you might make it up to there pavilion . if putting  in at mckeesport But river is very narrow and shallow around there . 

I have a 14' heavy Starcraft with a 15 hp.  As long as I followed the channel, I could make it from Coulter, all the way down to the confluence in Mckeesport but never much farther up than just past the rapids in Turner Valley.  I was bumping bottom once I got past the rapids up there and just tilted the motor and floated back down.

Definitely some deeper holes in that section and the channel right across from the launch is pretty deep.  Not sure how much you draft with that 18' boat though....
As with everything related to a river, water level means everything...

Got out for the second time this year, finally got off the schneid.  Fished the evening from 7:30 to about 11pm.  One small channel cat and one walleye (maybe a saugeye) about 19" at dusk.
 
To answer some questions, the pool at Coulter is pretty friendly to bigger boats. There is a distinct channel side with plenty of depth for bigger boats. As eyesandgillz stated, the most you'll make it without a jet or high water is just below the island at the Norwin Soccer Fields in Turner Valley. I've only drifted it a couple times, but I found the section from Boston to  Greenock to be wide and shallow.  I tend to go upstream when I launch and rarely go below the island at Alpsville. 

No meeting tonight.  There is a Facebook page, Yough Sports People Association.  There might be better contact information if you are interested in joining the club, but I don't have FB and can't access it.  There is also a web page, yspa.net, that is very dated and not alway up to date.  If you have access to FB, that is the better way to go.

I managed to get out on Wednesday.  The water is low and clear. Caught 2 channel cats.