I just used Starbrite from Walmart and a mild abrasive pad. Took several hours to hit the whole bottom and I still need to do it again to get it to 99% clean.

How bad was the bottom - any pics ? Any barnacles ? Any trailers or used tires stuck to it ?

It felt like sand paper, I would have figured a couple of miles per hour, but not restricting it that much. No pics, I just thought it was dirty and not pic worthy No tires that I saw.