[Fr. Frank]

You need a trailer that is rated at 135-140% of your max gross weight, which includes the empty trailer weight.

If you have figured the net weight of the boat when loaded at 4,250 lbs, add the weight of the trailer to that figure to get the max gross static weight. Under ordinary conditions, your trailer will undergo a momentary dynamic load of 135-140% of that total when it hits a bump. You also load one side of the trailer by itself to 80-100% of your total static load as you go around a corner.

4250 lbs boat, motor, fuel & gear
750 lbs empty trailer weight (Aluminum)
5000 lbs static load
X 140%
= 7000 lb trailer max gross capacity.

If your total towed vehicle weight exceeds 50% of your towing vehicle weight you need brakes!!

In Florida, if the trailer has a max gross capacity of 3500 lbs or more, trailer brakes are required by law, unless your trailer was manufactured before 1984.

In GA, trailers with a gross capacity of over 10,000 lbs must have electrically activated brakes or air brakes that operate off the tow vehicle's air system. I got a warning from the Georgia DOT a few years back for towing a 26' Wellcraft Scarab (on a trailer for a 30' boat) with tandem axles with a max gross of 12'000 (6K per axle), and only had surge brakes.