Anchored in a No Wake cove today and after lunch decided to do some pontoon and outboard cleaning. Felt little "bumps" on the outboard and found this. Some can be scraped off with my fingernail and some can be rubbed off with a rag. Some break when you try to scrape it and turns white. Some feel like they're not coming off! Any idea what the hell these are. They are only on the outboard no where else!