This week a team from the Atlantic Oceanographic and Meteorological Laboratory (AOML) is visiting the Little Cayman ICON station, designated LCIY2, working in collaboration with the Little Cayman Research Centre (LCRC). The AOML team consists of Lecia Salerno, NOAA Corps officer and AOML's Unit Dive Supervisor, and myself, Mike Jankulak, University of Miami researcher. We are being hosted by Brenda Gadd and Lowell Forbes of LCRC.
One of the purposes of this trip is to inspect and document the damage to one of the station's lower "hounds," which was first noted by Brenda and Lowell last Tuesday. We are also collaborating this week on a cleaning operation in order to provide "official" training for LCRC, who will be responsible for station maintenance. While we are here we are also installing the hardware and software required for radio communications between the research centre on land and the offshore station. This radio link can be used to download data that are more detailed than those transmitted by satellite, to fully monitor the instantaneous instrument readings on the station, or to upload changes to the datalogger program that runs the station. This blog entry will focus on the first of these three goals -- documenting the current state of the station in word and photo.
We will start with the situation above the water (see photo at left). The pylon has a noticeable lean to the left when viewed from land, i.e. it is leaning toward the west. I am told that the pylon when installed had a slight lean to the northeast, so this may be a newer development. Our surface pictures of the station were taken from the boat, which was attached to the mooring ball and resting downcurrent of the station to the west, so unfortunately in these pictures the station is leaning toward the camera. We will try to get pictures taken from the sides later this week.The surface pictures also show that there are tears in the rubber sheet that is wrapped around the station at the waterline. This piece of heavy, black rubber was wrapped around the underwater cables, which emerge from within the pylon above the waterline and are zip-tied along the pylon down to their connection points to the instruments. The rubber was held in place with long hose clamps also wrapped around the pylon. The rubber has torn away at the edges of the hose clamps and is now hanging in flaps. There is no noticeable sign of scuffing or scratching on the pylon that would suggest any kind of impact; it appears that the damage was done by wind and wave and the sharp edges of the metal hose clamps.
Below the surface, we will start with a view of the base plate (see photo at right). There are four "hounds" around the base that are attached by spectra lashings to the base plate pins. Each pair of opposite hounds consists of a single bar of allthread that is threaded through the pylon; on each side, from inside to out, is the following: a delrin load distribution washer, a flat washer, a convex locking washer, and a stainless steel eye nut threaded onto the end of the allthread bar. The photo shows where one of these "hounds" has broken off.
The broken hound is roughly to the south of the pylon, judging from its location under the southern-pointing underwater light sensor and its mounting platform. What has happened is that the allthread bar has broken at a point about one inch inside the pylon (see photo at left). The broken-off eye nut is still attached by its spectra lashings to its base plate pin, and is lying on the ocean floor. We have recovered the stainless steel flat washer but there is no sign of either the convex locking washer or, more seriously, the delrin load distribution washer.
Other comments about the base of the pylon: the eye nut attached to the other end of the broken allthread rod (i.e., 180 degrees opposite from the broken hound) is very loose. It easily twists from side to side in the hand (see photo at right), and the eye nut is holding tightly to the allthread itself which is also freely turning within the pylon. When looking at the broken end of the allthread inside the small hole left in the pylon where the hound broke away, you can see it moving when the eye nut is twisted on the other side. It seems possible that it will be relatively easy to twist out the entire length of the broken allthread when it comes time to replace it.The other comment is about the remaining two lower hounds. The lashings on these hounds are extremely taut, rock solid. They do not "give" to the hand when trying to pull or push. It had been suggested to me that these lashings should be tied much more loosely than this, that they should yield by about an inch in either direction when pushed or pulled, meaning two inches of "wiggle" altogether. When the repair work is done to replace the broken hound and correct the station's lean, these lashings will need to be loosened considerably during the operation, but they should also be re-tied to be much looser than they are now.
One final comment about the base: the first photo shows clearly that the pylon is rotated slightly counterclockwise from where it would "naturally" rest, i.e., with each hound directly above the base plate pin when viewed from head on (at the side). This is probably an artifact of how the station was installed but I mention it in case it is a more recently development.
There is one final area of damage to the station support hardware. One of the pins at the periphery, which is connected by spectra and chain to the upper hounds, has suffered some cracking of its concrete bed (see photo at left). I'm not sure how these pins are "officially" numbered, but I will assign my own numbering scheme to describe its location. One of the pins has a mooring ball attached to it in addition to its spectra/chain support line. You must move clockwise from this "mooring pin" by two pins to reach the pin with the damaged concrete. That is, if you numbered the pins in a clockwise sense from #1 to #8, beginning with the "mooring pin" as pin #1, the damaged pin would be pin #3.This puts the damaged pin to the north of the pylon, with a clear view of the CTD affixed to the north, and the southern-pointing light sensor obscured from view by the pylon. Note carefully, the lower hound broke off on the south (which might indicate stresses pushing the station to lean northward), the concrete cracked on the pin to the north (which might indicate stresses pushing the station to lean southward), and the station viewed from above the surface appears to lean primarily to the west. No formal assessment of this evidence has yet been done to hypothesize about causes of the damage, but contributing factors may include (1) prolonged heavy swells and strong winds throughout the past month, and (2) a magnitude-5.9 earthquake felt in the Cayman Islands on Tuesday, January 19th.
The broken hound was first sighted later on January 19th, and the cracked concrete, to my knowledge, was found during yesterday's dive, on January 26th. The lean to the west (to the left when viewed from shore) does not appear to be a new development, nor can it said to have worsened during the past month. [Although we are clearly paying more attention now, and we naturally assign more significance to the apparent lean than we once did.] The broken hound was last seen to be unbroken during the last cleaning operation, which would have been in early to mid December last.
I have brought some replacement parts with me on this trip to leave with LCRC. There is a new piece of allthread bar, two flat washes, two convex locking washers, two eye nuts and 41 feet of silver spectra. There are also two locking nuts which can be used to unscrew the broken allthread rod (if necesary) and to install the replacement allthread bar. Unfortunately at the time of travel we did not realize that one of the station's delrin load distribution washers had been lost, so we are still one part short of full readiness for repair.
In other news, all of the required software and hardware for the radio link has now been installed, and the LCRC computer is downloading six months' worth of data as I write this blog entry.
Many thanks to our hosts here at LCRC for their hospitality and their support of our diving operations. Thanks also to Mike Shoemaker and Jules Craynock for helping me with some of the background for this post. All photos were taken by Lecia Salerno and myself.
(signed)
Mike Jankulak