There are a lot of smart people on this site and I'm hoping for input. I'm building a 19 ft LOA dory from plans and intend to build some flotation tanks into the bow & stern. The plans do not make any provision for flotation. Has anyone got any idea on how much airspace i should plan on devoting to this? I want to keep the boat from going directly to the bottom in case it gets dumped in the middle of the St Claire River but also don't want to lose too much interior space. The thwarts will be removable as in a traditional dory so i won't be able to put foam or air tanks under them. I thought about putting foam between the floor frames and decking over that, but want to have inspection access in case of leaks, etc. Any ideas would be gratefully accepted.