I'm coming to Rhode Island and Cape Cod for a lighthouse adventure this Thursday 5/13 and leaving Sunday Morning 5/16.I'm planning on doing mainland Cape Cod lighthouses on Thursday, heading over to Martha's Vineyard (I don't think I have time for Nantucket also)on Friday, and a Rhode Island Lighthouse cruise on Saturday. I'm looking for advice on what particular order to see the mainland lighthouses so I don't have to back track, ones that are impossible to get to (that I should avoid due to limited time), Nantucket vs. Martha's Vineyard, etc. Thanks in advance!

I can't help with the Cape Cod lighthouses, but I find Lighthouse Friends, maps by state, very useful for planning the order. I also recently found this site for ordering out of state roads maps before a trip. Road Maps
It sounds like the cruise you are taking on Saturday might be the same one my sister and I are going on in June. Is it through SaveTheBay? I would really like to hear how it went for you. Have a great trip!

For the Rhode Island Lighthouse Cruise, I will be doing this one:

http://www.rhodeislandbaycruises.com/

Yes I the find Lighthouse Friends website very useful and have put the accessible Lighthouses addresses in my GPS.

I liked Martha's Vineyard more than Nantucket. The lighthouses are easier to see, for the most part, and I really liked all the Victorian buildings.