Since I just measured out my yak, I know of these numbers. My yak is 23.5 inches wide, 16 total feet long, 14.5 ft gunwalls and a 13ish ft long keelson. Its tradtional bent ribs with 3/4 inch keel and chine stringers. No skin touching any ribs. If you use forms, you should be more than fine. Keep in mind, that if you feel the need, you can add a chine that does not extend the whole distance of the boat.
Your numbers sound like an incredibly stable and fun yak, post pics.
Scott