13 footers mostly have smaller tubes and less space inside. That’s obvious!
Sometimes fishing folks will want a smaller raft for their needs on some smaller good fishing waterways. They can be run with shorter oars and fit through tighter runs.
If you frame out your boat for fishing, a 13 footer is quite full. If you have two fishermen and a rower aboard, you won’t have much space for cargo.
Take that into account when you look at your overall plans!