waterline question

Hey all:
After sailing in a somewhat-yukky lake yesterday, I noticed the light scum line on the hull was about 7" above the painted black waterline. This is only in the aft part of the boat - up front, under the bow, it's level with the line.
Does this merely mean that my friend and I are too fat (true - each about 230 or more...) and ought to try and sit more fore with that kind of weight, or does it possibly indicate something else about the boat that I ought to be aware of?
Also, is this waterline indicative of an EMPTY boat, and the idea is to keep it parallel with the actual waterline of a weighted boat?
Thanks in advance,
Carlos
After sailing in a somewhat-yukky lake yesterday, I noticed the light scum line on the hull was about 7" above the painted black waterline. This is only in the aft part of the boat - up front, under the bow, it's level with the line.
Does this merely mean that my friend and I are too fat (true - each about 230 or more...) and ought to try and sit more fore with that kind of weight, or does it possibly indicate something else about the boat that I ought to be aware of?
Also, is this waterline indicative of an EMPTY boat, and the idea is to keep it parallel with the actual waterline of a weighted boat?
Thanks in advance,
Carlos