It would be heavier and require more flotation than most materials. It doesn’t seem like it’d hold up as well either. It might work. I have owned boats, but I have no
experience with cob.
Are you talking about a houseboat and a separate structure on
land?
You might use bambo or
native cane at least for the boat, maybe with palm or grass thatching. I’m not sure what part of FL you are in.