If it is not changing anything when changing it there are two possibilities. First is that it has been disconnected. Second is that it is for somethig else as Baker said. Usually the front switches on a bass boat control Tilt up and Down, live well pumps, or navigation lights. What are the other switchs on the front for? Are they marked and operational? I do not exactly know the layout of your boat but am going by the switches on my 1990 Nitro 20 footer. A double throw switch as you described makes me think that Baker may be correct that it is for lights. If it isn't momentary on (stays in the up or down position without snapping back to the center) you can rule out the tilt function. The only way to know for sure is to remove the panel and see what is connected to what.