There really isn't a real close ramp b/c of no access in Grosse Pointe.
St Jean's can handle any boat you want to launch but the ramp is VERY steep.
Alter Road is closer but your boat had better not draft more than 2' of water as the canal is shallow.
9 mile and 10 mile are other alternatives that are not more than 3-4 miles from the north edge of the dumps.