a method and apparatus to implement a trolling device . the trolling device can assist maritime sports fishermen in defining the actual water depth and / or water temperature of the location at which a lure is situated in troll . the readings from the device enable an angler to adjust variables such as boat speed , length of line deployed and ballast weight to adjust to desired depth . the device comprises a temperature sensor , a pressure sensor , a micro - controller chip , a printed circuit board , an lcd display , and a cycle switch , all housed within a dense metal , water - proof body designed specifically for deep marine submersion and in - line trolling . the device has a pre - programmed data - logging algorithm that is activated by a fisherman via a magnetic controlled reed switch prior to letting out trolling line with the device set in - line to the trolling gear . upon retrieving the device , the fisherman can view the data to place or reset the trolling lures / rigs , as necessary , at the appropriate zone .