When rotted, for the most part. And if you have a soft floor, your stringers are probably bad. If all is solid, you are probably okay. More details can provide better answers.
take a small drill bit and drill the bottom of the stringer a small hole if the shavings come out damp or dark or the bit blows right threw its time to replace them.
The Fiberglass around the stringer was hard as a rock but the insides were gone ..
The out side can look fine but the inside looks like this .
You should never do that!!! Just look what it lead to I did the same thing and now am involved in an entire rebuild.
Seriously though, looks like you found the answer to the condition of your boat.
I did the same thing and now am involved in an entire rebuild.
