Steamer Quay Totnes is a great slip which I've used at all states of tide (sib) and yes it is free.
It is a lovely trip down the Dart to Dartmouth, but the 6 knot (or is it mph) does get a little tiresome after a while!
Another good place to launch, if your set up is light enough to take across a slightly muddy stretch, is Dittisham. Closer to Dartmouth and the sea if you want to venture out of the Dart.
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