Mooring winches are used to tie the ship to the berth when at a port. While loading and unloading the cargo on the ship, the mooring winches tighten or loosen suddenly. Any extra tightening or loosening of the mooring winches can lead to dashing of the ship with the berth or any other form of accident.
For this reason, load sensors are used on the mooring winches. Load sensors sense the tension on the mooring winches and adjust the tightening and loosing accordingly.
However, it is important that these load sensors are adjusted properly to get accurate results. The article will explain how to adjust the load sensors on the mooring winches.
Adjusting Load Sensor
Winches consist of strain gauges that sense the load. This strain gauge produces a small voltage when load is applied on it. The voltage produced will be different for different loading condition. This voltage is then calibrated to give out the readings on the panel of the winches. These gauges are required to be calibrated time to time and the procedure for the same is as follows.
1. A tool is fabricated as shown in the diagram with the dimension specified. The dimension may vary with different size of the winches; proportional dimensions may be calculated accordingly.
2. There are 2 holes in the rope drum and the measurement between the holes is 200 mm for the picture shown which may also vary with different winches.
3. For fabricating cut 2 pieces of plates 10-15mm thick and weld a distance piece of 25 mm between them, and in the bottom a plate to be welded for placing the hydraulic jack as shown.
How to Fill in the Formula?
The following calculations and measurement has to be taken and put which is marked in blue.
The example given above is for the MW 300 EA winches.
The winch tension is noted, a winch MW 300 EA is pulling 300 KN, and a MW 120 EA 120 KN etc.
The drum diameter is checked and noted. It can be measured on the winch, or can be taken from the manual by checking the mechanical dimensions.
The rope diameter is measured and noted.
The distances from the center of the shaft to the position where the hydraulic jack is to be positioned is measured and noted.
Finally the jack piston area is to be calculated cm2.
Download your own formula calculator below.
1. After all the measured values are inserted we need to get the jack load and the maximum pressure to be applied by the hydraulic jack.
2. Before adjusting safety precaution to be taken to avoid any accidents.
3. Bridge is informed that you are working on the winches.
4. Proper signs and placard are displayed for men at work so nobody will switch on the power by mistake.
5. Electrical permit to work to be filled and instructions should be followed so you don’t miss any safety point and prevent accident.
6. Switch off the power to the winch after putting the tool as seen in the picture.
7. The rope is made slack and a voltmeter is mounted between GND and SIGN. Trimmers P7 and P5 is adjusted until you have 0 V DC.
8. The reading should be zero as there is no load on the gauges, but if it shows any reading then it should be adjusted to zero as specified in above point.
9. Now engage the clutch and apply the pressure with the help of jack. The pressure applied is already calculated in the form above.
10. When the maximum pressure is reached, check the reading in the voltmeter by mounting the two leads between SIGN and GND.
11. Now adjust trimmer P6 amplification by turning with a small screw driver until you have approximately 3 V DC and the value on the “Load meter” in the control panel is maximum.
12. Release the hydraulic pressure and now the reading on the control panel should read approx. 0 V DC.
13. If reading is not zero then re-adjust trimmer P5 load sensor for fine tuning.
14. It is recommended to put back the pressure again to be sure that it goes back to max value.
Image Credits: Maersk shipping