MahReda:
What governing safety restrictions exist to limit your operations when the winds and waves are this high (too high)? Should you even be performing a lift under these severe conditions? I would still involve the crane owners/manufacturers in this discussion/analysis, they know much more about their equipment crane/barge combination than any of us do. You have provided very little meaningful info. about what is really going on here. Exactly what conditions are causing these shock loadings? Are the two crane/barge combinations of equal cap’y. (500t each) and/or do they carry the same proportion of the load as a percentage of their cap’y? You say.... “The overload sensors shut down all motors when this happen even the pontoon weight is 460 tons and both floating cranes have sum of 1000 tons lifting capacity.” 1000t/460t = 2.2 is not a particularly high FoS for this kind of lifting work. I’ll bet both cranes don’t shut down at the same time, during the same incident. If crane ‘A’ is in a wave trough, while its end of the pontoon is high on a wave, during a lift, then in a matter of a few seconds the relative elevations switch, the lifting lines will go from slack to being jerked into high tension, with many parts of wire rope elongation, boom deflection, barge buoyancy considerations due to added load, etc. etc. Now, at the same time, consider the fact that the pontoon has unloaded slightly at crane ‘B’ and/because it is actually floating at its far end, which is also moving vertically. Now, the static loading at crane ‘A’ is actually higher than you had first calc’ed., due to the sum of these actions. It is not hard to imagine that one of the cranes might be overloaded for a short period of time, and its sensors might trigger a shut down. But, this shut down might not prevent the additional overload.
We get all tangled up in trying to calc. some acceleration or shock loading or dynamic loading, with so many variables involved in that analysis, that the Good Lord could not come up with an answer; and then we don’t even really understand, nor can we explain, what is really happening. I don’t know how you select the variable values accurately, with any confidence, let alone calc. an answer which you think is correct. The crane sensors are telling you something, listen to them.
