Tweitz probably has more details but IIRC the Rams Head Inn is actually on what they call Ram Island even though it is connected by an isthmus to the rest of Shelter Island. If you were at the Coecles Harbor Marina look across the water and you are looking at "Ram Island". We took a long bike ride (over 2 isthmus and actually all the way to the spit of sand to your right as you enter Coecles Harbor) to check it out and it seems more of an Inn than a resturant, but we didn't look inside. I don't think there is any water access.
Wickford/Narragansett Bay RI