Re: trailer tire pressures
The only time you might want to run less than maximum pressure would be if you have a small boat on a heavy duty trailer and the tires and suspension are carrying significantly less than their rated load. The oversized suspension will be stiff and produce a rough ride, which could be hard on the hull, especially with a roller trailer. A modest reduction in air pressure would soften the ride at the expense of somewhat increased rolling resistance. For an idea of how much a tire can carry at reduced pressure, look up the maximum load and pressure specifications for same-sized, similar construction tires with a lower load range.
As for the O.P., a 4740 lb boat plus a trailer will be pretty close to if not over the 5260 lb rating of the 4 tires, so it's max pressure for sure.
