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Why doesn't my cutter dredge pivot on the stern spud?
Posted by Christian Shaw, Last modified by
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on 30 November 2016 02:19 PM

Why doesn't my cutter dredge pivot on the stern spud? 

We get this questions very often here in HYPACK support. It is a very east fix and there are TWO things that can cause the dredge not to pivot off the stern spud of the dredge. 

1. GPS offsets in HYPACK are not correct. Typically GPS systems on dredges now are two gps antenna array's. For example Trimble ships with two antennas. There is a primary (position) and secondary (heading) antennas. The starboard and forward primary antenna should be offset to the center of the trunnion pin. If the measurement is off just by a few feet or inches then the lever arm to the stern of the dredge is off proportional to the length of the dredge and the heading. 

2. Boat Shape in HYPACK is not to scale. The boat shape (*.SHP) that you make in the boat shape editor should be made exactly to scale. When making the shape in the Boat Shape Editor the origin of the shape (0,0) is the center of the trunnion pin. The Y axis should be mad in a negative fashion to the stern. It is important to either shoot the dredge coordinates in with total station or make sure that the physical measurement with the tape measure is very close. If you are off just a bit then the dredge stern could drift based on the length of the dredge and the heading.