You needed a beefier axel. It sounds as if it was overloaded. Most small boat trailers are good for about 600 - 1000 lbs. The only way to remove the torsion you saw on the wheel bearings is to apply your load to both sides of the wheel.
Nick
Current Boat Looking for one
Previous Boats '84 H16 '82 H18 Magnum '74 Pearson 30 St. Louis, MO