From floor to hull...???

[Passtime207]

Ok, talked about the floor in the general maint. section entitled "Broken Floor" recap is soft spot in floor don't know what is underneath it yet, bad stringers, ect. Well now I noticed small blistering on the hull just ahead of the transom. My question is before I start working on the floor what is this blistering and since it shouldn't be there is this an easy fix or with the floor issue and now a hull issue (?), dare I say look for another boat. Hope it doesn't go that way. Thank you for any help with this situation.