30 Jun - Now you see it...
Date: Sunday 30th June 2002.
Position @ 1200 (UTC): 53°37.6 North, 000°11.3 East. Alongside Immingham.
Next destination: Port of Aberdeen
Current weather: Overcast, with rain showers.
Wind: Sou'Westerly, Force 3
Barometric pressure: 1014.9 mb.
Sea state:. Moderate..
Air temperature: 15.2°C.
Sea temperature: 14.0°C.
No Ship's Position reports are available during our stay in the N.Sea since we cease doing Met.observations.
NOW YOU SEE IT, - NOW YOU DON'T !
This week, the Ernest Shackleton is keeping a very 'low profile' and has been a rare sight in the North Sea. The reason ? No, not camouflage precisely, just the ability to lay alongside in Immingham and let everybody just 'forget her'.
Not quite 'camouflaged', but managing to keep out of sight alongside in the port of Immingham.
The work continued throughout, starting at the beginning of the week just off the coast of Easington, but moving out to the Leman Field in the South before heading back to port for the 12-hour crewchange on Thursday. The Stolt crew were ready for a rotation, and so we all looked forward to a few hours alongside and taking a break from the steady plod of ROV'ing along the pipelines of the Lancelot and Leman fields. But once alongside Quay 2 of Immingham, the ROV Crane was given the 'once over' and deemed to be in need of some urgent repairs ashore. Thereby extending our stay alongside.
NOW YOU SEE IT - NOW YOU DON'T . Not only the ship, but the blue ROV Crane disappeared from view this weekend too. The photographs speak for themselves.
Whilst we were 'ROV Crane-less' this weekend, it is envisaged that it will return back to it's place in prominence early during this next week and then we can once again get out into the Southern North Sea and back to surveying.
This unexpected break allowed the Client (Stolt) to send their people home for the duration of our port call. So it was on Saturday morning that 24 of them departed the ship for a World-Cup
weekend at home, regardless of where that home may be. Several of those departing were Norwegians and so flights were arranged, last minute, and it is anticipated that it will take a 24-hour
period to get them all back when we have a definite date for our departure.
The Shackleton Webpage takes a closer look at just what is entailed in a D.P.Desk.
DP Desk from a novice DPO. For the time the Ernest Shackleton is out of the ice, she earns her living in the North Sea inspecting pipelines, but to be able to do that she needs a special Dynamic Positioning System. (DP).
Although the ROV does the actual inspection of the pipeline, the Shackleton has to be able to keep in position relative to the ROV very precisely in open waters. It becomes even more critical when the ROV is working around an Oil installation - this sort of work means the ship has to be very close to the platform sometimes as close as 10 metres or less. The ship is 80m long x 17m wide and weighs around 5,500 tonnes. Imagine, for a moment, something the size of a warehouse suspended besides your home. 10 m is not a lot of room !!!
DP uses a computer generated 'model' of the ship to estimate how she will be affected by environmental conditions (wind, sea state, etc) and also the likely outcome of a failure in any of the critical elements of the system. eg. thrusters, propeller. There is also an added margin of safety in the Shackleton's system - the ship has duplicate DP Computers, Gyros, Compasses, Wind sensors, Motion Reference Units, Position Reference Systems and an Azimuth Thruster should the Main Propeller fail. If any unit fails, the standby is selected, allowing the ship to be manoeuvred to safety in a controlled manner, allowing time for the ROV to be recovered to the deck.. Additionally when the ship is inside a Platform's 500 m zone, the Main Engines supply power exclusively to the propeller and thrusters - as well as this, the main engines cannot normally 'declutch'.
The ship's ability to maintain her position when in 'DP mode' comes firstly from the high accuracy of the position references. At least two at one time are needed (These can be selected from Satellite Navigation Systems such as DGPS (Differential Global Positioning Systems), also HPR (Hydrocoustic Positioning Reference), a LTW (Light Taut Wire) or a Fanbeam.
The ship will then maintain this position using Main Propeller for the thrust ahead and astern, the tunnel thrusters (a propeller mounted in a tunnel which runs across the hull of the ship) for movement from one side to the other, and the Azimuth Thruster ( a propeller extended beneath the hull of the vessel that can rotate through 360 degrees, so providing thrust in any direction whatsoever).
Whilst the ship is protected from 'single point failure' (ie a situation where one problem causes the ship to loose ability to maintain position ) it is possible for the vessel to maintain position for a short time by referring to the model it has already built up internally. Failing this, manual control of the ship is possible by using the 'rotate' and 'joystick' controls (see photo).
This is the job of the D.P.O (DP Officer) who specializes in this kind of system. An experienced DPO can detect the symptoms of a failure in the early stages, perhaps selecting/deselecting a position reference system, or increasing/decreasing power to thrusters or taking any other precaution.
Author DPO Alan Newman.
Forthcoming events: Reassemble the Stolt's team and re-commission the ROV crane. Then depart Immingham to resume our work on the Leman Field.
Contributors this week : Many Thanks to Wavey-Davey and to Alan Newman for his in-depth review of the Dynamic Position Equipment on the Ernest Shackleton.
Diary 6 will be written on 07th July 2002 and for publication on 08th July 2002
S teve B
Wavey-Davey's Weekly Whit-spot.
Davey Says :-An Albatross and a Penguin having a conversation: The Albatross said to the Penguin,... 'Did you know there was a biscuit named after you ???'. 'What ?' said the Penguin,... 'ERIC ???'.