Seismic Pressure

THE POLARCUS NAILA roams the ocean like a restless ghost, drifting slowly back and forth, day and night, over the same lonely patch of sea. And then, suddenly, she is gone; vanished again – off to haunt some other waters, in some other part of the world. She is a ship that never stops moving, thanks to a crew that never falters

THE NORTH SEA. FOG, THICK AND WHITE, hangs over the water and wraps around the bridge of the Polarcus Naila, where Sunil Pagnis, the ship’s Chief Officer, sits alone drinking coffee. This is the beginning of a new five-week rotation for him, a fresh start after spending a relaxing vacation with his family back home in India.
Like Sunil, the Polarcus Naila is starting afresh as well. This is the ship’s first seismic project since leaving dry dock in Amsterdam with a brand new twin fin propulsion system, the first of its kind in the world.
It was a fast retrofit – just forty-five days – but even so, the decision to take the vessel out of the water for that relatively short length of time was not made lightly. It was a matter of necessity. With operating costs of $200,000 per day, downtime is not an option for this ship – eighty-five percent of her lifetime will be spent at sea – and in a perfect world, she would never stop moving. It is an investment Polarcus is counting on making back in less than three years, through efficiency gains like reduced fuel consumption and improved reliability.
But three years at sea is a long time, especially when there is no room for error. Each day the crew must work to safeguard their ship’s operations, or risk tarnishing Polarcus’s hard-won reputation as one of the best seismic operators in the business. And in this industry, reputation is everything.

CONSTANT BEARING, DECREASING RANGE

The time is 07.00 hours when the radio crackles with an urgent message from the guard boat Aquarius, whose hazy shape is just visible far ahead off the starboard bow: Aquarius has been unable to make radio contact with a cargo ship, just 10 kilometers away, that is heading straight for the Polarcus Naila.
If the Polarcus Naila were any other type of ship, she could simply change course. But for seismic vessels, the solution is not so simple. Size is one issue: the twelve massive streamers she is towing make her effectively 19,685 feet long – that is 6 kilometers– of sensitive, and expensive, seismic equipment (each streamer costs about $3,000,000). Any sudden change in the ship’s direction could easily tangle and damage them.

HOW THE POLARCUS NAILA COLLECTS DATA

- Twelve seismic sources, suspended off the stern, shoot compressed air into the water at a force of 2,500 pounds per square inch.

- The compressed air creates vibrations that travelthrough the water and layers of rock on the ocean floor. The streamers, trailing the sources, pick up these vibrations using receiving devices known as hydro- phones.

- The hydrophones convert the vibrations into electrical energy, which is digitized and transmitted to the recording system in the instrument room.

- The seismic team analyzes the data for the presence of hydrocarbon deposits.

DATA COLLECTION

Then, there is the problem of the ship’s data collection. The Polarcus Naila is travel- ling at exactly five knots along a pre- programmed plotline, forty-six kilometers long. Every six seconds, the ship release acoustic pulses, vertically downward, through the layers of rock below the ocean floor. Meanwhile, the streamers, capture the reflected acoustic waves and convert them into digital data. The streamers then transmit that data to the instrument room, where the seismic team carefully analyzes it for the presence of hydrocarbon deposits far below.
Any change in speed during these delicate operations would create irregulari- ties and superfluous noise in the data. And if the ship were to deviate from the plotline even slightly, the crew would have to resurvey the entire line – a financially unacceptable risk.
It takes an around-the-clock, carefully coordinated balancing act between the seismic and maritime crews to prevent such devastating losses. As the seismic crew monitors the Polarcus Naila’s course, making micro-adjustments to correct for even the smallest changes in current, the maritime crew on the bridge makes mod– ifications to the vessel’s speed in increments of .1 knot at a time.
Other ships, meanwhile, are required to navigate around the Polarcus Naila, giving a wide enough berth – usually of a couple of nautical miles – to keep from interfering.

SITUATION CRITICAL

Another vessel is detected on the radar. With it’s current course it will cut straight over the streamers on tow. Sunil hails the vessel to ask it to change course. It could be that the other vessel’s officer on watch has his radio turned down. Or he could be asleep. Either way, there is no time left to lose. If he does not respond in the next couple of minutes, the Polarcus Naila will have to change course. In a final effort to attract attention, Sunil commands Aquarius to fire flares across the cargo ship’s bow. For backup, he calls up 2nd Officer James Winterton from the dining room and orders him to do the same from the bow of the Polarcus Naila.

James is a good-natured Brit who bears a passing resemblance to the actor Clive Owen, and it is with an action hero’s speed and confidence that James throws on his safety gear and grabs the flares from the storage box. As he walks outside to the bow, he pauses to remark that his wife, who works in the military, would laugh at the size of the gun he was firing.

FOLLOWING PROTOCOL

According to protocol, Sunil must also notify Captain Johnny Johannessen of the situation. The Captain is a Norwegian gentle giant whom the crew loves, and that they call him Johnny in no way dimin- ishes the respect they feel for him. He is so alert and focused when he arrives on the bridge to take command that the only indication of his having been asleep just moments ago is his slightly disheveled hair. And now he stands, watching through binoculars, as green flashes cut through the fog. The atmosphere has grown quiet and watchful, with the exception of Sunil’s calm but insistent calls over the radio.

Agonizing seconds pass. At last, the reply comes: the other ship’s officer on watch sheepishly apologizes, claiming to have had the radio turned down. It seems the flares have worked, and Chief Officer Sunil and Captain Johnny watch with great relief as the cargo ship slowly veers off.
Another watch-keeping shift has come to an end; another day’s work done. Sunil is modest by nature, so it does not occur to him that his actions today hint at where his daughter’s strength of character comes from. He’ll see her and the rest of his family again in five weeks, but in the meantime there is a seismic vessel to operate, and now it is time for some well-deserved rest. As Sunil descends below deck, James takes his place on the bridge, where for the next twelve hours, he’ll keep watch – and do his part to ensure the Polarcus Naila travels safely over the unpredictable seas.

TWIN FIN PROPULSION SYSTEM

For vessels working in tough conditions, such as offshore supply vessels in arctic seas, current propulsion alternatives have their drawbacks. Traditional propulsion systems with higher level of complexity, sometimes face reliability and downtime issues, and long conventional shaft lines take up space in the hull and can be difficult to retrofit. Now, primarily for diesel-electric new builds and retrofits, there is a fresh opportunity: twin fin propulsion.

TWIN FIN ADVANTAGES:

- Increased thrust and efficiency
- Reduced maintenance and easy access for service
- No need to dry dock in case of repairs
- Increased reliability and flexibility
- Reduced fuel consumption and green concept
- Increased cargo space and deadweight
- Well-proven for safety in the arctic Easy to retrofit with very short yard stay

READ MORE AND WATCH THE FILM:

catpropulsion.com/twinfin