Originally Posted by Last Tango
I noticed when I was into hard boats that the wider trailers that your laws allow meant that the boat chines could sit lower between the wheels whereas ours needed the boat to be set above the wheels. We have been given and extra 3 inches recently but "EU type approval" still has us using 1940's style rod operated drum brakes.
Not so much the trailer laws as how the hull is shaped, hard boat vs RIB.
Hard boats are narrower towards the keel, which allows them to sit down between the fenders or wheels (or both), with the keel/axle/crossmember interaction limiting how low you can go.
With a RIB, there is much less taper (i.e. the hull is a flatter form) as you move from the tube to the keel, which means the boat has to sit higher at the keel to allow the tubes to clear the wheels.