As above, so long as you’re cautious of the weather and fog, which is a factor that time of year (they call it fogaust for a reason!), 18 is plenty. I fished out of a 17ft harbercraft for years and could fish all the banks and outside structure depending on weather/sea state. I will add from my experience in a smaller boat you really want to pay attention to the forecast for the direction of the prevailing swell vs prevailing wind - when they’re 90 degrees to each other the resulting slop is very uncomfortable in a small boat no matter where u are! Also, depending on where you are be aware of building aftn wind, particularly if fishing in the lee of islands. I’ve had my most harrowing boat rides fishing a bit too long at Effingham/Cree only to find the wind from the NW was howling and wind waves across London channel were in the 5-7 ft range at a 4-6sec period ... scary **** in a small boat!
For fishing inside, find bait you should find fish. That time of year you often don’t have to go far plus there should be coho around. Harbour mouth, light house to little beach, red can, food islets and chrow island are all close and mostly protected. A bit further afield Great Bear/ Alley rock area is good that time of year. South bank, lighthouse bank and Wya point aren’t too far of a run with good seas and a stable forecast. Of course, a run through the broken group is beautiful if it’s not foggy in the sound and lots of areas to fish on the south side - meares/effingham, cree, Gibraltar and swale rock.
I’m jealous, good luck and tight lines!
Cheers!
Ukee