I used to go to the old Thompson's Clambar in Harwichport once in a while for lunch. You could tie up right there but they are long gone I think. When I go to Hyannis now I am usually just there to drop off my boat for service at Hyannis Marina in the fall. I know they have dockage. I wonder if you can tie up this time of year at the slips over by the HyLine dock. There is a harbor masters office right there, if memory serves. I would think after Labor Day there might be slips available there but I am just guessing. As for the Vineyard I have gone over to OB and tied up at their docks. Made for a nice day. Have not done that in quite a while either, perhaps this weekend if it is nice.
I think someone that lives over on the Cape or the Vineyard would have better and more up to date info than I and could comment. Where do you keep your boat here?