Hi Sushi,
I have had alot of luck in the past using the following techniques:
Fast-Trolling cut-plug herring in 20-40 ft of water using whatever means you have available to keep your presentation at that depth. Maintain a speed of 3-6 knots. I have landed both Blackmouth and Coho using this method... Mostly Coho. Others may disagree, but I have always preferred a faster troll because you cover more ground, the fish seems to hit the bait harder because it presents more of a challenge to them, and I can achieve the action on the bait that I desire. However, If you dont nail any of them at that speed try going 1-2 knots, just fast enough to keep a nice spiral on your bait. You dont want a spiral where the bait is going in a loop that is 2-3 foot wide in diameter, try to make the bait spin like a torpedo. Practice, on cutting the bait and rigging it ,makes perfect.
Also try dragging a hoochie behind a flasher using the same depths and speeds. I usually use a solid pearl or white color, or a white-green with success.
Mooching/Motor mooching also works well with cut-plug herring. Rig up with a 3-4 ounce weight and a 6ft. leader...and let your setup drop to bottom, then retrive so you clear the bottom by about 15-20 ft. Put your kicker in gear for 20-30 yards at a time to lift the bait, then stop for a minute or so to let it drop back down to depth, then repeat.
Good Luck and let us know how you fare!
Sky-Guy
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