Thanks for all of the input guys. I will check into those Goodyear Marathon tires when I buy new ones. The tires that came on the trailer are bias ply tires and recommended 50 PSI. I kept a good check on them because, even though my boat is aluminum, it is fairly heavy, especially in the back because of the 20 gallon fuel tank and three batteries. I talked to a lady at a local tire shop. She didn't tell me the brand, but said she had a 6 ply radial tire that would wear better than a bias ply tire.
The Lord is good. His mercy and love endures forever.