The eastern prom ramp in Portland is absolutely NOT all tide. I've seen skiffs unable to launch.
What would be most useful info in your listing would be the depth of water at the ramp at 0.0 feet of tide. For instance, the eastern prom at 0.0 feet of tide has 9" of water off the ramp. If your boat needs, say 2'-9" then you check the tide chart for when the tide level is above 2'.