Black stains from cover
 

So I just got a new snap cover for my 02 Sanger and whenver I take it off, the whole engine cover panels are brown with round black stains all over. If I leave it in the sun for about 4 hours, they almost completely go away. I make sure the boat is dry before putting the cover on everytime.

Anybody had this before? If so, any idea how to stop it from happening?

There was a near exact thread on MC owners just recently. I suspect the cover is black or dark cover?

I think they deduced that somewhere in the life of the boat, the vinyl had its protective coating stripped off and that causes it. Some guys have it with their MC cover and other guys don't. Even with the same years, same conditions, same original vinyl. The guys who replaced the vinyl had the problem go away, even when continuing to use the same cover.

cover
 

My cover is gray or green (color challenged here). I put a bed sheet on the engine cover - all the way across the back, then put the boat cover on. Its the dampness at night that causes the bleed through.

I have the same issue with my 2010 VLX. My dealer actually caught this when I took it in for service. It is the factory cover and only happens when left in the sun. I keep my boat under an awning, so there was never any issue when I would pull the boat out and go. At the dealer, the boat was left outside, and when they pulled the cover off, the vinyl was stained black. When left in the sun for a few hours, it goes away. I also left the cover on at the river one day when we didn't use the boat, the next day the same issue. He said it is a defect with the vinyl, and they will warranty it out and replace everything. He said just bring it in at the end of the season and they'll take care of it. check with your dealer

Yeah, that definitely makes sense! I used the boat in salt water so I am assuming that's what happened to the protective layer of the vinyl! I will try the sheet idea and reupholster it this winter. It seems to be the worst when it gets rained on and then the sun comes out which makes sense. Thanks alot guys!

Staining Vinyl
 

The cover materials that are Solution Dyed do not cause any staining.

The issue lies within the vinyl characteristics where glues and foam backings cross contaminate the vinyl surface setting the conditions for staining to occur.
Additionally the staining can also be mold growth in the foam section that bleeds to the vinyl surface from the backside.
Lack of a high quality top coat adds to the poor resistance of vinyl reacting to organic coumpounds that come in contact with it.

Although a sun pad which is in direct contact with the cover may stain so will a seat bottom which is a significant distance for the cover. There are cases where an uncovered boat on a hot day and not under sun exposure with this type vinyl will discolor. Once put in the sun it dissapears.

If you're experiancing the problem choose a Light Gray color cover alternative which the OE's offer. It should help.

Certain boat brands exhibit this staining problem while many others do not.
Higher quality vinyls resist any staining or discoloration.