A job we were getting ready to do in close to the coast was to work on this yellow thing.
It is a SPM, Single Point Mooring.
Here is a borrowed pic from the net to explain what it is.
The yellow float is an over sized buoy, there are anchor chains below keeping it in place, then there is a PLEM (pipe line end manifold) on the sea bed, from the PLEM is a riser hose which flexes with the SPM movement connecting the 2. The SPM can rotate around 360 degrees and still have the gas or oil passing. On the surface is a floating hose which connects to the vessel for loading. Also is the floating mooring line.
We went in side the anchor pattern to do some position testing to see if we could squeeze our 120 meters in between two chains close to the SPM sideways.
It kind of went wrong.....
The top pic which I took a few hours before it went tits up shows a small orange thing floating to the left, this is the mooring line which the ships tie up to.
The small Grey Vessel had the task of holding that mooring line and the hose out of our way.
They kind of ..... ummm....... let the mooring line go and it floated around and wrapped around 1 of the 2 main stern thrusters.
The fun bit is, we lost a thruster as it tripped out. That makes it hard to keep in position, but, we had to stay in position precisely to cut ourselves away from the mooring line.
The mooring line is 8 strand rope about 150mm dia.
The guys on the bridge managed to keep us in position so that the rest of the surface lines could be recovered, and we then cut ourselves away and move out.
We moved into sheltered waters and dropped anchor. The ROV went for a swim to have a good look about.
The Propeller is in a Round housing called a nozzle.
Here is some of the rope leading down to the Prop.
And now showing the prop and its housing that holds it to the vessel. It is shaped like the lower end of your typical outboard motor with a ring around the Prop.
We had to put the divers in to cut it away, took a large chunk of the day to do it.
Thankfully no damage, and we went back to work.