to service the RAPID-26N moorings, I thought I'd give a bit more information on what our scientific moorings are like.

They are basically long plastic-covered wire ropes (or synthetic fibre ropes), with a lot of floats to hold the top end up, and a big lump of steel to hold the bottom end down. The scale of them can be impressive though, with our tallest mooring rising approximately 5150m from the seabed, meaning it would dwarf a skyscraper if it were stood next to it .

The height of our mooring called MAR1 relative to some famous landmarks. We are currently steaming towards this mooring and will be working on it on Thursday.

Yet for all their length, the wire diameter is less than 8mm, and the majority of the buoyancy is provided by glass! The hollow glass spheres are packed in plastic "hard-hats" to protect them from impacts, but they are designed to withstand the pressure at a depth of 6000m (600 times atmospheric pressure). Sometimes, however, even these implode due to the enormous pressures.

Glass buoyancy recovered from a mooring today. Usually glass spheres reside inside plastic hard hats. Here the enormous pressure the spheres were under from the ocean has caused the glass to disintegrate into white powder. The force of the implosion can be seen in the damage to the plastic hard hats.

As the mooring is deployed, self-logging instruments - built into titanium or stainless steel pressure cases - and additional buoyancy are clamped to the wire ropes or inserted inline between joins in the wire. The mooring is assembled as it goes over the stern, and once all the wire, floats and instruments are streaming aft of the ship, the anchor is attached and dropped into the water. The whole mooring is then pulled down as the anchor sinks and it eventually stands upright with the top of the mooring stopping about 50m below the surface. The mooring is then left in place collecting data until we come to collect it in 18-months time.

To recover the moorings we use an acoustic release that when given the correct coded acoustic signals lets go of the anchor allowing the mooring to float to the surface. The ship manoeuvres in to pick the top of the mooring up, and then the rest is winched aboard with the instruments taken off and the data downloaded. A replacement mooring is deployed and we move to the next site.

Darren