You can install an inexpensive durable ramp for small boats without pouring concrete. Ramp is for light duty, foot traffic, not for motorized vehicles, and minimizes impact on waterline.To see my related Instructables, click on "unclesam" just below the title above or in the INFO box to the right. On the new page that appears, repeatedly click "NEXT" to see all of them.
Step 1: Precast pavers cover the ramp surface
This ramp design uses precast unreinforced pavers over a crushed stone bed that gradually slopes to the waterline and pavers on a pressure-treated wooden tray that runs into the water. I bought wet-cast pavers 2' by 3', 2" thick that have a nonslip surface cast into them, rather than dry-cast pavers that are not durable. Each weighs 75 pounds, so it will remain in place, and I used two 2' by 2' pavers to transition between the overland section of the ramp and the section in the water.
My tray is made from 12' lenths of 2" wood treated to 1.5 pounds per cubic foot retention level, some boards 8" wide and some 6" wide to make up the width I needed. It was so heavy I assembled in on skids near the water line at low tide and slid it into the water once the tide rose. A rim of pressure-treated wood strips contains the pavers on the tray, and cross-cleats underneath hold the boards together and keep the tray from sliding away from the shoreline.