hi there,
i was searching for some information on the grave which i have found of John Collins and thought it may be of interest to you.i know from the history of Bristol that we used to have ships sailing very frequently to Ireland which you mention in your post.
This 'Pirate grave' which is in a small church in Bristol UK is the only one i have ever seen (please see attached photo)as they were criminals i didnt think they were buried with any kind of headstone etc.
cheers
Marcus