August 3, 2006 Options

[Steve_Stevenoski]

August 3, 2006

Preparation for our third deployment of the seismic gun cage began with a
safety briefing in the main lab at midnight. Steffen and Russell had the
compressors up and ready. There were fewer Coast Guard representatives at
the meeting. Given that this was the third deployment, very few things had
changed in the procedures that would be followed on deck. Minor changes had
been made to the cable tube and the position of the towlines. Two
additional tag lines had been added.

Large air bubble released when guns are triggered produces low frequency
sound that is detected by seismic instruments


I was on the starboard tag line ad the cage was lowered over the transom.
With the cage partially submerged, we hit some ice that caused the cage to
spin. We lifted the cage above the transom again and then pulled the slack
out of the tag lines. The cage returned to its proper orientation and the
cage was then lowered to its towing depth of six meters below the surface.

Final check of the air guns


The ramp up of the guns went smoothly. The ice was not affecting the cage
or the thrusters like it had in the past deployments. Moments later the
ship entered a hard blue ice ridge. With thrusters at full, the ship came
to a stop. The cage sank heading downward. Reversing direction at this
point to back and ram could damage the cage and the ship. The bridge was
notified to hold position as we shut down the guns and lifted the cage above
the waterline. Pressure to the guns was released to prevent their
accidental firing.

In the rush to raise the cage, tag lines went slack and the cage rotated 90
degrees. The tube was c aught on the top of the cage and the towlines were
tangled. The cage was position with the top of the cage at deck level. All
on deck worked to untangle the lines and get the cage back in the water.
2:00, first gun was firing and we were in the full ramp up to eight guns.
The ship set course at 3Kn and we started to collect data, one shot every
sixty seconds.

3:00, we were at a new record for having the seismic gear in the water and
working. 2 hours, 5, 10 hours, and things were still working. We had
passed instrument number two on the ice and were headed for number three.
The seismic watch standers started to work a rotation, going from the aft
fantail, up to the aft control, and checking compressors. Mark had
installed a kill switch in the event that the cage came out of the water.
Triggers were on the fantail and the aft con.

At 10:30 we had lost a gun to an air leak, but other than that, no problems.
I headed to the gym and took a nap. At 2:20, Matt came into the room and
said, "We lost a gun, they had to shut everything down and bring the cage
in. Kevin had to use the kill switch, one of the guns fired out of the
water."

By the time I got to the aft con, they were pulling the cage up. You could
see the right bottom Bolt gun hanging by one bolt and the bottom left gun
was gone. Hoses and wires hung in space. I stayed off the deck until the
cage was secured, then I put ion a hard hat and mustang to see the damage.
It was 3:05. We had collected data for almost thirteen hours straight. The
final downfall was three hard ridges in a row that bashed the cage with
incredibly hard blue ice. By the time we hit the third ridge the ship was
nearly stopped. We would have had to pull the cage to back and ram.

There was some disappointment that we had lost the gun, but when you think
about it, we were able to collect data for nearly 13 hours through over 90%
ice cover with a system that had never been tried before. This is easily
one of the most difficult places on Earth to do anything. Yes, we will have
to make some repairs, but we collected data, and we will be ready to do it
again in a day or so.

At 4:35, the helicopter headed out to collect instruments 1,2, and three.
Once on the ship we will download the data the collected while we were
firing. Tomorrow will be more helicopter ops and more coring. Everyone
will be busy, and tomorrow is also Coast Guard Day.

Two meter block of ice forced out by the ship's propellers