Dynamic Positioning (a.k.a. DP)

The ship stays over the drilling hole despite the wind and waves. How? I spent an hour talking with the captain about the dynamic positioning system of the JR. He used this analogy of a canoe, so I’m going to repeat it. He clearly loves his job which he has been in for eight years.

First, think of yourself rowing a canoe in a river. You want to stay in over the same fishing hole. You spot a tree (using your eyes as your sensors). Your brain processes the incoming sensory data. A signal is sent through your nervous system to your muscles to either paddle faster or slower to stay in one place. Maybe the wind starts blowing in your face and then you paddle faster. Or the current picks up so you need to slow down.
That is how the dynamic positions system works. There are several sensory systems on board– two GPS sensors, two anemometers, a beacon on the seafloor that sends a ping every second and five hydrophones to hear the pings, plus more. The brain is a set of two computers that run independently. If you have haven’t noticed, there are two of just about everything, just in case one system fails. When you are in the middle of the ocean, two weeks from the nearest land, you want to make sure that you have at least one backup system.

 

dynamic postioning panel
The muscles are the twelve thrusters. These are propellers that move the ship from sides to side. On the JR, the thrusters can be moved from the sailing position, tucked in the hull, to the drilling position when they are lowered. Each thruster has one 800 horsepower motor. The other muscle of the JR are the main propellers (two of them), which move the ship forward. They each have 6 motors on the them, making them more powerful than the thrusters.
Right now, we are floating over 137 meters of water. That means we have a pipe going down 137 m in the water plus the length into the seafloor (more than 500 m). We need to stay over the top of the hole. In shallow water, there is a little leeway in how much the ship can move side to side. Right now the captain has it set for the ship must stay within a 7 m circle. And the DP system hold us right there, with just a few meters drift back and forth all the time. Amazing.

Captions:  1. Thruster in the bow of the ship.  2. Panel to control the dynamic positioning system.