CarPoop,

I am using this as an example: 10 foot of water

If you are in 10ft of water and have the unit set on 200 khz that means that you are running the unit in single beam. The coverage you will get from this is 3 ft of coverage. If you are running 200khz/83khz you are running dual beam. The coverage you will get from dual beam would be 10 ft of water 10ft of coverage.

If you are running I would use only 200 khz.