31 July - A full week of work
Date: Sunday 31 July 2005
Position @ 1200 Local (GMT+1): 60°09' North, 001°09' West - Alongside in Lerwick, the Shetland Islands
Next destination: Schiehallion Field, to the West of the Sheltand Islands
ETA: Monday 01 August, 2005
Distance to go: 118 nmiles to the next worksite
Distance sailed from Immingham and Crew change : Not Available due to various courses and manoeuvering.
Total distance sailed: Not known.
Current weather: Cloudy, fine and clear. Overcast
Wind: 350°, 20 kts
Sea state: Calm in the sheltered waters alongside
Barometric pressure: 1013.5 mmHg
Air temperature: 13.8°C
Sea temperature: 11.7°C
Again you can see that the ship’s position is obscured by a heavy overcast of ‘yellow stuff’ and again, Bergen is the place to be !
This Week on Shackleton
Was a full week of work on the Forvie Oil Field to the east of the Shetland Islands. One day was very much like the next, with a 24-hour a day routine of Preparing, Toolbox talks, Permits to Work, Diving the ROV’s (Remote Operated Vehicles) and Surveying. The ‘Posreps’ or ‘position reports’ all read pretty much the same from day to day. The upshot of this being that the workscope is getting completed and our end-of-project demobilization looks scheduled to go ahead this weekend. We demobilize this project and mobilize up again for the next.
If you are wondering whatever happened to those ‘lunar landers’ reported in last week’s webpage, they were successfully laid on the sea-bed and their associated beacons interrogated to verify correct operation and orientation of the array. Using the ship’s 50 Tonne main crane, they were lowered the 130 metres below the surface and dropped almost exactly into place. The precision of the placement of these was not too exact (within a couple of metres), so long as the exact ‘lat’ and ‘long’ was subsequently recorded for each landing. Once done, it was on to the next task on the work list.
WAVEY DAVEY’S WEEKLY WIT SPOT
Back home, Wavey Davey is treated like a God. He is given burnt offerings every evening ?
But after dinner, it’s straight to bed with his old friendly Teddy Bear which he’s had since he was a nipper.
‘It’s called Fred’ insisted Davey.
‘Why do you call it Fred Bear ?’ I enquired ?
‘Because it is’ says Davey.
Additionally this week, Wavey Davey (who is not noted for speed) was on the Monkey Island, and look what he found ?
‘Amazing’, say Davey. ‘They’ll put Speed Cameras up anywhere !’.
When is a Speed Camera, not a Speed Camera ???
… When it’s an NDB (Non-Directional Radio Beacon).
RRS Ernest Shackleton, like many vessels with a Helicopter Deck, boasts an NDB or Radio Beacon.
Typically in the frequency range 500-1250khz, a NDB puts out radio frequency waves that can be picked up by appropriate Radio Frequency Receivers and ‘points’ to the origin of the radio signals. Such a receiver is an ADF (Automatic Direction Finder).
‘The Bellini-Tosi Medium Frequency direction finding receiver was the first radio aid to navigation used in Australia. Designed for ship-to-shore use in 1911, it was in common use in Europe when introduced here in 1935.’
As they developed, these single frequency beacons became more sophisticated and now include superimposed intelligence on top of the base frequency. This means an identification signal can be superimposed on top and for RRS Ernest Shackleton, the letters ‘PQN’ can be heard in morse code if you tune to our frequency. (This is a testimony to the original name of the vessel, the Polar QueeN). We use our NDB for visiting helicopters. Should the visibility be marginal or should the helicopter pilots require confirmation of the location of (what is effectively) our mobile platform, they can adjust to our frequency, and their ADF will ‘point’ exactly to where the vessel is sailing. Clever, eh ?
Here’s what the encyclopaedia has to say about the NDB/ADF system :-
The Radio Range, is a geographically fixed radio transmitter that radiates coded signals in all directions to enable aircraft and ships to determine their bearings. An aircraft or ship can determine its line of position and drift if it knows it’s bearing relative to the radio transmitter and the geographic location of the transmitter. By taking successive bearings on two or more radio ranges the craft can determine its geographic position. Radio ranges are usually unattended; they emit either repeated call letters or steady signals that are periodically interrupted by station identification letters in Morse code. The aircraft or ship obtains its bearings relative to the radio range by picking up these signals with a receiver having a directional antenna, usually a loop antenna. The strength of the signal received depends on the orientation of the antenna relative to the radio range. By varying the orientation of the antenna and observing the changes in signal strength, the bearing of the vehicle can be obtained. When the antenna is driven automatically, the instrument is called an automatic direction finder (ADF). Both manual and automatic direction finders are also called radio compasses, although in aircraft the radio compass usually means an ADF. Another type of radio range called an A-N range transmits two coded signals via directional antennas so that a pilot on one of four fixed courses hears a continuous tone in his or her receiver when the craft's bearing is correct; if it veers off course either a Morse A or N is heard depending on the direction in which the error is made. Radio ranging is being made obsolete by the Global Positioning System (GPS), which uses a network of orbiting satellites to precisely locate the position of an aircraft or ship.
Acknowledgement to The Columbia Electronic Encyclopaedia, 6th ed.
Click images to investigate the Shackleton NDB… or ‘speedcamera’
Whilst out on the Forvie Oil Field, the Shackleton received an intership transfer from a visiting vessel, the Maersk Assister. The Assister had arrived on the ‘field’ from Lerwick, and had brought an important implement required for the onboard operations. Occasionally, these types of ‘rush arrivals’ are sent out to the vessel by Helicopter, but we are not due to have one of those until the middle of August. As the Assister was due out to the Forvie to begin a project of ‘trenching’ anyway, she was able to deliver the necessary parts to us. This was on the Monday 25th. This operation, although looking frightfully complex, was simply a case of two DP Vessels (Dynamic Positioning) moving slowly alongside each other until the crane could span the space between them and land the item onto our helideck. As you can see from the series of pictures, the ships get awfully close, but always in control despite the wind, seas, and swell.
Once the operation was completed, the Shackleton returned to the ROV survey of the Grant Tee sub-sea manifold, and the Assister went off to commence it’s trenching operations.
Finally, they say a picture is worth a thousand words! Since I do not have 1000 words to hand this week, I shall let the photographs speak for themselves. Here are a number of images for the work that has been going on around-the-clock on the Shackleton.
Click on images above to enlarge them and see ROV operations during the day and night.
Forthcoming Events: Crewchange and depart Lerwick for the Schiehallion Field and continue with the Stolt Summer Charter schedule.
Contributors this week: Thanks to an anonymous ROV crewmember for the snapshots of the North Sea operations.
North Sea Diary No.7 should be written on Sunday 06th August for publication on Monday 07th August, operations permitting.