Posted by: adorsk | October 5, 2007

Underwater Rodeo

It’s been a while since I’ve last posted. After the Long Corer cruise I went home for a week, then came back down to WHOI to sail on my new ship, the Oceanus. The ship’s internet went out while we were at sea, so I’m finally catching up now.

The O-Boat

The Oceanus is a rather different boat from the Knorr. Riding the Knorr is like riding an elephant; she has an imperturbable stability, a certain wisdom in her motion. Riding the Oceanus is like riding a drunken rabbit; she hops up & down the waves and rolls.

She’s about 180 ft long, a little more than half the size of the Knorr. In addition, her deck is much closer to sea level. I like to say that she has a swimming pool on every deck because Water washes up on deck all the time. She’s really quite exciting to sail on.

oceanus_sunset

I just got back from my first cruise on her, a mooring recovery cruise. The people I meet at sea never cease to amaze me. The crew of the Oceanus is great. They work out in the waves, maintaining perfect balance, facing off against the water that splashes over the stern. The science party is equally inspiring. B, the chief sci, is probably the world’s expert on surface moorings. His team knows all about the complicated logistics of mooring recovery. We were an international bunch. There were people from France, England, China, Pakistan, Lithuania, and Barbados.

B, the chief scientist was after the bottom part of a mooring that had broken in the Gulf Stream. The bottom part wasn’t useful for anything, but B wanted to know why the mooring broke. A single mooring can be quite expensive when ship time is taken into account (> 1 M $), so it makes sense to figure out why they break.

Mooring recovery is like aquatic rodeo. First you have to track down the maverick mooring, then you chase it down, and then you rope it in. Tracking down the mooring is the easy bit. The ship sends out an acoustic ping, which the mooring responds to with a ping of its own. If you know the speed of sound in the water you can figure out how far away the mooring is.

The next parts are more difficult. To chase the mooring down you have to know about how it will float up to the surface. Fortunately We have a device on the ship called the ADCP (acoustic doppler current profiler) which figures out what currents look like at various depths. Once you have an idea of what the currents look like, you send the mooring a special acoustic signal which will cause it to let go of its anchor and float to the surface. Then the chase is on.

As the mooring rises to the surface, the ship tries to use acoustic pinging to track the mooring. It’s kind of like playing ‘marco polo’ in a swimming pool. All you know is about how far away the mooring is. If you’re lucky, you can predict how the mooring will rise with the currents and position the ship accordingly. If you’re unlucky, the mooring heads off in a different direction until it is out of range, or doesn’t make all the way to the surface. Then you have to try to lasso it under the surface by using the ship to form a giant noose out of wire. Fortunately for us the mooring rose to the surface in about three hours along the path that B’s team predicted.

This set us up for the last step: recovery. This was also a tricky bit. First you have to spot the mooring on the surface. The only thing to really see are the yellow plastic ‘hard hats’ (plastic coated glass balls which provide flotation for the mooring). Hard hats are small. The ocean is big. Assuming you can find the mooring on the surface, the ship comes along the mooring slowly, taking great care not to entangle the mooring line in the propellors. Then the crew and science party try to hook the line and bring aboard with winches. Remember that all this is being done with waves splashing everywhere and the ship rocking the whole time.

mooring

October at WHOI

Now I’m back at WHOI. The air is just starting to turn crispy and cool, just perfect for morning bike rides along the bike path.

Time in port seems to be bittersweet for me. On the one hand, I miss the science party that just left.  To me it’s always very hard when the wonderful people I just sailed seem to vanish in a flurry of crane lifts and boxes. But on the other hand I’m excited for my next cruise. We’ll be going into the gulf of Maine for ten days to study Red Tide.

And that’s all I’ve got. Thanks for reading.

Miscellaneous Pictures

Hardhats on the dock at WHOI
hardhats

Have you checked the expiration date on your liberty?
sailing_board

The end of the bike path
bikepath_end

The view from my new office
oceanus_office

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Responses

  1. […] Mooring recovery is one of the most labor intensive activities the ship does. It requires many people on deck, involves high-tension lines and chains, and it takes a long time. I wrote about it one of my earlier posts: Underwater Rodeo. […]


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