and you think a 18 foot jet boat is going to exceed the weight rating for the tires he put on there? nope. the common car is 3k lbs...
BFG's- 215/60r14- 1345 lbs
'trailer tires'- 205/75-14- 1430lbs
I run a triple axle equipment trailer, with truck radials. 12,000 lbs empty, and has been loaded to over 30,000 lbs, on LT235/85R16's
'Trailer tires' might last 20,000 miles, LT radials last 75k+ miles. (Towed with 1 Ton CC Chevy)
Sidewall flex has never been a problem.
Radials on the boats and car flatbed, too.
Dan'l