Morrison, most aluminum hulls of this size do not use stringers. Instead they use ribs. I will include a picture of my Lund while I had the deck removed and it should give you a good idea of what's under yours. Again it maybe a bit different but still the same principal.
Notice the hole in the center of the ribs. I believe this is were your water may be collecting and not draining back the way it should be. Could be rain water, leaking connection and hopefully not some lose rivets. This is why I suggested tilting it up it it is just collecting rain water/splash.
Sea Nymphs are normally pretty sturdy hulls from my experience. Also I find it easiest to use photobucket to attach pictures to these posts.
