Originally Posted by johnovice
86-(11+11)=64" c to c, so a 68 wide frame results in 2" wide of center on each side; seems fine. My possible 66 frame on a 60 c to c results in 3" beyond center on each side. I know c to c is considered the minimum; I was wondering how far beyond c to c is still good.
Sounds from the responses here that 3" per side is still reasonable.
You could go wider if you wanted... but 66" is certainly reasonable, but you could go wider if you wanted. With 22" tubes you could go as much as 6 inches wider the C-C on either side it side decks and such were important to you.
FWIW, I did pretty much what pinemnky did, I drew my boat and frame to scale in ACAD and figured out a bunch of things in the process. It's a good idea if you're trying to maximize space, get things exactly so or what not but its not necessary. You can certainly have plenty of success simply getting a few inches wider than C-C.
My personal preference is for a wide frame and on my new boat I wanted side decks over a double rail frame. The boat is 65" C-C and the frame is 77" wide. It's a wide boat 88" overall with 23" tubes and both sets of rails lie on the tubes. That's how I built it in the end, put the double rails together, set them on the tubes were they wanted to be and measured the spacing. - came out within an inch of my drawing. In the end I adore the width. I have 11" decks on both sides, my kids and dogs walk back and forth all day and in 30 days on the water this year not one of them fell in (pretty remarkable for my family). Now with all that said, my frame, with anchor system, seats, decks and floors weighs about 160 lbs. If I wanted to go light I could get it down to between 70 and 90. The frame Nazi's will explode with laughter at that weight but the result is perfect for my use... So I could give a shit what they say. This is why I originally said it's really personal preference...
Moral of the story is, think about your use and decide if you want; a simple, light factory sizing or if you want something else. The beauty of modular frames is you can make them any size you want, aluminum is easy to cut and easy to drill. If you want a 68" NRS frame buy 72" and cut 4 inches off one end, redrill a half dozen holes and you're good to go. It's not rocket science. 66" will work fine for your boat, but you could go wider if it suited your needs...