Heavier sizes can be jigged below the boat over hard-bottom points. Depth and speed are the key factors. But, color can be important. Try chartreuse for dingy water and more natural colors for clear. But, don't be afraid to experiment and use natural colors when visibility is low.
Sluggish fish demand a finesse approach.
Use 8- to 12 pound line. The lighter your line, the deeper your crankbait will dive. Cast it, let it fall to the bottom, let it sit a few seconds and twitch it. Then, bring it back to the boat quickly, cast again and let it sit. Fish will strike fast if they are there.