The Bar Check is used to calibrate a depth sounder for draft and can also be used for calibrating the speed of sound throughout the water column in survey sites with a maximum water depth of 50 to 75 ft.
The BarCheck is designed for very low drag to minimize offset from the transducer due to water current or boat drift. The BarCheck has a small, low-stretch and low-drag Kevlar line marked with flags in foot or meter increments. The line is attached to an 8” diameter 10‑pound cast zinc disc with a flat top and parabolic bottom. The zinc disc serves as an acoustic target for calibrating the depth sounder and low drag weight to keep the line vertical.
The BarCheck is used to verify the draft setting by lowering the BarCheck a short distance below the transducer and adjusting the draft until the reading matches the BarCheck depth. The BarCheck can then be used to determine the speed of sound of the water column by lowering the bar check through the water column to near the bottom. The depth sounder’s speed-of-sound is adjusted so the indicated depth matches the BarCheck target depth. The BarCheck can be raised at intervals to define any vertical gradient in the water column speed of sound.