Field Report 2015-08-07: Retrieve Flow Sensor from Akumal Bay

Gabriel, Patricia Beddows, Marco A. Montes Sainz

Left to Right: Gabriel Sanchez Rivera / Patricia Beddows  / Marco A. Montes Sainz

I was up pretty late downloading the loggers from Rio Secreto the day before, so we had a late breakfast at Turtle Bay Bakery & Cafe the next morning. While the only decent coffee in Akumal has become something of a necessity for my aging brain, our corner table is also something of an office away from home for Trish, who knows so many people in the area that sometimes it’s hard to escape from all the hugs and hand-shakes.  With sufficient caffeine in my bloodstream I was ready to hit the reef with Marco, who had been keeping an eye on our little loggers through the Sargasso seaweed invasion that has affected coastlines throughout the Caribbean this year. He had already taken south bay unit out of the water due to a zip tie failure on the support rod.  I wondered if those dense floating mats had snagged the shallow unit, putting enough stress on the ties to break them?

Removing B4 from float line

Pulling B4 from it’s anchor rod.  (photo by Marco)

Since the B3 logger was already dry, that left only the Pearl at the north end of the bay. This B4 unit is the oldest continuously running logger on the project (it’s first underwater stint was back in March 2014) and is still running on it’s original Tinyduino core. Since the sensor is now well past my original one year design goal, I am tempted to retire it to the “bookshelf museum” as these old dogs feel like Russian tanks next to the new builds. But this project also embodies what the guys over at Boston Robotics distill down to “Build it, Break it, Fix it”, so I really want to see how long this DIY flow sensor will last.  As far as I know, this is the longest marine exposure test anyone has ever done with JB weld, or Loctite E30Cl epoxy on hardware store PVC.

And the little loggers did not disappoint, delivering a gorgeous four month record of water temperature, and tilt angle (my proxy for flow velocity)

Data from B4 Cave Pearl Data logger

This gave me another look at that June 13/14 event, and it must have been something! It almost doubled the relative flow velocities (probably more than that due to non-linearity, etc) and it pulled the mid-column temperature in the bay down by three degrees Celsius. To put sixty five degrees of deflection in perspective, here is a video clip of the relative motion of the floating logger, on the day we retrieved it:

This thing was brand new 4 months ago

That pivot joint was brand new four months ago…

I’m happy that the unit wasn’t ripped from it’s mooring by the storm, and that I installed the new super duper PVC pivot joints on that last trip. I am sure the old zip-tie swivels would have completely let go. In addition to the rough conditions, there is marine life colonizing all exposed surfaces.  When I took a closer look, the pivot joint was making some distinct “crunchy” noises – indicating something was trying to take up residence inside the tubing. The logger itself is now so hairy that I think the buoyancy is being affected. Hmmmm….

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