When you're chasing the big ones way offshore, look to the Lowrance X136 and Furuno FCV series of fish finders to help you find the big fish schools. 

High Power and Dual Beam sonar technology helps find the fish at in the deep seas! Use the lower frequency, wider cone angle to search a greater volume of water to find where those fish are located.  Then, switch to the higher frequency, narrow cone angle to pinpoint the exact location and depth for more accurate readings and fish finding.