What does your boat weigh?
Until now I have never worn out a boat trailer tire. Two years ago I pulled my boat to Lake Okeechobee which was about a 1000 mike round trip. When I bought my current boat (99 Duracraft, 40 Yammy, etc) I put two new tires on it. They were the run of the mill Carlisle 4ply 5:60X12.
When I got back from my trip I noticed they were worn to the point I wouldn't trust them to make another trip. I found some 6 ply ones on e-trailer.com and ordered two of them. I made the trip to Florida this year and they still look new.
The first set had a max load rating of 850#/tire or 1700 tax for the pair. This new set has a 1100#/tire rating or 2200 for the set.
One of my buds told me you can go to Lowe's Truck Stop and weigh your boat, so I did that today. My 16.5 ft aluminum boat with 40 motor and all the other crap we haul around topped out at 1900 pounds. No wonder the tires were worn out. It's a miracle I didn't have a blowout. I never would have guessed the rig was that heavy.
By the way, if the weight is under some set amount the don't charge you to weigh it. Don't know what the amount is but it is more than 2000 pounds. They used to weighing those big rigs, not a scrawny fishing boat.