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    This story is about a large split barge, which, by the way, had already been briefly mentioned in my post about oil spills. For those of you who don't know - split barges are used to transport dredged materials and they are called "split" because they have a longitudinally split hull, hinged on the deck level, which can split open to dump the load. The mechanics of that particular barge was of the simplest kind - two hinges, two massive hydraulic cylinders and an elementary hydraulic circuit to drive them, which consisted of a gear pump, a manual distributor, and an over-center valve - not more not less (schematics).

    So, one day I was asked to assist an apparently easy to solve problem - the barge wouldn't close completely on the stern side, leaving a good three inch gap in the bottom, and since it was being used for dredging mud - even such a small opening allowed a lot of mud to escape. The owner, as well as the crew, were convinced that it was a hydraulic problem. They were also convinced that the problem could be solved by simple adjustments, if they, naturally, were to be performed by a skilled enough professional. To top it up - the barge was working in Spain at that time - quite a long way from where we were...

    After five hours of driving I finally got to the barge. The hydraulic cylinders were under water, but it was still visible that the split hull was lacking a couple of inches to close at the stern side. Surprisingly, it was hard to determine when exactly the malfunction had appeared. I learned from the crew that not so long before the thirty-year-old hull had undergone some serious repairs with many steel panels replaced and re-welded, and there were even a couple of crew members who kind of recalled that the hull didn't close "right" the first time the barge hit the water after the overhaul, but for some reason nobody could tell for sure. Since then the barge had been transporting rocks and boulders, so the slightly opened hull made no difference till the day they had to transport mud.

  A quick check of the hydraulic system revealed no malfunctions. It was a very simple circuit, and it was working at a relatively low pressure - around 150 bar, which was more than enough to close the hull and keep it closed when loaded. I opened and closed the barge a couple of times, and the hydraulic system was working flawlessly. I measured pressures in the cylinder lines to make sure that there was no back pressure - it was all OK, so I called the captain, showed him the readings and explained to him that the problem was not being caused by the hydraulic circuit but rather was of a "mechanical" nature, meaning that something was jamming the movement. The way I saw it there were several possibilities  -

a) a malfunction inside the hydraulic cylinder wasn't letting him close completely (like an unscrewed piston nut)
b) a foreign object below water line was jamming the hull
c) excessive wear/play in the pivot points, like the cylinder eyes and pivot pins or the hull hinges
d) the whole hull structure was "crooked" for some reason, which made the already closed bow end the active mechanical stop 

   I also informed him that no matter what I did with the adjustments I wouldn't be able to solve the problem.

   The crew members told me that the first thing they did after noticing the partially opened hull was inspect it for foreign objects - and none were found. The crooked hull theory was discarded as impossible, even though some "circumstantial" evidence and "unofficial rumors" stated that the malfunction was already present when the boat left the shipyard. In any case it turned out that despite the very extensive repairs of the hull, the two enormous  cylinders weren't serviced, in fact even the hydraulic hoses (that were in an extremely deteriorated condition) weren't replaced. So it was assumed that the problem was most likely "cylinder related". Since there was nothing else I could do, I headed back to Lisbon, and the problem got temporarily solved by landing the dredge over a shallow beach during a low tide and then welding a steel stripe to cover the gap. The repair of the cylinders was scheduled for the next pit stop.

   A year passed, and I had already forgotten about that assistance call, which involved ten hours of driving and one hour of testing, when we were contacted by the same client and over the same matter. It turned out that after repairing the cylinders the problem remained.  And again, as before, the owner, the skipper and the crew were convinced that the problem was being caused by the hydraulic system. This time the barge was working on the Tagus river not far from our shop, so I didn't have to drive for more than thirty minutes to get there. Again, I made all the tests, and again I came to the same conclusion - the problem was mechanical and not hydraulic, and I did all I could to convince the "audience", but still nobody was believing my conclusions.  >>> Next Page