Welcome to the boat mate.
When using the sonar your self the only way to get an accurate range is to be sure you have the sonar pointed at the very center or the target, move the head left and right till you find center. Than when you ping a target you will get a pretty good range, not great but good enough to start a plot or firing solution. The more off center, the worse the range will be. The sonarman can't seem to do this.
Magic