Blackstone Valley has plenty of boat ramps for motor boating and paddling

Lincoln_Woods State Park in the Blackstone_Valley-credit-RI Commerce Corporation
Lincoln Woods State Park

2 Manchester Print Works Road Lincoln, RI, 02865 Phone: 401-723-7892

Inland park with freshwater swimming, boating, trails, horseback riding

This wooded inland park has a freshwater lake and beachfront for swimming and fishing and paddling. Motor boats are allowed, but with limitations. Motor boats are not allowed on the lake on weekends and holidays, Memorial Day through Labor Day. Boat motors must be less than 10 horsepower. Also Eastern Mountain Sports operates a kayaking school at the park (800-310-4504). See full description of Lincoln Woods State Park.
Woonasquatucket Reservoir / Stillwater Reservoir / Stump Pond

Log Road Smithfield, RI Phone:

This is a site for launching hand-carried boats and it is also a portage. There is also access to the reservoir on the west side, where there is a slab boat ramp, with parking. The shoreline there is also better for launching hand carried boats.
Keech Pond

Indian Trail Glocester, RI Phone:

Take Route 44 Glocester to Chestnut Hill Road, to Indian Trail, to end. Boat ramp is on the left. 10 HP limit. Parking is available. 
Bowdish Reservoir

Putnam Pike (Route 44) Glocester, RI Phone:

After George Washington Campground entrance, take third left to boat ramp, which is concrete slab. 10 HP limit, Parking available.
Pascoag Reservoir (Echo Lake)

at Jackson Schoolhouse and Widow Smith roads Glocester, RI Phone:

This site, managed by the state Department of environmental Management, has a gravel parking lot and a cement plank boat ramp. This is a popular lake in the summer and the shoreline is heavily developed. No motors above 10 hp may be used from this boat ramp between the Saturday before Memorial Day and the day after Labor Day. This is a busy aterway; watch out for paddlers and boaters.
Wilson Reservoir

East Wallum Lake Road Burrillville, RI Phone:

This cement plank boat ramp is for launching boats from trailers; also canoes and kayaks. There is a 10hp limit on motors. Parking is available.