Detector (s) used. MXT, TDI, Whites Dual Field, Goldmaster VSAT, Fisher CZ 21. Apr 2, 2009. #1. I just completed my homemade 2 1/2 inch dredge. I floated it in the lake to find out what the displacement was and it was almost perfect. The front was about 5 to 10 lbs light but with the water in the sluice, it should weight the front end down some ...