Next time try bucktailing a fly in the wake of the boat. Those Silver salmon just love playing in the prop wash for some reason. Use a fast troll speed so the fly pops up to the surface and then down again. If the bite is really slow tie a flasher to a heavy cord with a swivel and troll that about 10 feet in front of the fly. One warning you really have to watch the flasher to keep its line out of the prop when you make sharp turned or stop the boat to land a fish and restart again.
Make sure your flies are spare with a good amount of flash.