Rubber seal on cover....CRUD?

[KC_Jones]

Ok I managed to figure out how to clean this mess up (see pictures), but I am wondering what they heck this is?! Does anyone have any idea what is the typical cause of this crud/staining on the seal at the bottom of the cover? Also I am curious what others have done to clean this up? I know what I used, but curious what others have had success with.

 

[nccatfisher]

Mildew, usually gets on there during the winter. Boat will draw moisture and that is some hateful stuff to get off. My boat is under a shed but outside. Whole boat will have a light coat of it. Good cleaner and light % of bleach will usually work with the boat with a pressure washer. In the areas that I miss it only gets worse over the years.

 

[DaleH]

Mildew - Add ¾ cup bleach to 1 gallon water in a bucket ...