Problems with cargo cranes. Some problems with cargo cranes that occur on the ship

Some problems with cargo cranes that occur on the ship.

Deck crane hoisting limit switches

While checking hoisting limit switches, due to incorrect setting of the hoisting limit switch on deck crane no. 1, noticed that the system differs from the ones on other sister ships. Hoisting up limit switch is no longer activated by means of a small weight that slacks the chain when the hook touches it, thus activating the micro switch, as on the previous sister ships; instead it has been put on the cam limit switch together with lowering limit. This means that the hoisting up limit is no longer fixed, to hook being about 2 meters below the boom head regardless to the boom angle; but that it is activated when the exact amount of wire rope is wound up on the drum. 

Therefore, the limit switch activation depends on the boom angle. This is obviously ineffective due to the fact that for lower angles of the boom the limit is not even functional, increasing the risk for crane damage. On board, it is set to activate the limit switch when hook is 1 meter from the boom head with the boom angle 40 degrees and when the angle is increased the distance between the hook and the boom head is increased as well (for example for 55 degrees the distance is about 5 meters). Below boom angle of 37 degrees the hoisting limit switch can’t be activated at all.

Deck crane air heaters

The heaters inside the deck cranes have low insulation resistance on all 4 cranes (varying between 1 and 10 MΩ when measured cold). When the heaters are switched on the insulation resistance soon drops to 0 MΩ and the 440v low insulation alarm is sounded in ECR. Each crane has 9 heaters in star connection. To determine which heater is causing the low insulation, all connections were removed and insulation resistance of all heaters, one by one, was carried out, but without obvious success. 

The problem is that, while disconnecting the heaters, the heaters cool off a bit and insulation resistance rises, disabling the proper evaluation of their insulation values.  Although a couple of the heaters measured this way had insulation resistance of 0.5 MΩ, it has been noticed that the insulation resistance of each heater drops significantly when hot. Also please note that we don’t have any instruction books or drawings for these heaters.