Search and recovery in silt?

[DetectorGuy]

A Magnetometer would be best but these are expensive to rent if you can even find one to rent. Side scan sonar will also penetrate loose silt, but I would try a swim over the area to see if you can see a depression in the silt. In 1964 a small plane crashed in the deepest part of Spectacle Lake. We found the area and to this day there is a 3' deep depression in the 8' deep silt where it was removed at 50' deep. The sides of this depression are still vertical in really loose silt. Once you narrow down the area, a 10' long piece of conduit can work for a probe to push down into the silt and 'feel' objects in the silt. I made one of these with 1/8th inch aircraft cable running through it with a large trebble hook on one end and a loop on the other that I can attach a lift bag to. This way I can probe down into the silt, hook the object, and lift bag it with one device and not need to mark it for a later recovery. Obviously some objects won't hook with a trebble hook but you get the idea. Once the object is found you could deploy a dog bone buoy from underwater right over the object to get a better GPS location of the object if a different recovery method is needed. A metal detector could be used to stick down 5' to 8' into the silt but my detector will only read objects 18" from the coil. For body recoveries they use a gang of trebble hooks pulled behind a boat, but a drowning victim is 18 pounds negative if it is a male, and 14 pounds negative if it is a female, so bodies tend to get hung up on the surface of the silt and the hooks are more effective. We did drop a firemans training dummy through the ice into 30' deep water and 8' of silt. The training dummy was 250 pounds on land and 200 pounds negative in the water. It went into the silt like a lawn dart and was hard to locate even directly below the ice hole. Good luck with the search and recovery.
John