"John H" wrote in message
news
Therefore, at a given rate of deceleration, a more heavily loaded
trailer will have a greater differential pressure between itself & the
tow vehicle, than a lighter trailer, & therefore the hydraulic
pressure from the surge brake coupler will be higher for a heavier
trailer than the more lightly loaded trailer."


This is just another way of saying that surge brakes are a "negative
feedback" system: the more the trailer weighs, the more it pushes on the
tow vehicle during deceleration, which in turn creates a greater hydraulic
pressure which applies the trailer brakes harder.

In other words, it is self compensating. The trailer brakes work reasonably
well when the boat is floating on the lake and you are running the trailer
around the parking lot. It works just fine with the boat on the trailer as
intended. It still works good when you have just loaded the rig up with ice
chests, camping gear, full load of gas, tools, etc., etc., etc.


The size of the brake shoes, wheel cylinders and master cylinder needs to be
selected based on the total gross weight of the trailer, but the system is
very forgiving.

Rod