Posted by: Waterbird on Sep-05-12 6:50 PM (EST)
This is a personal choice. I don't like to store, load, or transport long or heavy kayaks. It also depends on the conditions, whether flat or rough.
The minimum would be 12' with two hatches. Most people would consider that too short for touring, but I know of at least one or two twelve footers that would work for touring. Example: Delta 12.10 (Okay, that's more than twelve feet.)
14'-15' is a nice middle ground. 14' is certainly sufficient.
How much you can store in the hatches is a function of the length, but may depend even more on the depth of the kayak, especially at the ends.