Have to agree with Breezy, heck if I can find a difference.
Sorry to keep posting but clam chowder variations are something that have confused me.
A few years ago read an piece in a book that said there were only three variations: Manhattan, New England, and Rhode Island. And I do not remember exactly what the Rhode Island variation was supposed to be (and cannot find the book now). But, as I recall, and please don't trust my memory, it was supposed to be a grayish, not very thick, soup. Sorta like a New England chowder but without the milk products. Whether it was supposed to be made from a roux, I do not remember.
Have Googled many times and finally decided that I could not find such a thing.
Found a recipe from the last governor of the state, Lincoln Almond, The ingredients seemed just like good old New England clam chowder, except it left out the bacon/ fat back (there was plenty of flour, and milk and cream). Seems just like the New England version.
So I guess if there is an authentic 'Rhode Island clam chowder' made without milk/cream, the ex-governor either does not like it or has never heard of it.
If anyone knows anything more about Rhode Island clam chowder would love to hear it.
What I have found is that the major difference between the 'white chowders' seems to be in the amount of flour used.
Went to Jasper White's book. He specifically shuns the addition of any thickener, relying only upon the starch from the potatoes to add what thickening they do. But he sure does add cream.
Other recipes utilize varying amounts of flour and fat (roux).
That is all I know about clam chowder, but would love to learn more.