Yo! 'yo,
Welcome aboard and sorry about the slow response, the Everett Coho Derby weekend is a bit of a busy one for us!
Congrats on drift boat #3 and the Skagit is a wonderful place to work on your drift boat silver salmon program.
In September, I like the Lyman to Sedro Wooley stretch and while it's more jet sled than DB water there are still spots to anchor and work the coho over.
The unique thing about silvers are that they hang out in frog water that no other self-respecting salmon would get caught dead in.
Look for blind stream channels/back waters and throw Mag Warts in fire tiger finish and Vibrax spinners. Work these lures right back to the rod tip and the strike can come at virtually any point in the retrieve.
Dick Nites in the current edges fished on 4' leaders with 3/4oz drop sinkers will also put coho in your fishbox.
As September fades into October, keep following the coho upstream to the more tradional drift boat water and keep in mind that fresh coho will be found entering the Skagit River right through December!
Good Luck!
