Keck Expedition 2004
August 7, 2004 Day 9
Historical perspective on seismic observatory development - by Taimi Mulder
Update for August 7—Completion of the KXBB broadband installation on the Explorer Plate. (by Debra Stakes)
Dawn was clear and beautiful, defying our assumptions about working so far north. It is always a good sign on a cruise when people are peaceful enough to stroll on deck for sunrises and sunsets. Let’s not forget the shared experience of being at sea together, something perhaps at risk with the development of cabled observatories. The pilots launch the vehicle before breakfast to return to the KXBB site and complete the broadband installation. They knew it would be a long tedious day trying to get the caisson vacuumed deeply enough. Fortunately, after yesterday, all of the equipment is onsite waiting for the ROV to arrive. Although we know the ROV can locate our equipment with the acoustic beacons, we are still amazed when the elevator comes into view with no time wasted nervously searching for it. I never tire of seeing the elevator appear out of the deep sea “fog”—almost seems like being home again. Wait a minute! Something else has moved into our elevator and seems determined to retain possession. We thought for a while that he (she/it..) was trying to unfasten the beacon so that we would not take her new perch from her. Dives on the Mendocino Transform Zone in 2002 and again in 2003 documented many octopi that found hard bottom in our research areas for brooding their eggs.
The caisson still has a few inches showing all around the rim. We want the caisson to be flush with the seafloor to avoid any current noise being transmitted to the sensor. Care in the installation is what will provide the highest quality data. So the pilots once again begin to vacuum the sediment and do “porch jumps” in which the ROV porch is used to push down the caisson. The suction tool has been modified following lunchtime brainstorming sessions between the pilots and the crew. Because there are video monitors everywhere on the ship—labs, mess hall, staterooms, bridge, etc—everyone has an opportunity to participate in the dive and contribute to solving such problems. The hole is finally deep enough or maybe even a little too deep. Paul now worries whether there are enough glass beads in the hopper to completely fill the hole to make a flat surface and avoid any turbulence over the sensor. The bead hopper is released from the elevator and deftly dropped over the caisson by new pilot Randy Prickett. The pilots release the bead hopper foam pack so that the structure sits firmly over the hole. The foam pack, with its 250 pounds of buoyancy, jets to the surface in less than 30 minutes, to be scooped from the sea by the small boat, leaving a space of several inches at the top. Fortunately, we have some extra buckets of beads on the elevator. Two trips with the ROV and we top it off. Otherwise we would have considered making a “mini-elevator” and tossing another bucket or two down from the ship.
The final step is to clean up the site, placing the white buckets into the drawer and returning the now empty bead hopper to the elevator. The bead hopper is guided onto two rods and then secured in place by a series of hooks. The ROV pilots decide to use the manipulators to release the elevator from its anchor. The lever is pulled and ,,,,and…it just sits there. We confirm the handle is indeed released. Then we look down. All four feet are stuck in the mud! The pilots gently nudge the elevator, but the mud is very sticky. They next try to rock the elevator and one foot is free. Finally the vehicle sits on the bottom and uses the big manipulator to pull the entire elevator slowly from the muck. We watch it rise slowly to the surface. The elevators have served us well during this cruise. But this success was the result of many days (and weekends) of effort by the Marine Operations Tech Mike Conway. Here Mike talks about his experience with designing and building the elevators for the Keck cruise:
“Each time we use the elevator we learn something, or
come up with a better idea of how to do something.
We learned from practicing in Monterey Bay that the glass beads do not
flow downhill underwater like they do when they are dry in air.
The glass beads are about the same size as grains of sand, so just like
sand they stick together when wet. Originally
the bead hopper was attached directly to the elevator about four feet above the
deck. The beads were supposed to
flow down a long hose and into the caisson.
Our experience showed us that the hopper had to be directly over the
caisson so the beads could fall vertically into the hole.
Hence the removable hopper was designed. The hooks that hold the hopper were first secured using
elastic “bungee” cords. But
these cords had to be stretched very tightly to hold the heavy hopper to the
elevator swinging in the air during launch and recovery.
These tight cords proved difficult to use underwater, allowing too little
working room. So the bungee cords
were replaced with yacht type braided cord secured with cam cleats.
These cam cleats are typically used on sailboats to secure sail halyards.
The hopper itself was purchased from an agriculture supply company, of
the type used to contain fertilizers or pesticides.
The bottom was cut out and fitted with a custom-made aluminum funnel that
allows all the glass beads to flow out. A
3-inch diameter fire hose valve controls the flow of the glass beads. This valve
was modified by the addition of springs that return the valve to the closed
position when the manipulator arm releases it. These are a few examples of what we go through to make things
work miles below the surface of the ocean.
We can’t always run to a store and buy exactly what we need.
That is what makes this job challenging and fun.
I’m always a bit nervous when the elevator is launched, will it sink,
will it stay on the bottom when it is empty, will it come up when the anchor is
released? If I did my calculations correctly it should all work,
but there is always the uncertainty. I
think we all are relieved when the equipment is installed and working on the
bottom and the elevator is safely back on deck.”
by Mike Conway